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WorksheetsCell Bio MCB 2210 Exam 1
Total questions: 139
Worksheet time: 1hrs 10mins
All of the following statements are true about modern Cell Theory except:
all living creatures are made of one or more cells
the cell is the structural unit of life
on the earth today, cells only arise from division of pre-existing cells
earlier versions of cell theory thought that contemporary living cells could arise from non-living material
all are true statements
Which of the following is/are NOT true statements of evidence supporting the idea that RNA probably evolved before DNA and proteins to serve important functions in the prebiotic world?
a.
proteins can substitute both for DNA and RNA
b.
DNA and enzymes are only present in the most advanced cell types today
c.
RNA can both code for genetic information and act as a catalyst
d.
many cells today do not use RNA
a, b, and d are all NOT true statements
Brain cells produce proteins that allow synapses to form, liver cells produce liver enzymes, muscle cells produce sacromeric proteins. If all cells have the same DNA, how can this occur?
a.
transfection
b.
differential gene expression via specific transcription factor activity
c.
differential gene expression via DNA methylation and/or Histone acetylation
d.
differential gene expression caused by endogenous miRNA expression
b, c, and d
What characteristics distinguish prokaryotic and eukaryotic cells?
Eukaryotes have membrane-bound organelles; prokaryotes do not.
Prokaryotes have relatively little DNA; eukaryotes generally have much more.
Eukaryotic chromosomes are linear; prokaryotic chromosomes are circular.
Prokaryotes possess a unique flagellum.
all of the above
The key difference between a plant cell and an animal cell is:
The presence of a plasma membrane.
The presence of a nucleus.
The presence of internal membranes.
The organization of DNA.
none of the above
Which statement about multicellularity is false?
Both prokaryotes and eukaryotes can form multicellular organisms.
Different cell types in a multicellular organism express different genes.
Multicellular organisms can be much more complex than single cell organisms.
Single-celled eukaryotic organisms are in general less complex cells than the individual cells that comprise multicellular organisms.
Some multicellular organisms can form from the gathering of individual cells rather than the fertilization of an egg by a sperm.
Evolutionary relationships between groups of organisms are most precisely determined using which of the following types of information?
a.
Comparison of nucleotide sequences.
b.
Comparison of structural features.
c.
Comparison of biochemical pathways.
b and c are both correct.
none of the above
Which of the following is an example of an epigenetic phenomenon?
Several proteins share amino acid sequences that mediate calcium binding.
Methylation of the DNA associated with a gene resulting in the transcription of that gene being inhibited over multiple cell generations.
A genetic mutation leads to an altered protein structure causing disease.
The actin gene is transcribed into an mRNA that is translated into the actin protein.
A change in a gene sequence causes a change in the phenotype of an organism.
Which statement about light microscopy is true?
A light microscope can generate contrast using interference of out of phase light.
The resolution of light microscopes is limited primarily by the magnification of the lens used.
Resolution is the only important aspect of visualizing cellular structures.
Light microscopy has the same resolving power as all types of microscopy.
none of the above
What is defined as the ability to see two neighboring points in a field as distinct entities?
revolution
magnification
resolution
tintinnabulation
aberration
If two parts of a specimen are not separated by sufficient distance, what happens?
a.
Magnification is impossible.
b.
diffraction is impossible
c.
the images of the two parts of the specimen cannot be resolved
d.
the images of the two parts of the specimens can be seen to be distinctly separated
a and b
Which of the following things directly determine resolution in microscopy?
a.
color of the specimen itself
b.
the wavelength of illumination light
c.
the numerical aperture of the objective
b and c can limit resolution
e.
the magnification power of the ocular lens
The method in which antibodies are conjugated to a fluorophore and used to determine the location within the cell of a specific protein is called ________.
immune surveillance
immunotherapy
polarization microscopy
immunofluorescence
differential interference contrast microscopy
You wish to measure calcium concentration changes in living cells. Which of the following microscopic techniques do you think would be most useful?
Transmission electron microscopy
scanning electron microscopy
Fluorescence microscopy using a calcium-sensitive indicator dye that is able to cross a living cell's plasma membrane.
none of the above
The absorbance of light by a compound and the subsequent release by that compound of some of the energy as longer, visible light wavelengths is known as _______.
fluorochrome
luminescence
fluorescence
fluorophore
phosphorescence
In which light microscope technique does a molecule absorb energy from light and glow with a bright color or colors against a dark background? The method is often used to localize specific molecules within a cell.
dark field microscopy
bright field microscopy
phase contrast microscopy
fluorescence
polarization microscopy
In a fluorescence microscope, ______-wavelength incident light is absorbed by the specimen and reemitted at a _______ wavelength.
long, longer
short, longer
short, shorter
long, shorter
medium, shorter
The resolution limit of a typical fluorescent microscope is ~200 nm. If two ribosomes that are 50 nm in diameter and 500 nm apart are labeled with a fluorescent antibody, what will you see?
You won’t be able to detect the ribosomes at all because they are below the resolution
limit of the microscope.
You won’t be able to detect them because you need an electron microscope to see such small objects.
You will be able to detect the ribosomes, but they will appear merged as a single spot.
You won’t be able to detect them because the wavelength of light is not short enough to resolve them.
none of the above
Which of the following conditions would result in the worst resolution in a light microscope?
Red light and 0.95 N. A.
Blue light and 0.95 N. A.
Blue light and 0.7 N. A.
Red light and 0.7 N. A.
Green light and 0.95 N. A.
What is the name of the fluorescent protein that is obtained from a jellyfish and can be used to follow a specific protein through the cell and reveal the dynamic activities in which the protein participates?
fluorescein
rhodamine
green fluorescent protein
phosphescein
verdine
How is green fluorescent protein (GFP) attached to a protein for which it serves as a label allowing that protein's dynamic activities to be tracked?
The GFP protein is chemically attached to the desired protein in vitro.
A RNA is produced by attaching the GFP mRNA to the mRNA of the desired protein.
GFP adheres specifically to the desired protein via weak interactions.
The coding region of the GFP gene is joined to the coding region of the gene of the protein being studied in an expression plasmid, using recombinant DNA technology.
GFP protein is attached to the coding region of the gene of the protein being studied.
You engineered a new gene which includes GFP fused to the cytoplasmic domain of a transmembrane protein. You then added a cardiac-specific promoter and incorporate this new gene into the genome of the mouse. When you examine cells from these mice in the fluorescent microscope:
You will see the fluorescence throughout the cytoplasm of all the cells of the mouse.
You will see the fluorescence throughout the cytoplasm of all cardiac cells in the mouse.
You will see the fluorescence from the protein in the membrane of all cardiac cells in the mouse.
You will see the fluorescence in the membranes of all the cells of the mouse.
all of the above will be seen
Which of the following is true of fluorescence microscopy?
Conventional fluorescent microscopy is useful for thicker specimens because fluorescence emitted throughout the illuminated specimen yields clear images.
Fluorescence microscopy is useful because it presents images in three dimensions.
Fluorescence microscopy overcomes resolution problems inherent in light microscopy.
Fluorescence microscopy can be used to view dead specimens only.
To view thicker specimens, a confocal microscope will yield the best image
Why does using a conventional microscope to view a whole cell in epifluorescence microscopy result in an image that is not very crisp?
a.
the specimen has a significant thickness, and thus multiple potential planes of focus
b.
looking at specimens in a normal light microscope damages the specimen
c.
light coming from parts of the specimen above and below the focal plane of interest interferes with the light coming from the part in focus
d.
such specimens have a single, large plane of focus
a and c
The confocal scanning light microscope produces an image of a _____ focal plane called a(n)_______situated within a much _______ specimen.
thick, optical section, thinner
thick, microtomal section, thinner
thin, optical section, thicker
thin, microtomal section, thicker
thin, optical section, wider
Why do electron microscopes provide much greater resolving power than light microscopes?
because more electrical power is involved in running an electron microscope
because electron beam wavelength is much shorter than that of visible light
because electron beam wavelength is much longer than that of visible light
because the numerical aperture is much larger in electron microscopes
because the numerical aperture is much smaller in electron microscopes
Which statement is true about electron microscopy?
Biological specimens can be alive during electron microscopy.
Scanning electron microscopy (SEM) cannot be utilized to examine the surface of objects.
To build the image, accelerated electrons are used instead of light.
The image formed in a scanning electron microscope is that of biological material itself.
All of the above statements are true.
A scientist is examining motile protozoa. She wishes to determine their direction of movement without the use of antibodies. Which of the following microscopic techniques is least likely to be useful?
phase-contrast microscopy
differential interference contrast microscopy
immunofluorescence microscopy
none will be useful
Why does both direct and indirect immunofluorescence provide remarkable image contrast?
a.
Antibodies are bigger than most proteins and thus easier to see in the light microscope.
b.
Antibodies absorb large amounts of light and are therefore more visible in the light microscope.
c.
Only the proteins bound by the antibody are visible because of the fluorescent label.
d.
All of the unlabeled materials remain invisible in the microscope because no fluorescent material is attached to them.
c and d are correct
You are examining the subcellular localization of a putative membrane protein using immunofluorescence microscopy. Which is a true statement about what you might expect?
If the antibody you are using was raised to a portion of the protein that is expected to be exposed to the cytoplasm, you will not need to permeabilize the membrane with detergent.
Although the lipid bilayer is ~ 4nm across, you would expect to observe an apparent structure ~ 200 nm across due to the resolution limit of light microscopy.
If the proteins are located 50 nm apart from each other, you will observe a dotted appearance of the membrane due to the separation of each labeled protein.
none are true
What do PALM and STORM refer to?
methods for generating antibodies.
a technique used by NFL running backs to block a defender and proceed rapidly up field.
microscopy methods that break the resolution limits of light microscopy by the sequential activation of isolated subsets of “switchable” fluorophores, generating a composite image map of the centers of their Airy disks.
microscopy method that uses pinholes to break the resolution limit of light microscopy.
microscopy method that uses pinholes to generate an “optical section” with reduced interference from light above and below the focal plane.
What is the name of the procedure in which proteins separated on a polyacrylamide gel are transferred with the application of a current to a nitrocellulose filter placed against the gel and subsequently identified by their interaction with specific antibodies?
southern blot
northern blot
eastern blot
western blot
east northeastern blot
Antibodies can be used to
visualize proteins in fixed and permeabilized cells
identify specific proteins on an immunoblot (western blot)
precipitate proteins from cellular extracts
identify and isolate organelle fractions
all are correct
Which technique depends on the use of antibodies made specifically against a particular protein (antigen)? The antibodies are then conjugated to a substance that makes them visible under the light or electron microscope.
immunolocalization
immunocompetence
immunization
immunofenestration
negative staining
Why is it a good idea to use cultured cells in research?
Cultured cells can be grown in large quantities.
A wide variety of different cell types can be grown in culture.
Many different cellular activities can be studied in cell culture, including endocytosis, cell movement, cell division, membrane trafficking, macromolecular synthesis
Cells can be made to differentiate in culture.
all of the above
Which would allow you to visualize the dynamics of an intracellular protein in a living cell?
using a fluorescently labeled antibody raised against the protein.
using phase contrast microscopy
using a gold-labeled antibody in combination with transmission electron microscopy
immunoprecipitating the protein from a cytosolic extract
none of these would achieve that goal
Which of the following is a technique used to isolate a particular organelle in bulk so that its function can be studied or so that an enzyme can be isolated from it?
differential interference contrast microscopy
differential & gradient centrifugation
affinity chromatography
selective precipitation
autoradiography
Under what set of circumstances will organelles not move to the bottom of a centrifuge tube in a centrifugal field?
a.
if the organelle is too small- say smaller than a ribosome
b.
if the organelle has very high fat content (fat/lipids are not very dense)
c.
if the organelle is less dense than the surrounding medium
d.
if the organelle is more dense than the surrounding medium
a, b, and c
Which is not true of phospholipids in a bilayer?
a.
Phospholipids are uniform in tail length, making the bilayer a uniform thickness.
b.
Phospholipids can rotate rapidly around their long axis.
c.
Phospholipids can easily move from one leaflet to the other leaflet by diffusion.
a and b are not true.
a, b, and c are not true
Phospholipid molecules in a membrane are arranged with their ____ on the exterior and their ____ on the interior of the bilayer.
Hydrophobic heads ... hydrophilic tails
Hydrophilic heads ... hydrophobic tails
Nonpolar heads ... polar tails
Hydrophobic tails ... hydrophilic heads
Hydrophilic tails ... hydrophobic heads
Which of the following increase bilayer thickness?
a.
Phospholipids with long, saturated fatty acyl chains.
b.
Phospholipids with short, unsaturated fatty acyl chains.
c.
Cholesterol interacting with lipids with shorter unsaturated chains.
d.
Certain cytosolic proteins.
a and c are correct
Of the following types of macromolecules, which one is not a component of cell membrane?
proteins
lipids
nucleic acids
carbohydrates
all are
Membrane lipids may not significantly do one of the following:
Spontaneously flip-flop from one membrane leaflet to the other.
Move laterally within one membrane leaflet.
Aggregate with membrane proteins to form lipid rafts.
Be unequally distributed in the two membrane leaflets.
Be present in varying amounts in different cellular membranes.
Which statement(s) is/are inaccurate?
a.
DNA is likely to have evolved as the first genetic material.
b.
RNA is capable of acting as an enzyme.
c.
DNA is utilized primarily as an informational molecule in cells.
d.
Epigenetic information is encoded in DNA sequence of cells.
a and d are inaccurate.
Which statement is not true of membranes?
The lipid bilayer is a flexible two-dimensional structure.
Membrane proteins can be embedded in the lipid bilayer.
Membrane proteins cannot easily leave the membrane once inserted.
Proteins can move easily from one side of the membrane to the other.
Some membrane proteins are able to diffuse laterally in the plane of the membrane.
Which of the following are functions of membranes?
a.
Provide a scaffold for biochemical reactions.
b.
Allows the cell to create and maintain an internal environment different from the exterior.
c.
Information storage.
a and b are correct
a, b, and c are correct
Which statement(s) about the non-uniformity of lipid bilayers is/are correct?
The two leaflets of the lipid bilayer making up the plasma membrane have identical composition.
A given leaflet of the bilayer of the plasma membrane is entirely homogeneous in its composition with no regions of differing composition.
All membranes in a particular eukaryotic cell type have the same composition.
a and b are correct
none is correct
The type of motion least common in biological membranes is:
Flip-flop diffusion of phospholipid from one monolayer to the other.
Lateral diffusion of individual lipid molecules within the plane of each monolayer.
Random motion of the fatty acyl side chains in the interior of the phospholipid bilayer
a and b are both uncommon
a and c are both uncommon
Specialized, cholesterol-rich regions of the membrane which possess a distinctive lipid composition may be called _______.
a.
microdomains
b.
life rafts
c.
lipid rafts
d.
cholesterolemias
a and c
Alpha helix formation
primary
secondary
tertiary
quaternary
protein domain or functional domains
A mutation in the DNA that changes the amino acid sequence always alters this
primary
secondary
tertiary
quaternary
protein domain or functional domains
A region of a protein that confers a specific function such as phospholipid binding
primary
secondary
tertiary
quaternary
protein domain or functional domains
The crystal structure of an individual protein informs this
primary
secondary
tertiary
quaternary
protein domain or functional domains
Which is true concerning protein synthesis?
Protein folding can start only after the entire polypeptide is synthesized.
Proteins can be made from either C-terminus to N-terminus or vice versa.
Proteins are directly synthesized using the information template in the DNA.
Proteins are completely folded inside the ribosome and then released.
Chaperones and chaperonins help some proteins fold to the right final conformation.
Which is true about chaperones like HSP70?
Chaperones protect cells from heat stress.
Chaperones help fold proteins into proper conformations.
Chaperones use ATP to help fold proteins
All of the above are true about chaperones.
none are true
What is the purpose of molecular chaperones like HSP70?
They bind to unfolded and misfolded RNA’s and help them regain their native structure.
They bind to unfolded and misfolded DNA’s and help them regain their native structure.
They bind to unfolded and misfolded carbohydrates and help them regain their native structure.
They transport secretory proteins into secretory vesicles.
none of the above
You are studying the cellular basis of protein synthesis. You have two proteins- protein A and protein B- and you know the following about them. Protein A adopts different conformations if it is translated in a test tube with purified ribosomes, mRNA, tRNA’s, and amino acids than if it is translated in vivo. When protein B is immuno-isolated from cells and denatured by heating in a test-tube, it spontaneously refolds into the right conformation. Which of the statements below is correct?
Protein A but not protein B likely folds with the aid of chaperones and chaperonins in cells.
Protein B but not protein A likely folds with the aid of chaperones and chaperonins in cells.
Both proteins require chaperones and chaperonins to fold properly.
Neither protein appears to require chaperones and chaperonins to fold properly.
Protein A and B are bound stably in a complex that you expect to last for 10’s of minutes. The Kd is 10-9 M. A regulatory protein binds to the complex, changing the Kd for the interaction between A and B to 10-7 M. Which describes the most likely ensuing events?
Nothing happens.
The complex becomes more stable, and will likely persist for hours.
The complex becomes less stable and is likely to fall apart more quickly.
A and B will likely collide with each other more often.
none is correct
The Kd for a binding interaction is 10-9 M. You set up a binding assay with a column
containing protein A. If a 10-7 M solution of protein B is incubated with the column, which statement best describes the situation?
Because the concentration of B is above the Kd, most of A is likely complexed.
Because the concentration of B is above the Kd, most of A is likely free.
Because the concentration of B is below the Kd, most of A is likely free.
Because the concentration of B is below the Kd, most of A is likely complexed.
none of the above is correct
Protein A binds to protein B with a high Kd, and to protein C with a low Kd. Which of the following statements is most likely to describe correctly the interactions of protein A with proteins B and C?
For a given and equal concentration of proteins B and C, protein A probably collides with protein B more often than protein C.
For a given concentration of proteins B and C, protein A probably collides with protein C more often than protein B.
For a given concentration of proteins B and C, protein A probably collides with both proteins equally often, but stays bound to protein B for a relatively longer time than it stays bound to protein C.
For a given concentration of proteins B and C, protein A probably collides with both proteins equally often, but stays bound to protein C for a relatively longer time than it stays bound to protein B.
Membrane proteins:
a.
Can associate with the membrane by virtue of covalent attachment to lipid groups.
b.
Can associate with the membrane by virtue of covalent attachment to carbohydrate moieties.
c.
Are composed of the same 20 fundamental amino acids found in soluble proteins.
d.
Can diffuse laterally in the membrane unless they are anchored.
a, c, and d are true
Peripheral membrane proteins:
Are covalently bound to membrane lipids.
Can be released from membranes only by treatment with strong detergent(s).
Can simultaneously have functional domains on both sides of the membrane.
Penetrate deeply into the lipid bilayer.
none is true
All of the following are true about integral membrane proteins except:
The transmembrane domain of a single pass integral membrane protein is made up of primarily polar amino acids.
They can associate with just one plane of the bilayer.
They can span through the lipid bilayer.
They can be immobilized in the membrane by interaction with molecules inside or outside the cell.
none of the above
What kind of membrane protein can be found at the extracellular or cytoplasmic surface of the bilayer, covalently linked to a lipid that is situated within the bilayer?
a.
Integral protein.
b.
Lipid-anchored protein.
c.
peripheral proteins
b and c are both correct
a and b are both correct
What kind of membrane protein penetrates into the hydrophobic part of the lipid bilayer?
a.
integral proteins
b.
lipid-anchored proteins
c.
peripheral proteins
b and c are correct
a and b are correct
What kind of membrane protein is found entirely outside the bilayer on either the extracellular or cytoplasmic surface? These proteins are associated with other membrane proteins by noncovalent bonds.
a.
integral protein
b.
lipid-anchored protein
c.
peripheral proteins
b and c are correct
a and b are correct
What kind(s) of membrane protein(s) does/do not typically have amino acids embedded within the hydrophobic core of the lipid bilayer?
a.
integral protein
b.
lipid-anchored protein
c.
peripheral proteins
a and b are correct
b and c are correct
A hydropathy/hydrophobicity plot is used to:
Determine the water-solubility of a protein.
Deduce the quaternary structure of a membrane protein.
Determine the water content of a native protein.
Extrapolate for the true molecular weight of a membrane protein.
Predict whether a given protein sequence contains membrane-spanning segments.
A membrane-associated protein is isolated and found to contain multiple alpha helices that contain many hydrophobic amino acids. This protein is most likely a:
Transmembrane protein that spans the membrane once.
Peripheral membrane protein.
Lipid-anchored protein.
Transmembrane protein that spans the membrane more than once.
none of the above
You determine the amino acid sequence of a novel protein. You find that it has a single alpha helical domain. The alpha helix has primarily hydrophobic amino acids on one face of the helix, and primarily polar (hydrophilic) amino acids on the other (an amphipathic helix). Which statement(s) is/ are false?
a.
This protein cannot exist as an isolated single pass transmembrane protein.
b.
This protein cannot be a membrane protein.
c.
This protein is almost certainly an isolated single pass transmembrane protein.
d.
This protein could be part of a multimeric protein complex that spans the bilayer to allow
transport of hydrophilic molecules through the lipid bilayer.
b and c are both false statements
What kind of membrane protein directly penetrates the hydrophobic part of the lipid bilayer?
a.
integral membrane protein
b.
lipid-anchored protein
c.
peripheral proteins
b and c
Which statement(s) about the non-uniformity of lipid bilayers is/are correct?
a.
All membranes in a particular eukaryotic cell type have the same composition.
b.
A given leaflet of the bilayer of a plasma membrane can vary in its composition from location to location.
c.
The two leaflets of the lipid bilayer making up the plasma membrane do not have identical composition.
b and c are correct
none is correct
The shortest α helix segment in a protein that can span a membrane bilayer will have about _____ amino acid residues.
5
20
50
100
200
What kind of protein structure is a beta sheet?
quaternary
primary
secondary
tertiary
none of the above
Which amino acids would most likely reside in the transmembrane alpha helix of a single pass transmembrane protein?
acidic amino acids
basic amino acids
hydrophobic amino acids
hydrophilic amino acids
alpha helices are not made of amino acids
Which of the following is a function of membranes?
compartmentalization
selectively permeable barriers
mediates intercellular interactions
helps cells respond to external stimuli
all of the above
You are studying membrane proteins in a cell, trying to deduce their topology. You treat the outside of the cell with trypsin, and a protein you are particularly interested in is partially digested and becomes smaller. Which statement below is true?
a.
The protein of interest cannot be protein 4.
b.
If the protein of interest is not reduced in size any further when the experiment is repeated in the presence of detergent, then it must be protein 2.
c.
If the protein of interest is not reduced in size any further when the experiment is repeated in the presence of detergent, then it must be protein 3.
all are true statements.
both a and b are true statements
You have a membrane protein such as CD2 fused to GFP so that the GFP is on the extracellular side of the membrane. What would you see when you looked in the fluorescence microscope after you added a protease to the cytoplasm that specifically cleaved (cut once, not digested) the protein between the end of its transmembrane domain and its intracellular domain?
a.
You would still see fluorescent membranes.
b.
You would see no fluorescence at all.
c.
You would see fluorescence in the cytoplasm.
d.
You would see fluorescence in the culture medium.
a and c are correct
Two cells with different cell-surface markers (labeled membrane proteins) are fused in the presence of polyethylene glycol (PEG). The cells are then placed at 0oC. What do you expect to observe about the individual cell markers?
The markers will evenly disperse throughout both membranes.
Only one marker will disperse while the other remains stationary.
Both sets of markers will not mix, but will migrate to opposite poles from one another.
The molecules will essentially remain where they are, with little migration.
The markers will be endocytosed by the fused cell and then redistributed as fused markers.
You are studying an integral membrane protein that you think binds to the cytoskeleton and is therefore immobile. Which choice is the correct set of FRAP and particle trajectory data shown below that you would expect to observe?
a.
A, II
b.
D, I
c.
B, II
a and c are likely to be observed
none of the above are correct
You have fused a mouse cell with a human cell. You then treated the resultant fused cell with antibodies to specific proteins, one of which is found on the mouse cells and one which is found on the human cells. The antibodies to the mouse protein are labeled with a green fluorescent dye, while the antibodies to the human protein are labeled with a red dye. What will the cell look like a long time after fusion?
a.
The cell will be half red and half green if neither protein is mobile.
b.
The red and green labels will be uniformly distributed across the entire membrane if both proteins are mobile.
c.
The red and green labels will be distributed in intermingled patches no matter what the mobility of the proteins is.
a and b are correct
b and c are correct
You express a recombinant membrane protein and put it into an artificial lipid bilayer. You tag it with a fluorescent antibody and measure its mobility using FRAP. You find that it is highly mobile. However, when you do the same experiment on a cell that naturally expresses that protein, you find that it is not mobile. Which explanation could account for these results?
a.
In the cell, the protein binds to the cytoskeleton.
b.
In the cell, the protein binds to other immobile membrane proteins.
c.
In the cell, the protein binds to other mobile membrane proteins.
a and b could
a and c could
You modify the DNA sequence for an integral membrane protein so that the cytoplasmic portions of the protein are deleted. When this DNA sequence is inserted in cells, what might be an effect you would see on the mobility of the modified protein in the membrane?
It moves much greater distances than the intact protein.
It move much smaller distances than the intact protein.
The intact protein was mobile, but now it does not move at all.
Integral membrane proteins are not inserted into the membrane so nothing can be learned about their mobility.
It now flip flops across the bilayer.
Which of the following statements about lipid rafts is false?
They can be regions enriched in lipids with saturated fatty acid chains.
They can be cholesterol rich regions.
They can have a different complement of membrane proteins than other regions of the bilayer.
They are slightly thicker than the rest of the bilayer.
all are correct
Molecules that are _______ and _______ will pass _______ through the lipid bilayer.
a.
small, hydrophilic, most easily
b.
small, hydrophobic, most easily
c.
large, hydrophobic, least easily
d.
large, hydrophilic, least easily
b and d are both correct
Which of the following molecules will diffuse slowest (or effectively not at all) across an artificial phospholipid bilayer?
A hydrophobic molecule such as glycerol.
Water.
Helium gas.
Calcium ion.
all will diffuse similarly
Which of the following would readily cross a lipid bilayer without the aid of a transport protein?
calcium ions
glucose
oxygen
amino acids
DNA
In osmosis, water always moves toward the ____ solution: that is, toward the solution with the ____ solute concentration.
isotonic, greater
hypertonic, greater
hypertonic, lesser
hypotonic, greater
hypotonic, lesser
If the volume of a cell decreases when it is placed in an aqueous solution, that solution is said to be __________ to the cell.
hypertonic
isotonic
hypotonic
subatomic
hypotonic
If the volume of a cell increases when it is placed in an aqueous solution, that solution is said to be __________ to the cell.
hypertonic
isotonic
hypotonic
subatomic
gin and tonic
Which of the following is most directly responsible for determining the value of the resting membrane potential of neurons and other cells.
voltage-gated Na+ channels
the Na+/K+ ATPase
K+ leak channels
the Na+H+ exchanger
none of the above
Which of the following is critical to maintaining the resting potential of neurons and other cells over time?
voltage-gated Na+ channels
GLUT transporters
the Na+K+ pump
the Na+H+ exchanger
none of the above
Consider a typical cell with the standard extracellular fluid (ECF) and intracellular fluid (ICF) conditions and a membrane potential of -75 mV. If the sodium conductance decreases:
The membrane potential will become more negative.
The membrane potential will become more positive.
There will be no change in the membrane potential.
Cannot be determined from the information given.
none of the above
Consider a typical cell with the standard ECF and ICF conditions and a membrane potential of -75 mV. If the potassium conductance decreases:
The membrane potential will become more negative.
The membrane potential will become more positive.
There will be no change in membrane potential.
Cannot be determined from the information given.
Consider a typical cell with the standard ECF and ICF conditions and a membrane potential of -75mV. If the extracellular concentration of K+ increases dramatically:
a.
The membrane potential will become more negative.
b.
The membrane potential will become more positive.
c.
There will be no change in the membrane potential.
d.
The Nernst potential for K+ would change.
b and d are correct
The K+ ion channel is a transmembrane protein complex that transports K+ ions across the plasma membrane. Based on what you learned in lecture about K+ channels and transmembrane proteins, which statements about the protein complex are likely true?
Hydrophilic faces of transmembrane helices will likely face the pore channel.
Most of the hydrophobic amino acids in the transmembrane alpha helices will interact with the lipid portion of the membrane.
The protein complex is likely to contain multiple amphipathic alpha helices.
The proteins will be glycosylated.
all of the above
A cell with the standard ECF and ICF composition with a membrane potential of -75mV will experience a change in membrane potential if which of the following conductances is changed? (Bonus: Cl-? What is ECl & driving force on Cl- here?)
K+
Na+
Ca2+
a and c
all of the above
In a standard cell under standard ionic conditions, if the membrane potential is -75 mV, which statement is correct?
Na+ is passively flowing into the cell through leak channels.
K+ is passively flowing out of the cell through leak channels.
The Na+/K+-ATPase must act to keep the ionic gradients from changing.
The net current moving across the membrane is zero
all are true statements
Which is a false statement about ion channels?
Ions can only move from the high concentration side to the low concentration side of the membrane.
Channels can be opened and closed by stimuli like ligands or changes in membrane potential.
Channels can be selective for the type of ion transported.
Ions can move in both directions through an ion pore.
Channel activity can be monitored via the patch clamp technique.
The specificity of the potassium channel for K+ over Na+ is mainly the result of the:
differential interaction of the ions with the selectivity filter protein.
hydrophobicity of the channel.
phospholipid composition of the channel.
presence of carbohydrates in the channel.
presence of cholesterol in the channel.
Based upon the patch-clamp tracing shown below, which one of the following conclusions can be drawn?
a.
There are at least two ion channels present in the membrane.
b.
The direction of ion flow across the membrane reverses each time the channel opens.
c.
The channel must be abnormal because there is variation in the period it remains open.
d.
The channel present must be a ligand-gated ion channel.
a and d are correct
A ligand-gated ion channel is:
A charged lipid in the membrane bilayer that allows ions to pass through.
A membrane protein that permits a ligand to pass through the membrane only when opened by the appropriate ion.
A membrane protein that permits ions to pass through the membrane only when opened by the appropriate ligand.
A molecule that binds reversibly to the membrane thereby allowing ions to pass through.
Always requires a second ligand to close the channel once it is opened.
In facilitated diffusion of an uncharged solute, the rate of transport is determined by the:
a.
the concentration gradient
b.
the electrical gradient across the membrane
c.
the number of transporters present
a and c
all of the above
Which of the following is NOT a characteristic of passive transport of molecules like glucose?
It requires binding of the molecule to be transported to the transporter.
It is specific for the molecule being transported.
The energy for transport is generated by the chemical gradient of the substance being transported.
The energy for transport is generated by ATP.
Transport of the substance requires a conformational change in the transporter.
Substance X is an uncharged polar molecule. It is found at higher concentrations inside of cells than outside. How might substance X enter cells?
a.
Diffusion through a channel.
b.
Diffusion directly through a lipid bilayer.
c.
Active transport.
b and c are correct
none of the above
An ion is at lower concentrations inside of cells than outside. How might the ion exit cells?
a.
Passive transport through a channel.
b.
active transport
c.
Because the ion is small, it will likely diffuse directly through the lipid bilayer.
a and b are correct. (think combined electrochemical gradients)
all of the above
Which statement correctly describes differences between carriers and channels?
a.
Channel proteins undergo pronounced conformational changes whereas carrier proteins do not.
b.
Carrier proteins undergo pronounced shape change whereas channel proteins do not.
c.
Channel proteins have a higher binding affinity for solutes than carrier proteins do
d.
Neither carrier or channel proteins readily bind to solutes.
both b and c are differences
The patch-clamp technique is used to:
measure the strength of an electrochemical gradient.
study the properties of individual neurotransmitters.
infuse different kinds of ions into of an axon.
study the properties of ion channels.
none of the above answers are correct
A “passive” membrane transport protein:
a.
Requires hydrolysis of ATP for transport to occur.
b.
Can only transport a solute ‘down’ a chemical gradient.
c.
Can be a channel or a diffusion facilitator (carrier).
d.
May be able to move an ion ‘up’ a concentration gradient if a membrane
potential exists.
c and d are correct
Which of the statements regarding the equilibrium distribution of solutes across membranes is false?
a.
The equilibrium distribution of a charged molecule across a membrane depends on the chemical gradient (concentration) and on the electrical gradient (membrane potential).
b.
Uncharged molecules are not sensitive to membrane potentials, so they will be at equilibrium only when at the same concentration on both sides of the membrane.
c.
Charged molecules can be at equilibrium even if the concentration inside and outside are different.
both a and b are false
all are true
Which of the following statements about the sodium-potassium pump is true?
It transports hydrogen ions out of the cell.
It transports 3 sodium ions out of the cell in exchange for 2 potassium ions.
It transports 2 sodium ions out of the cell in exchange for 2 potassium ions.
It transports 2 sodium ions out of the cell in exchange for 3 potassium ions.
it transports water directly out of the cell
In the mechanism of action of a V-type ATPase proton pump, the role of ATP is to:
Cause a proton to bind to a carbohydrate.
Cause a cell to take up protons by endocytosis.
Cause a cell to release protons by exocytosis.
Transfer protons to the inside of a cell.
Transfer protons to the outside of a cell or to the inside of a membrane bound compartment.
In the cotransport of glucose and sodium ions:
Glucose molecules are transported down their concentration gradient.
Sodium ions are transported down their concentration gradient.
The transport of glucose powers the transport of sodium.
ATP causes a conformational change in the carrier protein.
An antiport carrier protein is involved.
Lysosomal membranes contain a proton pump that utilizes the energy of ATP hydrolysis to pump protons into the lysosome, thereby maintaining the lumen at a low pH. Which statement is correct:
This is an example of secondary active transport.
This is an example of primary active transport.
This is an example of passive transport.
This is an example of a symporter.
This is an example of an antiporter.
Blocking the Na+/K+-ATPase in a typical cell will:
Immediately depolarize the cell to ENa
Cause the intracellular [K+] to increase over time.
Cause the intracellular [Na+] to increase over time.
Increase the driving force for Na+ - glucose cotransport
Cause the cell to immediately swell and explode. (it would slowly swell)
The Na/Glucose cotransporter can bring glucose into the cell when there is more glucose inside than outside. The energy input needed to drive the transport comes
Directly from ATP cleavage.
From the Na gradient.
From the glucose gradient.
From simple diffusion.
From phosphorylation of the transporter.
The type of membrane transport that uses ATP as the direct energy source is:
facilitated diffusion
passive transport
primary active transport
secondary active transport
simple diffusion
In the cotransport of glucose and sodium ions:
Glucose molecules are transported up their concentration gradient.
Sodium ions are transported up their concentration gradient.
The transport of glucose powers the transport of sodium.
ATP causes a conformational change in the carrier protein.
An antiporter is involved.
Which statement is FALSE regarding carrier and channel membrane transport proteins?
a.
Carrier proteins have to undergo larger shape changes to transport solutes than channels do.
b.
An individual transported ion remains associated with a channel for a much longer time than an individual solute remains associated with a carrier protein.
c.
For transport to work, all gates on an ion channel must be open, whereas for a carrier to work, at least one gate must always be closed.
a and b are false
all statements are false
The electrical signal of the action potential is first converted to a chemical signal at which step during synaptic transmission?
Influx of Ca2+ at presynaptic terminal triggered by voltage-gated Ca2+ Channels.
Binding of Ca2+ to receptors on synaptic vesicles.
Release of neurotransmitter into the synaptic cleft.
Binding of neurotransmitter to receptors on post-synaptic membrane.
none of the above
The permeability to ______ is the most important for generating the peak positive potential during an action potential.
sodium ions
calcium ions
chloride ions
all of the above
none of the above
As an action potential is initiated, the membrane is _____. This is caused by the _____ of _____ ions.
hyperpolarized, efflux, Na+
depolarized, influx, Na+
depolarized, influx, K+
hyperpolarized, influx, Na+
depolarized, efflux, Na+
What restores the ion gradients across a neuron’s membrane following many action potentials?
a.
The Na+/K+-ATPase
b.
A gated Na+ pump
c.
The gated Na+ channel
d.
The Na+ -glucose cotransporter
a and d
What happens after a sub-threshold depolarization?
a.
A full action potential.
b.
A partial action potential.
c.
No action potential.
d.
A proportional action potential.
b and d occur
The refractory period, when it is difficult or impossible to trigger another action potential, is caused by:
a.
Open voltage-gated K+ channels causing a brief, hyperpolarizing “overshoot”
b.
Closing of the voltage gated K+ ion channels
c.
Depolarization of the membrane
d.
Inactivation of the Na+ channel
a and d can contribute to the refractory period
Action potentials are transmitted in one direction because:
The sodium channels only open transiently.
The structural polarity of the neuron only allows signals to move in one direction.
The sodium channels have a period after opening when they are inactivated.
The K+ leak channel only opens transiently.
The calcium channel only opens when the membrane is depolarized.
Of the steps of the action potential listed, which is the fourth after a cell is initially depolarized by a current-passing electrode?
Voltage gated sodium channels open.
The membrane becomes repolarized.
The membrane rapidly depolarizes to near the sodium equilibrium potential.
Voltage-gated Na+ channels inactivate and Voltage-gated K+ channels begin to open.
Voltage gated K+ channels close.
Tetrodotoxin, an extremely potent poison produced by pufferfish, binds tightly to voltage-gated sodium channels and blocks the flow of sodium ions but does not affect either potassium or chloride ion channels. Tetrodotoxin directly blocks which phase of the action potential?
depolarization
repolarization
hyperpolarization
neurotransmitter release
the refractory period
In a typical cell, the purpose of the K+ channels in the plasma membrane is:
To allow K+ to flow out of the cell down its electrochemical gradient.
To allow K+ to flow into the cell during propagation of the action potential.
To allow K+ to flow into the cell down its electrochemical gradient.
To contribute to the depolarization of the cell during an action potential.
To prevent the forward propagation of the action potential.
Arrange the following events in the proper sequence they occur in the generation of an action potential, caused by the stimulation of a cell with a current-passing electrode:
I. K+ channels open and K+ rushes out of the cell. II. Na+ channels inactivate
III. Na+ channels open, membrane further depolarizes, and “threshold” reached. IV. The stimulus depolarizes the membrane toward threshold. V. Vm rapidly spikes toward ENa.
II, III, IV, I
III, IV, II, I
II, IV, III, I
I, II, IV, III
IV, III, V, II, I.
What helps the membrane potential return to a negative value in a neuron after an action potential has been triggered?
a.
A temporary rise in the permeability to all ions across the membrane.
b.
Opening of voltage-gated Na+ channels.
c.
Inactivation of voltage-gated Na+ channels.
d.
Opening of ligand-gated Na+ channels.
a and c are correct
Which of the following events cause an increase in cytosolic calcium ion levels?
a.
Interaction of an extracellular messenger with a G protein coupled receptor causing the activation of phospholipase C.
b.
Extracellular messengers signaling through receptor tyrosine kinases to activate members of the MAPK subfamily.
c.
Phosphorylation of transcription factors by activated Protein Kinase A.
d.
Action of GLUT transporters after insulin-stimulated membrane localization.
b and d
The activity of Ras GTPase is carefully regulated by two other proteins: Ras GEF (guanine nucleotide exchange factor) which stimulates binding of GTP by Ras, and Ras GAP (GTPase activating protein) which stimulates GTP hydrolysis by Ras. The activities of these regulatory proteins are, in turn, also regulated. Ras activity increases cell proliferation. Which of the following changes in GAP and GEF proteins might cause a cell to decrease proliferation?
a.
a nonfunctional GAP
b.
a permanently active GAP
c.
a permanently active GEF
d.
a nonfunctional GEF
b and d could cause a cell to decrease proliferation
A given protein is regulated by a protein kinase and a protein phosphatase, and is active when phosphorylated. Which would you expect to decrease the protein’s activity?
a.
Expression of a mutant, nonfunctional kinase that blocks the activity of the cell’s normal kinases (a “dominant-negative” kinase).
b.
Expression of a mutant, nonfunctional phosphatase that blocks the activity of the cell’s normal phosphatases (a dominant-negative phosphatase)
c.
Expression of a mutant, hyperactive kinase.
b and c would both decrease the protein’s activity.
None of the above would decrease the protein’s activity.
Place the following events in the proper order.
1 – Cyclic AMP activates one or more cellular signaling proteins.
2 – Gα-subunit with its attached GTP activates the effector adenylyl cyclase.
3 - Conformational change in the Gα subunit causing a decreased affinity for the Gβγ subunit.
4 – Production of a second messenger, like cAMP.
5 - Replacement of GDP by GTP on the Gα after interaction with an activated GPCR.
6 - Dissociation of Gα from the G protein complex.
4–1–2–6–5–3
5–6–3–2–4–1
5–3–6–2–4–1
5–3–6–4–2–1
1–5–2–4–3–6
Increasing the activity of vesicular H+-ATPases would:
a.
Increase pH inside of vesicles.
b.
Decrease pH inside of vesicles.
c.
Increase the pH of the cytoplasm.
d.
Decrease the pH of the cytoplasm.
b and c
The proteasome is a macromolecular machine that:
a.
Synthesizes proteins in the cell.
b.
Degrades proteins in the cell.
c.
Recognizes proteins that are poly-phosphorylated by Uber kinases.
d.
Recognizes proteins that are poly-ubiquitinated by E3-Ubiquitin ligases.
b and d
In an unstimulated cell, NF-kB is localized in the cytoplasm, but in response to stress signals, NF-kB enters the nucleus. What accounts for this behavior?
a.
NF-kB is frightened, and runs into the nucleus.
b.
NF-kB has a Nuclear Localization Sequence (NLS) that allows it to enter the nucleus; in the absence of stress signals this sequence is hidden due to an interaction with a sequestering protein.
c.
Stress signals lead to poly-ubiquitination of the sequestering protein.
d.
Cytoplasmic NF-kB is degraded by the proteasome, and then re-synthesized in the nucleus.
b and c
Which of the following are true regarding Receptor Tyrosine Kinases:
a.
They require dimerization for activation.
b.
They are activated by secreted ligands.
c.
Activated RTKs in a dimer “cross-phosphorylate” each other on Tyrosine residues.
d.
Activated RTKs allow the recruitment of SH2 domain containing proteins.
all of the above are true
