Praxis Biology

Biology Praxis - Molecular & Cellular Biology

By E James

Biological Molecules

• Atomic structure

• Chemical bonding

• Organic and inorganic molecules

• Properties of water

• Macromolecules

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• Chemical structures

• Chemical and physical structures

• Thermodynamics

• Anabolic and catabolic reactions

• Oxidation-reduction reactions

• Enzymes​

• Regulation

Multiple Choice

If the atomic number of a neutral atom is 6, how many protons and electrons does the atoms have?

• 0 protons and 6 electrons

• 3 protons and 3 electrons

• 6 protons and 0 electrons

• 6 protons and 6 electrons

​The atomic number of this atom is 6, so it must have 6 protons. For the atom to be neutral, it must have the same number of protons and neutrons.

​

The correct answer is 6 protons and 6 electrons.

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Multiple Choice

The mass number of an atom is 23, and its atomic number is 11. How many protons, electrons, and neutrons does this atom have?

• 11 protons, 11 electrons, and 12 neutrons

• 11 protons, 11 electrons, and 1 neutron

• 11 protons, 1 electrons, and 11 neutrons

• 6 protons, 5 electrons, and 12 neutrons

The atomic number is the number of protons, so this atom has 11 protons.

An atom is neutral, an ion is charged; since this is an atom, ​the number of protons and the number of electrons are equal so this atom has 11 electrons.

The atomic mass is the sum of the number of protons and the number of neutrons . To determine the number of neutrons subtract the number of protons from the total mass. 23 - 11 = 12

​Correct answer: 11 protons, 11 electrons, and 12 neutrons​

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Multiple Choice

Which of the following describes an atom that has donated an electron to become a positively charged particle?

• anion

• cation

• compound

• molecule

An atom that loses an electron becomes a positively charged ion called a cation.

​

An anion is a negatively charged particle due to gaining electrons.

A compound​ is composed of two or more different atoms joined together.

A molecule is composed of two or more atoms.​

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​

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Multiple Choice

A carbon atom has four electrons in its valence shell, while a hydrogen atom has one electron in its valence shell. How many atoms of hydrogen can be covalently bonded to carbon?

• two

• three

• four

• five

The goal of chemical bonding is to complete the outer shell. In order to accomplish this, carbon needs four more electrons to get to a total of eight. Hydrogen needs to gain one more to get to two.​

Therefore, carbon needs to bond with four ​hydrogen atoms.

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Two or three would not be enough and five is too many.​

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Multiple Choice

Which of the following is an organic molecule?

• CO₂

• CH₄

• NH₃

• H₂

By definition, an organic molecule contains atoms of both carbon and hydrogen. So CH₄ is the correct answer.​

​

CO₂ - no hydrogen

NH₃ and H₂ - no carbon​

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Multiple Choice

Which of the following properties of water causes water droplets to form beads on surfaces, such as on a leaf?

• adhesion

• specific heat

• surface tension

• ability to dissolve substances

Surface tension​ pulls together the molecules on the surface of water, forcing them to form a bead.

​

Adhesion accounts for water's attraction to other types of molecules.​

The specific heat ​of water is high due to the hydrogen bonds formed between adjacent water molecules. Water heats slowly but maintains its temperature longer.

Water is often called the universal solvent because its polarity enables it to dissolve other polar substances.​

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Multiple Choice

Which of the following bonds gives rise to the properties of water that make it essential for life?

• the ionic bonds between water molecules

• the ionic bonds within a water molecule

• the hydrogen bonds between water molecules

• the hydrogen bonds within a water molecules

The hydrogen bonds that form among water molecules hold these molecules together tightly and influence all the important properties of water.

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Water moleules do not bond to each other through ionic bonds.

Hydrogen atoms are bound to the oxygen atom in water by covalent bonds.

Hydrogen bonds form between (and within) polar molecules.​

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Multiple Choice

Proteins are built from which of the following monomers?

• monosaccharides

• nucleotides

• amino acids

• fatty acids

Amino acids are the building blocks of proteins.

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Monosaccharides are the monomers of carbohydrates.

Nucleotides are the monomers of nucleic acids.

Fatty acids and the monomers of lipids.​

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Multiple Choice

Which of the following scenarios would most likely result in a "membrane potential"?

• The concentration of K⁺ inside the cell is the same as the concentration H⁺ outside the cell.

• The concentration of K inside the cell is the same as the concentration of O outside the cell.

• The concentration of K inside the cell is greater than the concentration of K outside the cell.

• The concentration of K⁺ inside the cell is greater than the concentration of K⁺ outside the cell.

Membrane potentials generally form in response to differences in the concentration of a charged particle, an ion, across a cell membrane.

So the correct answer is:

The concentration of potassium ions inside the cell is greater than the concentration of potassium ions outside the cell.

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The other options would not create a difference in charge across the membrane.​

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Multiple Choice

Which of the following statements about thermodynamics explains why energy is required to move a hydrogen atom against a chemical gradient?

• The 1st law of thermodynamics states that energy can neither be created or destroyed.

• The 2nd law of thermodynamics states that energy must be conserved.

• The 1st law of thermodynamics states that entropy increases.

• The 2nd law of thermodynamics stated that entropy increases.

Without an input of energy, a hydrogen atom will move to areas of lower (not higher) concentration​ because this movement increases the entropy of the system.

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The conservation​ law refers to the amount of energy in the universe, whereas the question refers to the movement or transformation of energy.

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The 1st law of thermodynamics, not the 2nd law of thermodynamics, refers to the conservation of energy.

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The 2nd law of thermodynamics, not the 1st law of thermodynamics, refers to the tendency for the entropy of a system to increase.​

​

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Multiple Choice

Which is an anabolic reaction?

• 6CO₂ + H₂O -> C₆H₁₂O₆ + 6O₂

• 2H₂O₂ -> 2H₂O + O₂

• C₊H₁₂O₆ + 6O₂ -> 6C0₂ + 6H₂O

• 2NH₃ -> N₂ + 3N₂

​The equation for photosynthesis show sugars are synthesized from carbon dioxide and water. This is an anabolic reaction, which uses energy to build complex molecules.

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All of the other reactions are catabolic reactions, which release energy by breaking bonds.​

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Multiple Select

If the iron ion has an oxidation number of +3, which TWO of the following are true?

• Fe⁺³ can donate three electrons to form a chemical bond

• Fe⁺³ can accept an electron to form a chemical bond.

• Fe⁺³ is an oxidizing agent.

• Fe⁺³ is a reducing agent.

The iron ion can accept or gain three electrons from another molecule.

When the iron ion accepts electrons from another molecule, it becomes reduced, and the other molecule becomes oxidized, which makes the iron ion an oxidizing agent.

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An oxidation number of +3 indicates that the iron ion can gain three electrons.

Reducing agents lose, or donate, electrons to another molecule in a redox reaction.​

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Multiple Choice

Which of the following terms describes a molecule that inhibits the function of an enzyme by altering the shape of the enzyme's active site?

• coenzyme

• repressor

• activator

• substrate

A repressor molecule inhibits an enzyme from binding its substrate(s) by binding to the enzyme and changing the shape of the active site.​

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A coenzyme binds an enzyme to form an active enzyme that can catalyze a chemical reaction.

An activator binds an enzyme and changes the shape of the active site in a way that it can recognize and bind to the substrates.

The substrate bonds to the enzyme's active site during the normal functioning of an enzyme.​

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Multiple Choice

Enzyme X catalyzes the metabolism of Amino Acid G. When Amino Acid G is bound to Enzyme X, the affinity for Amino Acid G increases at the other active sites on Enzyme X.

This scenario describes ____.

• competitive inhibition

• noncompetitive inhibition

• positive cooperativity

• negative cooperativity

In positive cooperativity, when the substrate binds one of the active sites on an enzyme, the affinity for the substrate at the other active sites increasaes.

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Competitive inhibition is a type of feedback inhibition, which represses the action of the enzyme.

Noncompetitive inhibition is a type of feedback inhibition, which represses the action of the enzyme.

In negative cooperativity, a substrate bound to one active site on the enzyme decreases the affinity for the substrate at the other active sites on the enzyme.​

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Biochemical Pathways

• Photosynthesis

• ​Cell Respiration

  • ​Krebs cycle

  • electron transport chain

• Chemosynthesis

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Structure and Function of Cells​

• Organelles

• Prokaryotic and Eukaryotic Cells

• Plant vs Animal Cells

• Cell membrane​

• Cytoskeleton​

Multiple Choice

Why do some photosynthetic structures, like leaves, appear green?

• The epidermis of the leaf absorbs red and blue light.

• The epidermis of the leaf absorbs green light.

• The chlorophyll of the leaf absorbs red and blue light.

• The chlorophyll of the leaf absorbs green light.

Light passes through the epidermis and strikes the pigment chlorophyll, which absorbs the wavelengths of light that humans see as red and blue and reflects the wavelengths of light that the human eye perceives as green.

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Correct answer:

The chlorophyll of the leaf absorbs red and blue light.​

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Multiple Choice

The Calvin cycle produces one molecule of glucose from which of the following three molecules

• ATP, NADPH, & O₂

• ATP, NADPH, & CO₂

• CO₂, H₂O, & ATP

• CO₂, H₂O, & O₂

Glucose is produced from CO₂ by the energy stosred in ATP and the hydrogen atoms associated with NADPH.​

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​Although ATP and NADPH are substrates of the Calvin cycle, O₂, is not . O₂ is a product oh photosystem II.

ATP and CO₂ are needed for the Calvin cycle, but H₂O is not; H₂O is a substrate is photosystem II.​

When H₂O is split in photosystem II, O₂ is released; in contrast CO₂ is a substance in the Calvin cycle.​

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Multiple Choice

In the balance chemical equation for cellular respiration, C₆H₁₂O₆ + 6O₂ -> 6CO₂ + 6H₂O, which moleculel is oxidized and which is reduced?

• C₆H₁₂O₆ is oxidized and CO₂ is reduced

• C₆H₁₂O₆ is reduced and CO₂ is oxidized

• O₂ is oxidized and H₂O is reduced

• O₂ is oxidized and C₆H₁₂O₆ is reduced

In cellular respiration, glucose serves as the electron donor, and oxygen serves as the final electron acceptor.​

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• Although glucose is oxidized, carbon dioxide is the product of cellular respiration.

• ​Oxygen is the final electron acceptor in cellular respiration so it is reduced. Water is the product of the reduction of oxygen.

• ​Oxygen being oxidized and glucose being reduced is the exact opposite.

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Multiple Choice

Which of the following molecules is the final electron acceptor in lactic acid fermentation?

• NAD⁺

• NADPH

• pyruvate

• O₂

Pyruvate is reduced during fermentation;​ therefore, it serves as the final electron acceptor.

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NAD⁺ is produced during fermentation and recycled into glycolysis.​

NADPH is oxidized during fermentation.

Fermentation usually occurs in the absence of oxygen.​

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Multiple Choice

Which of the following is NOT a similarity between photosynthesis and chemosynthesis?

• The electron donor in photosynthesis and chemosynthesis is water.

• The final electron acceptor in photosynthesis and chemosynthesis is carbon dioxide.

• Carbon dioxide is reduced to sugars in both processes.

• An inorganic molecule is a product of both processes.

​Water is the electron donor in photosynthesis, but an inorganic molecule like hydrogen sulfide is the electron donor in chemosynthesis. The correct answer is A.

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In photosynthesis and chemosynthesis, carbon dioxide is reduced to organic molecules like sugars, so this is a similarity between the two processes.

The reduction of carbon dioxide to sugars is a similarity between two processes.

Oxygen is produced during photosynthesis. In chemosynthesis, when a molecule like hydrogen sulfide serves as an electron donor, s​ulfur is produced.

Multiple Choice

Which of the following is NOT bound by a cellular membrane?

• nucleus

• chloroplast

• ribosome

• lysosome

Ribosome can be found freely in the cytoplasm and not bound by a cellular membrane.

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All of the other organelles are bound by a cellular membrane.​

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Multiple Choice

Which feature distinguishes prokaryotic cells from eukaryotic cells?

• division by binary fission

• the presence of DNA

• an organized cell membrane

• a rigid cell wall

Binary fission is characteristic of all prokaryotic cells but dow not occur in eukaryotic cells.

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All of the other choices can be found in both prokaryotic and eukaryotic cells.​

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Multiple Select

Select the TWO metabolic reactions that occur in plants.

• 6CO₂ + 6H₂O -> C₆H₁₂O₆ + 6O₂

• C₆H₁₂H₆ + 6O₂ -> 6CO₂ + 6H₂O

• N₂ + 8H⁺ + 8e^- -> 2NH₃ + H₂

• CO₂ + 4H₂S + O₂ -> CH₂O + 4S + 3H₂O

​The first choice is photosynthesis and is definitely a metabolic pathway common to plant cells.

The second choice is cellular respiration. Plants synthesize sugars via photosynthesis and, like other eukaryotic cells, extract energy from those sugars through cellular respiration and store the energy as ATP.

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The third choice is nitrogen fixation​ - when prokaryotic cells convert atmospheric nitrogen into ammonia, which plants use.

The last choice is a chemosynthetic​ reaction carried out by hydrothermal bacteria.

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Multiple Choice

Which of the following is true about the phosolipids that make up the cellular membrane?

• The phosphate leads of the bilayer interact with the extracellular environment and the cytoplasm.

• The phosphate heads of the bilayer interact with the cytoplasm only.

• The fatty acid tails of the bilayer interact with the extracellular environment and the cytoplasm.

• The fatty acid tails of the bilayer interact with the cytoplasm only.

The bilayer forms with the polar heads on the outside and the fatty acid tails on the inside; therefore, the polar heads are exposed to both the external environment of the cell as well as the cytoplasm.

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Multiple Choice

Which of the following protein fibers of the cytoskeleton are primarily responsible for the crawling movement of cells such as white blood cells?

• flagella

• intermediate filaments

• microtubles

• microfilaments

Microfilaments are made of actine, and it is the arrangement of microfilaments that allows for crawling - a phenomenon observed in inflammation, clotting, wound healing, and in the spread of cancer cells.

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Flagella are rich in microtubules, these structures protrude from the cell surface.

Intermediate filaments are thick, ropelike fibers that give the cell strength.

Microtubules can play a role in movement, microfilaments drive the crawling movement of cells like white blood cells.​

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• Stages of cell cycles

• Cell cycle checkpoints

• Mitosis

• Meiosis

Cell Cycle and Cell Division

• Selective permeability

• Movement of water​

• Endocytosis & exocytosis

• Intercellular communication​

​Cell equilibrium and Communication

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Multiple Choice

Select the true statement.

• Sodium ions are pumped into the cell; potassium ions are pumped out of the cell.

• The formation of ATP drives the action of the sodium-potassium pump.

• The sodium-potassium pump uses facilitated diffusion to move ions across the membrane.

• The sodium-potassium pump is powered by the oxidation of ATP.

Hydrolysis of one molecule of ATP drives one cycle of the sodium-potassium pump and moves three ions of sodium versus two ions of potassium.​ Correct answer: D

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Sodium ions are pumped​ out of the cell; potassium ions are pumped into the cell.

ATP is broken down to provide energy for active transport in the pump.

Facilitated diffusion is a form of passive diffusion that does not require energy inputs.​

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Multiple Choice

Select the true statement.

• Facilitated diffusion is the movement of molecules from areas of low to high concentration.

• Small molecules may move through the membrane by the process of simple diffusion.

• ATP drives the facilitated diffusion of molecules across the cell membrane.

• The movement of molecules by facilitated diffusion does not require a carrier protein.

​In simple diffusion, small molecules pass through the membrane without the help of embedded proteins. Correct answer: B​

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In facilitated diffusion, molecules move down their concentration gradient.

ATP drives active transport, not diffusion.

A carrier protein is required to move molecules across the cell membrane in facilitated diffusion.​

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Multiple Select

Which TWO of the following statements are true of a solution with a high water potential?

• The solution consists of more free water molecules than a solution with a low water potential.

• The solution consists of fewer free water molecules than a solution with a low water potential.

• The concentration of solutes is high compated to a solution with a low water potential.

• The concentration of solutes is low compared to a solution with a low water potential.

A high water potential means a solution has a lot of free water molecules.

A high water potential means a solution has a lot of free water molecules, indicating that the solution has low osmotic concentration.

Correct choices: A and D​

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A solution with a high water potential has many free water molecules.

A solution with high water potential has many free water molecules; therefore, the osmotic concentration of the solution is low.​

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Multiple Choice

What will happen when a cell is placed in a hypotonic solution?

• Water will move from outside the cell to inside the cell.

• Water will move inside the cell to outside the cell.

• Solute will move from outside the cell to inside the cell.

• Solute will move from inside the cell to outside the cell.

The ​solute concentration inside the cell will be higher than the solute concentration of a hypotonic solution; therefore, water moves into the cell.

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hyper - more

hypo - lower

iso - equal​

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Multiple Choice

Which of the following facilitates exocytosis in a cell?

• carrier proteins

• vesicles

• pores in the cell membrane

• cell-surface receptors

Secretory vesicles carry the cellular material that needs to be excreted​ from the cell; these fuse with the cell membranes.

​

Carrier proteins are necessary for facilitated diffusion.

The pores through which materials are released from the cell form when the secretory vesicles fuses with the cell membrane.

Cell surface receptors mediate the interaction between the cell membrane and the large materials taht are brought into the cell via endocytosis.​

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Multiple Choice

During labor, the body releases oxytocin, a hormone that speeds up the time between contractions. AS contractions increase, more oxytocin is released, which speeds up the contraction, resulting in the release of more oxytocin. This cycle continues until the baby is born.

This phenomenon is an example of ___.

• positive feedback

• negative feedback

• homeostasis

• signal transduction

The release of oxytocin ultimately leads to the release of more oxytocin, which is the definition of positive feedback.​

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If this process was regulated by negative feedback, then an increase in oxytocin would ultimately lead to a decrease in oxytocin.

Homeostasis​ is the maintenance of a stable internal condition.

​Signal transduction is a cascade of chemical reaction triggered when an extracellular signaling molecule binds a receptor on the cell membrane (or occassionally inside the cell.)

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Multiple Choice

A cell spends most of its life in which phase?

• G₁ phase

• S phase

• G₂ phase

• M phase

In the G₁ phase, cells do much of the growing, carrying out processes like metabolism and gene expression.

​

In the S phase, the cell synthesizes new DNA.

in the G₂ phase, chromosomes condense, mitochondria are replicated and microtubules are produced.

The M phase stands for mitosis.​

Multiple Choice

Apoptosis prevents a cell from transitioning to which phase of cell division?

• G₁ phase

• S phase

• G₂ phase

• M phase

Apoptosis destroys damaged cells at the G₂ checkpoint before they enter the M phase.

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There is no checkpoint before the G₁ phase.

Cells that fail at the G₁ checkpoint often go into a G₀ phase, which is a stasis phase.

​There is not checkpoint between S and the G₂ phase.

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Multiple Choice

At the end of which phase are chromosomes first clearly visible under a light microscope?

• interphase

• prophase

• metaphase

• anaphase

The DNA replicated during interphase condenses into chromosomes, which are clearly visible under a light microscope by the end of prophase.​

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The DNA just begins to condense into chromosomes during interphase.

The chromosomes align at the center of the cell during metaphase.

Sister chromatids are separated and drawn to opposite poles of the cell during anaphase.​

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Multiple Choice

During which phase does the nucleolus reappear?

• prophase

• metaphase

• anaphase

• telophase

A new nuclear envelope, hence a new nucleus and nucleolus forms in telophase.

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Prophase prepares the sister chromatids for binding by the spindle fibers.

Metaphase prepares the sister chromatids for separation.​

Anaphase prepares the daughter chromosomes for the division of the ctyoplasm.​

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Multiple Choice

Select the process that occurs during anaphase I of meiosis.

• The spindle pulls homologous chromosomes to either side of the cell.

• The spindle pulls sister chromatids to either side of the cell.

• Chromosomes align along the metaphase plate.

• Two diploid (2n) daughter cells are formed.

It is the separation of homologous chromosomes in meiosis I that leads to the formation of four diploid (1n) cells in meiosis II.

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The spindle pulls sister chromatids to either side happens in anaphase of mitosis.

Chromosomes align along the metaphase plate happens during metaphase in both mitosis and meiosis.​

Two diploid daughter cells are formed only occurs in mitosis.​

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Multiple Choice

Select the true statement.

• The process of meiosis includes one nuclear division.

• Recombination occurs during the first phases of meiosis.

• Chromosomes replicate prior to meiosis II.

• Meiosis results in four diploid (2n) daughter cells.

Recombination, the chromosome swapping that happens between homologous chromosomes, occurs in prophase I.

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Mitosis​ involves only one nuclear division; meiosis involves two nuclear divisions.

No DNA replicates occurs between meiosis I and meiosis II.

Meiosis results in four haploid (1n) daughter cells.​

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• RNA Transcription

• mRNA Processing

• Translation

• Regulation of Gene Expression

​Protein Synthesis

• Structure of Nucleic Acids

• DNA vs RNA

• Chromosomes

• DNA Replication​

​Nucleic Acids

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Multiple Choice

Select the nucleotides that have two-ringed nitrogenous bases.

• adenine and thymine

• cytosine and thymine

• adenine and guanine

• guanine and cytosine

Adenine and guanine are made from a twp-ringed, nitrogen-containing organic molecule.​

​

Adenine and thymine are complementary bases, so one is 2-ring and the other is a single ring.

Cytosine and thymine are both single-ringed bases.

Guanine and cytosine and complementary bases.​

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Multiple Select

Select all of the true statements.

• Hydrogen bonds form between A-T and G-C bases.

• A sequence of RNA will not contain T bases but will contain U bases

• RNA is single stranded.

• RNA is double stranded.

RNA does not carry thymine bases but does carry uracil bases.

RNA is a long chain of nucleotides and it is single-stranded.​

​

​

A-T and G-C are complementary base pairs that form in DNA.

RNA does not form a double helix; DNA does.​

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Multiple Choice

All of the following properties are shared by chromosomes in an individual somatic cell EXCEPT

• size.

• shape.

• location of the centromere.

• presence of telomeres.

All chromosomes have telomeres.

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A chromosome will vary in size depending on the length of is DNA molecule.

Although all chromosomes are generally linear, chromosomes do differ in shape.

The centromere is not always located in the middle of a chromosome.​

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Multiple Choice

If a strand of DNA has the base sequence 5' AAGCCCTATAC 3', the corresponding base sequence in the complimentary strand of DNA would be

• 3' UUCGGGAUAUG 5'

• 3' TTCGGGATATG 5'

• 3' GTATAGGGCTT 5'

• 3' GUAUAGGGCUU 5'

The orientation of a complementary strand of DNA is the opposite of its template and has the complementary base pairs.

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DNA does not contain uracil so the first and last choices cannot be correct.

The base pairs in the third choice are correct but in the wrong orientation.​

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Multiple Choice

DNA is relicated during which cell phase?

• C phase

• M phase

• S phase

• G₁ phase

The S stands for synthesis so this is the stage of interphase when DNA is replicated.

​

Cytokinesis is the last phase of mitosis when the cytoplasm is split between two daughter cells. There is not a C phase.

M phase is mitosis and the DNA is already replicated.

G₂ phase is the last phase of interphase.​

​

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Multiple Choice

Select the steps of the processes of transcription and translation.

• RNA -> protein -> DNA

• DNA -> protein-> RNA

• protein -> DNA -> RNA

• DNA ->RNA -> protein

DNA must first be transcribed into a special kind of RNA before that piece of RNA can be translated into protein.

​

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Multiple Choice

If a strand of DNA has the base sequence 5' AAGCCCTATAC 3', the corresponding base sequence on the mRNA transcript would

• 3' UUCGGGAUAUG 5'

• 3' TTCGGGATATG 5'

• 3' GTATATGGGCTT 5'

• 3' GUAUAGGGCUU 5'

RNA polymerase transcribes DNA in the 5' to 3' with the complementary bases.

​

RNA does not have thymine so the 2nd and 3rd choices are not correct.

The base pairs are correct but oriented in the wrong direction.​

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Multiple Choice

RNA processing in a eukaryotic cell occurs in which of the followiong location?

• ribosomes

• cell membrane

• cytoplasm

• nucleus

DNA is transcribed into a primary RNA transcript in the nucleus of a eukaryotic cell; here, the RNA is processed into a nature length of mRNA​.

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Multiple Choice

The process of removing introns from the pre-mRNA molecules in a eukaryotic cell is called

• ligation

• splicing

• polyadenylation

• initiation

​Splicing is the process whereby the introns are removed from the pre-mRNA.

​

Ligation is the joining of exons after the introns have been removed.

Polyadenylation is the addition of a long stretch of A bases to the 3' end of the pre-mRNA transcript.

Initiation is the step in transcsription when RNa polmerase binds the promoter of a gene.​

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Multiple Choice

Which of the following is the site at which the tRNAs are released from the ribosome?

• P site

• E site

• elongation site

• termination site

The E site is where tRNAs exit the ribosome.

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The P site is where new amino acids are joined to the previously inserted amino acid by a peptide bond.

Elongation is a process in which tRNAs bring​ their amino acids to the mRNA and bind to the codon.

A stop codon at the termination site signals the end of translation.​

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Multiple Choice

At an ACU codon, the amino acid threonine will be inserted in the growing polypeptide. What is the anticodon of the tRNA molecule that brings threonine to the ribosome?

• ACU

• UCA

• TGA

• UGA

​Anticodons and codons are complementary so UGA is the correct answer.

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Multiple Choice

Select the true statement.

• Enhancers are a form of promoter is a bacterial cell.

• Enhancers are enzymes that help in the transcription of DNA.

• Enhancers are located at a distance to the promoter.

• Enhancers are proteins that bind and activate RNA polymerase.

Enhancers can exert their influence at a distance because ther DNA bends to form a loop.

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​In bacteria, transcription is initiated at a promoter, not an enhancer.

Enhancers are sections of DNA, not enzymes or proteins.

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Multiple Choice

In both prokaryotes and eukaryotes, the regulation of gene expression most commonly occurs at which point?

• post-transciption

• post-translation

• transcription

• translation

Most gene expression is controlled at the initiation of transcription.​

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​Cell Differentiation and Specialization

• Differential Gene Expression

• Stem Cells

Genetic Mutations

• Cause of Mutations

• Types of Mutations​

​

​Studying Celluar Processes

• ​Gel Electrophoresis

• Microscopy

• Spectrophotometry

DNA Technologies

• DNA Sequencing and PCR

• Gene Therapy

• Cloning

• Genetically Engineered Cells​

Multiple Choice

Cell A and Cell B carry the same genes, including Gene 1, Gene 2, Gene 3, and Gene 4. Which of the followiong scenarios best describes differential gene expression?

• Cell A expresses all four genes; Cell B expresses all four genes.

• Cell A expresses only Gene 1 and 2; Cell B expresses only Genes 1 and 2

• Cell A expresses only Gene 3 and 4; Cell B expresses only Gene 3 and 4

• Cell A expresses only Gene 1 and 2; Cell B expresses only Genes 3 and 4

Differential gene expression describes how specialized cells transcribe and translate only certain genes despite carrying all of the same genes.

Therefore the correct choice would be for one cell to express some genes while a different cell would express different genes.

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I explain this to my students by asking them if they want to grow a toe out o​f their back of a fingernail out of their eye. All cellls originate from the same cell so they are capable of expressing the same genes but they only express the ones for their specific function.

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Multiple Choice

If a fertilized egg can develop into every cell in an organism, it is classified as which type of cell?

• totipotent cell

• pluripotent cell

• multipotent cell

• unipotent cell

If a cell can differentiate to produce all the cells of an organism, then that cell is totipotent.​

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Most of the cell types of an organism are produced by a pluripotent cell; but not all cell types are produced.

Only similar or related cell types are produced by multipotent​ cells.

A unipotent cell will only differentiate into one cell type.​

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Multiple Choice

Ultraviolet light is known to cause _____.

• crossing over

• translocation

• recombination

• a mutation

Ultraviolet (UV) radiation is a known mutagen, which means it can cause a mutation.

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All the other processes are cellular processes.​

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Multiple Choice

If the sentence below represents a chromosome, which of the following answers represents a chromosome inversion?

This is a chromosome inversion.

• This is a chromosone inversion.

• This is emosomorhc a inversion.

• This is a inversion chromosome.

• This is a emosomorhc noisrevni.

An inversion is a segment that breaks away rotates 180 degrees and then rejoins the chromosome.​

The correct answer is B: This is emosomorhc a inversion. "a chromosome" was the segment that broke away from the sentence. and reinserted after a 180-degree flip.

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Multiple Choice

Which of the following mutations results when an adenine base is added before the first C in the DNA sequence CTGGGAATC?

• base substitution

• deletion

• insertion

• inversion

Added A before the first C results in an insertion and might also lead to a frame-shift mutation.

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In a base substitution​, one base is deleted and one is added, therefore, there is no change in the total number of nucleotides in the sequence.

A deletion mutation results in the loss of a nucleotide.

In an inversion, a piece of a chromosome breaks off, inverts and reinserts in the chromosome.​

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Multiple Choice

Nucleic acids carry an overall negative charge due to

• nucleotides

• sugar molecules

• phosphate groups

• nitogenous bases

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The phosphate group contains negatively charged oxygen ​atoms.

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Nucleotides carry three parts​ : a sugar, a phosphate group, and a nitrogenous base.

The sugar molecule or the nitrogenous bases do not confer a net negative charge.

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Multiple Choice

Select the proper equipment needed to study the structure of a virus particle.

• optical microscope

• electron microscope

• scanning electron microscope

• any of the above

The scanning electron microscope is the best choice because it passes a beam over the surface and captures a 3-D image.

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Viruses are usually too small to be seen by an optical microscope.

An electron microscope​ would work, but since this question asked about the structure of the virus, the scanning electron microscope is the best answer.

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Multiple Choice

A spectrophotometer cane be used to do which of the followiong tasks?

• distinguish between pigments in a plant cell

• measure enzymes in the blood of a heart attack patient

• determine how fast a pathogen grows in liquid culture

• all of the above

A spectrophotometer is able to do all of the tasks.​

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Multiple Choice

Which proteins make it possible to cut DNA from the genome of one cell and transfer that DNA to another cell?

• DNA polymerase

• RNA polymerase

• restriction enzymes

• ligases

Restriction enzymes are also called restriction endonucleases and are used to cut and splice DNA from one cell to another.

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DNA polymerase are enzymes used in DNA replication.

RNA polymerase are enzymes that catalyze the synthesis of mRNA from the DNA template.​

Ligases are enzymes that join two fragments of DNA together.​

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