WorksheetsBiochemistry Unit Test 1
Total questions: 30
Worksheet time: 19mins
When cytosine is treated with bisulfite, the amino group is replaced with a carbonyl group. Identify the resulting base.
Thymine
Uracil
5-methyl uracil
Inosine
A diploid organism with a 450 kb haploid genome contains 21% G residues. Calculate the number of A, C, G, and T residues in the DNA of each cell in this organism
A= 2.61x10^5, T= 2.61 x10^5, G= 1.89 x10^5, C= 1.89 x10^5
A=1.89 x10^5, T= 2.61 x10^5, G= 2.61x10^5, C= 1.89 x10^5
A=1.89 x10^5, T= 1.89 x10^5, G= 2.61x10^5, C= 2.61 x10^5
A= 21%, T= 21%, G=34%, C= 34%
Explain why increasing the NaCl concentration increases the temperature at which the two strands of DNA “melt” apart.
NaCl Denatures the dsDNA strands causing them to act like ssRNA molecule.
NaCl destabilizes the hydrogen bonds
NaCl stabilizes the stacking interactions
NaCl causes the DNA to be more acidic
What will happen to the polarity of any amino acid, if carboxyl group is added in its side chain?
It will remain unaffected
It will become negatively polar
It will become positively polar
It will become neutral
Over time, the glutamine residues of polypeptides are susceptible to deamidation, a reaction in which the amide group is replaced by a carboxylate group. What amino acid is produced when glutamine is deamidated?
Aspartate
Glutamate
Glycine
Arginine
Which amino acids have side chains that are capable of forming isopeptide bonds?
Glutamate
Valine
Methionine
Proline
Which peptide has greater absorbance at 280 nm?
A. Gln–Leu–Glu–Phe–Thr–Leu–Asp–Gly–Tyr
B. Ser–Val–Trp–Asp–Phe–Gly–Tyr–Trp–Ala
B will have greater absorbance at 280 nm
A will have greater absorbance at 280 nm
The absorbance is not related to amino acid composition hence both the peptides will have equal absorbance at 280 nm
Data is insufficient
Is Trp or Gln more likely to be on a protein’s surface?
Gln because it is uncharged polar, Trp is non-polar so it would be on innerside
Trp because it is non-polar, Gln is uncharged polar so it would be on inner side
Trp because it contains a phenol ring
Gln because it is negatively charged
Basic fibroblast growth factor binds to glycosaminoglycans in the extracellular matrix. Which amino acids would you expect to be abundant in this protein
Glutamate or aspartate
Lysine or arginine
Glycine or proline
Tyrosine or phenyl alanine
Which triacylglycerol yields more energy on oxidation: one containing three residues of linolenic acid or three residues of stearic acid?
one containing three residues of linolenic acid
one containing three residues of stearic acid
Both of the triacylglycerol will yield equal energy
None of them can be oxidized.
Choose the best description of an enzyme:
It allows a chemical reaction to proceed extremely fast.
It increases the rate at which a chemical reaction approaches equilibrium relative to its uncatalyzed rate.
It makes a reaction thermodynamically favorable.
All of the above
Consider the peptide DGNILSR, where N has a covalently linked galactose and S has a covalently linked glucose. What does it best describes?
O-linked glycosylation and N-linked glycosylation respectively
N-linked glycosylation and O-linked glycosylation respectively
Formation of glycosidic bond, irrespective of which molecule is involved
Formation of amino sugars.
Which of these is not a reducing sugar?
Sucrose
Maltsoe
Trehalose
Lactose
[H+] is one of the regulators of PFK-1. Which of the following best describes the role of [H+] in glycolysis?
PFK-1 is inhibited by increase in [H+]
PFK-1 is activated by increase in [H+]
Increase in pH decreases the rate of glycolysis
All of the above.
How much substrate level energy is gained by oxidative decarboxylation reaction of one mole of pyruvic acid?
3 ATP
1.5 ATP
0 ATP
2 ATP
The pK value for N1 of adenine is 3.64, whereas the pK value for N1 of guanine is 9.50. What does it signify?
i. Adenine is a weaker base than guanine
ii. Guanine can display both basic and acid properties: it accepts a proton in an acid medium and loses it in an alkaline one.
iii. Guanine is a weaker base than adenine
Choose the correct answer:
Only (i) is correct
Only (iii) is correct
Both (i) and (ii) are correct
Both (i) and (iii) are correct
Presumably, the mix of prebiotic compounds on early earth included both D- and L-amino acids. What are some hypotheses that attempt to explain why cells build proteins only from the L forms?
The enzymes involved are the aminoacyl-tRNA synthetases that preferentially bind L-amino acids.
Activation of malamide monomers by aminoacylation with simple amino acids such as Gly and L-Ala was catalyzed by simple proteins made from Gly and L-Ala.
Both (a) and (b)
None of the above
Hydrophobic residues usually appear at the 1st and 4th positions in the 7-residue repeats of polypeptides that form coiled coils. Why do polar or charge residues usually appear in the remaining 5 positions?
The 1st and 4th side chains of the 2 helices of a coiled coil form buried hydrophobic interacting surfaces but the remaining side chains are exposed to solvent and therefore tend to be polar or charged.
The 1st and 4th side chains of the 2 helices of a coiled coil form buried hydrophilic interacting surfaces but the remaining side chains are exposed to solvent and therefore tend to be nonpolar or uncharged.
The 1st and 4th side chains of the 2 helices of a coiled coil form buried hydrophobic interacting surfaces because they are polar or charged
None of the above.
In humans, the urge to breathe results from high concentrations of CO2 in the blood; there are no direct physiological sensors of blood pO2. Skindivers often hyperventilate (breathe rapidly and deeply for several minutes) just before making a dive in the belief that this will increase the O2 content of their blood. (a) Does it do so? (b) Use your knowledge of hemoglobin function to evaluate whether this practice is useful.
(a) yes (b) it decreases the pO2 in blood causing O2 to dissociate from heamoglobin
(a) yes (b) it increases the pO2 in blood causing O2 to bind with heamoglobin
(a) yes (b) it makes the Hb to configure as in T-state
(a) No (b) it makes the Hb to configure as in R-state
Human hemoglobin can react with sugars in the blood (usually glucose) to form covalent adducts. The a-amino groups of N-terminal valine in the Hb b-subunits react with the C-1 (aldehyde) carbons of monosaccharides to form aldimine adducts, which rearrange to form very stable ketoamine products. Quantitation of this “glycated hemoglobin” is important clinically, especially for diabetic individuals. Select the best methods by which glycated Hb could be separated from normal Hb and quantitated.
Modification of the N-terminus of a polypeptide will change the ionic properties and separation of modified and unmodified protein may be accomplished by ion exchange.
The two forms may also be separated using isoelectric focusing because they have different pI’s.
Addition of a glucosyl moiety will change the protein’s molecular weight. Mass spectrometry may also be used to detect and quantitate this modification.
All of the above.
Identify the FALSE statement among the following about non-competitive inhibition.
1. The inhibitor has no structural similarity to the substrate and forms an enzyme-inhibitor complex at a point other than its active site so that the globular structure of the enzyme is changed.
2. Even if the substrate is able to bind with the enzyme, catalysis cannot take place.
3. It is characteristic of allosteric and multisubstrate enzymes.
4. Km unaffected in simplest case. Vmax decreased by factor (1+[I])/KI).
Options:
1, 2 and 3
2, 3 and 4
1, 3 and 4
1, 2, 3 and 4
Mucopolysaccharides are gelatinuous polysaccharides formed from galactose and mannose. Slimy substances of bhindi, agar agar, alginic acid and carrageenin obtained from seaweeds are mucopolysaccharides. Select which of the following is not an example of mucopolysaccharides:
Chondroitin sulphate
Heparin
Keratin sulphate
Inulin
If the process of glycolysis is sub-divided into three major steps: (a) Phosphorylation, (b) Splitting of fructose-1, 6-diphosphate, (c) Formation of pyruvic acid. The regulation of these steps is crucial for the ongoing of glycolysis. Choose the correct pair for the regulation of glycolysis:
Hexokinase: [insulin] inhibitor
Phospho-Fructo kinase-1 :High [ATP] : [AMP] stimulator
Phospho-Fructo kinase-1 : [fructose 2,6-bisphosphate] allosteric stimulator
Pyruvate kinase: [Fru 1,6-BP] inhibitor
Which of the following is NOT a characteristic of a positive G0’ reaction
Free energy changes ( G) is 0 or negative
Increase substrates and/or decrease products
Reaction catalyzed by aldolase is an example of positive G0’
None of the above
Certain tissues effect Cl– secretion via a Cl– channel (CFTR protein-cystic fibrosis transmembrane regulatory protein). Cholera toxin abnormally opens the channel leading to a loss of NaCl. Treatment for cholera and sports drinks for electrolyte replacement is fluids high in Na+ and glucose. The presence of glucose enhances NaCl replenishment because:
Absorbing any nutrient causes Na+ uptake.
Glucose prevents Na+ excretion.
Na+ and glucose are transported in opposite directions.
Glucose is absorbed across intestinal epithelial cells via a Na+ -dependent cotransporter.
The transmembrane portion of a protein spanning the membrane is most likely to be composed of aminoacids that are-
basic
acidic
glycosylated
hydrophobic
A plot of enzyme velocity against temperature for an enzyme indicates little activity at 0 oC and 45 oC, with peak activity at 35 oC. The most reasonable explanation for the low velocity at 0 oC is that at this temperature
The hydrogen bonds that define the enzyme’s active site are unstable.
At low temperatures the substrate becomes an allosteric regulator.
The enzyme was denatured.
There is too little activation energy available.
Chaperone proteins:
a. All require ATP to exert their effect.
b. Cleave incorrect disulfide bonds, allowing correct ones to subsequently form.
c. Guide the folding of polypeptide chains into patterns that would be thermodynamically unstable without the presence of chaperones.
d. Of the hsp70 class are involved in transport of proteins across mitochondrial and endoplasmic reticulum membranes.
4-Hydroxylation of specific prolyl residues during collagen synthesis requires all of the following EXCEPT:
a. Fe2+
b. a specific amino acid sequence.
c. ascorbic acid
d. succinate.
Suppose the specific defect were a mutant pyruvate dehydrogenase (the first catalytic subunit) with poor binding of its prosthetic group. In this type of defect, sometimes greatly increasing the dietary precursor of the prosthetic group is helpful. In this case increasing which of the following might be helpful?
a. thiamine(TPP)
b. niacin (for NAD)
c. pantothenic acid (for CoA)
d. riboflavin (for FAD)
