Biochem Final Flashcards
The shift from the deoxy to the oxy state of hemoglobin happens simultaneously in all binding sites, even if some of these sites don’t have oxygen present. T or F
True
In the structure of Oxy-myoglobin, 4 ligands are bound to iron from the heme, one from the protein, and the 6th ligand is provided by the distal histidine. T or F
False
The hydrogen bonding pattern in a beta sheet occurs between beta strands rather than within the same strand. T or F
True
A biochemical reaction (A converted to B) has a delta G = -116 kJ/mol. Which of the following can you conclude about this reaction?
a. The reaction does require thermodynamic coupling.
b. The delta H (enthalpy change is likely to be small.
c. The reaction does not require thermodynamic coupling.
d. The delta S is likely to be the driving force of the reaction.
c. The reaction does not require thermodynamic coupling.
A mutation in several cultured cells renders their ribosomes unable to include proline in any amino acid sequences. Which one of the following would be unaffected by this mutation?
a. Tropocollagen production.
b. Production of proteins containing beta-turns in their secondary structure.
c. Amphipathic alpha-helix production.
c. Amphipathic alpha-helix production.
A positive delta S for water is the driving force behind the tendency of nonpolar molecules to self-associate, otherwise known as the hydrophobic effect. T or F
True
Which structural technique does not work well for studying large proteins?
a. NMR spectroscopy
b. Structural prediction
c. X-ray crystallography
d. SDS page
e. Cyro-EM
a. NMR spectroscopy
Fibroin is composed of stacks of beta sheets made of a hydrophobic 7 residue pseudo repeat in which every third residue is nonpolar. T or F
False
Flattening of the heme plane (upon binding to oxygen) is the basis of positive cooperativity in hemoglobin. T or F
True
In exclusion chromotography, small proteins elute before big proteins. T or F
False
The primary role of the distal histidine in Myoglobin is to:
a. Provide favorable delta H interactions to help the protein fold.
b. Promote positive cooperativity through allostery.
c. Promote oxygen binding via a hydrogen bond
d. Hold the heme in place by forming a covalent bond with the iron.
c. Promote oxygen binding via a hydrogen bond.
Which of the following is not an example of heterotropic regulation of hemoglobin?
a. Low pH resulting in the stabilization of the deoxy state of hemoglobin
b. The Bohr effect.
c. 2,3-BPG binding to the deoxy state of hemoglobin
d. Oxygen binding to alpha1 chain of hemoglobin.
d. Oxygen binding to alpha1 chain of hemoglobin.
A solution of carbonic acid (pKa=6.37) that is set to a pH of 8.0 is at its maximum buffering capacity (i.e., most effective at resisting changes in pH). T or F
False
A solution of L-cysteine at 50 mM concentration is adjusted to a pH of 5. What is the net charge of L-cysteine in this solution? (chart is shown)
a. -1
b. +1
c. +2
d. 0
d. 0
Among all the amino acids with an ionizable side chain, histidine is unique in which way? (chart is given)
a. It is small in comparison to the aromatic amino acids.
b. It can be covalently linked in the active site of some enzymes.
c. It can dissociate a proton near physiological pH.
d. It is the only titratable amino acid that has a ring structure on its side chain.
c. It can dissaciate a proton near physiological pH.
Hydrogen bonding is used to stabilize which of the following?
a. Intrinsically disordered proteins.
b. Beta turns
c. Disulfide bonds
d. Van der Waals interactions
b. Beta turns
What is the purpose of the amphipathic detergent in SDS PAGE?
a. Ensure that proteins are positively charged, and therefore migrate on the acrylamide matrix.
b. Ensure that proteins remain folded during electrophoresis.
c. Ensure that the disulfide bonds in a protein are all reduced.
d. Ensure that proteins are negatively charged, and therefore migrate on the acrylamide matrix.
d. Ensure that proteins are negatively charged, and therefore migrate on the acrylamide matrix.
You try to purify a protein using ion exchange chromatography, but you find that your protein did not “stick” to the column. What is a possible cause?
a. The protein has no affinity tag.
b. The protein was too big to enter the column matrix.
c. The pH of the buffer puts the protein close to its isoelectric point.
d. The protein is misfolded.
c. The pH of the buffer puts the protein close to its isoelectric point.
A chemical reaction is found to have an equilibrium constant (Keq) that is very, very small. Which of the following can you conclude regarding the reaction?
a. The acid involved in the reaction is only partially dissociated.
b. The concentrations of the reactants and products are equal.
c. The concentrations of the reactants are higher than the products.
d. The concentrations of the reactants are lower than the products.
c. The concentrations of the reactants are higher than the products.
A mutation of Myoglobin is discovered that results in stronger binding to oxygen. What can you expect from this new protein?
a. The P50 will decrease.
b. The P50 will increase.
c. This form of myoglobin will be an effective substitute for hemoglobin.
d. The Hill coefficient (nH) will increase.
a. The P50 will decease.
The classic experiment with Ribonuclease A demonstrated which of the following?
a. That disulfides promote misfolded structures of proteins.
b. That using urea to unfold proteins is a useful research tool
c. That the information needed to fold a protein is contained in the primary amino acid sequence.
d. That the information needed to form quaternary structures is contained in the primary amino acid sequence.
c. That the information needed to fold a protein is contained in the primary amino acid sequence.
Which of the following does not stabilize the structure of tropocollagen?
a. Hydroxylation of proline
b. The activity of lysyl oxidase.
c. The hydrophobic effect.
d. Disulfide bonds.
d. Disulfide bonds.
The following amino acid sequence is ⍺ helical. How many separate ⍺ helices are there? MAKLLGVEPETVHELAAHVDAAMSVCSTAEIGDDVVIAWTALSARSPAFLSITSANFDS
a. 4
b. 5
c. 3
d. 2
c. 3
An enzyme catalyst can only change which of the following?
a. hydrophobic effect
b. ΔG°‡
c. Keq
d. ΔG°
b. ΔG°‡
Lysine cross-linking, lysine hydroxylation, and proline hydroxylation are all examples of post-translational modifications that stabilize the structure of tropocollagen. T or F
True
A simple first order reaction is directly proportional to the concentration of the reactant. T or F
True
The following shows the Michaelis-Menten plot for an enzyme. Which of the following is true regarding the reaction order at the red arrow (i.e., concentration of substrate is much larger than Km)? (chart is given)
a. The reaction is second order overall.
b. The reaction is zero order overall.
c. The reaction is first order overall.
d. The reaction is first order with respect to substrate.
c. The reaction is first order overall.
A carbonyl oxygen of one residue that is hydrogen bonding to an amine hydrogen from 4 resiudes away is an example of this:
a. Tertiary structure
b. Primary structure.
c. Secondary structure.
d. An intrinsically disordered protein.
c. Secondary structure
A mutant form of hemoglobin is found that has negative charges lining the central (water-filled) cavity of the structure. What would you predict regarding this hemoglobin?
a. The P50 will be smaller than normal hemoglobin.
It will display a hyperbolic binding curve.
c. The P50 will be larger than normal hemoglobin.
d. It will have a higher denaturation temperature.
a. The P50 will be smaller than normal hemoglobin.
Transport across a membrane that is active and primary:
a. Requires symport with a solute that is going down a concentration gradient
b. Requires a solute to move up a concentration gradient
c. Is not classified as “facilitated”
d. Has transport kinetics that are linear
b. Requires a solute to move up a concentration gradient
The enzyme chymotrypsin has evolved to cleave a peptide bond right after which of the following residues:
a. Residues that are negatively charged
b. Residues that are large and hydrophobic
c. Residues that are small and neutral
d. Residues that are large and hydrophobic and located at the C-terminal end of a protein
b. Residues that are large and hydrophobic
Which molecule is an example of convergent evolution when compared to Chymotrypsin?
a. Elastase
b. Papain
c. Trypsin
d. Subtilisin
d. Subtilisin
Which of the following best describes a protein signal sequence?
a. A sequence in the mature protein that identifies the protein as a secreted protein
b. A polar, C-terminal sequence of resiudes that is cleaved by the signal peptidase
c. The part of the SRP that “signals” recognition of the SRP receptor
d. A nonpolar, N-terminal sequence of residues that is recognized by the SRP
d. A nonpolar, N-terminal sequence of residues that is recognized by the SRP
Which of the following coenzymes are NOT involved in oxidation, reduction reactions?
a. Nicotinamide adenine dinucleotide
b. Flavin adenine dinucleotide
c. Thiamine pyrophosphate
d. Lipoamide
c. Thiamine pyrophosphate
The signal sequence explains which of the following observations:
a. The C-terminal side of membrane proteins sometimes face the extracellular side of the plasma membrane
b. Membrane proteins with multiple hydrophobic helices are rarely found at the plasma membrane
c. The N-terminal side of membrane proteins are facing the extracellular side of the plasma membrane
d. The C-terminal side of the membrane proteins are modified to contain oligosaccharides
c. The N-terminal side of membrane proteins are facing the extracellular side of the plasma membrane
What describes the “steady state assumption” of enzyme kinetics?
a. The [ES] is assumed to be constant
b. The free [E] is assumed to be decrease as the enzyme resets
c. The [S] is assumed to be increasing
d. The [P] is assumed to be steady
a. The [ES] is assumed to be constant
When an enzyme is activated by a molecule other than its substrate, this is an example of:
a. Heteroallostery
b. Noncompetitive inhibition
c. Homoallostery
d. Competitive activation
a. Heteroallostery
An ES complex that does not require E and S to change shape is best explained by the induced-fit model of substrate binding. T or F
False
An enzyme accepts both cholesterol and pregnenolone as its substrates. According to the following table, the enzyme is most efficient with cholesterol as its substrate (table shown with cholesterol and pregnenolone values). T or F
True
You identify an new enzyme and find that it has a relatively large turnover number (kcat). Which of the following is also likely to be true?
a. There is not enough information to determine if the reaction velocity (Vo) is high
b. The Km must be small compared to the kcat
c. The Km must also large
d. The reaction velocity (Vo) is high
a. There is not enough information to determine if the reaction velocity (Vo) is high
Thiamine pyrophosphate is an example of a prosthetic group. T or F
True
Which of the following do not contribute to the favorable thermodynamics of a phospholipid bilayer?
a. Favorable enthalp resulting from van der Waals interactions
b. Favorable enthalpy resulting from disulfide bond formation between head group
c. Favorable entropy resulting from the hydrophobic effect
d. Favorable enthalpy resulting from hydrogen bonding
b. Favorable enthalpy resulting from disulfide bond formation between head groups
Which of the following amino acids is not capable of acid base catalysis:
a. Histidine
b. Cysteine
c. Phenylalanine
d. Tyrosine
c. Phenylalanine
The prosthetic group that is directly involved in formation of Acetyl-CoA is:
a. Lipoamide (LA)
b. Flavin adenine dinucleotide (FAD)
c. Thiamine Pyrophosphate (TPP)
d. Coenzyme A
a. Lipoamide (LA)
A Tm is measured for a bilayer that is made of the lipid PI (18/1:18/1). A second bilayer is determined to have a Tm that is 10 degrees higher. What is the likeliest composition of the second bilayer?
a. PI (18:2/18:2)
b. PI (20:1/20:1)
c. PI (18:1/18:1) with 10 % cholesterol
d. PI (16:1/16:1)
b. PI (20:1/20:1)
In which way are Carboxypeptidase A and trypsin similar?
a. They both use zinc to stabilize the transitions state
b. They both display a rapid burst phase followed by a slower stead state phase
c. They both recognize large, bulky hydrophobic groups in their specificity pockets
d. They both cleave at a peptide bond
d. They both cleave at a peptide bond
A membrane protein that moves two solutes in opposite directions of one another is an example of:
a. Active unipot
b. Facilitates symport
c. Passive antiport
d. Facilitated antiport
d. Facilitated antiport
Cholesterol “blurs the transition” between the gel phase and the liquid crystal phase of a bilayer. How does it do this?
a. It inverts between leaflets of the bilayer
b. It lowers the Tm to a more physiologically relevant level
c. It promotes more efficient tail packing between fatty acid tails
d. It decreases motional freedom between the neighboring fatty acid tails
d. It decreases motional freedom between the neighboring fatty acid tails
In serine proteases, the role of the serine residue is to serve as an essential nucleophile. T or F
True
Which of the following is an example of desensitization of a signaling event:
a. The activity of phosphodiesterases
b. The conversion of ATP into cAMP
c. The activation of adenylate cyclase
d. G-protein degradation
a. The activity of phosphodiesterases
The following structure is an example of a glycerophospholipid (shows an image of lipid with two tails). T or F
False
What is the correct label for the following fatty acid?
(shows image)
a. 20:5 c∆ 5, 8, 11, 14, 17
b. 20:5 t∆ 5, 8, 11, 14, 17
c. 19:5 c∆ 5, 8, 11, 14, 17
d. 20:5 c∆ 3, 6, 9, 12, 15
a. 20:5 c∆ 5, 8, 11, 14, 17
Which of the following is true regarding competitive inhibition?
a. It requires some form of allostery
b. The inhibitor is not likely to “look like” the substrate
c. The apparent Vmax decreases
d. The apparent Km increases
d. The apparent Km increases
Which of the following result in a more fluid membrane?
a. Increase in the fatty acid tail length
b. Decrease the size of the polar head group
c. Increasing the size of the polar head group
d. Decreasing the number of double bonds
c. Increasing the size of the polar head group
Triglycerols are not amphipathic and therefore are not components of membranes. T or F
True
The enzyme triose phosphate isomerase is a very efficient enzyme. Therefore, its ΔΔG°‡ must be a small number. T or F
False
In the “signal hypothesis”, the outcome of a deficient SRP receptor would be finding protein that is secreted, but still has an intact signal sequence. T or F
False
Lactate dehydrogenase in skeletal muscles:
a. Replenishes ADP so that glycolysis can continue to run
b. Maximizes energy production by oxidizing pyruvate
c. Generates NADH so that gluconeogenesis can run
d. Generates ATP so that gluconeogenesis can run
e. Replenishes NAD+ so that glycolysis can continue to run
e. Replenishes NAD+ so that glycolysis can continue to run
Under high blood glucose concentrations, ___ effectively traps glucose in liver cells.
a. Glucose-6-phosphate
b. Glucokinase
c. GLU2
d. Hexokinase
e. Phosphofructokinase-1
b. Glucokinase
In Complex V (ATP synthase; FOF1 complex), the proton pump consists of:
a. αβ-subunits
b. Oligomycin sensitivity conferral protein (OSCP)
c. Stator
d. a- and c-subunits
e. γδε-subunit
d. a- and c- subunits
In glycogenesis, almost all α(1→4) linkages are synthesized by:
a. Glycogen synthase
b. Branching enzyme
c. Debranching enzyme
d. Glycogen phosphorylase
e. Glycogenin
a. Glycogen synthase
Substrate level phosphorylation involves transferring a high energy phosphate bond from __________.
a. A phosphorylated molecule of ATP
b. ATP to another molecule
a. A phosphorylated molecule of ATP
A metabolic accident leads to 1 electron being transferred onto O2. The resulting molecule is:
a. Water (H20)
b. Hydrogen peroxide (H2O2)
c. Superoxide (●O2-)
d. Hydroxyl radical (●OH)
d. Elemental oxygen (O)
c. Superoxide (●O2-)
In glycogenesis, α(1→6) linkages are synthesized by:
a. Glycogen synthase
b. Glycogenin
c. Debranching enyzme
d. Branching enzyme
e. Glycogen phosphorylase
d. Branching enzyme
In skeletal muscles, electrons from cytoplasmic NADH are transported into the mitochondria via __________.
a. Glycerol-3-phosphate shuttle
b. Malate / Aspartate shuttle
a. Glycerol-3-phosphate shuttle
The two enzymes that directly digest dietary glycogen are __________ and isomaltase.
a. Maltase
b. α-amylase
b. α-amylase
The rate-limiting step in the TCA cycle is:
a. Succinate dehydrogenase
b. Isocitrate dehydrogenase
c. Citrate synthase
d. Malate dehydrogenase
e. α-ketoglutarate dehydrogenase
b. Isocitrate dehydrogenase
Fructose-2,6-bisphophate promotes the activation of __________ while inactivating __________.
a. phosphofructokinase-1; fructose-1,6-bisphosphatase
b. glycogen phosphorylase; glycogen synthase
c. glycogen synthase;
glycogen phosphorylase
d. fructose-1,6-bisphosphatase;
phosphofructokinase-1
e. pyruvate kinase;
pyruvate decarboxylase
a. phosphofructokinase-1;
fructose-1,6-bisphosphatase
ATP is exported out of the mitochondrial matrix by:
a. Adenine nucleotide translocase
b. ATP / ADP symport protein
c. Phosphate translocase
d. Complex VI
e. Complex V
a. Adenine nucleotide translocase
__________ decreases pyruvate kinase activity and increases the activity of pyruvate carboxylase.
a. ATP
b. Acetyl-CoA
b. Acetyl-CoA