BCH EXAM 2 PRACTICE

An insect aminopeptidase was purified and its catalytic activity was investigated using an artificial peptide substrate. The Vmax was 4.0 x 10-7 M/s and the KM was 1.4 x 10-4 M. The enzyme concentration used in the assay was 1.0 x 10-7 M. What is the catallytic efficiency of the enzyme?

A) 2.8 x 104 s-1. M-1

Which of the following would represent the reaction coordinate for a two-step reaction with an initial slow step?

A) A

Which is not a consequence of the cis double bonds of fatty acids?

A) A higher melting temperature

Which amino acid in the aquaporin channel hydrogen bonds with water to prevent the movement of protons?

A) Asn

Which of the following second messengers would NOT be found free floating in the cytosol?

A) DAG

Laminaria groenlandica is a type of kelp that grows along the rocky shores of Alaska. Due to its geographic distribution, this species is subjected to cold temperatures and potential freezes. Macrocystis pyrifera is a type of kelp that grows off the coast of South America and encounters much warmer temperatures. Which of these two species would you expect to have a higher composition of unsaturated fatty acid tails incorporated into its lipid bilayer?

A) Laminaria groenlandica

Some G protein-linked receptors are associated with a protein called RGS (regulator of G protein signaling). RGS stimulates the GTPase activity of the G protein associated with the receptor. What effect does RGS have on the signaling process?

A) This will shorten the duration of signaling

What is the relationship between KM and [S] when an enzyme-catalyzed reaction proceeds at 90% of Vmax?

A) [S] = 9 KM

Acetylcholine and nicotine competitively bind to nicotinic acetylcholine receptors to cause the same second messenger activation. Nicotine is considered an _______________ of the receptors.

A) agonist

The Na,K-ATPase is a(n) _____ that moves Na+ from _____ and K+ from _____.

A) antiporter; inside to out; outside to in

Which type of secondary structure present in integral membrane proteins is readily detectable in the primary structure?

A) membrane-spanning α helix

Rank the melting points of the following fatty acids. 1) cis-oleate (18:1) 2) trans-oleate (18:1) 3) linoleate (18:2)

B) 2 > 1 > 3

Glucose is added to cells and the rate of glucose transport is plotted against glucose concentration. In the presence of the galactose derivative 6-O-benzyl-D-galactose the curve is shifted to the right (with no other change). What kind of agent is this galactose derivative?

B) Competitive inhibitor

Prodrugs are inactive compounds that need to be cleaved in order to yield an active drug. A novel tumor therapy has recently involved the delivery of an enzyme, capable of catalyzing this cleavage reaction, to the tumor site. This is followed by administration of the prodrug, which in this instance is acting as the substrate. Suppose that there are two enzymes capable of catalyzing this reaction. Enzyme A has a KM for the prodrug of 1 µM and Enzyme B has a KM of 1 nM. Which enzyme would you use in patients?

B) Enzyme B

Activation of a G protein in response to hormone binding requires binding of _____ to the _____ subunit.

B) GTP; α

What is the major factor in determining the types of secondary structures that form in the transmembrane portions of integral membrane proteins?

B) Hydrogen bonding interactions of protein backbone groups

Which of the following amino acids could bind to the specificity pocket of Trypsin?

B) Lys

Hexokinase undergoes a large conformational change in order to exclude water from the active site. Would chymotrypsin undergo such a change upon binding its substrate?

B) No

Which of the following is true regarding the glucose transporter?

B) binding of glucose causes a conformational change so that the transporter is never open on both sides of the membrane

A patient suffers from premature zymogen activation, so that the pancreatic enzymes are activated in the pancreas rather than the small intestine -- causing damage to the pancreas. Which of the following would be the most effective in preventing these effects?

B) trypsin inhibitor

Which of the following curves shows the appropriate relationship between [ES] and time in steady state kinetics?

C) (c)

Alcohol dehydrogenase (ADH) converts ethanol into acetaldehyde in the liver. The acetaldehyde is then processed by acetaldehyde dehydrogenase (ALDH) to form acetic acid, according to the scheme below. Following ingestion of a large volume of ethanol, all all of the acetaldehyde cannot be processed and builds to concentrations that result in the physiological symptoms of intoxication. The ALDH enzyme is inhibited by the compound benzaldehyde (below).

C) 0.017 µmol/min

Sarin gas [(CH3)2CHO]CH3P(O)F is a fatal nerve agent that acts as an irreversible inhibitor of the enzyme acetylcholine esterase. Acetylcholine esterase hydrolyzes acetylcholine to render it inactive in the synapse. Atropine is an antagonist to acetylcholine. Latrotoxins (black widow venom) act as agonists to acetylcholine. Which of the following physiological features would you expect to find in an individual exposed to sarin gas? Would you treat this individual with atropine or latrotoxins to reverse the symptoms?

C) Increased muscle contraction; atropine

Yeast glucose-6-phosphate dehydrogenase can be inhibited by a number of cellular agents whose KI values are listed below. Which is the most effective inhibitor? Which inhibitor is likely to be completely ineffective under normal cellular conditions?

C) Most effective: NADPH; Ineffective: inorganic phosphate

The rate constant associated with the reaction below would be 2A --> B

C) Second order

A membrane consisting only of phospholipids undergoes a sharp transition from the crystalline form to the fluid form as it is heated. What would be the effect on this transition in a membrane containing 80% phospholipid and 20% cholesterol?

C) The shift from the crystalline to the fluid form would be more gradual.

Phorbol esters, which are compounds isolated from plants, are structurally similar to diacylglycerol. How does the addition of phorbol esters affect the signaling pathways of cells in culture?

C) They would activate protein kinase C.

Which of the following is FALSE regarding transition state stabilization?

C) Transition state stabilization refers to the shift in the equilibrium of the reaction

A molecule moves across a membrane from a lower to a higher concentration with the aid of a membrane protein. This process is known as:

C) active transport

In the reaction mechanism of the glycolytic enzyme aldolase, an active site tyrosine residue accepts a proton from the substrate. In this form the side chain of Tyr must be _________ and it is acting as a(n) __________ catalyst.

C) deprotonated; base

It is necessary to know the value of [E]t in order to determine the values of

C) kcat

Ligand binding to a receptor tyrosine kinase causes _____ of the receptor which then _____ the next protein in the signaling pathway

C) phosphorylation; phosphorylates

Which of the following lipid types are not found in animal membranes?

C) triacylglycerols

Which of the following statements about allosteric control of enzymatic activity is false?

D) Binding of the effector to the active site changes the conformation of the enzyme molecule.

Renin or chymosin is a protease similar to chymotrypsin, except that it belongs to a class of enzymes called aspartyl proteases -- in which asparatate residues are found in the active site rather than serine. Renin catalyzes the hydrolysis of a peptide bond in the protein angiotensinogen, converting it to angiotensin I, a precursor of a hormone involved in regluating blood pressure. Renin inhibitors are therefore potentially valuable in the treatment of high blood pressure. Two aspartate residues in the renin active site, Asp 32 and Asp 215, constitute a catalytic dyad, rather than the catalytic triad found in chymotrypsin. Given this information and the figure below, what type of catalysis is utilized by renin? Which of the two active site Asp residues will have the lower pK value?

D) Renin uses acid-base catalysis; Asp 32 has the lower pK value

The drug known as Botox is a preparation of botulinum toxin. How does this account for its use by plastic surgeons to alleviate facial wrinkles?

D) all of the above

There are few examples of inhibitors that decrease Vmax but do not affect KM, these inhibitors

D) all of the above

The GLUT transporter moves glucose through a transport protein in the same direction as its concentration gradient. The action of the glucose transporter is an example of _____________. The SGLT transporter uses the sodium concentration gradient created by the sodium potassium ATPase to move glucose against its concentration gradient. The action of the SGLT transporter is an example of _______________.

D) facilitated transport, secondary active transport

The complex formed between a lipid hormone and its receptor binds to _____ which are specific DNA sequences.

D) hormone response elements

Which of the receptors below is a tyrosine kinase?

D) insulin receptor

cAMP binds to the _____ subunits of protein kinase A allowing the tetramer to dissociate into _____.

D) regulatory subunits; two active monomers and an inactive dimer

The chymotrypsin/trypsin family of proteases has which combination of amino acids in the active site

D) serine, histidine, aspartic acid

All known porins are _____ proteins composed of _____.

D) trimeric; β-barrels

What is the membrane potential created by a sodium gradient where [Na+]out = 145 mM and [Na+]in = 12mM at 37°C?

E) -67 mV

Which of the following would be a proper representation of enzyme velocity?

E) Either B or C

Based on the reaction below, how would the enzyme catalyzing this reaction be classified?

E) Transferase

A pH/rate curve with an inflection point at pH~4 suggests the involvement of a(n) ________ in the catalytic step.

E) acidic amino acid

Which of the following will cause the opening or closing of a gated ion channel?

E) all of the above