Exam 2

Question 1

How many acyl chains are present in glycerophospholipids?

Answer 1

2

Question 2

The transformation of a monosaccharide into its ______ occurs easily and does not require the assistance of a catalyst.

Answer 2

anomer

Question 3

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

Answer 3

triacylglycerols

Question 4

All known porins are _____ proteins composed of _____.

Answer 4

trimeric; β-barrels

Question 5

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

Answer 5

antiporter; inside to out; outside to in

Question 6

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

Answer 6

GTP; α

Question 7

The concentration of cytosolic Ca2+ is _____ the extracellular concentration.

Answer 7

less than

Question 8

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

Answer 8

agonist

Question 9

When a receptor loses its ability to transmit a signal following continuous exposure to a ligand, the receptor is said to be _____.

Answer 9

desensitized

Question 10

The rate constant associated with the reaction below would be ______.
A –> B + C

Answer 10

First order

Question 11

Which type of isomer is represented by the pair of sugars below?
(D-Psicose and D-Sorbose)

Answer 11

Epimers

Question 12

What portions of the velocity versus substrate curve correspond to zero-order processes?

Answer 12

C (plateauing out)

Question 13

Which of the following terms describes all glycerophospholipids?

Answer 13

amphipathic

Question 14

What is one way that N-linked glycosylation differs from O-linked glycosylation?

Answer 14

The network for N-linked glycoproteins is less extensive than O-linked.

Question 15

Which of the choices below would be an accurate classification of the structure below?

Answer 15

aldohexose

Question 16

Which of the following curves shows the appropriate relationship between enzyme velocity and enzyme concentration? ***

Answer 16

E (linear)

Question 17

What is responsible for the extremely rapid propagation of action potential?

Answer 17

Axons are insulated with a myelin sheath which prevents ion movement except at the nodes between
myelinated segments.

Question 18

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

Answer 18

-affect kcat
-affect the catalytic function, but not the binding of substrate
-are called noncompetitive
[all of the above]

Question 19

Rank the melting points of the following fatty acids.

Answer 19

Linolenate

Question 20

You are constructing a velocity versus substrate curve for an enzyme whose KM is believed to be about 2
µM. The enzyme concentration is 200 nM and the range of substrate concentration is 0.1 µM to 10 µM. Is there anything wrong with this experimental setup and if so – how could you fix it?

Answer 20

The enzyme concentration is too high and needs to be decreased.

Question 21

Amylopectin contains primarily _____ glycosidic bonds with _____ glycosidic bonds as branch points.

Answer 21

α(1→4); α(1→6)

Question 22

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

Answer 22

phosphorylation; phosphorylates

Question 23

Which of the following is NOT a reducing sugar?

Maltose/sucrose/lactose

Answer 23

Sucrose

Question 24

Which of the following contains a glycosidic bond?

pic of and nTP, disaccharide and monosaccharide

Answer 24

A, B, C

Question 25

Which of the following is NOT a general feature of the lipid bilayer in biological membranes?

Answer 25

The bilayer is stabilized by covalent interactions between the lipids molecules and integral membrane
proteins.

Question 26

Bacillus anthracis, the cause of anthrax, produces a three-part toxin. One part facilitates the entry of the two other toxins into the cytoplasm of a mammalian cell. The toxin known as edema factor (EF) is an adenylate cyclase. What is the effect of this toxin?

Answer 26

The levels of cAMP rise and protein kinase A is activated.

Question 27

Tagatose is an “artificial” sweetener that is similar to sucrose in sweetness and replaces sucrose in Pepsi Slurpees. Tagatose is a C4 epimer of fructose. Which of the structures below is D-tagatose?

Answer 27

(B) 
     CH2OH
      |
      =O
      |
HO+H
HO+H
   H+OH
      |
     CH2OH

Question 28

The resting membrane potential maintained in most nerve cells is about -70 mV. Calculate the ratio of [Na+ ]in/[Na+]out at the resting potential.

Answer 28

0.062

Question 29

Shown below is the Fischer projection of D-mannose. Which of the choices below would be a proper representation of the Haworth projection of this molecule?

Answer 29

A (the one that looks like a train track)

Question 30

How does cAMP influence glycogen breakdown?

Answer 30

(A) cAMP activates protein kinase A, which phosphorylates the enzyme phosphorylase kinase, which
then activates glycogen phosphorylase to break down glycogen.

Question 31

For a cell with [Na+]out = 150 mM and [Na+]in = 15 mM at 37°C, what is the free energy for movement of
sodium ions from outside the cell to inside if the potential across the membrane is -60 mV?

Answer 31

-11.7 kJ/mol

Question 32

Acid-gated channel proteins include a set of Asp or Glu residues in their acid sensor that maintains the channel in a closed conformation. How does pH affect the opening of these channels?

Answer 32

Low pH would neutralize these residues and open the channel

Question 33

A 30-mM solution of hippurylphenylalanine was monitored for amide bond hydrolysis by monitoring the formation of product, phenylalanine. At the end of 50 days, 25 µM phenylalanine was detected in
solution. The amide bond in hippurylphenylalanine is hydrolyzed 4.7 x 1011 times faster in the presence of an enzyme. What is the rate of formation of phenylalanine in the presence of the enzyme (M/s)?

Answer 33

E) 2.7 M/s

Question 34

The action of phospholipase C results in the formation of 2 second messengers. Which of these is soluble in the cytoplasm?

Answer 34

C) inositol trisphosphate

Question 35

A galactosyl transferase that catalyzes the reaction below, β3-GalT, has recently been purified. The
reaction velocity was measured in the presence of UDP-[3H]Gal. Use the graph below to determine the value of KM and Vmax.

Answer 35

D) KM = 591 µM; Vmax = 2.27 x 103 µM/h

Question 36

How many acyl chains are added to a sphingosine backbone in order to form a sphingomyelin molecule?

Answer 36

B) 1

Question 37

In which of the following cases is the first product released before the second substrate binds?

Answer 37

C) Ping-pong mechanism

Question 38

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 value if kcat?

Answer 38

B) 4.0 s-1

Question 39

Which of the following is not an example of a passive-mediated transporter?

Answer 39

D) Na+/K+ transporter

Question 40

Mutant Ras proteins have been found to be associated with various types of cancer (uncontrolled cell growth). What is the likely effect of the mutation on Ras function?

Answer 40

B) Ras is unable to hydrolyze GTP.

Question 41

Which of the following components of the insulin response pathway are NOT enzymes?

Answer 41

D) adapter proteins

Question 42

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?

Answer 42

C) They would activate protein kinase C.

Question 43

Which of the following functon solely as structural molecules?

Answer 43

A) chitin

Question 44

What is the effect on phosphofructokinase in the presence of phosphoenolpyruvate and what type of interaction do they have?

Answer 44

Phosphoenolpyruvate allosterically inhibits phosphofructokinase; engage in feedback inhibition

Question 45

Which of the structures below would represent a sphingolipid?

Answer 45

C) C (the one with the P group)

Question 46

Which of the sterol-based molecules below would be the LEAST soluble?

Answer 46

A) A (bc it has NO electronegative atoms)

Question 47

Which statement does NOT accurately describe integral membrane proteins?

Answer 47

C) Integral proteins typically have covalently-bound lipids.

Question 48

ABC transporters are examples of

Answer 48

C) primary active transport

Question 49

Which of the following is true regarding membrane asymmetry?

Answer 49

E) none of the above

Question 50

Calculate the free energy change for the movement of Na+ into a nerve cell at the resting potential of -70
mV. Assume the temperature is 37oC. Is this process favorable?

Answer 50

E) -13.9 kJ/mol; favorable

Question 51

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 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).

Answer 51

C) 0.017 µmol/min

Question 52

Stachyose is a tetrasaccharide found in soybeans, which is composed of galactose, glucose, and fructose residues. Given the structure below, identify the glycosdic bonds between residues A and B, and between residues B and C. Which residue is glucose?

Answer 52

C) α(1 –> 6) between Residue A and B; α(1 –> 2) between Residue B and C; Glucose is #2

Question 53

Glucose-6-phosphate dehydrogenase catalyzes the following reaction:
G6P -(G6P dehydrogenase)-> 6PGL
Kinetic data for the enzyme isolated from T. maritima are in the table below. NADPH inhibits the enzyme. What kind of an inhibitor is NADPH and how does it alter the values of KM and Vmax listed in
the table? Does the enzyme prefer NAD+ or NADP+ as a cofactor?

Answer 53

D) Competitive inhibitor; KM increases; Vmax unchanged; prefers NADP+

Question 54

A sample of cells with a total receptor concentration of 50 µM was incubated with a ligand concentration of 100 µM. Following the incubation period, the concentration of unbound receptors was determined to be 15 µM. What is the Kd for the receptor-ligand interaction?

Answer 54

A) 28 µM

Question 55

You perform a series of experiments to isolate membrane proteins from cells using three different methods. Assume that the only proteins present are those associated with the membrane, as illustrated in the figure below.
For Experiment 1, you bathe the intact cells with a mild salt solution. In Experiment 2, you first rupture the cell membrane, and then proceed to bathe the cell extract in a mild salt solution. Experiment 3involves cell rupture followed by adding the cell extract to a strong ionic detergent (stringent conditions). Samples from each experiment are run on a denaturing SDS-PAGE gel, using proteins of known molecular weight (MW) as markers to estimate protein mass. Lane 1 contains the MW markers and Lanes 2, 3, and 4 contain the extracts from Experiments 1, 2, and 3, respectively. Which of the following figures would properly represent the successful results of your experiments?

Answer 55

A) A