Biochem Exam 2

Question 1

A peptide built from three amino acids must have

Answer 1

three side chains

Question 2

What happens soonest during the protein folding process?

Answer 2

Hydrophobic groups move to the protein interior

Question 3

At a pH above its pKa, the e-amino group of lysine is

Answer 3

deprotonated and neutral

Question 4

What is the N-terminal residue of the peptide AYSDG?

Answer 4

Alanine

Question 5

In an alpha helix, each carbonyl group

Answer 5

is a hydrogen bond acceptor

Question 6

Which of the following amino acids is generally absent from an alpha-helix?

Answer 6

Proline

Question 7

Which of the following is most critical for maintaining the tertiary structure of a protein?

Answer 7

hydrophobic interactions

Question 8

Three of the 20 amino acids that are incorporated into proteins are aromatic. They are:

Answer 8

tyrosine, phenylalanine, and tryptophan

Question 9

The predominant non-covalent interaction seen in alpha-helices and beta-sheets is

Answer 9

hydrogen bonds

Question 10

Which statement is FALSE about the classification of amino acids?

Answer 10

Glutamic acid and asparagine are negatively charged amino acids

Question 11

Which of the following best describes the side chains of the nonpolar amino acids (glycine is not included)?

Answer 11

They are primarily neutral hydrocarbon structures

Question 12

If an alpha-helical region of a protein contained 18 amino acid residues, how many helical turns would be present?

Answer 12

5

Question 13

Which of the following forces stabilize protein primary structure at physiological pH?

Answer 13

covalent bonds

Question 14

Which of the following statements about peptide bonds in FALSE. Peptide bonds are:

Answer 14

charged

Question 15

Amino acid residues with nonpolar side chains are mostly located in the protein interior because

Answer 15

nonpolar groups cannot interact with water molecules

Question 16

Which of the following statements about the peptide bond is FALSE?

Answer 16

It is a phosphodiester bond

Question 17

Which of the following is FALSE with respect to beta-sheets?

Answer 17

Amino acid side chains protrude from one side of the beta-sheet

Question 18

Which of the following statements about the alpha-helix and beta-sheet are TRUE?
1. They are both types of secondary structure.
2. They are both stabilized by hydrogen bonds between amino acid side chains.
3. The polypeptide backbone is fully extended in both structures.
4. They are both usually located in the interior of soluble globular proteins

Answer 18

1 and 4

Question 19

A domain is:

Answer 19

a folded segment of polypeptide with a separate hydrophobic core

Question 20

What is the primary driving force in the formation of protein tertiary structure?

Answer 20

The exclusion of non-polar substances from aqueous solution

Question 21

What ultimately determines the unique three-dimensional structure of soluble globular proteins?

Answer 21

The sequence of the amino acid residues

Question 22

A polypeptide that does not assume its proper three-dimensional structure

Answer 22

may be degraded, may re-fold, may accumulate

Question 23

To dislodge a protein bound to a carboxymethyl column, you should add a solution containing

Answer 23

a higher concentration of cations

Question 24

Hemoglobin’s oxygen-binding curve is sigmoidal because

Answer 24

O2 binding shifts hemoglobin to a high-affinity conformation

Question 25

Respiring tissues release CO2, which leads to

Answer 25

a shift to the T state of hemoglobin

Question 26

Calculate the fractional saturation for myoglobin when pO2 is a. 20 torr and b. 80 torr.

Answer 26

The fractional saturation at 20 and 80 torrs are 0.88 and 0.97, respectively, which indicate the myoglobin is 88% and 97% saturated with oxygen at these respective pressures

Question 27

A protein that consists of more than one polypeptide chain has

Answer 27

quaternary structure

Question 28

Which of the following statements is FALSE? In its interaction with hemoglobin, oxygen is:

Answer 28

a prosthetic group

Question 29

Structurally, myoglobin and hemoglobin are very similar proteins. In which of the following levels of structure do they differ most?

Answer 29

Quaternary structure

Question 30

Which cytoskeletal proteins are constructed from globular protein subunits?

Answer 30

actin filaments and microtubules

Question 31

The changes in cell shape that allow crawling are mainly the result of

Answer 31

actin filament assembly and disassembly

Question 32

Which type of structural protein is exclusively extracellular?

Answer 32

collagen

Question 33

Phalloidin, a peptide isolated from a poisonous mushroom, binds to F-actin but not G-actin. How does the addition of phalloidin affect cell motility?

Answer 33

cell mobility is impared

Question 34

The motor protein myosin has

Answer 34

two heads attached to a rigid neck lever

Question 35

Straight hair can be curled and curly hair can be straightened by exposing wet hair to a reducing agent, repositioning the hair with rollers, then exposing the hair to an oxidizing agent. What are the roles of the reducing and oxidizing agents?

Answer 35

The reducing agent breaks disulfide bonds; the oxidizing agent forms new disulfide bonds

Question 36

"Hard" keratins such as those found in hair, horn, and nails have a high sulfur content whereas "soft" keratins found in the skin have a lower sulfur content. Explain the structural basis for this observation.

Answer 36

Hard keratins have oxidized cysteine residues, which enhance stability through disulfide bonds

Question 37

Kinesin is known as a processive motor because

Answer 37

it remains attached to its track after each reaction cycle

Question 38

Which of the following amino acids has the most significant role in the molecular mechanisms of hemoglobin's function?

Answer 38

histidine

Question 39

Is myosin a fibrous protein or a globular protein?

Answer 39

it's both fibrous and globular

Question 40

Which of the following best describes the tertiary structure of myoglobin?

Answer 40

it contains heme, which is slotted into a hydrophobic pocket between alpha-helix E and alpha-helix F

Question 41

Which of the following statements about 2,3-bisphosphoglycerate (BPG) binding is FALSE?

Answer 41

BPG aids oxygen delivery to tissues by increasing the affinity of myoglobin for oxygen

Question 42

Which of the following statements about the structure of myoglobin is FALSE?

Answer 42

Myoglobin contains all three types of secondary structure

Question 43

A newly-identified protein has a sigmoidal curve in a graph of fractional saturation versus ligand concentration. What can be deduced about this protein?

Answer 43

The protein binds the ligand cooperatively

Question 44

Myoglobin and hemoglobin are both oxygen-binding proteins but have very different physiological roles. Which two of the following are the most important factors that contribute to their different functions?

Answer 44

Myoglobin is a monomeric protein, whereas hemoglobin is a tetrameric protien Hemoglobin binds BPG which stabilizes the deoxy (T) state

Question 45

Which of the following statements most accurately explains why hemoglobin is able to deliver oxygen to myoglobin in the tissues?

Answer 45

Myoglobin has a hyperbolic oxygen binding curve, whereas hemoglobin has a sigmoidal oxygen binding curve

Question 46

Why is BPG essential for the delivery of O2 to the tissues?

Answer 46

BPG stabilizes the T state conformation of hemoglobin

Question 47

Which of the following is a role of histidine in myoglobin?

Answer 47

A histidine residue forms a hydrogen bond with oxygen

Question 48

The binding of one O2 to a molecule of hemoglobin results in:

Answer 48

An increased affinity for O2 in the remaining subunits (Which have not yet bound O2)

Question 49

Which of the following statements about the structure of myoglobin is TRUE?

Answer 49

A heme prosthetic group is tightly bound to myoglobin via coordination bond

Question 50

What is the fractional saturation of myoglobin at pO2 = 7.2 torr, if P50 = 2.8 torr?

Answer 50

0.72

Question 51

Proteins such as hemoglobin are known as ______ proteins since binding of a molecule to one site alter binding to other sites

Answer 51

allosteric

Question 52

During the formation of microfilaments, which of the following occurs?

Answer 52

ATP hydrolysis is catalyzed by F-actin

Question 53

The idea that binding of one molecule of oxygen to hemoglobin enhances further binding of oxygen to hemoglobin is called

Answer 53

cooperativity

Question 54

Proteins such as hemoglobin are known as _______ proteins since binding of a molecule of one site alter binding to other sites

Answer 54

allosteric

Question 55

When oxygen is bound to the heme group of myoglobin, it is coordinated between

Answer 55

E7 His; Fe2+ of heme

Question 56

Which allosteric effector has the greatest ability to stabilize the deoxy state of hemoglobin?

Answer 56

BPG

Question 57

What is the prominent type of secondary structure observed in myoglobin?

Answer 57

alpha-helices

Question 58

The individual hemoglobin subunits and myoglobin share what similar structures but have what different structures

Answer 58

secondary and tertiary; primary

Question 59

Which amino acid is critical for crosslinking of collagen trimers?

Answer 59

Lys

Question 60

In a muscle cell, what is the name for the bundles of myosin tails?

Answer 60

thick filaments

Question 61

Which of the following fibers is correctly paired with the protein that forms fibers

Answer 61

microfilaments: actin microtubule: tubulin extracellular support fibers: collagen intermediate filaments: keratin

Question 62

Which of the following details the nucleotide-binding side when tubulin dimers assemble into microtubules?

Answer 62

the alpha site is bound to GTP; the beta site is bound to GDP

Question 63

Which of the following details the nucleotide-binding site when tubulin dimers assemble into microtubules

Answer 63

the alpha site is bout to GTP; the beta site is bound to GDP

Question 64

When a cell moves along a surface' actin _____ occurs at the leading edge while _______ occurs at the trailing edge

Answer 64

polymerization; depolymerization

Question 65

While the composition of hemoglobin in adult humans is alpha2 beta 2, in the developing fetus, ______ is observed

Answer 65

alpha2 y2

Question 66

In a solution of high pH (<12), all of the acidic and basic sites in an amino acid are

Answer 66

deprotonated

Question 67

Parallel polypeptide chains in a beta-pleated sheet conformation are held together by

Answer 67

hydrogen bonding

Question 68

Which of the following would be a correct representation of a portion of a protein "backbone"?

Answer 68

the one with two peptide bonds on either side of an amino acid

Question 69

Which of the following best describes the peptide backbones in a beta-sheet?

Answer 69

highly extended

Question 70

Glycine, the simplest amino acid, is different from all of the other standard amino acids in that it

Answer 70

does not have a chiral center

Question 71

The first step in the folding of disordered polypeptide chains into stable proteins is the formation of:

Answer 71

secondary structural elements

Question 72

Which one of these characteristics is not true for the alpha helix?

Answer 72

there is a requirement for glycine every third amino acid residue

Question 73

Which of the following amino acids is most likely to be found on the interior of a protein (Use the Hydrophobic Scale from your textbook)

Answer 73

methionine

Question 74

Molecular chaperones assist proteins in the formation of

Answer 74

tertiary structure

Question 75

Which of the following amino acids would be classified as a polar neutral amino acid?

Answer 75

The amino acid that has a neutral charge

Question 76

What enzyme is required to form a new phosphodiester bond when inserting DNA into a plasmid?

Answer 76

ligase

Question 77

Which bond is unable to rotate?

Answer 77

peptide bond

Question 78

Which of the following has the most dramatic influence on the characteristics of an individual natural protein:

Answer 78

the amino acid sequence

Question 79

Which of the following is a palindromic sequence?

Answer 79

GAATTC

Question 80

Which of the following statements concerning the tripeptide Val-Ala-Gly is correct?

Answer 80

The C-terminal amino acid residue is Gly