Chapter 2 - Protein Composition and Structure - part 2

Question 1

Polypeptide chains can change direction by making

Answer 1

reverse turns and loops.

Question 2

Unlike alpha helices and beta strands, loops do not have

Answer 2

regular, periodic structures.

Question 3

Alpha-Keratin is a member of a superfamily of proteins referred to as

Answer 3

coiled-coil proteins.

Question 4

In coiled-coil proteins, two or more alpha helices can entwine to form a

Answer 4

very stable structure, which can have a length of 1000 Angstrom or more.

Question 5

The two helices in alpha-keratin associate with each other by

Answer 5

weak interactions such as van der Waals forces and ionic interactions.

Question 6

The most abundant protein in mammals is

Answer 6

collagen.

Question 7

Hydroxyproline is

Answer 7

a derivative of proline that has a hydroxyl group in place of one of the hydrogen atoms on the pyrrolidine ring.

Question 8

What is myoglobin’s role in the body?

Answer 8

Acts as the oxygen storage protein in muscle.

Question 9

In an aqueous environment, protein folding is driven by

Answer 9

The strong tendency of hydrophobic residues to be excluded from water.

Question 10

The polypeptide chain folds so that its ________ side chains are buried and its _______ side chains are on the surface.

Answer 10

hydrophobic; polar

Question 11

Amphiphatic

Answer 11

Having both hydrophobic and hydrophilic parts.

Question 12

Motifs

Answer 12

Small regions of protein three-dimensional structure or amino acid sequence shared among different proteins.

Question 13

Domains

Answer 13

Polypeptide chains that fold into two or more compact regions that may be connected by a flexible segment of polypeptide chain, rather like pearls on a string.

Question 14

Domains range from _________ amino acid residues.

Answer 14

30-400

Question 15

Primary structure

Answer 15

The amino acid sequence.

Question 16

Secondary structure

Answer 16

The spatial arrangement of amino acid residues that are nearby in sequence.

Question 17

Tertiary structure

Answer 17

The spatial arrangement of amino acids residues that are far apart in the sequence and to the pattern of disulfide bonds.

Question 18

Subunit

Answer 18

Each polypeptide chain in a protein containing more than one polypeptide chain.

Question 19

Quaternary structure

Answer 19

The spatial arrangement of subunits and the nature of their interactions.

Question 20

The simplest sort of quaternary structure is the

Answer 20

dimer.

Question 21

Dimers consist of

Answer 21

two identical subunits.

Question 22

The amino acid sequence of a protein determines its

Answer 22

three-dimensional structure.

Question 23

Difference between cystine and cysteine

Answer 23

Cysteine is an amino acid, and cystine forms when two amino acids join together via a disulfide bond.

Question 24

A protein is said to be denatured when

Answer 24

the protein is converted into a randomly coiled peptide without its normal activity.

Question 25

The information needed to specify the catalytically active structure of ribonuclease is contained in its

Answer 25

amino acid sequence.

Question 26

Conditions that lead to the disruption of any part of a protein structure are likely to

Answer 26

unravel the protein completely.

Question 27

Proteins fold by progressive stabilization of intermediates rather than by

Answer 27

random search.

Question 28

Small proteins can fold is less than

Answer 28

one second.

Question 29

Levinthal’s paradox

Answer 29

The enormous difference in time between calculated and actual folding times in proteins.

Question 30

The essence of protein folding is to retain

Answer 30

partly correct intermediates.

Question 31

The free energy difference between the folded and unfolded states of a typical 100-residue protein is

Answer 31

42 kJ/mol

Question 32

Nucleation-condensation model

Answer 32

Unstable transition states must exist between the denatured and native state in proteins.

Question 33

The local sequence appears to determine only between __________% of the secondary structure of proteins.

Answer 33

60-70

Question 34

ab initio prediction attempts to

Answer 34

predict the folding of an amino acid sequence without prior knowledge about similar sequences in known protein structures.

Question 35

In knowledge based prediction methods,

Answer 35

an amino acid sequence of unknown structure is examined for compatibility with known protein structures or fragments therefrom.

Question 36

Intrinsically unstructured proteins (IUPs)

Answer 36

Proteins that, completely or in part, do not have a discrete three-dimensional structure under physiological conditions.

Question 37

Unstructured regions are rich in

Answer 37

charged and polar amino acids with few hydrophobic residues.

Question 38

IUPs appear to be especially important in

Answer 38

signaling and regulatory pathways.

Question 39

Metamorphic proteins

Answer 39

Proteins that appear to exist in an ensemble of structures of approximately equal energy that are in equilibrium.

Question 40

Chemokines are

Answer 40

small signaling proteins in the immune system that bind to receptor proteins on the surface of immune-system cells, instigating an immunological response.

Question 41

Amyloidosis

Answer 41

a rare disease that occurs when an abnormal protein, called amyloid, builds up in your organs and interferes with their normal function.

Question 42

Acetyl groups attached to the amino termini of many proteins makes the proteins

Answer 42

more resistant to degradation.

Question 43

The addition of a fatty acid to an alpha amino group or a cysteine sulfhydryl group produces

Answer 43

a more hydrophobic protein.

Question 44

The addition of sugars makes proteins more

Answer 44

hydrophilic.