Important Molecules

Question 1

How are peptide bonds formed?

Answer 1

peptide bonds are formed by linking a carboxyl group of one amino acid with a a-amino group of another amino acid

Question 2

What is a residue?

Answer 2

an individual amino acid part of a polypeptide chain

Question 3

What is the “backbone” of a polypeptide chain?

Answer 3

N-C-C-N-C-C

Question 4

What is an amino terminus?

Answer 4

the first end made during polypeptide synthesis

Question 5

What is a carboxyl terminus?

Answer 5

the last end made during polypeptide synthesis

Question 6

In the oligopeptide Phe-Glu-Gly-Ser-Ala, which residue has a free a-amino group, and which residue has a free a-carboxyl group?

Answer 6

Phe - amino group

Ala - carboxyl group

Question 7

What is a protease?

Answer 7

a proteolytic enzyme that cleaves peptide bonds

Question 8

What is cystine?

Answer 8

dimer of cysteine, residue that results from one cysteine residue besoms disulfide-bonded to another cysteine residue

Question 9

What is a denatured protein?

Answer 9

non-functional protein that is improperly folded. the protein’s shape is disrupted without breaking peptide bonds.

Question 10

How does urea affect protein?

Answer 10

urea disrupts hydrogen bonding by extremes of pH, extremes of temperature, and changes in salt concentration

Question 11

Primary Structure

Answer 11

simplest level of protein structure, the same as sequence

Question 12

Secondary Structure

Answer 12

initial folding of a polypeptide chain into shapes stabilized by hydrogen bonds between backbone NH and CO groups

Question 13

Parallel B-pleated sheets vs anti-parallel B-pleated sheets?

Answer 13

parallel sheets have polypeptide chains running in the same direction, anti-parallel have sheets running in the opposite direction

Question 14

If a single polypeptide folds once and forms a B-pleated sheet with itself, would this be a parallel or anti-parallel B-pleated sheet?

Answer 14

Anti-parallel

Question 15

Tertiary Structure

Answer 15

protein folding that concerns interaction between amino acid residues located more distantly from eachother

Question 16

Which of the following may be considered an example of tertiary protein structures?
I. van der Waals interactions between two Phe R-groups located far apart on a polypeptide
II. Hydrogen bonds between backbone amino acids
III. Covalent disulfide bonds between cysteine residues located far apart on a polypeptide

Answer 16

I and III

Question 17

What is a polypeptide subunit?

Answer 17

a single polypeptide chain that is part of a large complex containing many subunits

Question 18

Quaternary Structure

Answer 18

highest level of protein structure, the arrangement of subunits in a multisubunit complex

Question 19

What is the difference between a disulfide bridge involved in a quaternary structure and one involved in tertiary structure?

Answer 19

quaternary disulfides are bonds that form between chains that aren’t linked by peptide bonds. tertiary disulfides are bonds that form between residues in the same polypeptide.

Question 20

Why do fatty acids end in a carboxylic acid?

Answer 20

the chains are synthesized two carbons at a time for acetate

Question 21

How does the shape of an unsaturated fatty acid differ from that of a saturated fatty acid?

Answer 21

an unsaturated fatty acid is bent or kinked the double bond

Question 22

If fatty acids are mixed into water, how are they likely to associate with each other?

Answer 22

the long hydrophobic chains will interact with each other to minimize contact with water, exposing the charged carboxyl group the aqueous environment

Question 23

Would a saturated or an unsaturated fatty acid residue have more van Der Waals interaction with a neighboring alkyl chain in a bilayer membrane?

Answer 23

a saturated fatty acid would have more van Der Waals interactions. the bent shape of the unsaturated fatty acid means that it doesn’t fit in as well and has less contacted with neighboring groups

Question 24

What are the structural determinants of membrane fluidity?

Answer 24

degree of saturation, tail length, and amount of cholesterol

Question 25

How do double bonds affect membrane fluidity?

Answer 25

double bonds tend to increase membrane fluidity

Question 26

How does length affect membrane fluidity?

Answer 26

decreasing the length of a fatty acid tails increase fluidity

Question 27

How does cholesterol affect membrane fluidity?

Answer 27

increases fluidity at low temps, decreases fluidity at high temps; keeps fluidity at an optimum level

Question 28

How are linked phosphates able to provide so much energy?

Answer 28

linked phosphates act as a compressed spring waiting to fly open and provide energy