Biochemistry Chapter 1: AA, Peptides & Proteins (4 Stars)

Question 1

Amino acids have four groups attached to a central (alpha) carbon: an amino group, a carboxylic acid group, ______, and an R group

Answer 1

hydrogen atom

Question 2

The R group determines chemistry and ______ of that amino acid.

Answer 2

Function

Question 3

______ amino acids appear in the proteins of eukaryotic organisms.

Answer 3

20

Question 4

The stereochemistry of the alpha-carbon is ____ for all chiral amino acids in eukaryotes.

Answer 4

l

Question 5

d-amino acids can exist in ___________.

Answer 5

prokaryotes.

Question 6

All chiral amino acids except _____have (S) configuration.

Answer 6

cysteine

Question 7

All amino acids are chiral except ____,

Answer 7

glycine, which has a hydrogen atom as its R group.

Question 8

Nonpolar, nonaromatic: 7

Answer 8

glycine, alanine, valine, leucine, isoleucine, methionine, proline

Question 9

Aromatic: 3

Answer 9

tryptophan, phenylalanine, tyrosine

Question 10

Polar: 5

Answer 10

serine, threonine, asparagine, glutamine, cysteine

Question 11

Negatively charged (acidic): 2

Answer 11

aspartate, glutamate

Question 12

Positively charged (basic): 3

Answer 12

lysine, arginine, histidine

Question 13

Amino acids with long alkyl chains are _____, and those with charges are ______many others fall somewhere in between

Answer 13

hydrophobic hydrophilic

Question 14

Amino acids are ______; that is, they can accept or donate protons.

Answer 14

amphoteric

Question 15

The pKa of a group is the_____ at which half of the species is deprotonated;

Answer 15

pH

Question 16

At low (acidic) pH, the amino acid is ______.

Answer 16

fully protonated.

Question 17

At pH near the pI of the amino acid, the amino acid is a _______.

Answer 17

neutral zwitterion.

Question 18

At high (alkaline) pH, the amino acid is______

Answer 18

fully deprotonated.

Question 19

The isoelectric point (pI) of an amino acid without a charged side chain can be calculated by averaging the ____# ______ values.

Answer 19

two pKa values.

Question 20

The titration curve is nearly flat at the _____ values of the amino acid.

Answer 20

pKa

Question 21

The titration curve is nearly ______ at the pI of the amino acid.

Answer 21

vertical

Question 22

Amino acids with charged side chains have an additional _____ value, and their pI is calculated by averaging the _____ values that correspond to protonation and deprotonation of the zwitterion.

Answer 22

pKa

Question 23

Amino acids without charged side chains have a pI around ____

Answer 23

6.

Question 24

Basic amino acids have a pI well above____.

Answer 24

6

Question 25

Dipeptides have two amino acid residues; tripeptides have three. Oligopeptides have a _______

Answer 25

few amino acid resides (20).

Question 26

Forming a _____ bond is a condensation or dehydration reaction (releasing one molecule of water).

Answer 26

peptide

Question 27

The nucleophilic amino group of one amino acid attacks the electrophilic ______ group of another amino acid.

Answer 27

carbonyl

Question 28

Amide bonds are rigid because of ______

Answer 28

resonance.

Question 29

Breaking a peptide bond is a ______ reaction.

Answer 29

hydrolysis

Question 30

Primary structure is the

Answer 30

linear sequence of amino acids in a peptide and is stabilized by peptide bonds.

Question 31

Secondary structure is the local structure of neighboring amino acids, and is stabilized by ______ bonding between amino groups and nonadjacent carboxyl groups.

Answer 31

hydrogen

Question 32

alpha-helices are _____ coils around a central axis.

Answer 32

clockwise

Question 33

Beta-pleated sheets are rippled strands that can be _____ or _____

Answer 33

parallel or antiparallel.

Question 34

Proline can interrupt _______ structure because of its rigid cyclic structure.

Answer 34

secondary

Question 35

Tertiary structure is the three-dimensional shape of a single polypeptide chain, and is stabilized by _______ interactions, acid–base interactions (salt bridges), hydrogen bonding, and disulfide bonds.

Answer 35

hydrophobic

Question 36

Hydrophobic interactions push hydrophobic R groups to the interior of a protein, which increases _____ of the surrounding water molecules and creates a negative Gibbs free energy.

Answer 36

entropy

Question 37

Disulfide bonds occur when two cysteine molecules are ______ and create a covalent bond to form cystine.

Answer 37

oxidized

Question 38

Quaternary structure is the interaction between _____ in proteins that contain multiple subunits.

Answer 38

peptides