1: Amino Acids: Concept Summary

Question 1

Amino Acids have four groups attached to a central (alpha) carbon: ______, _____, ______, ______

Answer 1

Amino group, Carboxylic Acid Group, Hydrogen Atom, R group

Question 2

The _____ determines the chemistry and function of that amino acid.

Answer 2

R group

Question 3

_______ amino acids appear in the proteins of eukaryotic organisms

Answer 3

Twenty

Question 4

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

Answer 4

L

Question 5

____-amino acids can exist in prokaryotes

Answer 5

D

Question 6

All chiral amino acids except _____ have (S) configuration

Answer 6

cysteine

Question 7

All amino acids are chiral except ____, which has a hydrogen atom as its R group

Answer 7

glycine

Question 8

____ can be polar/nonpolar, aromatic/nonaromatic, charged/uncharged

Answer 8

Side chains

Question 9

Nonpolar, nonaromatic amino acids: (7)

Answer 9

Glycine, Alanine, Valine, Leucine, Isoleucine, Methionine, Proline

Question 10

Aromatic: (3)

Answer 10

Tryptophan, Phenylalanine, Tyrosine

Question 11

Polar: (5)

Answer 11

Serine, Threonine, Asparagine, Glutamine, Cysteine

Question 12

Negatively charged (acidic): (2)

Answer 12

Aspartate, Glutamate

Question 13

Positively charged (basic): (3)

Answer 13

Lysine, Arginine, Histidine

Question 14

Amino acids with __________ are hydrophobic

Answer 14

long alkyl chains

Question 15

Amino acids with ______ are hydrophilic

Answer 15

charges

Question 16

Amino acids are amphoteric. What does this mean?

Answer 16

they can accept or donate protons

Question 17

The _____ of a group is the pH at which half of the species is deprotonated; [HA] = [A-]

Answer 17

pKa

Question 18

T/F: Amino acids do not exist in different forms at different pH values.

Answer 18

False

Question 19

At pH near the pI of the amino acid, the amino acid is ____________

Answer 19

a neutral zwitterion

Question 20

At high (alkaline) pH, the amino acid is ___________

Answer 20

fully deprotonated

Question 21

The ____________ of an amino acid without a charged side chain can be calculated by averaging the two pKa values.

Answer 21

isoelectric point (pI)

Question 22

Amino acids can be _______.

Answer 22

titrated

Question 23

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

Answer 23

flat

Question 24

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

Answer 24

vertical

Question 25

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

Answer 25

pKa value

Question 26

Amino acids without charged side chains have a pI of around ___.

Answer 26

6

Question 27

____ amino acids have a pI well below 6.

Answer 27

Acidic

Question 28

____ amino acids have a pI well above 6.

Answer 28

Basic

Question 29

_____ have two amino acid residues

Answer 29

Dipeptides

Question 30

_____ have three amino acid residues

Answer 30

Tripeptides

Question 31

_______ have a “few” amino acid residues (<20)

Answer 31

Oligopeptides

Question 32

______ have “many” amino acid residues (>20)

Answer 32

Polypeptides

Question 33

Forming a peptide bond is a ______ or _____ reaction (releasing 1 molecule of water).

Answer 33

condensation, dehydration

Question 34

The ______ amino group of one amino acid attacks the ______ carbonyl group of another amino acid.

Answer 34

nucleophilic amino

electrophilic carbonyl

Question 35

Amide bonds are rigid because of _____.

Answer 35

resonance

Question 36

Breaking a peptide bond is a ______ reaction.

Answer 36

hydrolysis

Question 37

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

Answer 37

Primary structure

Question 38

______ is the local structure of neighboring amino acids and is stabilized by hydrogen boding between amino groups and nonadjacent carboxyl groups

Answer 38

Secondary Structure

Question 39

____ are clockwise coils around a central axis

Answer 39

Alpha-helices

Question 40

__________ are rippled strands that can be parallel or antiparallel.

Answer 40

Beta-pleated sheets

Question 41

_____ can interrupt secondary structure because of its rigid cyclic structure

Answer 41

Proline

Question 42

________ is the 3D shape of a single polypeptide chain and is stabilized by hydrophobic interactions, acid-base interactions (salt bridges), hydrogen bonding, and disulfide bonds.

Answer 42

Tertiary Structure

Question 43

_______ push hydrophobic R groups to the interior or a protein, which increases entropy of the surrounding water molecules and creates a negative Gibbs free energy.

Answer 43

Hydrophobic Interactions

Question 44

_______ occur when two cysteine molecules are oxidized and create a covalent bond to form cystine.

Answer 44

Disulfide bonds

Question 45

________ is the interaction between peptides in proteins that contain multiple subunits.

Answer 45

Quaternary Structure

Question 46

Proteins with covalently attached molecules are termed _________

Answer 46

conjugated proteins

Question 47

The attached molecule in conjugated proteins are termed ______, and may be a metal ion, vitamin, lipid, carbohydrate or a nucleic acid

Answer 47

Prosthetic group

Question 48

Both heat and increasing solute concentration can lead to loss of 3D protein structure, which is termed _______

Answer 48

denaturation