Unit 2.2a - Proteins (Amino Acids - General Info)

Question 1

composition of amino acids

Answer 1

• amino group
• carboxyl group
  (both bonded to the a-carbon)

Question 2

functional group of amino group

Answer 2

NH2 (positive)

Question 3

functional group of carboxyl group

Answer 3

COOH (negative)

Question 4

What does the carboxyl group dissociate into?

Answer 4

carboxylate anion (–COO-)
hydrogen ion (H+)

Question 5

Which group can accept electrons and which can donate electrons?

Answer 5

amino group: accept
carboxyl group: donate

Question 6

To which is the a-carbon bonded to?

Answer 6

to a hydrogen and to the side chain group, R

Question 7

portion of an amino acid that determines its identity

Answer 7

side chain group

Question 8

Two streoisomers of amino acids are designated as __- and __-amino acids based on similarity to glyceraldehyde.

Answer 8

L and D

Question 9

Two streoisomers of amino acids are designated as L- and D-amino acids based on?

Answer 9

similarity to glyceraldehyde

Question 10

molecules that differ from each other only in their configuration

Answer 10

stereoisomers

Question 11

Streoisomers are molecules that differ from each other only in their?

Answer 11

configuration

Question 12

All amino acids have at least one chiral center (a-carbon) and are chiral (stereoisomers), except?

Answer 12

glycine

Question 13

Except glycine, all amino acids have at least one ______ ________ (a-carbon) and are _______ (stereoisomers).

Answer 13

chiral center
chiral

Question 14

Vast majority of a-amino acids have the __ configuration at the a-carbon

Answer 14

L

Question 15

________ is usually in the L form

Answer 15

Proline

Question 16

Side chain carbons in amino acids other than glycine are designated with _______ symbols, starting at a-carbon.

Answer 16

Greek

Question 17

Amino acids can be referred to by ____-letter or __-letter codes

Answer 17

three
one

Question 18

group of amino acids that has nonpolar side chains

Answer 18

nonpolar amino acids

Question 19

9 nonpolar amino acids

Answer 19

Alanine
Valine
Leucine
Isoleucine
Glycine
Proline
Phenylalanine
Tryptophan
Methionine

Question 20

Structure (nonpolar)
Alanine
Valine
Leucine
Isoleucine

Answer 20

contain aliphatic hydrocarbon group

Question 21

Structure (nonpolar):
Proline

Answer 21

Has an aliphatic cyclic structure

Question 22

Structure (nonpolar):
Phenylalanine

Answer 22

Hydrocarbon is aromatic

Question 23

Structure (nonpolar):
Tryptophan

Answer 23

The side chains contain an indole ring (aromatic)

Question 24

Structure (nonpolar):
Methionine

Answer 24

The side chain contains a sulfur atom in addition to aliphatic hydrocarbon groupings

Question 25

group of amino acids that has polar side chains that are electrically neutral at neutral pH

Answer 25

polar-neutral amino acids

Question 26

Principle in polar-neutral amino acids

Answer 26

+ and - cancel out

Question 27

6 polar-neutral amino acids

Answer 27

Serine
Threonine
Tyrosine
Cysteine
Glutamine
Asparagine

Question 28

Structure (polar-neutral):
Serine
Threonine

Answer 28

the polar group is a hydroxyl (-OH) bonded to aliphatic hydrocarbon groups

Question 29

Structure (polar-neutral):
Tyrosine

Answer 29

the hydroxyl group (phenol) is bonded to an aromatic hydrocarbon group

Question 30

Structure (polar-neutral):
Cysteine

Answer 30

the polar side chain contains a thiol group (-SH)

Question 31

Structure (polar-neutral):
Glutamine
Asparagine

Answer 31

contain amide groups in their side chains

Question 32

2 Acidic Amino Acids

Answer 32

Aspartic Acid
Glutamic Acid

Question 33

Structure (Acidic):
Aspartic Acid
Glutamic Acid

Answer 33

have carboxyl groups in their side chains in addition to the one present in all amino acids

Question 34

In acidic amino acids, describe what happens to the carboxyl group.

Answer 34

carboxyl group can lose a proton, forming carboxylate anions

Question 35

In acidic amino acids, what is the charge of the side chains?

Answer 35

negatively charged at neutral pH

Question 36

3 Basic Amino Acids

Answer 36

Histidine
Lysine
Arginine

Question 37

In basic amino acids, what is the charge of the side chains?

Answer 37

side chains are positively charged at or near neutral pH

Question 38

Structure (Basic):
Lysine

Answer 38

side-chain amino group is attached to an aliphatic hydrocarbon chain

Question 39

Structure (Basic):
Arginine

Answer 39

side chain is a guanidino group bonded to an aliphatic hydrocarbon chain

Question 40

Structure (Basic):
Histidine

Answer 40

side chain is an imidazole group

Question 41

Average pKa of an a-carboxyl group

Answer 41

2.19

Question 42

Which is more acidic, a-carboxyl group or acetic acid?

Answer 42

a-carboxyl group (2.19)
**acetic acid’s pKa: 4.76

Question 43

Why do a-carboxyl groups have a greater acidity?

Answer 43

due to the electron-withdrawing inductive effect of the -NH3+ group

Question 44

Average value of pKa for an a-NH3_ group

Answer 44

9.47

Question 45

In a guanidine group, which is more basic, side chain of arginine or aliphatic amine?

Answer 45

side chain of arginine

Question 46

Basicity of guanidino group is attributed to the large ________ ___________ of the protonated form relative to the neutral form.

Answer 46

resonance stabilization

Question 47

side-chain imidazole group of histidine is a?

Answer 47

heterocyclic aromatic amine