Amino Acids Structures

Question 1

Answer 1

phe

neutral, nonpolar

aromatic

Question 2

Answer 2

asp

acidic, polar

• side chain is carboxyl after one CH₂

Question 3

Which amino acids are polar?

Answer 3

aliphatic - Ser, Thr, Cys, Gln, Asn

aromatic - Tyr

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Question 4

Answer 4

pro

neutral, nonpolar

not an amino acid, but a cyclic amino or imino acid

with a secondary amide contained within the ring

Question 5

the amine group has a pka normally around what?

and the carboxylic acid group?

Answer 5

the carboxyl group is normally around pH of 2

amine around pH of 9

Question 6

Answer 6

asn

neutral, polar

the amine in the side chain is NEVER protonated

• contains carboxamide (carboxyl w/ NH₂ replacing OH) attached to CH₂

Question 7

Answer 7

ser

neutral, polar

Question 8

Answer 8

alanine

Question 9

an amino acid has what 4 groups

Answer 9

a carboxyl, amine, carbon** side chain, and hydrogren

**except glycine has a hydrogen as the side chain

Question 10

What are the non-polar amino acids?

Answer 10

aliphatic - Met, Gly, Ala, Val, Leu, Ile, Pro,

aromatic - Phe, Trp

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Question 11

Which amino acids have acidic side chains?

Answer 11

Glu, Asp

• same as those with ‘negative’ side chains
• both have COOH groups

Question 12

Answer 12

tyr

neutral, polar

aromatic

• side chain is phenol

Question 13

Which amino acids have a net positive charge at neutral pH?

Answer 13

Arg, Lys, His

Question 14

Answer 14

met

neutral, nonpolar

• S comes after two CH₂s

Question 15

Which amino acids have basic side chains?

Answer 15

same as those with positive charge

His, Lys, Arg

• all also have N in their side chains

Question 16

Answer 16

leu

neutral, nonpolar

• one of the 3 brainched chain AAs

Question 17

Answer 17

thr

neutral, polar

2 chiral centers

Question 18

Answer 18

glu

acidic, polar

• side chain is carboxyl after two CH₂s

Question 19

Answer 19

Sec (Selenocysteine)

Neutral

Polar

• selenium replaces sulfur in cysteine’s thiol group

Question 20

Answer 20

ile

neutral, nonpolar

2 chiral centers (4 configurations)

Question 21

What amino acids have aliphatic side chains?

Answer 21

this is most easily remembered by just knowing the aromatic side chain amino acids and knowing that ALL others are aliphatic

Question 22

Which amino acids have a net negative charge at neutral pH?

Answer 22

Asp, Glu

Question 23

Answer 23

lys

basic, polar

• pka of side chain is more basic than amine
• side chain is an amino group after four CH₂s

Question 24

Answer 24

trp

neutral, polar

aromatic

• contains an indole (benzene + pyrrole) group attached to -CH₂ via the double bonded C of its pyrrole furthest from the N

Question 25

Answer 25

arg

basic, polar

• pka of side chain is more basic than amine
• side chain is guanidine after three CH₂s

Question 26

Answer 26

val

neutral, nonpolar

• one of the 3 branched-chain AAs

Question 27

Answer 27

gln

neutral, polar

• contains carboxamide (carboxyl w/ NH₂ replacing OH) attached to second CH₂

Question 28

Answer 28

his

basic, polar

aromatic

• side chain is imidazole attached to one CH₂ via the C furthest from the lone N

Question 29

Answer 29

cys

neutral, polar

• contains a thiol (R-S-H) on a CH₂

Question 30

What are the branched chain amino acids?

How can their structures be remembered?

Answer 30

Valine, Leucine and Isoleucine

• Valine is the simplest and contains a “V” of methyls branching off a carbon
• Leucine is just valine with an extra carbon
• Isoleucine is just leucine with its branching from the first carbon instead

Question 31

What amino acids have aromatic side chains?

Answer 31

Phe, Trp, Tyr, His

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Question 32

Answer 32

Glycine