amino acids

Question 1

Glycine

Accepted Answer

GLY Aliphatic, hydrophobic R= H Prefer an environment within a protein shielded from water

Question 2

Alanine

Accepted Answer

ALA Aliphatic, hydrophobic R= -CH3 Prefer an environment within a protein shielded from water

Question 3

Valine

Accepted Answer

VAL Aliphatic, hydrophobic CH3 | R= -CH3 | CH3 Prefer an environment within a protein shielded from water

Question 4

Leucine

Accepted Answer

LEU Aliphatic, hydrophobic CH3 | R= -CH2-CH3 | CH3 Prefer an environment within a protein shielded from water

Question 5

Isoleucine

Accepted Answer

ILE Aliphatic, hydrophobic CH3 | R= CH-CH2-CH2-CH3 Prefer an environment within a protein shielded from water

Question 6

Proline

Accepted Answer

PRO Aliphatic, hydrophobic CH2 / \ CH2 CH2 | | R= +H3N --- C-COO- | H Mainly aliphatic but difficult to fit into category, mainly hydrophobic Prefer an environment within a protein shielded from water

Question 7

Serine

Accepted Answer

SER Hydroyl R=CH2OH Hard to ionize (very high Pka) Relevant to enzyme mechanism

Question 8

Threonine

Accepted Answer

THR Hydroyl OH | R= -CHCH3

Question 9

Cysteine

Accepted Answer

CYS Sulfur R groups R= CH2SH Weakly polar, generally hydrophilic Sulfhydryl group is ionizable

Question 10

Methionine

Accepted Answer

MET Sulfur R groups R= -CH2-CH2-S-CH3 Weakly polar, generally hydrophilic

Question 11

Phenylalanine

Accepted Answer

PHE Aromatic R= benzene Hydrophobic

Question 12

Tyrosine

Accepted Answer

TYR Aromatic R= benzene - OH Some hydrophobic character but tempered by polar OH groups in side chain Can be ionized at high pH

Question 13

Tryptophan

Accepted Answer

TRP Aromatic R= SEE NOTES

Question 14

UV abs.

Accepted Answer

TRP, TYP & PHE conjugated rings exhibit strong UV abs. A280 (TYR, TRP) + A260 (PHE) (A280 responsible for most UV absorbance in proteins)

Question 15

Lysine

Accepted Answer

LYS Basic R= -CH2CH2CH2-NH3+ pKa2 ~9 Positively charged at physiological pH

Question 16

Arginine

Accepted Answer

ARG Basic R= -CH2CH2CH2-NH-C-NH2 || NH2+ pKa2 ~9 Positively charged at physiological pH

Question 17

Histidine

Accepted Answer

HIS
Basic (less basic than LYS and ARG)
R= SEE NOTES
pKa imidazole = 6.5-7.4
pKa free a.a. ~6
pKa in proteins ~7
Side chain can exchange protons near physiological pH. Often it plays role in enzymatic mechanisms

Question 18

Basic a.a. properties

Accepted Answer

strongly polar. Found on exterior surfaces of proteins. They are hydrated with surround aqueous environment

Question 19

Aspartic Acid

Accepted Answer

ASP Acidic O || R= -CH2C-O- pKa2 ~4 Carry negative charge @pH 7 Only if pH < pKa, carboxyl groups neutralized, becomes aspartate Tend toward protein surface + in contact with water

Question 20

Asparginine

Accepted Answer

ASN Acidic O || R= -CH2-C-NH2 Unlike acidic analog, have uncharged side chains though decidedly polar Like acidic analog tend toward protein surface + in contact with water

Question 21

Glutamic Acid

Accepted Answer

GLU Acidic O || R= -CH2-C-O- pKa2 ~4 Carry negative charge @pH 7 Only if pH < pKa, carboxyl groups neutralized, becomes glutamate Tend toward protein surface + in contact with water

Question 22

Glutamine

Accepted Answer

GLN O || R= -CH2-C-NH2 Unlike acidic analog, have uncharged side chains though decidedly polar Like acidic analog tend toward protein surface + in contact with water

amino acids

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