LECTURE 3: Amino Acids & Proteins

Question 1

How many substituents does the alpha-carbon atom have and what does that make it?

Answer 1

4 & Chiral

Question 2

What determines the identity and properties of the amino acid?

Answer 2

The R group

Question 3

All amino acids have mirror images, except which one? EXPLAIN WHY

Answer 3

Glycine - it is the only one that does not have a chiral centre, and therefore, it lacks stereoisomers or mirror images.

Question 4

What form are the amino acids in proteins in? (chirality)

Answer 4

L (laevus) form

Question 5

What form are the amino acids in bacterial cell walls in? (chirality)

Answer 5

D (dexter) form

Question 6

Best unit for expressing acid strength

Answer 6

pKa

Question 7

Higher pKa means

Answer 7

smaller Ka and weaker acid

Question 8

Lower pKa means

Answer 8

higher Ka

Question 9

Carboxyl group in zwitterion

Answer 9

Carboxyl group is deprotonated, COO-

pKa= 3.1

Question 10

Amino group in zwitterion

Answer 10

Amino group is deprotonated, NH3+

pKa=8.0

Question 11

What is a zwitterion

Answer 11

amino acids in solution at a neutral pH (7.0) exist predominantly as dipolar ions called zwitterions.

Question 12

Glycine, Gly, G

Answer 12

• R-group is -H
• shows no chirality
  -provides flexibility to proteins where other side chains would be too bulky

Question 13

Alanine, Ala, A

Answer 13

• R group is -CH3
• aliphatic side chain
• small size, no reactivity
• non-polar
• hydrophobic

Question 14

Proline, Pro, P

Answer 14

• pyrrolidine ring
• imposes tight restraints on the conformation of the protein
• found in proteins that need to be rigid e.g. collagen, and in turns of globular proteins.

Question 15

Serine, Ser, S

Answer 15

• R group is -CH2-OH
• hydroxyl functional group
• polar due to electronegativity values between O and H
• hydrophilic
• often found in active sites of enzymes

Question 16

Histidine, His, H

Answer 16

• R group imidazole ring
• pKa 6.7, can be neutral or positively charged
• found in active site of enzymes

Question 17

What is an imidazole ring?

Answer 17

A five-membered aromatic ring

Question 18

Cysteine, Cys, C

Answer 18

• R group is -CH2-SH
• thiol functional group
• hydrophobic amino acid
• pKa of 8.4

Question 19

Positively charged R group amino acids

Answer 19

Arginine
Lysine
Histidine

Question 20

Hydrophobic amino acids with non-polar R groups

Answer 20

Glycine
Alanine
Valine
Cysteine
Proline
Leucine
Isoleucine
Methionine
Tryptophan
Phenylalanine

Question 21

Polar amino acids with neutral R groups

Answer 21

Serine
Threonine
Tyrosine
Asparagine
Glutamine

Question 22

Negatively charged R groups

Answer 22

Aspartate
Glutamate

Question 23

Residue

Answer 23

Each amino acid unit within a polypeptide

Question 24

N-terminal

Answer 24

Amino acid sequences are written starting with the amino acid terminal residue

Question 25

C-terminal

Answer 25

End of amino acid sequence

Question 26

Purines

Answer 26

Adenine and guanine
- bigger looking structure

Question 27

Pyrimidines

Answer 27

Cytosine, thymine and uracil
- singular looking structure

Question 28

What type of inhibitor is PALA

Answer 28

competitive inhibitor