AMINO ACID CHEMISTRY

Question 1

Show the general structure of an amino acid and label the asymmetric carbon atom (LO)

Answer 1

draw 20 amino acid (esp GLY,GLU,HIS)

Question 2

Show the difference between D and L amino acids (LO)

Answer 2

L- Nh2 on the left ( found in nature)
D -NH2 on the right

Question 3

Define standard and non-standard amino acid with exp(LO)

Answer 3

Standard- AA for which at least one codon exists in the genetic code
Non-standard- consist of AA residues that have been chemically modified aft incorporation into polypeptide

Question 4

List few exp of amino acid modified post-translationally(SLS). (LO)

Answer 4

4-hydroxyproline- hydroxylation of proline residues aft incorporation into polypeptide chains. in collagen

5-hydroxylysine- hydroxylation of lysine residues aft incorporation into polypeptide chains. in collagen

gamma- carboxyglutamate- carboxylation of conversion of glutamate.in prothrombin

methyl lysine- methlyation of lysin. in histone proteins

Diphthamide- methylation of histine. in elongation factor 2( involved in DNA regulation)

Question 5

Amino acids are ampholytes

Answer 5

they contain both basic(amino) and acidic(carboxyl) grps.

Question 6

define alpha carbon

Answer 6

carbon that is linked to the carboxylate, amino and R groups

Question 7

Which amino acid does not have a primary amino grp?

Answer 7

Proline (secondary amino grp)

Question 8

pH 7.4

Answer 8

coo-,NH3+ formed ( Zwitter ion)

Question 9

what is asymmetric carbon atom/ chiral carbon?

Answer 9

A carbon atom attached to 4 dif types of atoms/ grp of atom

Question 10

Which standard AA is symmetric?

Answer 10

Glycine because its R grp is H atom.no chiral carbon. no optical rotation

Question 11

describe stereoisomers

Answer 11

• not superimposable
• mirror images called enantiomers
• D and L enantiomers have dif optical rotation

Question 12

state 5 common D amino acids

Answer 12

D-serine
D- aspartate
D- phenylalanine
D-alanine and D glutamate

Question 13

D-serine

Answer 13

• in mammal brains
• co- agonist of NMDA type glutamate receptors responsible for learning,memory and behaviour
• Alzheimers

Question 14

D- aspartate

Answer 14

-regulator in adult neurogenesis
- Alzheimers
- development of endocrine function ( mainly in pituitary gland and testes), regulation of the release and synthesis of LH

Question 15

D- phenylalanine

Answer 15

in cyclic peptide antibiotics tyrocidin and gramicidin S
-decrease pain

Question 16

D-alanine and D glutamate

Answer 16

in cell walls of gram positive bacteria
-involved in peptidoglycan biosynthesis

Question 17

dextrorotary behavior

Answer 17

+ form with clockwise rotation (rotate the plane of plane-polarized light.

Question 18

levorotary behavior

Answer 18

• form with anticlockwise rotation

Question 19

L enantiomer that is dextrorotary.

Answer 19

L (+) alanine

Question 20

which AA does not have D and L forms.

Answer 20

Glycine has H atom as a side chain
- does not have chiral C
-does not form stereoisomers
- no D or L configurations
- no chiral C, does not rotate the plane of plane-polarized light.

Question 21

Name AA with 2 assymetric C atoms. and num of their stereoisomers

Answer 21

Isoleucine and threonine
2 power of n= 4 stereoisomers possible

Question 22

which AA can be involved in buffering

Answer 22

GLU AND HIS

Question 23

Which amino acid is an imino acid

Answer 23

Proline

Question 24

standard amino acids

Answer 24

all 20

Question 25

non-standard AA

Answer 25

AKA Non-protein AA
post translationally modifies amino acids: hydroxyproline
derived alpha AA- Ornithine,Citrulline,Homocystein( high mean high cardio disease risk)
non-derived alpha AA- beta-alanine,GABA(gamma amino butyric acid)

Question 26

define post-translational modification of an AA

Answer 26

AA in protein from chemical modification of standard amino acids