amino acids and proteins

Question 1

amino acids are…

Answer 1

Organic acids that have an amino group bonded to the α carbon atom, next to a carboxyl group.
All a-amino acids are chiral molecules (except for glycine)
The chirality center is the asymmetric α carbon atom

Question 2

How are amino acids classified

Answer 2

Nonpolar (hydrophobic)
Polar (hydrophilic)
acidic (hydrophilic)
Basic (hydrophilic)

Question 3

Acid-Base properties of amino acids

Answer 3

Amino acids exist as dipolar ions (zwitterions) that have both formal positive and formal negative charges. The overall charge is neutral.
The ammonium ion acts as an acid and the carboxylate as a base.

Question 4

Isoelectric point (pI)

Answer 4

Point at which a compound is electrically neutral.

Question 5

how to visualise fingerprints

Answer 5

used ninhydrin which reacts with an amino acid which cause a purple colour

Question 6

what causes an amino acid to from an amide

Answer 6

acylating agents cause this reaction

Question 7

Peptides formation

Answer 7

amide bonds can from beween the amino group of amino acid and the carboxylic acid group of a second amino acid.

Question 8

Peptides and proteins are

Answer 8

composed of 2-50 amino acids bound together with amide bonds. Proteins contain many more amino acid residues. amide bond is planar due to C=N bond.

Question 9

Disulfide bonds in peptides and proteins

Answer 9

the cysteine residues within a peptide or a protein form disulphide bonds to maintain folding and stability of the molecule.

Question 10

Hydrogen bond in peptides and proteins

Answer 10

The peptide chains form hydrogen bonds between them.
This causes the protein to have highly ordered domains called β sheet and α helix domains
There are also random domains of hydrogen-bonded peptide chains that are called random coil

Question 11

Protein denature:

Answer 11

leads to denaturation of the protein and is usually irreversible and leads to loss of biological activity

Question 12

how to determine protein structure 1st step

Answer 12

break the disulfide bonds and sepearte the individual peptide chains with peroxy formic acid.

Question 13

2nd step to determination of protein structure

Answer 13

cleave the amide bonds and partially hydrolyse the peptide chains
use proteases to cleave.
Trypsin cleaves at the C-terminal side of basic residues, Arg, Lys but not His
Chymotrypsin: cleaves at the C-terminal side of aromatic residues Phe, Tyr, Trp

Question 14

3rd step to determine protein structure

Answer 14

screen the amino acis using chromatographic methods

Question 15

Edman Degradation

Answer 15

The peptide chains are treated with phenyl isothiocyanate, followed by acid hydrolysis.
This produces a shorter peptide chain and a phenylthiohydantoin derivative that corresponds to amino acid.
The N-phenylthiohydantoin is analysed by HPLC-UV