Amino Acids and Proteins, Slides of Chemistry

Download Amino Acids and Proteins and more Slides Chemistry in PDF only on Docsity!

AMINO ACIDS AND

PROTEINS

PROTEIN FUCTION

Catalyst  enzyme

Transport  blood, membrane protein

Nutrient  seed protein, ovalbumin, casein

Skeletons  collagen, keratin, fibroin

Defense  immunoglobulin, fibrinogen,

thrombin

Regulator  hormone

Protein is a polymer of “amino acid”

monomers

AMINO ACIDS IN SOLUTION

H

NH

2

COOH

C

R

H

NH

3

COO

C

R

Un-ionized Zwitterion (ion dipolar)

H

NH

2

COOH

C

R

H

NH

2

COOH

C

H

Glisin

AMINO ACIDS AT VARIOUS pH

H

NH

2

COO

C

R

H

NH

3

COO

C

R

H

NH

3

COOH

C

R

pH = 1 pH = 7 pH = 11

AMINO ACID

The R group of each amino acid is different

Structure

Size

Charge

Solubility

Amino acid groups:

Non-polar aliphatic R groups

Aromatic R groups

Polar un-charged R groups

Negatively charged R groups

Positively charged R groups

AMINO ACID “R” GROUP

CYSTINE

AMINO ACID

Examples of non-standard amino acids

• 4-hydroxyproline  plant cell walls
• 5-hydroxylysine  collagen
• N-methyllisine  myosin
• γ-carboxyglutamate  prothrombin
• Selenocysteine  glutathione

peroxidase

• Ornithine, citrulline in watermelon

AMINO ACID

Each amino acid has a specific titration curve

Each amino acid has different acid and base

properties.

TITRATION CURVE

Titration curve of 0.1 M Alanine

NINHYDRIN REACTION

PEPTIDE BONDS

PEPTIDE BONDS (cont.)

Two amino acids  dipeptide

Three amino acids  tripeptide

Several amino acids  oligopeptide

Many amino acids  polypeptide

(MW < 10,000)

Read from left (N-terminal) to right (C-terminal)

Peptide bonds are very stable  hydrolysis of

peptide bonds  exergonic reaction

Disulfide bonds are also very important especially

those that function extracellularly

Eg: insulin and immunoglobulin

PEPTIDE

Terminal amino residues

H

H

3

N C C

R

1

O H

N C C

R

2

O H

N C C

R

3

O H

N C C

R

4

O H

N C C

R

5

O

O

Terminal carboxyl residue

Pentapeptide

= R

= R