PROTEIN STRUCTURE

Primary Structure – the sequence of amino acids

PRIMARY STRUCTURE

Sequence of amino acids in protein linked by

covalent amide (peptide) bonds

CONDENSATION AMINO ACIDS: AMIDES OR

PEPTIDE BONDS

COHCH

NH2

CH3

O

C

O

NH2CH2 OH

C

C

O

CH

O

CH2CH2

NH2

NH2OH

+ +

CNCH

NH3

+

CH3

O

CNCH

CH3

O

C

C

O

CH

O

CH2CH2

NH2

O-H

H

alanine glycine glutamine

Peptide or amide bond

Amino acids condense

to form amides – or

peptide bonds

Protein chain made up

of amino acids

covalently bonded by

amide bonds

SEQUENCE MATTERS

Functioning proteins have

unique primary structure –

sequence of amino acids

in the chain

This primary sequence

determines how the

protein folds into 3-D

shape required for protein

function

Sequence has a free

amino end (N-terminal

amino acid)

Sequence has free

carboxyl end (C-terminal

amino acid

COHCH

NH2

CH3

O

C

O

NH2CH2 OH

C

C

O

CH

O

CH2CH2

NH2

NH2OH

+ +

CNCH

NH3

+

CH3

O

CNCH

CH3

O

C

C

O

CH

O

CH2CH2

NH2

O-H

H

alanine glycine glutamine

Peptide or amide bond

N-terminal amino acid

alanine (free amino end)

C-terminal amino acid glutamine (free carboxyl end)

SEQUENCE MATTERS

When 3 amino acids

reacted together, 6

possible different

tripeptides result

Sequence of amino acids

in proteins determined by

sequence of nucleotides

on m-RNA, which is

transcribed from DNA

COHCH

NH2

CH3

O

C

O

NH2CH2 OH

C

C

O

CH

O

CH2CH2

NH2

NH2OH

+ +

alanine glycine glutamine

Possible sequences

ala-gly-gln

ala-gln-gly

gly-ala-gln

gly-gln-ala

gln-ala-gly

gln-gly-ala

POLYPEPTIDE HORMONES

Vasopressin (antidiuretic

hormone

• 9 amino acid polypeptide

forms cyclic structure

• N terminal amino acid:

glycine

• No C terminal amino acid

(due to ring structure)

• Conserves body fluids

, reduces loss of water in

urine

• Leads to constriction of

blood vessels, increase in

blood pressure

POLYPEPTIDE HORMONES

Oxytocin

• 9 amino acid polypeptide with

cyclic structure

• N-terminal amino acid: glycine

• No C-terminal amino acid

• Well studied effects:• Stimulates milk production

• Stimulates muscle contraction

for birth

• Promotes maternal behavior

• Possible association with

development of human

bonding an interpersonal

relationships

• Compare structure to

vasopressin: 2 amino acids

different – very different

physiological effects!

PROTEIN PRIMARY STRUCTURE

Lysozyme

• Enzyme breaks down bacterial cell walls

• Found in egg whites, human tears

• Single polypeptide chain of 129 amino acids

• N-terminal amino acid is lysine

• C-terminal amino acid is leucine

Disulfide bonds considered to be part of tertiary structure.