Amino acids

R-groups non-polarpolaracidicbasic

proteins condensation between carboxylic acids and amines

+ + H2O

carboxylic acid amine amide

CO

OHNH C

O

N

Amides

amides resonance structure

alanine glycine Ala-Gly +H2O

dipeptide

CO

NC

O

N

CH2N

H

CO

OHCH3

CH2N

H

CO

OHH

CH2N

H

CO

H

CN

H

CO

OHHCH3

Polypeptides“backbone”

N1-C1-C1-N2-C2-C2-N3-C3-C3-

peptide bonds

_

H_H =

OOH

_

H_

H

=O

=

O

_R _R _

R

N-terminal residue

C-terminalresidue

biological activity = structure

protein structure 4 levels

Primary structure

sequence of amino acids

hemoglobin transports O2 and CO2 4 protein chains 300 amino acids

6th amino acid from N-terminus

Glu Val

-CH2CH2-CO2H -CH(CH3)2

R

Sickle cell anemia

water soluble water insoluble

Primary structure

study evolution

-chain 146 residueshorses - humans = 26 pigs - humans = 10 gorillas - humans = 11 successful change /

Primary structure -

10,000,000 years

selective hydrolysis

Phe-Val-Asn-Gln-His

His-Leu-Cys-Gly-Ser

Gly-Ser-His-Leu-Val

Gln-His-Leu-Cys

His-Leu-Val-Glu

Leu-Val-Glu-Ala

Phe-Val-Asn-Gln-His

His-Leu-Cys-Gly-Ser

Gly-Ser-His-Leu-Val

Gln-His-Leu-Cys

His-Leu-Val-Glu

Leu-Val-Glu-Ala

Secondary structure

hydrogen bonding backbone groups

H-bond donors

N1-C1-C1-N2-C2-C2-N3-C3-C3-

_

H_H =

OOH

_

H

_

H

=

O

=

O

_R _R _

R

H-bond acceptors

Two main secondary structures: -helix

-sheet

Alpha helix

Every C=O bonded to N-H 4 residues away

forms a helix core is backbone

R-groups outside

3.6 amino acids per turn

proline

breaks helix

=

O

C

no H-bondingC=

O

N

H

Beta sheet

Every C=O bonded to N-H far apart in 1o structureon different chains

peptide chains extended side-by-side

maximal H-bonding for anti-parallel chains

small R-groups above and below the sheet

if not -helix or -sheet random coil

Secondary structure

some proteins 1o structure amino acid sequence2o structure -helix

-sheet

-sheet silk

-helix collagen bone, teeth triple heliceskeratin hair, skin, wool, hooves

cross-linked with disulfide bonds

Disulfide bonds

cysteine -CH2-SH

S-H H-S C

H

N

C

C

H

N

C

reduced

[O]

S S C

H

N

C

C

H

N

C

oxidized

Protein function

enzymes biological catalystsimmunoglobulins antibodies

transport hemoglobin

hormones regulation

structural keratin, collagen

motion actin, myocin

function depends on structure