Proteins

1o structure amino acid sequence

2o structure - helix -sheet

H-bonding betweenC=O and N-H of backbone

- +

some proteins only have 1o and 2o structure:

fibroin (silk) -sheet

keratincollagen

hairskin

- helixinsoluble in H2O

non-polar residues

Fibrous

Gly-Glu- His-Ala-Phe-Ser-Ser-Val- His-Ile-Met-Arg-Asp-Val- Asn-

Tertiary structurePrimary structure sequence of amino acids

Alanine

Non-polar

Phenylalanine

Polar

Serine

Valine

Acidic or Basic

Glutamic acidHistidine

Isoleusine Methionine

Arginine

AsperagineAspartic acid

Glycine

Ala-Phe-Ser-Ser-Val-Glu-His-Ile-Met-Arg-Asp-Val-His-Asn-Gly

Tertiary structureAla-Phe-Ser-Ser-Val-Glu-His-Ile-Met-Arg-Asp-Val-His-Asn-Gly

arrange these in an -helix

Ala 1

Phe2

Ser3

Ser

4

Val 5Glu

6

His7

Ile8

Met9

Arg10

Asp11

Val 12

His13

Asn14

Gly15

non-polarpolarinterior

exterior

Tertiary structure

interaction of the R-groups-

-

+

-+

-

- +

proteins fold aroundnon-polar groups

globular proteins

hydrophobic residues inside

polar and charged residues outside

Tertiary structure

1. Hydrophobic interactions non-polar R-groups

LDF2. Hydrogen bonding

between H-bonddonors and acceptors

polar R-groups

3. Ionic bonds (salt bridges) acidic and basic R-groups

4. Covalent bonds (disulfide) cysteins

ion-ion

interactions of R-groups

CH3

NH+

N-terminus

C-terminus

Pro

Ala Phe

Arg

Asp

Pro

SS Cys

Cys

His

His

-O-CH O

= Fe2+

Quaternary Structuresubunits

hemoglobin heme groups 4 - Fe

globin chains 2 -chains2 - chains

held in position by interaction of R-groups

polar histidine inside - holds Fe2+

pKa = 6.1

C

H

H3N+

CO

O-

NH

N

Denaturationform is function

loss of native configuration denaturation

denaturation peptide bonds not affected

H-bondsdisulfide bondsionic bondsL.D.F.

disrupted

Denaturation

4o structure disrupted first subunits separate

3o structure disrupted protein unfolds

2o structure disrupted H-bonds broken

treatments are sometimes reversible renaturedsometimes irreversible

insulin

Denaturing treatments

1. Heat above 50-60oC frying eggsunburn

2. pH disrupt salt bridgesapproach pHI

3. detergents unfold globular proteins SDS

SO4-

Na+

-

-

+

-+

-

- +

Denaturing treatments4. reducing agents

S-S SH HS

5. Metal salts Hg+, Pb+, Ag+ S-Hg

C =O_O-

Hg+

6. H-bonding solvents alcoholacetone

7. “Chaotropes”

urea guanidine

oxidizing agents

CH2N NH2

O

CH2N NH2

NH

Words of Wisdom

3. detergents

6. H-bonding solvents alcohol

1. Heat sunburn