PROTEIN PROTEIN STRUCTURES &STRUCTURES &

FUNCTIONSFUNCTIONS

FUNCTIONSProteins function as:1. Enzymes:biological catalysts2. Regulators of catalysis-hormones3. Transport and store i.e. O2, metal ions sugars, lipids, etc.

FUNCTIONS4. Contractile assemblies

Muscle fibers

5. SensoryRhodopsin nerve proteins

6. Cellular defense (antibodies/Ig) 7. Structural (collagen)

Proteins play key roles in a Proteins play key roles in a living systemliving system

examples of protein functions

Catalysis:Almost all chemical reactions in a living cell are catalyzed by protein enzymes.

Transport:Some proteins transports various substances, such as oxygen, ions, and so on.

Information transfer:For example, hormones.

Alcohol dehydrogenase oxidizes alcohols to aldehydes or ketones

Hemoglobin carries oxygen

Insulin controls the amount of sugar in the blood

Amino acid: Basic unit of Amino acid: Basic unit of proteinprotein

COO-NH3+ C

R

HAn amino

acid

Different side chains, R, determin the properties of 20 amino acids.

Amino group Carboxylic acid group

20 20 Amino acidsAmino acidsGlycine

(G)

Glutamic acid (E)Asparatic acid (D)

Methionine (M)

Threonine (T)

Serine (S)

Glutamine (Q)

Asparagine (N)

Tryptophan (W)Phenylalanine (F)

Cysteine (C)

Proline (P)

Leucine (L)Isoleucine (I)Valine (V)

Alanine (A)

Histidine (H)Lysine (K)

Tyrosine (Y)

Arginine (R)

White: Hydrophobic, Green: Hydrophilic, Red: Acidic, Blue: Basic

Proteins are linear polymers Proteins are linear polymers of amino acidsof amino acids

R1

NH3＋

C CO

H

R2

NH C CO

H

R3

NH C CO

H

R2

NH3＋

C COOー

H＋

R1

NH3＋

C COOー

H＋

H2OH2O

Peptide bond

Peptide bond

The amino acid sequence is called

as primary structure A AF

NGG

S TS

DK

A carboxylic acid condenses with an amino group with the release of a water

Amino acid sequence is Amino acid sequence is encoded by DNA base encoded by DNA base sequence in a genesequence in a gene

・CGCGAATTCGCG・

・GCGCTTAAGCGC・

DNA molecule

＝

DNA base sequence

Amino acid sequence is Amino acid sequence is encoded by DNA base encoded by DNA base sequence in a genesequence in a gene

Second letterT C A G

Firs

t lette

r

T

TTTPhe

TCT

Ser

TATTyr

TGTCys

T

Th

ird le

tter

TTC TCC TAC TGC CTTA

LeuTCA TAA

StopTGA Stop A

TTG TCG TAG TGG Trp G

C

CTT

Leu

CCT

Pro

CATHis

CGT

Arg

TCTC CCC CAC CGC CCTA CCA CAA

GlnCGA A

CTG CCG CAG CGG G

A

ATTIle

ACT

Thr

AATAsn

AGTSer

TATC ACC AAC AGC CATA ACA AAA

LysAGA

ArgA

ATG Met ACG AAG AGG G

G

GTT

Val

GCT

Ala

GATAsp

GGT

Gly

TGTC GCC GAC GGC CGTA GCA GAA

GluGGA A

GTG GCG GAG GGG G

Basic structural units of Basic structural units of proteins: Secondary structureproteins: Secondary structure

α-helix β-sheet

Secondary structures, α-helix and β-sheet, have regular hydrogen-bonding patterns.

Three-dimensional Three-dimensional structure of proteinsstructure of proteins

Tertiary structure

Quaternary structure

Hierarchical nature of Hierarchical nature of protein structureprotein structure

Primary structure (Amino acid sequence)↓

Secondary structure （ α-helix, β-sheet ）↓

Tertiary structure （ Three-dimensional structure formed by assembly of secondary

structures ）↓

Quaternary structure （ Structure formed by more than one polypeptide chains ）