protein english aug 2006

8/2/2019 Protein English Aug 2006

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Fundamentals ofProtein Structure


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Proteins play key roles in a

living systemThree examples of protein functions

Catalysis:Almost all chemical reactions in a

living cell are catalyzed by proteinenzymes.

Transport:Some proteins transports varioussubstances, such as oxygen, ions,

and so on.Information transfer:For example, hormones.

Alcoholdehydrogenaseoxidizes alcoholsto aldehydes or

ketones

Haemoglobincarries oxygen

Insulin controlsthe amount ofsugar in theblood


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Amino acid: Basic unit of

protein

COO-NH3+ C

R

HAn amino acid

Different side chains,R, determin theproperties of 20amino acids.

Amino group Carboxylic

acid group


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20 Amino 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


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Proteins are linear polymers ofamino acids

R1

NH3 C CO

H

R2

NH C CO

H

R3

NH C CO

H

R2

NH3 C COO

H

R1

NH3 C COO

H

H2OH2O

Peptidebond PeptidebondThe amino acid

sequence is called as

primary structure

A AF

NG GS

T

S

DK

A carboxylic acid

condenses with an aminogroup with the release of awater


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Amino acid sequence is encoded

by DNA base sequence in a geneCGCGAATTCGCG

GCGCTTAAGCGC

DNAmolecule

DNA basesequence


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Amino acid sequence is encoded

by DNA base sequence in a geneSecond letterT C A G

Firstle

tter

T

TTTPhe

TCT

Ser

TATTyr

TGTCys

T

Thirdle

tter

TTC TCC TAC TGC C

TTA Leu TCA TAA Stop TGA Stop ATTG TCG TAG TGG Trp G

C

CTT

Leu

CCT

Pro

CATHis

CGT

Arg

T

CTC CCC CAC CGC C

CTA CCA CAAGln

CGA A

CTG CCG CAG CGG G

A

ATT

Ile

ACT

Thr

AAT

Asn

AGT

Ser

T

ATC ACC AAC AGC C

ATA ACA AAALys

AGAArg

A

ATG Met ACG AAG AGG G

G

GTT

Val

GCT

Ala

GATAsp

GGT

Gly

T

GTC GCC GAC GGC C

GTA GCA GAAGlu

GGA A

GTG GCG GAG GGG G


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Gene is proteins blueprint,

genome is lifes blueprint

Gene

DNA

Protein


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Each Protein has a unique

structure

Amino acid sequence

NLKTEWPELVGKSVEEAKKVILQDKPEAQIIVLPVGTIVTMEYRIDRVRLFVDKLDNIAEVPRVG

Folding!


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Basic structural units of proteins:Secondary structure

-helix -sheet

Secondary structures, -helixand -sheet, have regularhydrogen-bonding patterns.


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Three-dimensional structure of

proteins

Tertiarystructure

Quaternary structure


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Hierarchical nature of protein

structurePrimary structure (Amino acid sequence)

Secondary structure -helix, -sheet

Tertiary structure Three-dimensional structureformed by assembly of secondary structures

Quaternary structure Structure formed by morethan one polypeptide chains


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Close relationship between

protein structure and its function

enzyme A

B

A

Binding to A

Digestion

of A!

enzyme

Matching

the shapeto A

Hormone receptor AntibodyExample of enzyme reaction

enzyme

substrates

protein english aug 2006

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