Biosynthesis of protein

(translation)

1. Materials involved in

the translation

(1) mRNA

a. genetic code

b. the category of genetic

code

c. Triplet code

d. Open reading frame

(ORF)

c. character of the genetic

code

* non-spacer,non overlap

frame shift & frame shift

mutation

A

DNA 5’-ATG CAT GAC ATT TCG-3’

mRNA 3’-UAC GUA CUG UAA AGC-5’

* degeneracy(synonymous code)

& plurality

concept

significant

* wobble

①②③ mRNA 密码 5’—G C U—3’ 5’—G C C—3’ 5’—G C A—3’ tRNA 反密码 3’—C G I—5’ 3’—C G I —5’ 3’—C G I—5’ 3 2 1

U C A

I C G U

A U G

* Universality

(2) tRNA

* function

*charater

mRNA 5’-AAU CGA-3’

tRNA 3’-UUN GCN-5’

wobble

if the first code in anticode

of the tRNA is C or A there

is no wobble

* Type

initiation tRNA

concrpt

tRNAfmet ( prokaryotes)

kind

tRNAimet (eukaryotes)

elongation tRNA

concept

(3) ribosome & polyribome

prokaryotes :60s large subunite

40s small subunite

eukaryotes: 50s large subunite

30s small subunite

Polyribosome

in cytosol

biding to the rough endoplasmic

reticulum

(4) Soluble factors

initiaotion factors (IF)

elongation factors (EF)

termination factors (RF)

(release factors)

for eukaryotes

eIF, eEF, eRF

2. the process of synthesis

(1) activation & transfer of

amino acid

* enzyme

aminoacyl-tRNA synthetase

(5) Energy & enzymes

* Catalytic reaction

* type

type I & type II

* Charater

two site

high specificity

biding site

bind & activate

E

hydrolytic site

proofreading

(2) ribosome cycle----

initiation,elongation,termination of the translation

A. initiation stage

a. requirment

prokaryotes:

* dissociated of large & small

subunite

* The initiation signal in mRNA

5’ end

* Initiation tRNA

( tRNAfmet)

* Three types of initiation

factors

IF1— help IF3 to bind small subunite,make

large & small subunite dissociated

IF2---recongnize tRNAfmet , bind to

GTP to form triplet then to

bind small subunite , possess

GTPase activity

IF3---bind small subunite, make

large & small subunite dissociated

b.form of initiation complex

*initiation sequence

SD sequence

c.Form of 70s complex

mRNA 5’end SD sequence

base pair with the 16s rRNA

3’end

initiation code of mRNA base

pair with anticode of tRNAfmet

30S 起始复合物 + IF3

GTP 50S 大亚基

 

GDP IF1 IF2

 

70S 起始复合物

Elongation of peptide synthesis

aminoacyl-tRNA delivery

peptide bond formation

translocation

aminoacyl-tRNA delivery

* protein factors involved

* process

*character

GTPase activity of EF-tu

determined pace & fidelity of

protein synthesis

EF-tu

(have GTPase activity)

elongation

factor,EF

EF-ts

f-met-tRNAfmet 起始 tRNA 不能进入 A 位

 

ef--tu

met-tRNAmet

及携带其它氨基酸的 tRNA 阅读 mRNA 内部的 AUG 密码

peptide bond formation

large subunite has peptidyl

transferase activity

( transfer tRNAfmet or peptidyl-tRNA in the P site to A site

P site ---peptidyl site

A site ---amino acyl site

E site---exit site

Translocation

requirement:

*EFG( GTPase activity)

* direction of movement

mRNA

move one code from 5’to 3’

tRNA carry peptide

move from A site to P site

Newly peptide

elongate from N end to C end

* Process

acho

move

Summarize

energy requirements for the formation of one peptide bond

(activated of amino acid,aminoacyl-tRNA deleviry,translocation)

A

A

A

A

P A P A

锚定 移动

Termination of peptide synthesis

protein factor involved

RF1----act on UAA,UAG

RF2---act on UGA

RF3---release

The termination signal on A site

UAA.UAG,UGA

process

The character of the translation in eukaryotes

eukaryotes prokaryotes

Structure of 80s 70s

Ribosome (60s,40s) (50s,30s)

Structure of 5’ cap,3’tail 5’SD

mRNA sequence

Initiation tRNA met –tRNAimet fmet-tRNAfmet

Initiation factors many few

Form of initiation complex simple

Complex

Processing & polymerization of

subunites after formation of peptide

chain

* remove of met or fmet at the N

end

* the formation of –S-S

* Modification of specific amino acid

* Remove of the unnessary peptide

from the protein

concept of signal peptide

function of signal peptide

example

Processing of polyprotein

* polymerization of subunites

regulation of protein synthesis

* function of antibiotin

*factors affecting eukaryotes

Interferon

produce

function

Heme

22 ---globin

HB

four heme

感染 释放 WBC--α 干扰素 γ

病毒 细胞 蛋白质因子 成纤维细胞 --β 干扰素

免疫细胞 -- γ 干扰素

2. 2. 血红素调节血红素调节 HbHb合成的机制合成的机制　　 αα22ββ22—— 珠蛋白珠蛋白 HbHb

4 4 分子血红素分子血红素

血红素　，血红素　， HbHb合成　，反之亦然合成　，反之亦然　　通过通过 cAMPcAMP 依赖的蛋白激酶连续反应使依赖的蛋白激酶连续反应使eIFeIF

22 磷酸化，活性下降，蛋白质合成减少磷酸化，活性下降，蛋白质合成减少3. 3. 白喉杆菌素白喉杆菌素

Diphtheria bacillin

function