baisic of translation

translation occurs in ribosomes in the cytoplasm细胞质 or across the membrane of the endoplasmic内质网

ribosome 核糖体

ribosome is a complex of rRNA and protein
two subunits –smaller and larger

alt text
核糖体有4个RNA结合位点,一个mRNA,还有三个E,P,A

codons 密码子

is a consecutive groups of three nucleotides

一个 amino acid 对应多个codons
The codons are degenerate (简并的) or redundant(丰余的)
alt text

AUG编码methionine甲硫氨酸,是起始密码子

编码同一种的氨基酸的密码子称为synonymous codons同义密码子

一个RNA有三种翻译方式,根据起始位置而定,但是只有一种能翻译出所需的蛋白质
alt text

tRNA

transfer RNA

alt text

tRNA can fold into a secondary cloverleaf三叶草 structure, then fold into a tertiary structure of L-shape

上面有反密码子anticodon

还有3’CCA端共价结合氨基酸

tRNA与氨基酸的连接

Aminoacylation氨酰化, the attachment of an amino acid to a tRNA

Recognition and attachment of the correct amino acid depends on enzymes called aminoacyl-tRNA synthetase (氨酰-tRNA合成酶)

alt text

先形成一个AMP-氨基酸,然后氨基酸连到tRNA上

翻译区域

alt text

有一个5’UTR与核糖体结合启动翻译,有一个3’UTR终止翻译并post-translation modification翻译后修饰

Initiation

一个带着methionine的initiator tRNA起始tRNA与小亚基结合
小亚基识别mRNA的5’帽子然后结合
小亚基沿着mRNA移动,直到遇到AUG
起始因子解离,大亚基结合,P-site结合起始tRNA

The initiation of translation requires initiation factors起始因子 eIFs binding, GTP and ATP

alt text

Elongation

The elongation of translation requires elongation factors eEF1α, eEF1βγ, eEF2 and GTP

1. Aminoacyl-tRNA delivery 氨酰-tRNA转运

P已经有一个polypeptide多肽,A过来一个tRNA

alt text

2. Peptide bond formation 肽键形成

alt text

3.Large subunit translocation 大亚基移位

大亚基往3’移动,P到E,A到P

alt text

4.Small subunit translocation 小亚基移位

小亚基往3’移动,E上的tRNA掉下去

alt text

Termination

stop codons (UAA, UAG, or UGA)

Release factors (释放因子) bind to ribosome with a stop codon positioned in the A site

催化一分子水加到多肽链末端离开tRNA

然后散开

alt text

其他

polysomes 多聚糖体

alt text

Co-Translational Protein Folding

蛋白质可以在翻译过程中折叠

Molecular Chaperones 分子伴侣

heat-shock proteins(hsp)分子伴侣的一种

可以识别不正确的构型by their exposure of hydrophobic surface然后拆开让蛋白质重新折叠直到正确

alt text

从多肽到有功能的蛋白质

折叠
共价修饰(糖基化,磷酸化)
与其他subunit assemble