Sunday, April 24, 2011

Genetics: Protein Synthesis: Translation

Translation: the process by which mRNA is used to code for proteins.

Location: Ribosome/Cytoplasm

- 3 nucleotides code for one amino acid
- these groups of 3 nucleotides are called codons (there are 64)
- UAA UGA UAG are all stop codons
- AUG is the start codon
- the third base wobble: sometimes, more than one codon codes for the same amino acid. The third nucleotide may differ. This allows for less tRNA (which we will learn about shortly).
- translation occurs from 5 prime to 3 prime also
- amino acids have anticodons complimentary base pairs to those on the mRNA

tRNA: tRNA is known as transfer RNA. It is composed of a string of nucleotides in the shape of a clover. Its shape is secured by hydrogen bonds. It possesses an anticodon on the leaf side where mRNA can bind using hydrogen bonds and a 3 prime end where amino acids can bind by a unstable covalent bond. The third nucleic acid on the anticodon is angled inwards resulting in the third base wobble.

Ribosome: Ribosomes are manufactured in the nucleolus. Their structure helps to form the peptide bind between amino acids. They are made of rRNA and proteins. They are composed of a large and small sub unit. They also have 3 sections: E, P and A.

The steps:

mRNA, ribosomal subunits and initiator tRNA (for AUG) are brought together by initiation factors.

-An enzyme called aminoacyl-trna synthetase attaches amino acid to tRNA.
-tRNA brings the amino acid to the ribosome and binds to the A site. The tRNA containing the polypeptide chain is on the P site. The tRNA from the A site moves to the P site adding its amino acid to the chain and the tRNA that used to be on the P site is now empty and moves to the E site where it will exit.

The end codon codes for a release factor, and the polypeptide chain is complete!

Here is an animation of the process, enjoy!

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