GENETICS Processes Translation

 

- Info:

- Translation is process of synthesising protein by combining amino acids as defined by mRNA.

- mRNA strand created by Transcription travels to protein-making machinery called ribosome located in cytoplasm.

- Ribosome reads mRNA sequence and translates it into amino acid sequence of the protein.

- Ribosome starts at the sequence AUG and reads 3 nuceloids at the time.

- Each 3 nucleotide "codon" specify particular amino acid.

- Different codons can specifiy the same amino acid like for instance UUU and UUC both specifying phenylalanine.

- The stop "codons" (UAA, UAG and UGA) tell the ribosome that the protein is complete.

- Following explanations and examples are based on example started in Transcription tutorial.

- This tutorial is based on:

http://learn.genetics.utah.edu/content/begin/dna/transcribe

http://www.sparknotes.com/biology/molecular/translation/section3.rhtml

 

- Inititation:

- Small subunit of the ribosome binds via complementary base pairing to specific sequence on the mRNA chain.

Length of this sequence is about ten nucleotides which start anywhere from 5 and 11 nucleotides from start codon.

- Initiator tRNA, carrying methionine, is attracted to the region and binds to the starting triplet code AUG.

- This then attracts the large ribosomal subunit which binds to the small subunit.

- This formes so called initiation complex where Initiator tRNA occupies P site while E and A sites remain empty.

- Next mRNA codon is placed below A-site (CUA in our example).

- Elongation:

- tRNA with anti-codon GAU and attached leucine comes into the A-site of the ribosome.

- Peptide bond, catalyzed by the enzyme peptidyl transferase, forms between the methionine and leucine.

- Methionine-specific tRNA leaves the P-site and goes off to gather another methionine.

- Leucin-specific tRNA now contains Leucin with methionine attached to it with peptide bond.

- Translocation:

- Ribosome shifts 3 nucleotides so that the P-site now contains the next mRNA codon with the attached leucine tRNA.

- A site is now left open to accept Aspartic-acid-specific tRNA.

- Next mRNA codon CAC is now place below the A-site.

- Initiator tRNA is moved to E site through which it exits ribosome.

- Termination:

- Process continues until stop sequence gets into A-site.

- Ribosome detaches from the mRNA and splits into its two parts.

- Phenylalanine-specific tRNA releases its phenylalanine and leaves.

- The new protein floats away

 

- Example:

- To get the actuall result of the above proceess first we have to locate starting sequence AUG.

Then we divide mRNA in clusters of 3, called codons, each defining specific amino acid.

 

    

U

A

 

A

U

G

 

C

U

A

 

C

A

C

 

G

U

G

 

U

U

C

 

U

A

G

 

G

A

 

- Using Universal Genetic Code, codons are decoded into amino acids:

Methionine Leucine Aspartic Acid Valine Phenylalanine Stop