Translation -Synthesis of protein from RNA

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Translation -Synthesis of protein from RNA

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Genetic code:

Genetic code

The Genetic Code:

4 The Genetic Code Codon : A sequence of three ribonucleotides in the messenger RNA chain that codes for a specific amino acid; also a three-nucleotide sequence that is a stop codon and stops translation. Genetic code: The sequence of nucleotides, coded in triplets ( codons ) in mRNA, that determines the sequence of amino acids in protein synthesis,of the 64 possible three-base combinations in RNA, 61 code for specific amino acids and 3 code for chain termination.

Mutation:

Mutation A changes to the nucleotide sequence of the genetic code. The most common changes are substitutions, additions or deletions of one or more bases The chemical nature of base can be altered either by environmental or chemical means. Physical or chemical agents that that causes a mutation is a mutagen

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Types of base pair mutations CATTCACCTGTACCA GTAAGTGGACATGGT CAT G CACCTGTACCA GTA C GTGGACATGGT CAT C CACCTGTACCA GTA G GTGGACATGGT transition (T-A to C-G) transversion (T-A to G-C) CATCACCTGTACCA GTAGTGGACATGGT deletion CAT G TCACCTGTACCA GTA C AGTGGACATGGT insertion base pair substitutions transition: pyrimidine to pyrimidine transversion: pyrimidine to purine normal sequence deletions and insertions can involve one or more base pairs

Types of mutation - According to consequence of the change:

Types of mutation - According to consequence of the change SILENT mutations occur when a base pair change in a coding region does not affect the amino acid that is encoded. MISSENSE mutations occur when the base pair change in a coding region results in a change the amino acid that is encoded. NONSENSE mutations occur when the base pair change in a coding region results in the creation of a stop codon. Proteins will be truncated as a result of this type of mutation. Frame-shift mutation occur when a deletion or insertion of a nucleotide to a gene results in an altered reading frame in the base sequence in that gene.

ACTIVATION OF AMINO ACIDS :

ACTIVATION OF AMINO ACIDS Activation of an amino acid occurs before it binds to its specific tRNA. This process, as well as the formation of the amino acyl-tRNA complex, is catalysed by aminoacyl tRNA synthetase. The activated amino acid is joined covalently by an ester linkage through its carboxyl group to the CCA- sequence at the 3' terminus of the tRNA.

Initiation :

Initiation Binding of initiation factors to the 40S ribosomal subunit Formation of a complex, initiator tRNA , plus 40S ribosomal subunit . Binding of mRNA ( facilitated by the methyl Cap ) form a 40S initiation complex. Which scans the mRNA for the initiator codon AUG. Binding of the 60S ribosomal subunit to the 40S complex to form the 80S initiation complex. The ribosome has three binding sites for tRNAs carrying amino acids ( A - P and E - sites). At the completion of the 80S complex, the initiator tRNA will be occupying the P-site on the ribosome, leaving the A-site free.

ELONGATION OF THE POLYPEPTIDE CHAIN :

ELONGATION OF THE POLYPEPTIDE CHAIN binding of an aminoacyl-tRNA to the A-site Proper binding of the incoming aminoacyl-tRNA requires assistance from GTP and certain elongation factors peptide bond formation. A component (23S rRNA ) of the 60S ribosomal subunit known as peptidyl transferase catalyses the transfer of the amino acid at the P-site to the A-site, and a peptide bond is formed between the two amino acids. Peptidyl transferase is an example of a ribozyme (an RNA molecule acting as an enzyme). translocation . This involves a movement of the ribosome and mRNA in relation to one another in such a manner that the ribosome will move along each time, by one codon , towards the 3' end of the mRNA. Elongation factor eEF-2 and GTP are responsible for the transfer of the peptidyl-tRNA from the A-site to the empty P-site,

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