Biology

BIOLOGY

Part 1 : Genetics - From Genes to Proteins , Mutations (Chapter 10

The base sequence of RNA after transcription is

5 '-AUGGGUUUACAUCGGUGA-3

The resulting amino acid sequence is

Methionine-Glycine-Leucine-Histidine-Arginnine-Opal /Stop

The first codon is usually AUG and this is considered as the start codon for most proteins . The codon AUG codes for methionine and this generally acts as the initiation site for protein translation (Garber 2002 . The UGA codon is also known as the opal or stop codon . This codon is considered as a termination sequence because it triggers the

release of the growing protein chain or polypeptide from the ribosome (Raven et al , 2007 . The release of the protein chain is also influenced by the presence of release factors instead of transfer RNA molecules that generate additional amino acids to the growing polypeptide chain (Campbell and Reece , 2004 C ) Original sequence 3 '- TACCCTTTAGTAGCCACT-5

mRNA sequence 5 '-AUGGGAAAUCAUCGGUGA-3

Amino acid seq . Met-Gly-Asn-His-Arg-Opal

Mutated sequence 1 ) 3 '-TACGCTTTAGTAGCCATT-5

mRNA sequence 5 '-AUGCGAAAUCAUCGGUAA-3

Amino acid seq . Met-Arg-Asn-His-Arg-Ochre

Mutated sequence 2 ) 3 '-TAACCTTTACTAGGCACT-5

mRNA sequence 5 '-AUUGGAAAUGAUCCGUGA-3

Amino acid seq . Ile-Gly-Asn-Asp-Pro-Opal

The protein sequence of mutated sequence 1 will be changed at the second position , from Gly to Arg . This mutation is known as a sense mutation because the protein sequence is now different from that of the original protein sequence . The sixth amino acid is changed from opal or stop codon to an ochre stop codon . Since both opal and ochre are stop codons , this does not affect the protein sequence...