Genetic code and the structure of RNA
DNA is confined to the nucleus to reduce the risk of mutation, why is this a problem?
- because protein synthesis needs to take place outside the necleues in the cytoplasm
how is this overcome?
- the desired section of DNA is transcribed onto a single stranded molecule of RNA
- this mRNA is small enough to leave the nucleus through nucleur pores and enter the cytoplasm where the genetic code it contains is used to determine the sequence of amino acidss in the proteins being synthesised.
describe the structure of mRNA
- single stranded
- complimentary, not identical to DNA strand
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The genetic code
describe 5 features of the genetic code
- each amino acid in a protein is coded for by a 3 nucleotide bases known as a codon
- a few amino acids have only one codon, however the code is degenerate so one amino acid is often produced by different codons.
- three codons code for no amino acid these are known as stop codons
- the code is non overlapping, every base is read only once
- it is a universal code, applies to all organisms with a few minor exceptions
Describe the structure of RNA
- a polymer made up of repeating mononucleotide subunits
- forms a single strand
- each nucleotide has the pentose sugar ribose, one of the orgnanic bases, AUGC, and a phospate group
- the only two types in protein synthesis are mRNA and tRNA
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