protein synthesis Flashcards
consists of 2 stages: Transcription
Translation
TRANSCRIPTION:
∙one strand of DNA acts as a template for the production of mRNA. this occurs in the nucleus
(each gene has its own promoter: DNA sequences which tell RNA polymerase where to start)
1) the enzyme DNA helicase breaks down the H+ bonds between the bases, causing the DNA to unwind
2) the enzyme RNA polymerase binds to the template strand of DNA (synthesises RNA in the 5’-3’ direction opposite to the template DNA strand)
3) free RNA nucleotides align opposite template DNA strand, RNA polymerase moves along and forms bonds between bases
the result is pre-mRNA
at the end of the gene is a terminator, this tells RNA polymerase to leave the DNA
RNA processing:
there are 3 main stages to this- capping
tailing
splicing
∙capping- cap structure added to the 5’ end
∙tailing- string of A bases added to the 3’ end
∙splicing- introns removed, exons spliced
structure of final mRNA= has untranslated regions (UTR’s)
= coding sequence translated
TRANSLATION:
∙the sequence of codons on the mRNA is used to generate a specific sequence of amino acids. it takes place on a ribosome and involves tRNA
Ribosomes:
made of 2 sub-units (tRNA attaches to the larger sub-unit)
smaller sub-unit= mRNA goes through
3 main steps:
1) initiation
2) elongation
3) termination
INITIATION:
1) ribosome attaches to a start codon at the end of mRNA molecule
2) tRNA molecule with an anti-codon complementary to the mRNA attaches to ribosome. the bases are joined with H+ bonds
ELONGATION:
1) the 2 amino acids are close enough that an enzyme can catalyse a peptide bond between them
2) the first tRNA leaves the ribosome, it returns to the cytoplasm to bind to another copy of its specific amino acid
3) the ribosome moves one codon along the mRNA strand, the next tRNA binds
TERMINATION:
1) the sequence repeats until a stop codon is reached
