protein synthesis Flashcards
(8 cards)
describe what transcription is
the process of making pre-mRNA using part of the DNA as a template
how is pre-mRNA made
-DNA helicase breaks down H bonds between 2 strands
-complimentary RNA nucleotides move into place and form H bonds with the bases on the exposed DNA nucleotides on one of the DNA strands
-RNA polymerase joins RNA nucleotides by forming phosphodiester bonds
-this happens along the length of the gene to make a strand of pre-mRNA
-once pre-mRNA synthesised RNA polymerase detaches from the DNA
-DNA goes back to normal structure
-pre-mRNA leaves nuclear pore and goes into cytoplasm for translation
what is the sense strand
-the strand of DNA the pre-mRNA has the same base sequence as except thymine has been replaced with uracil
what is the template/antisense strand
the strand of DNA the pre-mRNA is complimentary to
what is the role of splicing
-converts pre-mRNA into functional mRNA
-by getting rid of non coding regions–> introns
-makes mRNA small enough to leave nucleus through nuclear pore
why doesnt splicing occur in prokaryotes
introns uncommon in prokaryotes
describe the stages of translation
-mRNA moves to cytoplasm
-small subunit of ribosome binds to mRNA at the start codon
-tRNA with complimentary anticodon to the start codon attatches to mRNA
-held in place by H-bonds between complimentary base pairs on the mRNA and tRNA
-second tRNA molecule with an anticodon complimentary to the second codon on the mRNA
-peptide bond formed between amino acids on tRNA
-catalysed by peptidyl transferase–> part of ribosomal RNA moleculed
-formation of peptide bond requires energy from ATP
-ribosome moves onto next codon and the first tRNA released which are later attatched to amino acids in cytoplasm by enzymes
-ribosomes moves down mRNA till polypeptide formed and reaches stop codon and then ribosome detatches
how can a large number of polypeptide molecules be formed
multiple ribosomes acting on mRNA and tRNA
