protein synthesis Flashcards
what are the 2 steps in protein synthesis
Nuclear (occurs in nucleus) = transcription
Cytoplasmic (occurs in cytoplasm) = translation
why does transcription have to take place
to transfer the genetic material out nucleus by messenger RNA
how does protein synthesis differ in eukaryotes and prokaryotes
transcription occur in nucleus of cell in eukaryotes but not in prokaryotes as prokaryotes have no nucleus
briefly describe transcription stage
In nucleus
RNA polymerase transcribes DNA into RNA=>
- messenger RNA (mRNA) Directs synthesis of polypeptide
- Ribosomal RNA
Part of ribosomes
3.Transfer RNA (tRNA)- single stand of nucleic acid . Carries amino acids to ribosome for reaction
Transcription is synthesis of RNA from DNA and is catalysed by enzyme RNA polymerase. Allowing message to leave cell, by mRNA to cytoplasm where message is translated to final functional protein
RNA polymerase starts process by recognising appropriate site on DNA. Therefore, determining which genes in body need switched on and off
briefly describe translation stage
Requires 3 different RNAs:
Message RNA –from nucleus (mRNA)
Transfer RNA to carry amino acids (tRNA)
Ribosomes to do the actual work, and contains ribosomal RNA (rRNA)
explain the full process of translation stages
For this process to start, the small units of the ribosome must read the sequence contained within the mRNA until it finds a specific code within that (AUG) as this is the start codon
1- Initiator tRNA is always bound to the amino acid methionine, for process to begin. so the tRNA then attaches to a start codon for process to begin
2- large and small ribosomal subunits join to form a functional ribosome and initiator tRNA fits into position on the ribosome
3- anticodon of incoming tRNA pairs with next mRNA codon beside initiator tRNA
4- amino acid on initiator tRNA forms a peptide bond with amino acid beside it. and the initiator tRNA unattaches from the amino acid so the peptide chain can form
5- tRNA leaves the ribosome; ribosome shifts by 1 codon; tRNA binds to newly exposed codon; steps 3-5 repeat
6- protein synthesis stops when the ribosome reaches stop codon on mRNA
stop codons are – UAG, UAA, UGA
what are ribosomes made up of
Ribosome is made up of small and large subunits, large subunit helps to catalyse process of translation, and small subunit helps recognise and read the cods that’s contained within the mRNA
what do stop codons do
Terminate process as not attached to any amino acid so no new amino acid to add to chain so growing polypeptide is cleaved
what happens to the polypeptide one made
Released polypeptide may be post-translationally modified
e.g. glycosylation.
Finally folds to produce a mature functional protein. in quaternary structure
