Protein Synthesis Flashcards
Why does protein synthesis occur
Chromosomal DNA is too large to leave the nucleus to supply the coding information needed to determine the protein’s sequence of amino acids (primary structure).
What are the two main stages in protein synthesis and where does each one take place
The first stage is transcription which takes place in the nucleus
The second stage is translation which takes place on a ribosome
What is the first stage of transcription
In the first stage of transcription, DNA helicase breaks the hydrogen bonds between the two polynucleotide strands.
What happens after the first stage of transcription
Complementary RNA nucleotides then move into place and form hydrogen bonds on the exposed nucleotides on one of the DNA strands.
What is the second stage/ second enzyme involved in transcription
The enzyme RNA polymerase joins the RNA nucleotides by forming phosphodiester bonds between them.
What does RNA polymerase continue until
It continues along the DNA until they reach the end of the gene.
After these transcription stages what occurs
A strand of mRNA has now been formed
What is the mRNA complementary to
It is complementary to the antisense or template strand which runs from 3’ to 5’.
What is the strand that the mRNA is not complementary to called and in which direction does it run
The other strand is called the sense strand and it runs from 5’ to 3’.
Once the mRNA has been synthesised what happens
The RNA polymerase detaches from the DNA and DNA returns to its double helix structure. The mRNA then moves out of the nucleus through a nuclear pore.
How long are mRNA molecules
They are hundreds of nucleotides long
What happens once the mRNA are in the cytoplasm
They can take part in translation
How are the mRNA nucleotides read and what are they called
mRNA nucleotides are read as a series of triplets, and the triplets are called codons.
What is the mRNA sequence used to determine in translation
It is used to determine the amino acid sequence of a polypeptide.
What does the start codon determine
Where to start translating the mRNA molecule.
What is required for the mRNA to be read
Another type of RNA which is tRNA is involved which is needed for the mRNA to be read.
What is the structure of tRNA
At the top of tRNA is a binding site for an amino acid.
At the bottom there is a triplet of bases called the anticodon.
The tRNA anticodon is complementary to the mRNA codon for that amino acid.
What happens once the mRNA moves from the nucleus to the cytoplasm
The small subunit of a ribosome binds with the mRNA at the start codon.
What do ribosomes contain
They contain a type of RNA called ribosomal or rRNA.
What is the purpose of ribosomal RNA or rRNA
It is important in maintaining the structural stability of the protein synthesis sequence and plays a biochemical role in catalysing the reaction.
After it binds to the small subunit of the ribosome what happens
A tRNA molecule with an anticodon complimentary to the codon attaches.
What are the codon and anticodon held together by
They are held in place by hydrogen bonds between the complementary bases on the mRNA and tRNA.
What does the second tRNA molecule then do
It then moves into place, and has an anticodon which is complementary to the second codon on the mRNA.
What forms between the amino acids on the tRNA and what catalyses the reaction
A peptide bond then forms between the two amino acids which is catalysed by peptidyl transferase, which is part of the ribosomal RNA molecule.
What does the formation of this peptide bond require
It requires energy which is provided by ATP.
What does the ribosome then do
It moves to the next codon and forms a peptide bond to the next amino acid and the first tRNA molecule is released.
What do the released tRNA molecules do
They are then attached to their amino acids by enzymes in the cytoplasm.
What does the ribosome continue to do
Moving down the mRNA forming a polypeptide/protein.
What happens when the ribosome gets to the stop codon
It detaches and the polypeptide chain is released.
How can multiple ribosomes translate the same mRNA
Once the first ribosome has started moving along another ribosome can attach to the start codon and start translating.
What does multiple ribosomes translating the mRNA mean
That a large number of polypeptides can be produced rapidly.
Once the protein has folded what can it do
It can then carry out its functions in the cell.
Where may the protein be further modified
It may undergo further changes in the Golgi apparatus.
