Gene Expression- Translation Flashcards
(22 cards)
What sections are present on a gene
Enhancer- binds particular proteins that specifically active a gene
Promotor- specific sequences that allow specific transcription factors to bind
Transcription begins after the promoter
What sections does the mRNA strand consist of
An untranslated leader sequence AUG start codon Reading frame Terminator codon Trailer sequence that is not transcribed and protects the
Untranslated regions UTR
What do the subunits of ribosomes consist of
Ribosomal proteins and rRNA
What are the names of the two subunits of a ribosome
Large subunit 60s
Small subunit 40s
All together they make an 80s protein
What do the small and large subunits consist of
In the large subunit there are 28s rRNA 5.8s rRNA 5s rRNA Approximately 50 ribosomal proteins
In the small subunit there are
18s rRNA
30 ribosomal proteins
What are the sites on the large subunit of the ribosome
Peptidyl P site- first tRNA will bind to this site
Amino acetyl A site- adjacent tRNA binds here
How is the peptide chain formed in the ribosome
First tRNA that has the complementary antI codon for the codon coding for the amino acid binds to the P site and then the second tRNA binds to the A site and this causes the amino acids to come in contact so that a peptide bond is formed
The tRNA on the P site is no longer charged so will leave the P site and the tRNA with two amino acids attached to it now will move into the P site to allow the next tRNA to bind to the A site
Structure of tRNA
Acceptor stem, at the 3’ end there is CCA which is where the amino acid is attached
There is a discriminator base between the acceptor stem and CCA terminus that distinguishes which amino acid will bind to the tRNA
Anticodon loop, this is where the anticodon is which is complementary to the codon for the amino acid which binds to the 3’ end of the tRNA
What is the name of the enzyme which allows tRNA to be charged
Aminoacyl-t RNA synthases
What is the name of the process in which an amino acid is added to a tRNA
Aminoacylation- charging
How many aminoacyl-t RNA synthases are there
There are 20 different enzymes as there are 20 different amino acids that could be added to the tRNA molecule
How are tRNA molecules charged with amino acids
The enzymes have specific binding sites that are the correct shape to allow the amino acid to bind
This is an energy consuming process so an ATP binds adjacent to the amino acid which causes a slight change in shape of the enzyme
The ATP loses two phosphate groups and binds to amino acid as AMP
tRNA binds to a second pocket on the enzyme which requires energy AMP is released and this causes a change in enzyme shape and structure and tRNA binds to the amino acid
Once the charged tRNA is released the enzyme goes back to its original conformation to then allow another tRNA and amino acid to bond
Which bonds are formed between the enzyme and the amino acid and tRNA molecules
Bonds are formed between the enzyme and the carbonyl group in amino acids and the OH group on the tRNA molecule
How is translation initiated at the ribosome
The small subunit scans for the start codon and attaches at the AUG start codon then the tRNA molecule attaches at the start codon and then the large subunit attaches to form the full 80s ribosome and then translation begins
What is the name for the formation of the peptide chain
Elongation of the peptide chain
How is translation terminated
At the stop codon a release factor reads the triplet and translation will end a terminator sequence factor will bind and cause the polypeptide, small and large subunits to release
What is a polysome
Why are they important
A cluster of ribosomes held together by a stand of mRNA.
Several ribosomes can translate the same strand of mRNA until the correct quantity of protein has been produced
This is important as mRNA is very unstable therefore translation has to be quick
Silent mutation
A point mutation or mutation in the intron that then has no effect on the polypeptide sequence of amino acids as the genetic code is degenerate
Missense mutation
The amino acid sequence has been slightly altered and is not as it should be
The closer to the terminator the less of an effect the mutation will have on the protein
Nonsense mutation
This is when a base has been changed to mean that the terminator sequence is now been moved in the sequence so the peptide is terminated much sooner than should have been
This therefor means that the peptide chain is too short to produce a functioning protein
What is frameshift and what causes it
Frameshift is caused my addition or deletions of bases in the genetic code
This means that the genetic code is shifted and this could cause an extensive missense or an immediate nonsense
How could an insertion or deletion not cause a frameshift
If three bases are added to the genetic code then this could not cause a frameshift
