Week 6 lecture material Flashcards
Is genetic code the same as gene sequence?
NO
What are the reading frames for aa sequence?
Start reading from 5’ AUG and go towards 3’.
Do translation and transcription start from the same site?
No, transcription has promoters and the start later on, translation has a start codon AUG and immediately start from there.
What are the 3 types of mutations that can occur when you have nucleotide base pair substitution?
- Silent mutation: change in single base pair yet codes for the same aa
- Missense: New amino acid code
- Nonsense: Codes for stop.
What do TRNA’s do?
- They recognise codons on mRNA nad bring the proper aa
- TRNA’s are about 80 nucleotides long
- Has 5’ end and 3’ end transcribed as usual
- It base paris with itself in regions (double helical regions)
- Aa gets attached to 3’ end
- ANticode binds to the mRNa anti parallel and complementart
- There are modified bases
Which position is flexible in TRNA?
The 3’ on the mRNA and 5’ on the TRA are the flexible positions.
How is redudency managed for translation?
There are two strategies:
1) More than 1 tRNA for many aa
2) Some tRNAs can recognise and base pair with more than 1 codon
Do eukaryotes have more flexibility than bacteria in codon and anticodon?
No, bacteria has more flexibility than eukaryotes and I = inosine often in 5’ antiwobble position
How do you make sure right aa is made on TRNA?
we relie on base pairing and aminoacetyl-tRNA synthetases.
Aminoaceltyl synthases take the right aa and use ATP to attach the right aa on the TRNA. there are 20 aminoacetly synthases, 1 for each aa
If mistakes happen with aminoacetyl-tRNA how is it fixed?
By hydrolytic editing
Which end on the TRNA is the acceptor arm?
The 3’ end, it recognises the right aa
How is recognishion achieved in TRNA?
- Identify the tRNA anticodon nucleotides, this is done by glutamine aminoactlyl-trna synthase
- Regognise the nucleotide sequence (at the acceting arm 3’ end)
- Reading the nucleotide at additional places.
How many sub units does ribosome have?
2 subunits, large (many proteins many ribosomal RNA) and small (many proteins 1 ribosomal rna).
How many sites does ribosome have and what are they?
A: aminoacyl site
P: peptidyl site
E: exit site
Where are the ribosomes located in eukaryotes?
In the endoplasmic reticulum and in the cytosol
Where is peptide bond formed in the ribosome?
It is formed in the peptidyl transferase activity in the rRNA in the large subunit
What are ribozime?
RNA molecule that posses catalytic activity
For quality control and check what does EF-tu do in eukaryotic cell?
EF-Tu doesnt exsist in eukaryotic cell, this is in bacterial cell it checks the amino acyl trna. Humans have EF-1
Then it goes with it at the A site, it also checks if the base pariing is correct, if it is nit EF-Tu wont release and peptide bond wont form.
If it is correct, GTP gets hydrolysed and EF-tu is released.
There is a slight delay before the polypeptide bond is formed as there is one last checking
After the checking and attaching onto the Psite how is it moved into the A site?
EF-G (in prokaryotes) and EF2 in humans helps the ribosome to move the mRNA forward one codon and helps to speed up the elongation of the polypeptide chain.
Can ribosomes perform protein synthesis without the aid of elongation factor?
ye but its slower and inefficient
What is the role of elongation factors?
Improve speed and efficiency and error checking funtion
What is the elongation mediated by?
GTP hydrolysis and release of EF-Tu (bacteria), EF-G (bacteria)
EF-Tu binds aminoacyl-TRNA (EF1 in humans)
EF-G: helps ribosome move mRNA 1 codon (EF2 in humans)
Do bacteria have poly A tail and caps?
NO
What is polycistronic mRNA?
Multiple proteins coding for one mRNA in PROKARYOTES
What are ribosome binding sequence also called in prokaryotes?
Shine Dalgaro Sequences
What basepairs in ribosomal subunits in bacteria or prokarytoes?
Shine Dalgano Sequences or ribosome binding sites
How does initian of translation take place in prokaryotes or bacteria?
Ribosome binding sites or Shine -Dalgarno sequences on mRNA base paris with rRNA in small ribosomal subunits
Positioning of small subunits to initiating AUG codons on mRNA also requires Inition factors
fMethionine aminoacyl trna binds to inititor codon
Large ribosomal subunit binds.
How does translation termination occur?
Human release fator or proteins (not TRNA) are used.
What do both eukaryotes and prokaryotes have?
Polyribosomes or polysomes. They are ribsomes essentially one after the other. It is relatively slow. The gap is about 80nt.
How is protein folded?
These are proteins that help in the protein folding as they emerge after translation.
what are post translation modifications to the proteins?
- Phosphorylation and Glycosylation is required for most proteins.
Some need covalent modifications to make proteins active and recruit protein to correct membrance or organelle.
How are old proteins destroyed in cells?
a target protein called polyubiquitin chain is attached to the protein and taken to proteasome, proteases sees this and degregates it.
What are antibiotics?
Many inhibitors that hurt bacteria by screwing up bacterial translations
