Translation Flashcards
What is Transfer RNA?
A transfer RNA is a small RNA molecule that:
- binds a specific amino acid
- recognises the corresponding codon in messenger RNA by base pairing (anticodon)
What is the start codon? (Bases)
AUG
What does the start codon do?
Specified the beginning of translation. Codes for methionine.
What are the 3 stop codons?
UAG, UGA, UAA
What do the stop codons do?
Specify the end of translation
Which directions do anticodons go?
5’ to 3’
Which direction do codons go?
3’ to 5’
What is the secondary shape of tRNA?
Clover leaf- in reality an L-shape molecule- 3 loops folded on top of each other with a stem (loop because they do not base pair to one another
What does aminoacyl-tRNA synthetase do?
Joins the correct amino acid to the tRNA
Why can some tRNAs recognise more than one codon?
Because of imperfect “wobble” base pairing
Where does the imperfect “wobble” occur?
At the third position of the codon
How are T & C, and A & G similar?
Are chemically similar
Where does protein synthesis take place?
Ribosomes.
What are ribosomes?
Complex structures containing RNA and protein
What are ribosomes made up of?
Has two subunits- 1 large and 1 small. Has binding sites for mRNA and for tRNA (E,P,A sites)
What is the difference in colour between the large and small subunits of a ribosome?
The large is lighter green
Describe protein synthesis (the basics)?
. Messenger RNA binds to ribosome
. Aminoacyl-tRNAs recognise and bind to base triplets in mRNA
. The ribosome transfers the growing polypeptide to the new amino acid
. Protein is extended from amino terminus to carboxy terminus
. Initiation, elongation and release factor proteins assist the process
What is the initiation mechanism?
Process involves initiation factor proteins:
- Methionyl-tRNA (in eukaryotes) or formylmethionyl-tRNA (in bacteria) binds to P site in small subunit of ribosome
- mRNA binds to the small subunit; start codon binds to tRNA anticodon
- Large subunit of ribosome binds
- Aminoacyl-tRNA for second amino acid binds A site on ribosome
- Protein synthesis proceeds as for elongation
Describe the elongation mechanism
- Messenger RNA is bound to the small subunit of the ribosome. The growing polypeptide is attached to tRNA in the P site of the ribosome
Aminoacyl-tRNA for the next amino acid recognises and binds to the mRNA bade triplet in the A site of the ribosome - The ribosome transfers the growing polypeptide from the peptidyl-tRNA in the P site to the new aminoacyl-tRNA
- The large subunit moves relative to the small subunit
- The ribosome is “reset” so that the next tRNA can bind
- The “spent” tRNA is ejected from the E site and the next aminoacyl-tRNA binds
(If the wrong tRNA comes along it will be rejected)
What is the P site?
Where the growing polypeptide chain is
Where does the energy for protein synthesis come from?
The hydrolysis of GTP
Describe how GTP is used to provide energy in protein synthesis
- EF-Tu (in bacteria; called EF1 I’m eukaryotes) carries aminoacyl-tRNA to the ribosome. EF-Tu also binds GTP. If bade pairing is correct, EF-Tu releases aminoacyk-tRNA and hydrolyses GTP to GDP and phosphate
- EF-G (I’m bacteria;called EF2 in eukaryotes) with bound GTP binds to the A site. It hydrolyses GTP and resets the ribosome ready for the next aminoacyl-tRNA
Describe the termination mechanism of translation
Translation ends at the first in-frame stop codon (UAA or UAG or UGA).
- Release factor protein binds to A side instead of tRNA
- Peptidyl-tRNA bond is hydrolysed, releasing newly synthesised protein
- Ribosome dissociates into large and small subunits (so that the process can start again)
Give examples of model organisms
. Escherichia coli (bacteria) . Saccharinyces cerevisiae (yeast) . Fruit flies . Mice . Humans
Cells only rise from pre-existing cells. What are the requirements for this?
. Raw materials
. Energy source
. Information- this is what the genes provide, along with the structure
What is responsible for the differences between organisms?
. Differences between gene products (sequence of amino acids in proteins)
. Differences in patterns of gene expression (under what circumstances genes get turned on and off)
Compared to ribose what does deoxyribose lack?
An O on the 2’ carbon
How many hydrogen bonds are between A and T?
2
How many hydrogen bonds are between G and C?
3
DNA and RNA are chemically similar but RNA has…
. Ribose (extra O to DNA) instead of deoxyribose
. U instead of T. Only difference between the two is the presence of a methyl group makes no difference to the base pairing
How are the amino acids in proteins joined together?
By peptide bonds- the carboxylate group of one amino acid and the amino group of the next in the chain (results in the loss of water)
What is transfer RNA?
A small RNA molecule that:
- binds a specific amino acid
- recognises the corresponding codon in messenger RNA by base pairing anticodon if the transfer RNA
Describe Aminoacyl-tRNA synthase**
Group of enzymes that decides which amino acid to put into the transfer RNA). Joins the correct amino acid to the tRNA at its terminus which requires energy from ATL hydrolysis, but in the case below it requires a lot of energy so it actually hydrolyses ATO-ADP and then to adenosinemonophosphate, releasing 2 phosphates and therefore getting more energy than if you only went from ATP-ADP
Describe the structure of ribosomes
Contains RNA and protein. Rach ribosome has two subunits-a small one and a large one. The ribosome has bonding sires for mRNA and for tRNAs (E, P, A sites)
Describe the basics of protein synthesis
. Messenger RNA binds to ribosome
. Aminoacyl-tRNAs recognise and bind to base triplets in mRNA (transfers polypeptide to the amino acids)
. The ribosome transfers the growing polypeptide to the new amino acid (is transferring the polypeptide to the amino acid)
. Protein is extended from amino terminus to carboxyl terminus
. Ribosomes get help from a additional proteins called the: initiation, elongation and release factor proteins assist the process
Describe the first step of the initiation mechanism
. Methionyl-tRNA (in eukaryotes) or formylmethionyl-tRNA (in bacteria) binds to P surge in small subunit of ribosome. First codon is AYG however, I’m bacteria the methylene group is chemically modified by the addition of the formyl group. So bacteria start with cornel-methylene
Describe the second step of the initiation mechanism
MRNA binds to the small subunit:start codon binds to tRNA anticodon (which would be CAU) this positions the messenger RNA in the right place to start protein synthesis
What happens in stages 3,4 and 5 in the initiation process?
- Large subunits of ribosome binds
- Aminoacyl-tRNA for second amino acid binds to A dire on ribosome
- Protein synthesis proceeds as for elongation
What happens in the first rage of the elongation process?
mRNA is bound to the small subunit of the ribosome. The growing polypeptide is attached to the tRNA in the P site of the ribosome. Have the large subunit attached. Amino acid-tRNA for the next amino acid recognises and binds to the mRNA bade triplet in the A-sure if the ribosome m. If the tRNA does not match the codon then it is rejected so, the tRNA will not bind until it is the right one. The tRNA is ejected so, the E-sure stands for ejected
What happens in the second stage of elongation?
The ribosome transfers the growing polypeptide from the peptidyl-tRNA in the P-sure to the new aminoacyl-tRNA (if the wrong tRNA comes along it will be rejected). So the polypeptide chain has grown by A single amino acid in length.
What stages in stages 3,4 and 5 of the elongation process?
- Large subunit moves relativ to the small subunit. So, the small subunit stays where it was
- The ribosome is reset, by sliding in 2 steps, so that the next tRNA can bind. So opposite
- The “spent” tRNA is ejected from the E site and the next aminocyl-tRNA binds
What are he roles of elongation factors?
- EF-Tub(in bacteria; called EF1 in eukaryote) carries aminoacyl-tRNA to the ribosome. EF-Tu also binds GTP. If base pairing is correct, EF-Th releases aminoacyl-tRNA and hydrolyes GTP to GDP and phosphate (EF-Tu and EF1 are pretty much the same thing)
- EF-G (calmed EF2 in eukaryotes) with bound GTP binds to the A sure. It hydrolyses GTP and resets the ribosome ready for the next amino acid-tRNA
What happens in the termination mechanism?
- Release factor protein binds to A site instead of tRNA. This is shown with AUG as it has no tRNA
- Peptidyl-tRNA bond is hydrolysed, releasing newly synthesised protein
- Ribosome dissociates into large and small subunits (process can start again)
