Translation Flashcards
What is translation?
When mRNAs sequence is translated three bases at a time (codon) by base-pairing to a tRNA with a complementary anti-codon. Each tRNA is attached to a specific AA, and the AAs delivered by the tRNAs are joined together to form a polypeptide (protein)
Where are proteins made on free ribsosomes usually headed? Rough ER ribosomes?
Free - destined to stay in the cells. Rough ER- destined to exit the cell, become an organelle, cell membrane
Where does translation take place?
On ribosomes
In what direction is mRNA translated?
5’ to 3’
What is a polysome?
When multiple ribsomes are on a given transcript. This happens depending on how much of a protein is needed.
What is the first tRNA brought to the ribosome? Why does it matter?
N-formylmethionine-tRNA. It is specific for initiating translation
How close do two AAs need to be to form a peptide bond?
2 tRNAs must be side by side on the ribosome with their anticodons h-bonded to the mRNA at adjacent codons
How many tRNAs for the 20 amino acids?
20
What is the wobble mechanism?
As long as the first two positions of th codon are paired, the 3rd position is less critical. The 3rd position is called the wobble position
What is the purpose of Aminoacyl-tRNA synthetase?
It loads the AA onto the correct tRNA
When is a tRNA charged or uncharged?
Charged when carrying an AA and the tRNA is uncharged when not carrying an AA
Decribe the rxn for tRNA synthetase adding an AA to a aminoacyl-tRNA
AA and ATP bind to tRNA Synthetase, ATP is hydrolyzed to AMP to release energy that is temporarily stored in the enzyme, and that energy is used to bind the AA to aa-tRNA
Which classes of tRNA synthetase add the AA to which OH group?
tRNA synthetase class 1 adds the AA to the tRNA backbones 2’ OH group and class 2 adds to 3’ OH group
How many tRNA synthestases are there for the 20 amino acids?
20, its a 1 to 1 ratio
What is the overall goal of the ribosome?
To allow the mRNA and tRNA in close proximity so that they can h-bond between anticodon and codon which allows the transfer of AAs during elongation.
Where on the ribosome does the tRNA bind? The mRNA?
Large subunit - tRNA and small subunit - mRNA
What are ribosomes made up of? What are they considered?
rRNA and protein, considered to be ribonucleo proteins
What is the size of the prokaryotic large subunit and its rRNAs? Small unit and its rRNA? Assembled?
50S has 5S and 23S rRNAs, 30S has 16S rRNA, Assembled = 70S
What is the size of the eukaryotic large subunit and its rRNAs? Small unit and its rRNA? Assembled?
60S has 28S, 5.9S and 5S rRNAs, 40S has 18SrRNA, Assembeled = 80S
How does translation initiate?
70S ribosome comes apart in to 50S and 30S
Initiation Factor 1 and Initiation Factor 3 do what?
Guide the small 30s subunit to the shine dalgarno sequence. Recognized by IF1 and IF3 only in prokaryotes? From there 50S moves to start codon (AUG).
When is IF2 recruited and what does it do?
Once 30S is on start codon, IF2 will carry the charged tRNA to the start codon site. Uses GTP energy. Now the initiation factors dissociate, This recruits the 50S subunit
What is the only amino acid that can initiate translation in prokaryotes?
formyl-methionine
What are the 3 sites inside the large ribosome?
Acceptor - where charged tRNA first binds, Peptidyl ,Exit
Write out elongation steps of translation.
Write it out
What brings tRNA to A- site?
EF-Tu with GTP hydrolysis energy
What pushes the ribosome along?
EF-G with GTP hydrolysis energy
Which rRNA has proof reading capabilities? Then what happens?
16rRNA scans the incoming tRNA for the correct base pairing with the codon, if the nucleotides match, the RNA structure changes and the GTP is hydrolyzed
Write out the termination steps of translation.
Write it out
What is a point mutation?
A single nucleotide or very few nucleotides has been changed by an insertion, deletion or substitution of an incorrect base compated to the original DNA sequence.
What is a missense mutation?
A single nucleotide change results in a codon that codes for a different AA. This changes the overall protein product
What is a nonsense mutation?
Mutation that causes a premature stop codon. Results in truncated protein
What is an insertion mutation?
When one or more nucelotides is added to a DNA sequence. Completely changed protein sequence
What is a deletion mutation?
When part of the sequence is lost. Changes the whole sequence
What is a frameshift?
Shift caused by insertion or deletion mutation. Shifts the whole codon sequence
How do antibiotics only target prokaryotic translation machinery?
Eukaryotic translation machinery is different enough but bacterial cells can methylate their RNA so it isnt recognized by antibiotics
How many initiation factors do eukaryotes have?
Over 12 some with many subunits
What is the initiator tRNA ?
tRNAi-met
Instead of shine-dalgarno guiding ribosome, what happens in eukaryotes?
The small subunit binds near the 5’ cap, and the polyA tail is also involved by helping the transcript form a circular loop to allow for multiple rounds of translation
What do eIF2 and eIF5b do?
Bind GTP and assemble with tRNAi-Met and bring it to the P site of the large subunit
How does the 40S recognize the correct start codon?
The adjacent Kozak sequence
Transcription and translation are coupled in what kind of cells? How is it coupled?
In prokaryotes/E.coli. Coupled by NusG and NusE / S10
Where does transcription and translation occur in eukaryotes?
Transcription is in the nucleus and translation is in the cytoplasm
Proteins in high demand can be translated by what?
Polyribosomes, both in prokaryotes and eukaryotes
What are the final stages of protein synthesis?
Protein folding into its tertiary structure so it can function. It is aided by chaperones (proteins)
What is important for proper protein folding?
Chaperones prevent against improper folding
How do heat shock proteins work?
HSP and ATP bind to hydrophobic regions to inhibit it from prematurely folding. As well as help it fold. Once protein reaches its final destination, ATP is hydrolyzed
How does a protein know where to go in prokaryotes?
Leader sequence guides protein to final destination.
