7.3 translation Flashcards
(16 cards)
what are the two subunits of a ribosome?
a protein and ribosomal RNA (rRNA)
Ribosome subunits and their binding
the small subunit binds mRNA on the surface
the large subunit has 3 binding sites for tRNA
what are the tRNA binding sites?
E site - exit, frees tRNA opening next codon on mRNA sequence.
P site - peptidyl, holds tRNA that carries polypeptide chain.
A site - aminoacyl, holds a tRNA carrying the next amino acid to be added to poly chain
what are the different ribosomes?
prokaryotes are 70s
eukaryotes are 80s
what is tRNA?
- has a basic T-shape
- has sections that become double-stranded by base pairing, it creates loops at 3 different spots depending on how many nucleotides.
what is the anticodon loop?
- tRNA loop that has 7 unpaired bases
- has 3 nucleotides that form an anticodon to the mRNA codon.
- each codon has a CCA base sequence at the 3’ ens that makes the amino acid binding site.
What is a tRNA activating enzyme?
- each tRNA molecule binds to a specific amino acid in the cytoplasm
- the reaction is catalysed by a tRNA-activating enzyme
- the tRNA activating enzyme is specific to the tRNA molecule and amino acid.
how does a tRNA activating enzyme work?
- it has an active site that binds to the specific amino acid and the tRNA
- requires energy as ATP
- ATP and amino acid are attached to active site of enzyme - two phosphates are cleaved from ATP to form adenosine monophosphate (AMP)
- this forms an amino acid - AMP complex.
- the amino acid becomes activated.
what is the process of translation?
happens in three stages:
- initiation
- elongation
- termination
what is the process of initiation?
- deeds three components: mature mRNA, tRNA and ribosome
- the ribosomal unit binds to the 5’ end of the mRNA and moves along until start codon
- initiator tRNA carrying the met amino acid binds to start codon on mRNA
- large ribosomal subunit binds to a smaller unit and locks initiator tRNA into the P binding site
what is the process of elongation?
- a second tRNA mol will move to a binding site of ribosome and the incoming tRNA/anticodon will pair with mRNA codon
- peptide bond is formed between amino acid is site A and the amino acid in site P
- the tRNA in the P site is deacylated and amino acid on site A carries the peptide chain
- the ribosome translocates moving the first tRNA into the E site from P site, this frees the first tRNA and opens up next codon to be translated at A site.
what is the process of termination?
- the process stops at the stop codon located near the 3’ and the polypeptide chain is released
- the stop codon recrutes a release factor (protein)
- breaks bond between the polypeptide chain and the last tRNA in the P binding site
what do free and bound ribosomes do?
- protiens that are synthesied by free ribosomes and will remain in the cell and generally used in the cytoplasm, mitochondria and chloroplast.
- protiens that are synthesied by bound rybosomes are mostly secreted from cell or used in lysosomes
translation in eukaryotes.
transcription occors in cytoplasm at the ribosomes
because of the compartmentalisation there is a delay between transcription and translation.
translation in prokaryotes.
- no delay between transcription and translation bc they can happen in the same place and time bc no nucleus.
- prokaryotic mRNA does not undergo modifications
what are polysomes or polyribosomes?
- look like beads on a string
- a group of ribosomes that move along a single strand of mRNA
- multiple copies of a polypeptide can be sythesied when more ribosomes move along the mRNA
