Translation Flashcards
Name parts of the machinery that drives translation: specifically: ribosomes, mRNA, tRNA, aminoacyl tRNA synthetases, initiation factors, elongation factors, and release factors.
(7) ribosomes, mRNA, tRNA, aminoacyl tRNA synthetases, initiation factors, elongation factors, and release factors.
What is the role of ribosomes, how many subunits/binding sites do they have?
The ribosome contains the catalytic center, contains both RNA and many proteins.it contains two subunits: in bacteria these are the 30S and 50S, and in eukaryotic these are the 40S and 60S. In a fully assembled ribosome, the mRNA and tRNA pass between the two subunits;
there are three tRNA binding sites: the A, P, and E sites.
What does the small (40S) ribosome subunit do?
The small subunit has the decoding groove through which the mRNA passes and the tRNAs read the message.
What does the large (60S) ribosome subunit do?
The large subunit contains the catalytic center (the peptidyl transferase center, PTC), which appears to be made entirely of RNA and thus the ribosome is a ribozyme (uses RNA to perform catalysis).
What is the role if mRNA
contains the nucleotide sequence that encodes the protein. There are 64 (4^3) possible codons, all are used.
What is the role of tRNA (and what are the main parts of the tRNA that are involved in performing that role)
adapters that “read” the message and deliver the right amino acid. tRNAs base-pair directly to the codons in the mRNA though the the tRNA’s anticodon loop. the acceptor stem has the amino acid attached that matches the anticodon. Some tRNAs can recognize more than one codon, due to wobble-pairing at the third location in the codon. The amount of each type of tRNA in the cell varies, usually matching codon frequency. The function of tRNA is dictated by its three-dimensional folded structure.
What is the role of aminoacyl tRNA synthetases
protein enzymes that put the right amino acid on the right tRNA.
What is the role of initiation factors
They bring the ribosome to the message and assist in getting the machinery assembled.
What is the role of elongation factors
They deliver tRNAs and move the ribosome down the message.
What is role of termination factors
They end the process at a stop codon, and dissociate the subunits so they can be used again..
What does degeneracy mean with regards to the genetic code?
there are multiple codons for a single amino acid
Describe Initiation in bacteria
the ribosome binds essentially right at the start codon due to the Shine-Dalgarno sequence and three initiation factors work to assembly the full ribosome.
Describe initiation in eukaryotes
initiation factor (eIF) 4E is required to bind to the 7-methyl guanosine cap on the 5’ end of the mRNA. This leads to binding of many other eIFs (4G, 4A, 4B, etc.) and eventually to binding of the small ribosomal subunit, which itself is bound by several factors (eIF3, eIF1A, eIF1, eIF2, etc.). The ribosome then scans down the message to find the AUG start codon. At that point, the large subunit can join the small, the factors are released, and the goal of initiation has been achieved.
Describe the elongation process (cycle)
aa-tRNA enters A-site (delivered by EF1A in eukaryotes, EF-Tu in bacteria), where its anticodon loop base-pairs with the right codon in the mRNA, “reading” the message. The peptide bond forms when the protein chain moves form the P-site tRNA onto the A-site tRNA. elongation factor catalyzes translocation, in which the message and tRNA move one codon over. Now, the empty tRNA form the P site is in the E site and the nascent peptide chain is attached to the tRNA in the P-site. This leaves the A site open and the cycle repeats for each codon.
Describe termination
Ribosome reads a stop codon at the end of the sequence, ending elongation, and dissociating the subunits. A stop codon is detected by a recycling factor in the A-site. Recycling factors are proteins that fit into the same space as a tRNA, but when they do, they trigger the termination of the peptide chain, and a series of events that lead to release of the peptide and dissociation of the subunits. The protein then goes off to fold, receive any modifications, etc.
