Flashcards in Biochemistry Lecture 6 - Protein Synthesis Deck (30):
What are the three stages of protein synthesis?
Initiation, elongation, termination
What are the ribunucleoprotein particles that synthesize proteins called?
What are the eukaryotic rRNA sedimentation coefficients (small, large, total)?
60S, 40S, 80S for entire combined unit
Which three small ribosomal RNA subunits associate with the large eukaryotic ribosomal subunit?
28S, 5.8S, 5S.
Which small subunit associates with the small eukaryotic ribosomal subunit?
What is meant by redundancy of the genetic code?
More than one codon codes for an AA
What two molecules initiate translation?
The special met-tRNA binds to the small 40S SUBUNIT first during initiation
What is tRNA's purpose in translation?
It acts as an adapter between the mRNA and the AAs.
What is the tRNA folding pattern?
How many bases comprise a tRNA and what kind of bases are they?
76-80 bases. The bases are "unusual."
What two purposes does linking the AA to the tRNA serve? Which end does the AA attach to?
1. It attaches the AA to the corresponding tRNA
2. It "energizes" the AA
The AA is attached to the 3' OH end of the tRNA
What enzyme catalyzes the AA to AMP linkage?
Aminoacyl tRNA synthetases.
What is the wobble hypothesis?
It is the idea that the third base of the anticodon is relaxed and can base pair with other atypical bases.
Describe the initiation process of translation (including when enzymes come in and bone out).
The Met-tRNA complex binds to a protein eIF-2 and GTP forming a ternary complex (eIF2-GTP-mettRNA). This complex binds to the 40S subunit. Then more initiation proteins, notably eIF4F come in, and the 40S complex binds to mRNA. The 40S complex moves from 5' to 3' looking for the start codon. Once the start codon is found, eIF2 is released and the 60S subunit comes in.
After the 40S complex with its associated proteins and tRNA find the start codon, what position is the met-tRNA in (P, S, or E)? What is the start codon?
Start codon is AUG. The met-tRNA is in the P site upon location of the start codon.
On which end of the tRNA is the end that the peptide bonds are formed?
The 3' OH end.
What protein is required to place incoming aminoacyl-tRNAs on the ribosome? Does the step require energy?
EF1 (very abundant in eukaryotes!). GTP is hydrolyzed in this step.
What protein is required for translocation? Does this step require energy?
EF2. This step hydrolyzes GTP.
To which site is the nascent peptide chain transferred after peptide bond formation?
What enzyme catalyzes peptide bond formation and where does it come from?
Peptidyl transferase is the enzyme and its a component of the 28S RNA.
What are the three stop codons?
UAA, UAG, UGA
What factors are involved in termination (stop recognition, and ester bond hydrolysis)?
Release factor (RF1 or RF2) recognize the stop codon and RF3 catalyzes hydrolysis of the ester bond.
How close can polyribosomes be on a mRNA?
What is another term for base substitution? What can it result in?
AKA point nt mutation. Can result in a missense mutation (single AA replacement).
What is a nonsense mutation?
A nt mutation that results in the generation of a termination signal.
What is a missense mutation?
A nt mutation that results in a single AA replacement.
How can missense mutations affect splice sites?
They can generate cryptic splice sites.
During periods of stress like AA starvation, what is one way a cell halts translation?
The cell will phosphorylate EIF2, which is the inactive state of the protein. This prohibits 40S-tRNA from combining.
What is an IRES? What does it do?
Internal ribosome entry site. It is a viral component that recruits the pre-initiation complex to the start codon of viral RNA in a 5' cap independent manner.