Ch. 11 Control of Translation Flashcards
Viruses are totally dependent on the host cell for translation of mRNA. W
True. Very few virus encode any translational machinery.
What do viruses do to host cell machinery?
They modify it for their own benefit.
What is the direction mRNAs are read?
What is the direction of peptide synthesis?
5’ to 3’; Amino to Carboxy
What is the location of translation?
Ribosomes
How long is the 5’ untranslated region?
3-1000 nucleotides Usually 50-70
What causes the start and stop of translation?
Start and stop codons (initiation and termination)
What follows the stop codon?
the 3’ Untranslated region. regulates speed of translation, stability, and initiation
Are the majority of eukaryotic mRNA mono or poly cistronic?
mono. poly means there are several start and stop codons in one mRNA
What are the components of the ribosome? What carries out their catalytic activity?
Small subunit (40S): 18S rRNA and 30 proteins; Large subunit (60S): 5S, 5.8S, 28S, and 50 proteins.
The RNA
What are the structural characteristics of tRNA
CCA sequence that binds amino acid; anticodon on opposite end; 70-80 nucleotides long; highly base paired L-Shape
What are the three steps of translation? Which is rate limiting? How many proteins participate in this step?
Initiation, elongation, and termination.
Initiation is rate limiting
At least 11
What three proteins promote dissociation of ribosome in order to start initiation?
ElF1A, elF3, and elF6
What is the role of secondary structure in the 5’ UTR?
a stable 2ndary structure in 5’ region inhibits translation by blocking ribosome movement
What does elF4A do?
It has RNA helicase activity that helps in unwinding of dsRNA near the 5’ end. (helps eliminate 2ndary structure)
What is the start codon?
Aug (for over 90% of mRNA)
A purine at the -3 position does what?
It allows start codon to be recognized most efficiently.
What is the role of ElF1?
It selects the initiation codon
What are the other start codons for viral mRNA? Why does this work?
ACG, GUG, and CUG;
Parts of viral mRNA mimic tRNA to occupy P site and allow initiation to take place at A site
What is one way that virus prevents cellular mRNA translation?
Cleavage of ElF4G with a protease which prevents cellular initiation complex from forming, since the cleaved protein can only translate at the IRES (internal ribosome entry site) Poliovirus
What is ribosome shunting?
When the ribosome bypasses secondary structure in 5’ UTR
What does Reinitiation do?
It produces 2 proteins from a single mRNA
What is ribosomal frameshifting?
The ribosome moves back or forward one nucleotide, which is present in viral and cellular systems
To what extent can a virus take over the host machinery?
The virus can completely change synthesis towards viral proteins.
What are cellular defenses?
Release of interferon leads to an antiviral state;
RNA activated protein kinase (Pkr) are produced, which phosphorylates elF2alpha and inhibits translation. Can happen in presence of dsRNA
What are some viral defenses against Pkr?
Adenoviral protein VA-RNA I inhibits Pkr;
Vaccinia virus E3L sequesters dsRNA;
some proteins act as a pseudosubstrate;
in HSV1, ICP 34.5 dephosphorylates elF2alpha
