Translation (Lecture 14) Flashcards
What does the ribosome consist of?
40S and 60S subunits
What is the only region where we translate? What characterizes this region?
open reading frame that always starts with start codon AUG and ends with a stop codon
How many open reading frames do polycistronic transcripts have and why?
many since they have multiple start and stop codons
What is pre-initiation?
getting the ribosome and other components to bind to transcript so that it can begin scanning transcript until it reaches start codon
What is polyprotein synthesis?
whole genome gets transcribed which will get cleaved into separate proteins by proteases
When does polyprotein synthesis occur?
post-translation
What is the leaky scanning method of transcription?
ribosome skips start codon and finds another downstream start codon where it will start making protein off of
When does leaky scanning occur?
during translation
What is ribosomal frameshifting?
overlapping ORFs || ribosomes are shifting that open-reading frame because a sequence in the transcript causes a tRNA molecule slippage in reading the sequences so the next tRNA will bring in a different amino acid than what it was supposed to bring
When does translation begin?
at the start codon AUG
What does ribosomal frameshifting cause?
mutations in the protein sequence = makes different protein products
What are internal ribosomal entry sites?
ribosome enters mRNA downstream and starts translating downstream of 5’ cap
What role do secondary structures play in translation?
can be a site where small subunit to bind and begin scanning or a marker for subunit to past and scan
What is ribosomal shunting?
small ribosome will skip secondary structure and start at one AUG past it or may skip to another start codon
What is important in eukaryotic translation?
initiation step
What 3 things form the pre-initiation complex? What binds to the 5’ cap?
40S small subunit, initiator tRNA molecule, initiator factors (eIF2a)
What is the purpose of initiation factors?
ensures translation doesn’t start until the AUG start codon
What are some reasons why a cell would need to stop/pause translation?
amino acid deprivation, ER stress, virus detection in the cell (such as detection of dsRNA)
How does the cell pause/stop translation?
targets the eIF2a via eIF2a kinases that phosphorylate eIF2a so that eIF2B can sequester and permenantly hold onto eIF2a until it gets dephosphorylated
What is the enzyme that gets activates when dsRNA is detected?
Pkr
What is Pkr?
a steady state monomeric protein
What is Pkr induced by?
interferons = immune proteins produced by immune system; if cell detects viruses = will turn on interferon production
What is the sequence of events of Pkr?
Pkr binds to dsRNA and activates »_space;> dimerizes and phosphorylates each other and eIF2a »_space;»» translation paused/stop
How do viruses stop the phosphorylation of eIF2a?
targets Pkr but can also inhibit eIF2 and target Perk (induced upon ER stress during protein production)
