MCAT BIO CH. 4 PART 3 Flashcards
When does termination of elongation in translation occur?
When a stop codon appears in the A site
What happens when a stop codon appears in the A site?
The A release factor enters the A site
What does the release factor cause to happen?
The peptidyl transferase to hydrolyze the bond between the last tRNA dn the completed polypeptide
How many release factors do prokaryotes have?
Three release factors
What are the purpose of the first two release factors, RF1and RF2?
RF1: Recognize termination codons UAA and UAF
RF2: Recognizes UAA and UGA
What is the purpose of RF3?
RF3 is a GTP-binding protein that leads to dissociation of RF1RF2 after peptide release
RF3 recognizes a stop codon T/F
False
How is the N-terminal amino acid different from prokaryotes and eukaryotes?
Euk: Met
Prok: fMet
What do eukaryotes used during translation instead of the Shine-Dalgarno?
There are 5’ UTR sequences in eukaryotes that function in starting translation
What is a common eukaryotes sequences that start translation?
Kozak sequence
What does eukaryotic translation begins with?
Eukaryotic translation begins with formation of the initiation complex
What complex forms in the beginning on eukaryotic translation?
43S pre-initiaion complex forms
What is the 43S pre-initiation complex composed of?
Composed of the 40S small ribosomal subunit, Met-tRNAMet and proteins called eIFs
What are eIFs?
Eukaryotic initiation factors
What happens once the 43S pre-initiation complex is assembled?
Complex recruited to the 5’ capped end of the transcript by an initiation complex of proteins (with eIFs)
What does the initiation complex do to the mRNA?
Scans the mRNA from the 5’ end to find the start codon
What happens once the initiation complex finds the start codon on the mRNA?
The large ribosomal subunit (60S) is recruited and translation can begin
What eIFs proteins are essential?
- eIF3
2. eIF4A, eIF4E and eIF4G
What is the purpose of the eIF3 protein?
Binds the small ribosomal subunit and prevents it from prematurely associating with the 60S subunit
What is the purpose of eIF4A?
A helicase and unwinds mRNA
What is the purpose of eIF4E?
Binds to the 5’ cap of the mRNA
What is the purpose of eIF4G?
A scaffold protein
What is the importance of the levels of the eIFs proteins?
Their levels are a rate-limiting step for translation
Higher amount of the three eIFs proteins means……? A lower amount means…?
Higher: Cell can perform more translation
Lower: Decreases translation