10: Ribosomes and Prokaryotic TX Termination Flashcards
In prokaryotes, what are the two types of transcription terminators?
Intrinsic (rho-independent)
Rho-dependent (extrinsic)
What are the two components of intrinsic terminators?
Dyad symmetry and a string of T’s in the DNA sequence
Intrinsic terminators form a secondary structure in the mRNA necessary for termination. What is its name?
A stem-loop or hairpin structure
What comes after the stem-loop/hairpin in newly transcribed RNA that is terminated intrinsically?
A string of U’s
In intrinsically-terminated RNA, what exists between areas exhibiting dyad symmetry?
A 7-nucleotide spacer
In intrinsic termination, what affect does the hairpin have on RNA polymerase?
It makes RNA polymerase pause
In intrinsic termination, what causes RNA polymerase to fall off the DNA?
A string of weak U:A basepairs
What is the first step in rho-dependent TX termination?
The rho-utilization (rut) site in the DNA is transcribed in the RNA
Where does the rho protein bind in rho-dependent TX termination?
The rho-utilization (rut) site
In what direction does the rho protein move in rho-dependent TX termination?
Toward the 3’ end of the RNA (toward RNA polymerase)
How does the rho protein terminate transcription (last step in termination)?
The rho protein causes the RNA to dissociate from DNA either by pushing RNA polymerase or pulling RNA (unknown which)
What are the two parts of a ribosome?
Large (50S) subunit and small (30S) subunit
In what direction do ribosomes translate mRNA?
From 5’ to 3’, from the protein N-terminus to C-terminus
Can multiple ribosomes translate the same gene at the same time?
Yes
In prokarotes, ribosomes can start translating an mRNA even before RNA pol has finished transcribing it.
Why is this not true in eukaryotes?
In eukaryotes, TX & TL take place in different locations (TX in nucleus & TL in cytoplasm)
Why don’t prokaryotic cells fill up with too much mRNA and protein? (2 reasons)
- Cell divison: cells need enough RNA and protein to divide quickly
- Degradation: mRNA and proteins have limited lifespans
In prokaryotes, on what part of mRNA does translation start?
Ribosome binding site (RBS)
What two things are together sufficient to initiate prokaryotic translation?
RBS consensus sequence + start codon AUG
Where are rRNAs found?
In the ribsosomal subunits
How does the 3’ end of the 16S rRNA allow ribosome binding?
It basepairs with the RBS consensus sequence
Could a change to the RBS be a null mutation, hypermorph, or both?
Both - null if the RBS was deleted, hypermorph if it increased the match of RBS sequence to the consensus
