lecture 6 Flashcards
(39 cards)
what is the function of ribosomes?
translation
- about 50,000 per cell (depending on the growth rate)
what is the average size of a bacterial protein?
~300 amino acids
is mRNA or the coded protein bigger?
mRNA
why do bacteria lack a membrane enclosed nucleus?
They have to respond to changes very quickly
- the ribosomes can readily access mRNA once it is made
what are the advanges to bacteria having no membrane enclosed nucleus?
-prevents accumulation of non-functional transcripts in the cytoplasm
- avoids the formation of RNA-DNA loops
- Regulation of transcription pausing by translation: gene regulatory mechanism
what is the structure of the bacterial ribosome?
a large multi protein complex (70S)
- two subunits; 30S (small), 50S (large)
RNA and protein
how is RNA stabilised?
by alot of small proteins
what is the difference between bacterial and mammalian ribosome structure?
mammalian ribosome is slightly larger
what are the steps involved in bacterial translation?
- initiation
- elongation
- termination
- recycling of the ribosomes
what stabilises RNA?
a lot of small proteins
what are the tRNA binding sites on the ribosome?
A, P, E
what is the function of the A tRNA binding site?
aminoacyl-tRNA enters the ribosome
what is the function of the P tRNA binding site?
hold tRNA carrying the nascent chain
what is the function of the E tRNA binding site?
tRNA dissociated from the ribosome
how is the ribosomes polysome arranged?
to avoid direct collision during elongation
- the ribosomes can communicate within the cell to stop them from bumping into each other
how is transcription regulated by the rate of translation?
Global rates of transcription and translation is influenced by nutrient availability and growth rate
- transcription can be interruped by pauses
what is direct coupling in transcription pausing?
an mRNA hairpin programed pause
- causes transcription to be paused of stoped
the hairpin is an mRNA secondary structure
how is an mRNA hairpin pause releated?
by translation
- the ribosome pulls the mRNA from transcription and detangles to mRNA secondary structure (hairpin)
how is bacterial transcription regulated by leader regions in direct coupling?
Charged tRNA is abundant
leads to
Rapid translation
leads to
Formation of a terminator loop
charged tRNA is deficient
leads to
Slow translation
leads to
Formation of an anti-terminator loop
what is the structure of the Expressome?
- ribosome and RNAP are bridged by dedicated transcription factors
- NusG has domains specific for the two interactions
- RNAP binds to the 30S head domain
- RNAP Beta’ subunit zinc finger domain (ZF) is closest to the ribosome surface
- NusA is rotated in expressome compared with paused elongating RNAP
what is the expressome structure in situ with Cryo-ET imaging?
in-cell architecture of a transcripting and translating expressome: abundance, structural variability, mobility, functional analysis
what are the effects of the drugs on the expressome?
- translation inhibito
- Transcription inhibitor
how are ribosomes profiled?
- deep sequencing of ribosome- protected mRNA fragments
- Genome-wide investigation of translation
- Monotoring protein translation in different conditions
what is the function of tunning the synthesis of protein products?
majority of multiprotein complexes: a single polycistronic mRNA
- gene order does not explain differential synthesis rates
- synthesis rates are generally determined by the frequnecy of translation initiation
Proportional synthesis: tuning synthesis rates to the subunti stoichiometry (acheived through translational control (not transcriptional control)
