MCB Lecture 20 Protein Synthesis Flashcards
What is mRNA?
Messenger RNA
Translated into proteins
What is rRNA?
Ribosomal RNA that makes up the structure of ribosomes
Untranslated
What is tRNA?
Translational RNA
Delivers codons and amino acids
Untranslated
What is snRNA?
Small nuclear RNA
Makes up the spliceosome
Removes introns from hnRNA
Differentiate between RNAP in prokaryotes and eukaryotes.
What are the similarities and differences?
There is only one in prokaryotes and three in eukaryotes
The structure of eukaryotic RNAPs are quite similar to prokaryotic ones, except they have more associated subunits
How do RNAP differ from DNApol?
They do not have proofreading mechanisms
Ey do not require primers
What is the function of RNA pol I?
Synthesised ribosomal RNA
What is the function of RNApol II?
Synthesised mRNA
What is the function of RNApol III ?
Synthesises tRNA
How do promoter regions differ in prokaryotes and eukaryotes?
There is much more variation in eukaryotic promoter regions
What makes up the transcription preinitiation complex?
RNApol
TFIID: TBP and TAF
And the other four GTFS
What are GTFs?
How many types are there?
General transcription factors
There are 5
What is TFIID comprised of?
TBP and TAF
What is TBP?
Where does it have a role?
TATA binding protein
It forms part of the preinitiation complex in transcription by binding it to the promoter region
What is TAF?
What does it do/associate with?
TBP associated factor
Makes up TFIID which has a role in the pre-initiation complex
Describe the process of the preinitiation complex formation
- TBP and TAF combine with RNA pol
- TBP binds to the TATA box in the promoter
- The four other GTF bind
Describe the function of the mediator
The mediator connects the RNA Pol to the activator and thus enhancer region of the DNA
Describe the function of the activator
The activator binds to the enhancer region upstream from the promoter and thus increases gene expression
What do the Chromatin Modifying Proteins do?
Name one
SAGA is an example of chromatin modifying proteins
It moves the nucleosomes out of the way so that transcription can occur
Describe how the enhancer, activator and mediator work together
Enhancer is a region of DNA upstream from the promoter
The activator is a molecule that binds to the enhancer to increase gene expression
The mediator connects the activator and the RNA pol
Which enzyme opens up the DNA strands (like helicase) in transcription?
TFIIH
What happens to the preinitiation complex when elongation starts?
The GTFs dissociate from the RNA Pol
What is the CTD of RNApol? What is special about it?
The C terminal domain
It has had it’s phosphorylation changed
Ser-5 -> ser-2
Transcription elongation requires the recruitment of many other …
eIF
Elongation initiation factors
What happens when specific termination sequences are transcribed?
When the termination sequence is transcribed, certain proteins are recruited and bound to the sequence and the mRNA strand is cleaved from the RNA pol
What is CstF?
Cleavage stimulation factor
What is CPSF?
Cleavage and Polyadenylation Stimulating Factor
What is PAP
Poly adenylase polymerase
What is PABP?
Poly adenylase binding protein
How does the mRNA get cleaved from the RNAP?
What happens next?
- Specific sequence is transcribed
- CstF and CPSF bind to the mRNA
- mRNA is cleaved
- PAP adds nucleotides to the 3’ end
- PABP associates with poly-A tail and determines its length
What are the three differences in protein synthesis between prokaryotes and eukaryotes?
Prokaryotes lack post-transcriptional modifications/processing
Only one RNA pol
No histones or nucleosomes
What is hnRNA?
This is the immature mRNA
It still has introns
What are the three main processes that occur in post-transcriptional modification?
5’ capping
Poly a tail
Splicing
Describe the process of 5’ capping
- After 20-30 nucleotides, guanyl-transferase adds 7methyl guanosine to the end of the transcript
Which enzyme adds the 5’ cap?
Guanyl transferase
When does G-capping occur?
After 20-30 nucleotides have been synthesised in the mRNA transcript
What is the function of the 5’ cap?
Orientation on the ribosome
Prevent degradation
What is the structure of the poly-A tail?
Many adenine nucleotides added
Which enzyme synthesises the poly-A tail?
PAP
Poly adenine polymerase
What are consensus sequences and in what process are they important?
These are specific sequences of nucleotides in an mRNA transcript
These sequences are recognised by spliceosomes
The spliceosome recognises that region as an intron and then cuts it out
What is the structure of a spliceosome?
Thus, it is …
snRNA And protein
Ribonucleoprotein
What is the RNA in a spliceosome called?
snRNA
What is snRNP?
What does it do?
Small nuclear RNA + protein
Ribonucleoprotein
It recognises the consensus sequences in introns so that they can be cut out
What is the structure of ribosomes?
Thus it is a …
rRNA and protein
Ribonucleoprotein
List some structures that are ribonucleoproteins
- Spliceosome, snRNPs
- Ribosome
- Telomerase
What are the two subunits of the ribosome?
40S and 60S
What are eIF?
Elongation initiation factors
These are required for addition of nucleotides to the mRNA transcript by the RNA pol
It moderates RNApol’s action
and rmoves histones
Describe initiation of translation
eIF bring together the 7mG of 5’ cap, the 40S subunit of ribosome and MET tRNA
When does the 60S subunit bind?
Wen the start codon is reached in the 40S subunit
Describe the steps in translation elongation
- Empty A site
- Complimentary tRNA codon enters a site
- Bond forms between the amino acids in the A and P sites
- 60s shifts along
- tRNA in the E site is expelled, 40S moves along
Describe the process of termination of translation
When the stop codon is in the a site, instead of a tRNA coming in, a termination factor comes in instead.
This causes the two subunits to dissociate
What is the protein component of a spliceosome for?
The protein part of the spliceosome actually breaks the phosphorite steer bonds between nucleotides
What is the other name for a spliceosome?
snRNP or SNURP
