Genes and proteins: Transcription of DNA into RNA Flashcards
What is DNA transcription?
Part of gene expression process.
Why is RNA translated?
To produce functional proteins.
Where is genetic information from DNA transferred?
To proteins.
What is DNA?
The primary store of inherited information.
Critical resource for cell, organism, population.
How can information from DNA be accessed?
It is un-packed.
Un-wound.
What happens to DNA after it is un-wound, un-packed?
It is exposed.
More susceptible to damage.
How are DNA sequences/genes present?
As 1-2 copies per cell.
How many of proteins/products of genes are required at one time?
Thousands.
Why do DHA genes present as 1-2 copies per cell and thousand of their proteins are required at one time?
To make few ‘copies’ of a sequence –> use –> make hundreds products –> used by cell.
What is DNA transcription?
The process of copying DNA genes into RNA.
What are the characteristics of RNA?
- Chemically similar to DNA.
- Has a ribose sugar unit, not a deoxyribose sugar.
- Includes: A, C, G, U = bases.
- RNA Polymerase –> transcription –> template DNA strand and 4 bases copied.
Which are the leading strands of synthesis in DNA transcription?
Template DNA strand + 4 bases of RNA copied.
3’-OH.
How many types of RNA exist in prokaryote and eukaryote cells?
3.
What are the 3 types of RNA in organisms required for?
Protein production.
Which are the 3 types of RNA in organisms?
- Ribosomal RNA (rRNA).
- Transfer RNA (tRNA).
- Messenger RNA (mRNA).
What types of RNA does DNA transcription produce?
All 3 types.
Which type of RNA focusses on converting inherited information in genes to proteins?
mRNA.
What do some cells contain except from coding RNA?
Non-coding RNA.
What are the types of non-coding RNA?
- Small nuclear RNA (SnRNA).
- Micro RNA (miRNA).
- Small interfering RNA (SiRNA).
- Heterogeneous nuclear RNA (hnRNA).
What is the function of non-coding RNA species?
Regulation of transcription and translation.
What is the function of tRNA?
It transports amino acids to protein synthesis site.
What is the function of rRNA?
It combined with proteins –> form ribosomes to protein synthesis site.
What is the function of mRNA?
It directs amino acid sequence of proteins.
What is the function of SnRNA?
It processes mRNA to mature in eukaryotes.
What is the function of SiRNA?
It affects gene expression.
Used by scientist –> knock out a gene.
What is the function of miRNA?
It affects gene expression.
Important in growth and development.
For which organism was In vitro transcription demonstrated?
For Escherichia coli RNA Polymerase.
Who and when was the first In vitro transcription demonstrated?
By Weiss and Hurwitz, in 1960.
Where could they see RNA Polymerase?
On DNA.
Producing ‘tails’ of RNA in electron microscopy.
Why is the simple in vitro system easy to understand?
It does not have other factors that regulate gene expression.
Of how many stages does transcription consist?
3.
Which are the 3 transcription stages?
- Initiation.
- Elongation.
- Termination.
Which of the 3 stages of transcription could be interrupted to control gene transcription?
Any of the 3.
Which factors target the transcription stages?
Antibiotics.
How many subunits compose the E. coli RNA polymerase (RNAP) enzyme?
5.
Which are the 5 subunits of RNA Polymerase?
2 α β β' ω
What does the Holoenzyme include as the fifth subunit?
Sigma: σ.
What is Sigma in the Holoenzyme?
A very large protein complex.
What does RNAP synthesize?
mRNA.
rRNA.
tRNA.
For what is the RNAP/Core enzyme required?
For the polymerization.
For what is σ factor required?
For correct transcription.
How does σ factor work?
It targets gene’s upstream region/operator: -35 and -10 sites.
Why do bacteria have different Sigma factors?
To regulate different gene groups.
What is Sigma factor in bacteria?
The highest-order mean that regulates bacterial gene expression.
Where does Escherichia coli RNA Polymerase bind?
To DNA.
By which factors is transcription controlled?
By non-coding DNA sequences.
Of what do genes consist?
Of a central ‘coding’ sequence.
In what is the central ‘coding’ sequence of genes translated?
In amino acids sequence.
What do amino acids translate from genes make?
Protein.
Up-stream region.
Down-stream region.
What do the up-stream and down-stream regions control?
Gene expression.
What is the difference between eukaryote gene structure and prokaryote one?
Eukaryote is more complex.
What do eukaryote gene structure and prokaryote have in common?
They include coding and non-coding sections.
What does the σ subunit recognise in transcription?
The promoter sequence.
What does the σ subunit allow once it recognises the promoter sequence in transcription?
Holoenzyme binding to DNA.
Where does initiation of transcription occur?
At the start of transcription.
Where does initiation of transcription occur?
Within the promoter.
Which is the progress initiation of transcription take place?
5’- 3’direction.
From 3’- OH of RNA.
What does the σ factor do after initiation stage ends?
It dissociates from the core enzyme.
When does termination occur in transcription?
At/after transcriptional stop site –> Rho (p) factor binds –> termination occurs.
What does RNA polymerase holoenzyme recognise first in initiation stage of transcription?
The promoter at -35 region.
Where does RNA polymerase holoenzyme bind once it recognises the promoter at -35 region in initiation stage of transcription?
To the full promoter.
Where does RNA polymerase bind as initiation occur?
At the -10 region of the promoter.
What happens once RNA polymerase bind to -10 region of the promoter?
DNA untwisting.
As DNA untwists what happens?
RNA polymerase is orientated and begins transcription at +1.
What happens in DNA untwisting process?
The two DNA strands melt apart.
Base-pairing first nucleotide to coding strand.
What does Termination stage of transcription involve?
Hair-pin loop formation near mRNA end.
What does the termination site include?
A GC-rich direct repeat + short poly-U sequence.
What is the poly-A tail in eukaryotic mRNA?
Much longer.
How is the poly-A tail in mRNA used?
Uses poly-T anchor –> Isolates mRNA from active genes.
How is transcription and translation in prokaryotes?
Tightly coupled.
Which factors line up along mRNA in prokaryotes to produce proteins, as RNAP goes along DNA to produce mRNA?
Ribosomes.
How is transcription-translation possible in vitro?
With 3H production.
14C-labelled proteins.
What do 3H and 14C-labelled proteins production from transcription-translation production, allow?
Investigation of protein functions not able to occur in cells/cell lysates.
What is the difference of coupled transcription in prokaryotes and eukaryotes?
Prokaryotes: Translation is the rule.
Eukaryotes: Translation does not occur.
What is the difference of coupled transcription in prokaryotes and eukaryotes?
Prokaryotes: Translation is the rule.
Eukaryotes: Translation does not occur.
When and where does transcription occur in prokaryotes and eukaryotes?
Prokaryotes: In cytoplasm, at any stage of cell cycle.
Eukaryotes: In nucleus, at G1, G2 phases of cell cycle.
Which factors synthesize mRNA, tRNA and rRNA in transcription, in prokaryotic and eukaryotic?
Prokaryotic: A single RNAP.
Eukaryotic: RNAPs 1, 2, 3.
What happens to RNA in order to produce proteins in eukaryotic transcription?
It is heavily modified before use: capping, tailing, splicing, export.
What characteristic do eukaryotic RNAPs have?
Larger complexes.
Contain more subunits.
Maintain basic structure like prokaryotes RNAPs.
Where do modifications in eukaryotic mRNA undergo?
In nucleus.
When do modifications occur in eukaryotes’ nucleus?
Before being exported and translated.
What do the modifications of mRNA in eukaryotes include?
5’ capping.
3’ poly-A tailing.
Splicing.
What is ‘capping’?
A 3-step process.
What are the 3 steps/enzymes of RNA ‘capping’?
- RNA triphosphatase.
- Guanylytransferase.
- Methyltransferase.
When are the 3 capping RNA enzymes functional?
When they are attached to RNA polymerase 2 to produce RNA transcript.
What do the 3 capping RNA enzyme do when they are attached to RNA polymerase 2?
They modify RNA transcript –> produce 7-methylguanosine cap at 5’ end.
By what is the 3’ segment of the born pre-mRNA cleaved off?
By proteins.
What do the proteins that cleave off the 3’ end of pre-mRNA then synthesize?
The poly A tail from the 3’ end.
Where can the poly A tail then be added?
At one of the several possible sites.
What does the addition of poly A on the sites allow?
Different transcripts mRNA to be produced from a single gene –> polyadenylation.
Why is the tail important?
For nuclear export.
Translation.
mRNA stability.
What happens to the tail over time?
It shortens.
What happens to the mRNA when the tail is short enough?
It is enzymatically degraded.
What does polyadenylation promote once it occurs in bacteria?
RNA degradation.
What do eukaryote genes include?
Short protein-coding regions: exons.
Non-coding regions: introns.
How are the introns removed from the RNA?
By ‘splicing’?
Why are introns removed from the RNA?
To produce mature mRNA.
Are exons removed from RNA during splicing?
Maybe.
Why are exons removed from the RNA if they do?
To produce different mRNAs with lost protein sequences.
By what factor hoes pre-mRNA undergo editing?
By the spliceosome.
Why does pre-mRNA undergo editing by the spliceosome?
To remove introns and join exons, precisely –> produce mRNA
Where does RNA splicing take place?
In the nucleus.
When does splicing take place?
During/immediately after transcription.
What is the spliceosome?
A complex of small nuclear ribonucleoproteins(snRNPs).
What do self-splicing introns/ribozymes do?
They catalyse their own excision from their parent RNA molecule.
What do alternative splicing patterns do?
Remove exons.
Link introns.
Related proteins expressed.
What does transcription transfer?
Genetic information from DNA to RNA.
What is the function of alternative processes intracting with transcription?
To change the outcome.
Why is gene expression regulated?
For the cell to change in transcription –> respond to external conditions.
Why can transcription be interrupted?
For the gene to be expressed.
By what factor is pre-RNA modified?
By polyadenylation.
Why is pre-RNA modified by polyadenylation?
To control stability.
To determine sequential coding end.
Why does splicing remove exons?
To produce series of proteins which function relatively in different situations.
What can be the result of mutations in regions?
Different genetic conditions.
