Transcription & RNA processing Flashcards
Where is DNA converted to RNA
In the nucleus DNA is converted to RNA
Why must genetic code be copied and transferred out of nucleus
Because the DNA found in nucleus is too big to move out (carried from DNA in nucleus to ribosomes in cytoplasm)
Define proteome
All protein in a cell
Enzymes that synthesise RNA from DNA are called _____
RNA polymerases (Pol II)
RNA is synthesised from which strand of DNA and in what direction
RNA is synthesised from the TEMPLATE (antisense) DNA strand which runs 3’—5’
In which direction does RNA polymerase synthesise complementary RNA
RNA is synthesised 5’—3’ as we synthesise RNA from the template strand so complementary base pairing means it’s the right way round 5’—3’ when it’s made (in RNA U instead of T)
What are the 5 steps of mRNA synthesis
INITIATION: polymerase binds to gene
ELONGATION: polymerase transcribes gene
TERMINATION: polymerase stops transcribin gene
PROCESSING: pre mRNA—> mature mRNA is formed
EXPORT: mRNA leaves nucleus through nuclear pore to be translated
What region initiates transcription that the RNA polymerase binds to at beginning
RNA polymerase binds close to PROMOTER REGION to initiate transcription
The promoter acts as a template for assembly of ______. This brings Pol II to gene. Once bound, polymerase can transcribe
The promoter acts as a template for assembly of PREINITIATION COMPLEX. This brings Pol II to gene. Once bound, polymerase can transcribe
What are the polymerase positioning elements
• TATA box= initiator
• upstream + downstream elements that bind +ve & -vely acting transcription factors (enhancers + silencers)
What happens in elongation stage of transcription
RNA polymerase synthesises complementary RNA in 5’—3’ direction using NTPs ( ribonucleoside triphosphates)
List difference between RNA & DNA
- different pentose sugar: deoxyribose in DNA, ribose in RNA
*DNA is double stranded; RNA is single stranded
*DNA has Thymine (T), RNA has Uracil (U)
How many bonds between
Thymine and Adenine
Uracil and Adenine
2 bonds between T & A
2 bonds between U & A
How many bonds between Guanine and Cytosine
3 bonds between G & C
What type of linkages form backbone of both DNA & RNA
PHOSPHODIESTER linkages form backbone of both DNA & RNA
Primary mRNA transcript needs to be modified before it’s exported into cytoplasm, explain the 2 caps and their role
5’ cap helps with efficient translation, prevents degradation of unstable mRNA molecule. Also directs pre mRNA splicing
3’ cap helps prevent degradation, assists splicing + nuclear export of mRNA
What is the role of poly A and where is it
Poly A is AAAA at 3’ end of RNA it provides the mRNA with stability and prevents degradation.
Describe RNA splicing (going from pre mRNA to final mature mRNA)
Cuts out INTRONS (non-coding RNA regions) are spliced out of pre-mRNA leaving the EXONS in the final mature mRNA
Define intron
Non coding region
Define exon
Coding region
Alternative splicing of mRNA forms what?
Alternative splicing forms different ISOFORMS of a protein
I.e. pre-mRNA—> alt splicing—> isoform 1 + isoform 2
These isoforms are fundamentally the same proteins but with slightly different features
Describe process of mRNA termination
RNA polymerase reaches TERMINATOR SEQUENCE —> transcription stops, mRNA is released
Describe process of mRNA processing
Polyadenylated region (at PolyA tail on 3’ region) is CLEAVED, the rest of mRNA degrades.
Mature mRNA is ready to be released into cytoplasm
What is the function of non-coding regions on DNA
Non-coding DNA corresponds to the portions of an organism’s genome that do not code for amino acids (build proteins).
Some non-coding DNA sequences are known to serve functional roles: e.g. regulation of gene expression, while other areas of non-coding DNA have no known function
When we want to infer mRNA sequence, we know complementary base pairs line up to form non-template sense (?’) strand (but with U instead of T) from the template antisense (?’) strand
When we want to infer mRNA sequence, we know complementary base pairs line up to form non-template sense (5’) strand (but with U instead of T) from the template antisense (3’) strand
Give some examples of Mis-regulated gene expression + disease
• general transcription factors can be mutated = e.g. cMyc-one is commonly amplified oncogene (large number of transcription factors important for development)
• mutated splice sites = e.g. cancer BRCA1 + 2, spinal muscular atrophy (SMN2), atypical cystic fibrosis (CFTR)
• mutated splicing machinery= retinitis pigmentosa, spinal muscular atrophy
Where is information that codes for proteome stored
Information to code for proteome is stored in DNA
Primary transcripts must be processed by 3 things:
Capping
Splicing
Polyadenylating
— this all forms mature mRNA that can be exported to ribosomes in cytoplasm
_____ in transcription factors (activating + inactivating) + splice sites affect gene expression + cause disease
MUTATIONS in transcription factors (activating + inactivating) + splice sites affect gene expression + cause disease
What’s the function of preinitiation complex
Regulates transcription + allows polymerase to attach to right part of the gene in order for transcription to be initiated
What is the UTR + why is it important
Untranslated region (UTR) they are all the regions before + after stop and start codon
They’re important as it’s where RNA polymerase will bind, it’s where termination factors will bind, where preinitiation complexes bind. I.e. controls all proteins that control transcription but don’t contain any sequence that is translated
We read DNA 5’ to 3’. We read RNA 5’ to 3’, why do we need to used 3’ to 5’ to synthesise RNA strand in 5’ to 3’
Because we use the template antisense strand (3’ to 5’) as RNA polymerase can complementary base pair to this strand and therefore form RNA 5’ to 3’ ( so RNA will be a copy of the 5’ to 3’ strand just with U instead of T)
What determines alternative splicing and what exons are kept
Different proteins in different cells will determine where the splicing will occur. It requires proteins to bind to splice sites depending on cell. So always different
In regards to exon splicing, how many can you splice out but still maintain function of protein
Depends on protein! Depends where functional domains are within the protein.
If you get mutations in transcription factors that will affect _____
If you get mutations in transcription factors that will affect TRANSCRIPTION OF THE GENE I.e. transcription factor isn’t moving away after initiated transcription so the patient will be transcribing gene continuously. If this gene regulates growth or cell division= unregulated growth/ cell division = cause cancer
Define oncogene
A gene in viruses (v-onc) + mammalian cells (c-onc) that can cause cancer. It results from a mutation of a normal gene
