RNA Synthesis Flashcards
Which is the biggest and smallest chromosome in the karyotype?
1= biggest and 22= smallest
What protects the ends of the chromosomes?
Telomere
What is the definition of a gene?
Unit of hereditary, or a DNA segment containing instructions for making a particular product
Why is the promoter region important?
Turns the gene on/off
Which of introns/Exons is expressed?
Exons are Expressed (remember the E’s)
Introns are spliced out
Where would you find an untranslated region (UTR)?
Part of the first and last exon
What is transcription? (General overview)
Synthesis of mRNA from DNA
What is translation? (General overview)
Nucleic acid ->protein
What genes do RNA polymerase 1 transcribe?
Most ribosomal RNA (rRNA)
What genes do RNA polymerase 2 transcribe?
Protein coding, miRNA and non coding RNA
What genes do RNA polymerase 3 transcribe?
tRNA, 5s rRNA and other small RNAs
How does the cell respond so quickly to changes in its environment?
Lots of polymerases can work simultaneously on the gene to make lots of copies of the gene
What molecules do you need for RNA synthesis?
- DNA template
- RNA polymerase 2
- ribonucleotide
- buffers
- transcription factors
What is a transcription factor?
Proteins required to initiate or regulate transcription in eukaryotes
How do transcription factors work?
- TATA box (promoter) recognised by the TBP subunit or TFIID
- other transcription factors bind then RNA polymerase2 assembles at the promoter forming the transcription initiation complex
- TFIIH (helicase) pulls apart the helix and phosphorylates RNA polymerase 2
- phosphorylated RNA polymerase 2 is released from the complex and begins transcription
What does TBP stand for?
TATA binding protein
Why is there a 5’ UTR?
Regulation of translation
Why is there a 3’ UTR?
MRNA stability and miRNA binding
What are the three steps in RNA processing?
Capping, polyadenylation and splicing
What is capping and how does it work?
5’ end modification.
Forms a 5’-5’ triphosphate bridge and is methylated at the 7 position
What does capping do?
Allows for co-transcriptional modification
can stimulate splicing
Used for the recognition of mRNA by the translation machinery in the cytoplasm of the cell
What is polyadenylation and how does it work?
At some point there is a cleavage (joining) signal. Then an adenine tail is added by poly (A) polymerase
What is the point of capping and polyadenylation?
Stability
Allows for the transport to the cytoplasm
And increases the integrity prior to translation
How many introns are in one gene?
7-9
What is the size of an intron?
<100->700,000 nucleotides (median 1800 nucleotides)
How many nucleotides does an exon have on average?
123 nucleotides
What are the steps of splicing?
- GU and pyramiding rich region get recognised by proteins and they undergo splicing
- ends join up
- then the 3’ end gets cut and the two Exons join up
Why do introns exist?
Alternative splicing - allows you to select different Exons to make up your mature proteins
Means you can make up many more proteins with less genes
What do you need to export the RNA from the nucleus?
Cap binding complex (CBC)
Transcription-coupled export complex (TREX)
Exon junction complex
Give some examples of where alternative splicing takes place
Alternative promoters (eg myosin)
Alternative polyadenylation in ubiquitously expressed genes
