Gene expression Flashcards
What is the process of transfering information from RNA to DNA
Reverse transcription
Can information be transfered from protein to DNA
No
What is TATA box
A specific Promotor
What binds onto the promotor
Enhancer (A TF)
What binds onto the enhancer
What’s it’s function
Activator Protein.
It recruits more TF to form a complex
What’ s the complex formed by activator protein for
Make it easier for RNA polymerase to attach on
What is the nature of CTCF
A protein
What sequence does it bind to
CCCTC (found in all insulator)
What does CTCF prevents
The binding of enhancers onto promotor
In Direct methylation, where is the methyl group added
Cytosine on CCCTC
Does Direct Methylation raise or drop a gene’s expression level from
It depends on the underlying genetic sequence
What is the function of mediator
- Mediator binds to RNA which controls transcription of gene
- May be an enhancer or silencer
What are the steps in transcription
A. Initiation
1. TATA-box binding protein binds to the DNA at the TATA box sequence in DNA.
- Transcription factors assemble at a specific promoter region along the DNA
- Other components of TFII (transcription factor 2) and RNA polymerase II bind.
- A mediator complex protein arrives carrying the enzyme RNA polymerase
- RNA polymerase is inserted into place between the strands of the double helix - Transcription factors at cis-acting enhancers thousands of bases away can trigger elongation.
- Initiation process requires contact between the transcription initiation complex and activator proteins
regions)
B. Elongation
1. Elongation of the RNA occurs 5’ to 3’ simply with the template strand. The coding strand goes around the ‘outside’ and is not actually directly involved.
- RNA polymerase unzips a small portion of the DNA helix, exposing the bases on each
strand
- Only one strand is copied, acting as the template for the synthesis of a protein
molecule
C. Termination
1. In some cases this occurs in response to a particular DNA sequence, in others randomly after the end of the gene to be transcribed.
What molecules contribute the nucleotides of mRNA
Ribonucleotide triphosphate
What is the product of the above transcription
pre-mRNA or primary transcript
What mineral is required for the RNA polymerase
Why is energy input required
Mg 2+
To break the high-energy triphosphate bonds
What are the 3 steps done to the aforementioned product
5’ capping, 3’ Polyadenylation, splicing
What are the 4 purpose for 5’ capping
To stabilze the RNA
– Regulation of nuclear export (1 mark)
– Prevention of degradation by exonucleases (1 mark)
– Promotion of translation (1 mark)
– Promotion of 5’ proximal Splicing(1 mark)
What is the enzyme used for 3’ PolyAdenylation
What are the 4 functions of 3’ Polyadenylation
Poly A polymerase
– Protect mRNAs from degradation by exonucleases (1 mark)
– Participate in transcriptional termination (1 mark)
– Facilitate export of the mRNA from the nucleus (1 mark)
– Participate in translation (1 mark)
What is splicing
What is the protein required for splicing
Splicing is the process by which non-coding sequences (introns) in the pre-mRNA are removed and the remaining protein-coding sequences (exons) are ligated together. (2 marks)
spliceosome
Different cells will splice the primary transcipt in different ways.
What the name of the process
Alternate Splicing
In what organelle is translation done
Ribosome
How many subunits are in the ribosome
2
Name the nucleic acid component of ribosome
Ribosomal RNA (rRNA)
What is the code on mRNA called
Codon
Does codon always corresponds to an amino acid
No, it can be a stop codon
If the codon is 5’ AAC’ 3’, what is the anticodon
3’UUG 5’, ie 5’GUU 3’
What is the region in Ribosome that the tRNA is checked by matching the codon and anticodon
A
What is the region where the amino acid is detached from the tRNA
P
What is the region that the tRNA is ejected
E
What are the procedures for Translation
A. Initiation
The first stage of translation involves the assembly of the three components that carry out the
process (mRNA, tRNA, ribosome)
1. The small ribosomal subunit binds to the 5’-end of the mRNA and moves along it until it reaches the start codon (AUG)
- Next, the appropriate tRNA molecule bind to the codon via its anticodon (according to
complementary base pairing) - Finally, the large ribosomal subunit aligns itself to the tRNA molecule at the P site and
forms a complex with the small subunit
B. Elongation
1. A second tRNA molecule pairs with the next codon in the ribosomal A site
- The amino acid in the P site is covalently attached via a peptide bond (condensation
reaction) to the amino acid in the A site - The tRNA in the P site is now deacylated (no amino acid), while the tRNA in the A site
carries the peptide chain
C. Translocation
1. The ribosome moves along the mRNA strand by one codon position (in a 5’ → 3’ direction)
2. The deacylated tRNA moves into the E site and is released, while the tRNA carrying the peptide chain moves to the P site
3. Another tRNA molecules attaches to the next codon in the now unoccupied A site and the process is repeated
D. Termination
The final stage of translation involves the disassembly of the components and the release of a
polypeptide chain
1. Elongation and translocation continue in a repeating cycle until the ribosome reaches a stop
codon
2.These codons do not recruit a tRNA molecule, but instead recruit a release factor that signals
for translation to stop
3. The polypeptide is released and the ribosome disassembles back into its two independent
subunits
