Introduction to Molecular Biology 3 Lecture Flashcards
31/10/24
Which base is unique to RNA?
Uracil, rather than Thymine.
What makes deoxyribose sugar different from ribose?
Deoxyribose has a missing oxygen from the ‘OH’
What different structures can DNA and RNA adapt?
DNA is always a double helix.
RNA can take the form of a STEM loop, a Hairpin loop, and a Pseudoknot.
What is the function of RNA?
- Acts as a cataylst - rRNAs in the formation of a ribosome
- Spliceosome - snRNA
- Adaptor - tRNA
- Genetic messenger - mRNA
What is the function of DNA?
Storage of genetic information
Describe the process of transcription
DNA helicase breaks hydrogen bonds.
One strand acts as a template, free RNA nucleotides bind and RNA polymerase created phosphodiester bonds 5’ to 3’ direction. Transcription is not as accurate as replication.
Where does transcription take place?
Downstream of the promoter. The terminator region signals polymerase to stop.
Which RNA polymerases are responsible for the different types of RNA?
RNA Pol. 1 - rRNA
RNA Pol. 2 - mRNA
RNA Pol. 3 - tRNA
What is the TATA box?
A short DNA sequence found around 25 bases upstream of the start region. It facilitates the binding of RNA polymerase and a transcription factor.
What is CAAT box?
CAAT box is found in the promoter region, 70-80bp upstream of the starting site. It is responsible for recruiting RNA polymerase and serves as a binding site for groups of transcription factors.
What is the SPI gene?
Codes for a transcription factor.
What is the role of enhancers?
They boost the rate of transcription, and can be far upstream or downstream, or even in introns.
Provide binding sites for transcription factors.
They loop DNA to bring the enhancer to the promoter attracting RNA polymerase. Enhancers are opposed by silencers.
How is mRNA stabilised?
At either end, there is a 5’ cap, and a poly-A-tail. This is to protect mRNA from exonucleases, to aid export of mRNA, and to assist with its identification.
What are introns/exons?
Introns are coding segments of DNA, while exons are non coding segments of DNA.
What is an open-reading frame?
A continuous stretch of nucleotides that carry the potential to be translated into a protein.
Briefly summarise the process of transcription (1st 1/2 to protein synthesis)
Gene → pre-mRNA (transcription) → introns removed to become mRNA (splicing) → mature mRNA exported from nucleus to cytoplasm
Describe the process of splicing
Spliceosomes (proteins and RNA) assemble on a pre-mRNA molecule, where introns meet exons. It identifies the 5’ start of the introns and cuts, forming a lariat structure. It then loops the intron out, cuts the other end and joins adjacent exons together.
What is alternative splicing?
The formation of different protein isoforms, by excluding/including certain exons, or intron retention. A variation in splice sites.
