Introduction to Molecular Biology 3 Lecture

Question 1

Which base is unique to RNA?

Answer 1

Uracil, rather than Thymine.

Question 2

What makes deoxyribose sugar different from ribose?

Answer 2

Deoxyribose has a missing oxygen from the ‘OH’

Question 3

What different structures can DNA and RNA adapt?

Answer 3

DNA is always a double helix.

RNA can take the form of a STEM loop, a Hairpin loop, and a Pseudoknot.

Question 4

What is the function of RNA?

Answer 4

1. Acts as a cataylst - rRNAs in the formation of a ribosome
2. Spliceosome - snRNA
3. Adaptor - tRNA
4. Genetic messenger - mRNA

Question 5

What is the function of DNA?

Answer 5

Storage of genetic information

Question 6

Describe the process of transcription

Answer 6

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.

Question 7

Where does transcription take place?

Answer 7

Downstream of the promoter. The terminator region signals polymerase to stop.

Question 8

Which RNA polymerases are responsible for the different types of RNA?

Answer 8

RNA Pol. 1 - rRNA
RNA Pol. 2 - mRNA
RNA Pol. 3 - tRNA

Question 9

What is the TATA box?

Answer 9

A short DNA sequence found around 25 bases upstream of the start region. It facilitates the binding of RNA polymerase and a transcription factor.

Question 10

What is CAAT box?

Answer 10

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.

Question 11

What is the SPI gene?

Answer 11

Codes for a transcription factor.

Question 12

What is the role of enhancers?

Answer 12

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.

Question 13

How is mRNA stabilised?

Answer 13

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.

Question 14

What are introns/exons?

Answer 14

Introns are coding segments of DNA, while exons are non coding segments of DNA.

Question 15

What is an open-reading frame?

Answer 15

A continuous stretch of nucleotides that carry the potential to be translated into a protein.

Question 16

Briefly summarise the process of transcription (1st 1/2 to protein synthesis)

Answer 16

Gene → pre-mRNA (transcription) → introns removed to become mRNA (splicing) → mature mRNA exported from nucleus to cytoplasm

Question 17

Describe the process of splicing

Answer 17

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.

Question 18

What is alternative splicing?

Answer 18

The formation of different protein isoforms, by excluding/including certain exons, or intron retention. A variation in splice sites.