Biological Molecules 3

Question 1

Describe the differences between RNA and DNA

Answer 1

RNA - presence of hyrdroxyl group on carbon two makes it more unstable than DNA, also means it is more susceptible to hydrolysis. Contains base uracil and is more structurally more complex due to the different single stranded conformations (Stem-loop, hair-pin and psudoknot
DNA- Thymine base, and is found in a double helix.

Question 2

What is the coding strand?

Answer 2

The non-template strand of DNA, therefore is the same as the mRNA produced but contains thymine instead of uracil.

Question 3

How do RNA polymerase know where to begin?

Answer 3

They bind to specific start sequences called start codons. The start codon is found in the promoter section and this is where RNA polymerases are found.

Question 4

What RNA polymerase is used in the protein coding for RNA?

Answer 4

RNA polymerase II

Question 5

What is the promoter for RNA polymerase II and give some features?

Answer 5

TATA boxes. They facilitate the binding of RNA polymerase II and transcription factors. These are 25 bases long and are found upstream of the start site.

Question 6

What helps recruit RNA polymerase II. (what helps it bind to DNA)

Answer 6

The binding of trans-acting factors to cis-acting promoters. The RNA polymerase II will then bind to this complex as it is unable to bind directly to the promoter.

Question 7

What is a transcription factor?

Answer 7

A protein that can float in the nucleus and act at multiple locations in the genome.

Question 8

Describe the difference between houskeeping genes and transcriptionally regulated genes

Answer 8

Housekeeping gene - Cells need it to be expressed at a constant level all the time (actin)
Transcriptionally regulated gene - Transcription of this gene is tightly controlled (Insulin).

Question 9

What is an enhancer?

Answer 9

These stabilise transcription machinery and are opposed by silencers.

Question 10

Describe the two ways in which mRNA is processed.

Answer 10

Addition of a methyl group at the 5’ end (5’cap) and a poly -A-tail at the 3’ end. These increase stability and allow it to be identified as mRNA.

Question 11

Describe the process and reason for mRNA splicing

Answer 11

Reason - removes introns to produce a mature mRNA strand.
Process - Takes place through two esterification reactions and the use of spliceosomes containg snRNA to identify the correct sequences and have a catalytic activity

Question 12

What is the function of alternate mRNA splicing?

Answer 12

To create different proteins from the same strand of mRNA