FHMP 003 control of transcription

Question 1

What is transcription?

Answer 1

The process of making RNA from DNA

Question 2

What is reverse transcriptase?

Answer 2

an enzyme that catalyzes the formation of DNA from an RNA template in reverse transcription.

Question 3

What is translation?

Answer 3

the decoding of an mRNA message into a protein

Question 4

What are the differences between DNA and RNA?

Answer 4

DNA: double-stranded, longer, has deoxyribose sugar, bases: A, T, G, C
RNA: single-stranded, shorter has ribose sugar, bases: A, U, G, C

Question 5

describe transcription in prokaryotes

Answer 5

• prokaryotes have no nuclear membrane, so transcription and translation occur in the same compartment at the same time (coupled)
• the expression of their proteins depends on the environment to reduce waste of materials and energy
• some proteins are always expressed at a constant amount, regulated by ‘house keeping genes’
• use operons

Question 6

What is an operon?

Answer 6

• a unit made up of linked genes that is thought to regulate other genes responsible for protein synthesis.
• found in both prokaryotes and eukaryotes
• a cluster of genes under the control of a single promoter
• 3 components = promoter region ( where RNA polymerase binds), operator region ( where a repressor binds and inhibits RNA polymerase from binding), structural sequence (a sequence that codes for the protein)

Question 7

What is the lac operon?

Answer 7

• A collection of genes that are important in coding for enzymes that metabolise lactose.
• the structural genes code for lactose permease and beta-galactosidase which allows lactose to be metabolised
• without lactose, the operator region is repressed, blocking the promoter region so RNA polymerase cannot bind and the proteins are not transcribed
• with lactose, it blocks the repressor protein, so RNA polymerase can bind and the proteins are transcribed

Question 8

describe transcription regulation in eukaryotes

Answer 8

• eukaryotes can compartmentalise transcription and translation as they have membranes
• regulation is different as they are found much further upstream at transcription start sites on the same or different chromosome
• have mediator complex which transmits signals from transcription factors to RNA polymerase to regulate transcription

Question 9

describe the mechanism of transcription

Answer 9

• DNA template is unwound, unzipped and is transcribed to the RNA transcript which is complementary to the DNA strand but U instead of T
• RNA is process and a 7- methyl guanosine cap is added to the 5’ end
• the RNA transcript is spliced by spliceosome, to remove the introns to produce mature RNA
• A poly (A) tail is added to the 3’ end and now mRNA is ready for translation

Question 10

What is initiation in transcription?

Answer 10

• transcription factors and recruitment factors bind to the TATA box on DNA, and also to RNAPII (RNA polymerase 2) where the start site is just above the start site and on the promoter region to stimulate or inhibit transcription

Question 11

give an example of a splicing mutation disease

Answer 11

• Beta thalassemia = 1 of the bases is mutated from G to A so the intron will not be removed as it is not recognised, so the protein will be longer and mutated with the added intron

Question 12

describe 4 ways of regulating genes

Answer 12

1. transcription factors
2. mRNA splice variants/alternative splicing
3. mRNA editing
4. Epigenetic