DT - Transcription

Question 1

What is the structural difference between ribose and deoxyribose?

Answer 1

Ribose contains an extra -OH in the 2’-position

Question 2

What are the 5 types of RNA? (*Main types)

Answer 2

1. mRNA*
2. rRNA*
3. tRNA*
4. snRNA
5. miRNA

Question 3

What is the function of mRNA?

Answer 3

Acts as the template for protein synthesis

Question 4

What is the function of rRNA?

Answer 4

Major component of ribosomes

Question 5

What is the function of tRNA?

Answer 5

Carries amino acids, when active, to the ribosome

Question 6

What special sequences determine the start of transcription?

Answer 6

Promoter sequences

Question 7

What occurs during transcription initiation?

Answer 7

1. RNA polymerase binds to a region of a gene called the promoter
2. DNA unwinds allowing the enzyme to move along one of the DNA strands

Question 8

What occurs during transcription elongation?

Answer 8

RNA chain complementary to that of the template is synthesised in the 5’ to 3’ direction

Question 9

What occurs during transcription termination?

Answer 9

The transcribing RNA polymerase releases the DNA template strand and the transcribed RNA strand

Question 10

How are transcription and translation different in prokaryotes compared to eukaryotes?

Answer 10

In prokaryotes, transcription and translation can occur together

Question 11

What are the 3 factors that influence gene expression?

Answer 11

1. Nuclear membrane- separates transcription and translation
2. RNA processing
3. Complex transcriptional regulation

Question 12

What 2 ways are Eukaryotic pre-mRNA processed?

Answer 12

1. Addition of polyA tail to the RNA transcript
   - Increases stability and specifies export to cytoplasm
2. Addition of a cap to the end

Question 13

What regions are spliced from the newly synthesised RNA?

Answer 13

Introns

Question 14

What large complex performs splicing?

Answer 14

Spliceosome

Question 15

What happens in the lac operon when lactose is present?

Answer 15

Lactose or Allolactose bind to the repressor proteins, activating them, and preventing them to bind to the operator region. Hence structural genes are transcribed and Lactose is metabolized

Question 16

What do the terms: constitutive expression, regulated expression and polycistronic mRNA mean?

Answer 16

Constitutive expression- Genes which are always expressed
Regulated expression- Genes expressed under specific conditions
Polycistronic mRNA- An mRNA transcript encoding many different proteins

Question 17

Why may eukaryotic gene expression control be more complicated?

Answer 17

The gene to be transcribed may be inaccessible in condensed chromatin.
- Chromatin remodelling may need to occur

Question 18

Why may eukaryotic gene expression control be more complicated?

Answer 18

The gene to be transcribed may be inaccessible in condensed chromatin.
- Chromatin remodelling may need to occur

Question 19

What are the 2 types of transcription factors?

Answer 19

BASAL transcription factors- Bind to promotors (common in most genes)
REGULATORY transcription factors - Binds to
promotor-proximal element (Unique to a particular gene)

Question 20

What is the function of miRNA?

Answer 20

Acts as a guide to base pairing complementary sequences within mRNA, resulting in the silencing of specific mRNAs