Lecture 16: Gene Expression: Transcription

Question 1

What is gene expression?

Answer 1

The process by which information from a gene is used in the synthesis of a functional gene product: protein or non-coding RNA

Question 2

What is a gene?

Answer 2

A defined region (sequence) of DNA that produces a type of RNA molecules that has some function

The “gene” (DNA) may contain sequences:

• responsible for the regulation of the synthesis of the
  RNA.
• that produce the RNA.
• responsible for the further processing of the RNA.

Question 3

Which DNA strand is transcribed?

Answer 3

DNA has two strands which are complementary in sequence

one strand is known as the coding strand (5’ → 3’), the
other is the template strand (3’ → 5’) (a.k.a. the non-coding strand)

Question 4

what are the three phases of transcription?

Answer 4

1. initiation
2. elongation
3. termination

Question 5

what happens during initiation?

Answer 5

1. Transcription factors bind to
   the TATA box and other
   regions of the promoter.
2. RNA pol II binds, forming a
   transcriptional initiation
   complex together with the
   transcription factors.

3. The two DNA strands
separate and RNA pol II
starts mRNA synthesis
without the need of a
primer.

Question 6

what happens during elongation?

Answer 6

RNA pol II uses the template strand, which runs in the 3’ → 5’ direction, as a template, and inserts complementary RNA nucleotides in the 5’ → 3’ direction

Question 7

What is coding sequence?

Answer 7

portion of a gene’s dna that is translated into a protein

Question 8

what is a promotor?

Answer 8

DNA segment recognised by RNA polymerase to initiate transcription

Question 9

What is UTRs (UnTranslated RegionS)

Answer 9

Transcribed but (usually) not translated

Contain regulatory elements (sequences) that influence on gene expression at the transcriptional and/or translational level

5’ UTR facilities the addition of the 5’ G cap

3’ UTR facilitates the addition of the polyA tail

Question 10

What is 5’ G cap

Answer 10

Prevents mRNA degradation, promote intron excision and provides a binding site for the small ribosomal subunit

Question 11

What is Poly- A- Tail

Answer 11

Prevents mRNA degradation and facilitates export of the mRNA from the nucleus to the cytoplasm

Question 12

Summary of Eukaryotic Gene Structure Elements

Answer 12

Contains non-coding DNA regions upstream and
downstream of the coding sequence as well as within
the coding sequence

These non-coding DNA regions can be transcribed but
are not translated

These non-coding DNA elements are involved in
regulating gene expression

Changes (mutations) in these non-coding gene
sequences may ‘disrupt’ normal gene expression