L-16

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 such as a protein or a non-coding RNA

Question 2

What is a gene?

Answer 2

A defined region of DNA that produces a type of RNA molecules that have some function

Question 3

What is Transcription?

Answer 3

DNA-dependant RNA synthesis that is catalysed by the enzyme RNA polymerase. RNA polymerase synthesises mRNA by catalysing the formation of phosphodiester bonds between ribonucleotides

Question 4

Which strand of DNA is used to synthesise mRNA? What is the other strand called?

Answer 4

The template strand

The coding strand

Question 5

What are the 3 stages of transcription?

Answer 5

• initiation
• elongation
• termination

Question 6

Outline the 3 steps of initiation?

Answer 6

• Transcription factors bind to the TATA box and other regions of the promoter
• RNA pol II binds, forming a transcriptional initiation complex with the transcription factors
• the 2 DNA strands separate and RNA pol II starts with mRNA synthesis without the need of a primer

Question 7

What occurs during Elongation?

Answer 7

RNA pol II uses the template strand running in the 3’-5’ direction as a template and inserts complementary RNA nucleotides in the 5’-3’ direction

Question 8

What is splicing?

Answer 8

Splicing occurs between transcription and translation and is the removal of introns from the coding sequence to leave only the exons to be translated

Question 9

What is a coding sequence?

Answer 9

Portion of a genes DNA that is translated into a protein

Question 10

What is a promoter?

Answer 10

DNA segment recognised by RNA polymerase to initiate transcription

Question 11

What are the 4 functions of UTRs

Answer 11

• transcribed but not (usually) translated
• contains regulatory elements (sequences) that influence on gene expression at the transcriptional and/or translational level
• 5’ UTR facilitates the addition of the 5’G cap
• 3’ UTR facilitates the addition of the polyA tail

Question 12

What is the function of the 5’G cap?

Answer 12

Prevents mRNA degradation, promotes intron excision and provides a binding site for the small ribosomal subunits

Question 13

What is the function of the polyA tail?

Answer 13

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