L10 - Regulation of gene expression - concepts

Question 1

Why is gene expression regulated?

Answer 1

• Microorganisms adapt their profile of expressed genes in order to utilize available nutrients.
• Cell differentiation and development programmes are driven by changes in gene expression.
• While many transcripts will be switched on or off under different growth conditions/ different cell types, some genes are constitutively expressed. This means the expression of some transcripts does not alter

Question 2

What is the meaning of constitutive and inducible genes?

Answer 2

Constitutive genes are those that are always active.

Inducible genes are those that have variable activity, depending on the needs of the cell.

Question 3

What are the two mutation types affecting gene expression?

Answer 3

Cis (within the same gene) or trans (in a different gene).

Mutations in cis affect nucleotide sequences within the DNA required for gene expression. Whereas trans mutations affect factors that regulate the expression of a target gene.

Question 4

Trans-acting factors can act to up or down regulate expression. What do these mean?

Answer 4

• Factors that cause activation are known as trans-acting activators (under positive control).
• Factors that cause downregulation are known as trans-acting repressors (under negative control).

Question 5

What is an inducer and a corepressor?

Answer 5

Inducer - molecule mediating the upregulation e.g. enzyme encoding genes can be unregulated in the availability of substrate.

Corepressor - active molecule that mediates enzyme-encoding genes that can be downregulated in the presence of a product.

Question 6

What does it mean if a gene can be autoregulated?

Answer 6

the gene product influences its own expression