Control of Gene Expression

Question 1

What are switched on genes?

Answer 1

Permanently expressed genes.

E.g the genes that code for essential chemicals.

Question 2

What are switched off genes?

Answer 2

Permanently not expressed.

E.g the gene for insulin in cells lining the small intestine.

Question 3

What are totipotent cells?

Answer 3

Cells such as fertilised eggs, which can mature into any body cell.

Question 4

The ways in which genes are prevented from expressing themselves include:

Answer 4

• Preventing transcription and hence preventing the production of mRNA.
• Breaking down mRNA before its genetic code can be translated.

Question 5

What are stem cells?

Answer 5

Totipotent cells which exist in mature animals.
They are undifferentiated dividing cells that occur in adult animal tissues and need to be constantly replaced.
They’re found in the inner lining of the small intestine, the skin and the bone marrow.

Question 6

What are embryonic stem cells?

Answer 6

The stem cells that occur at the earliest stage of development of an embryo, before the cells have differentiated.

Question 7

For transcription to begin what needs to happen? What are they called?

Answer 7

The gene needs to be stimulated by specific molecules that move from the cytoplasm into the nucleus.
These are called transcriptional factors- they each have a site that binds to a specific region of the DNA in the nucleus.
When it binds it stimulates this region of DNA to begin the process of transcription.
mRNA is produced and the genetic code it carries is then translated into a polypeptide.
When a gene is not being expressed, the site on the transcriptional factor that binds to DNA is blocked by an inhibitor molecule which prevents transcription.

Question 8

What shape is mRNA?

Answer 8

Clover leaf

Question 9

Starting with mRNA, describe how the process of translation leads to the production of a
polypeptide.

Answer 9

mRNA attaches to ribosome;
codon on mRNA;
binds to an anti-codon on tRNA;
each tRNA brings a specific amino acid;
sequence of codons/bases on mRNA determines order of amino acids; formation of peptide bonds/amino acids joined by condensation reactions;