15 Control of gene expression

Question 1

What is a transcription factor? (2)

Answer 1

1. (Protein/molecule) that moves from cytoplasm
   to DNA;
2. (TF) binds to specific gene/genes/ to specific
   part of/site on DNA/ binds to promoter/RNA
   polymerase;
3. Leads to/blocks (pre)mRNA production /
   allows/blocks binding of RNA polymerase (to
   DNA)/allows RNA polymerase to work;

Question 2

Give 2 characteristic features of stem cells (2)

Answer 2

Will replace themselves/keep dividing/replicate;
Undifferentiated/can differentiate/develop into other
cells/totipotent/multipotent/pluripotent;

Question 3

Callus is a mass of undifferentiated plant cells.
Plantlets are small plants.

Explain the evidence from the table that the cells from the stem tip are totipotent. (2)

Jun11-6a

Answer 3

1. Gives rise to new plants/plantlets;
2. So must be able to develop into different tissues / other
   specialised cell types / differentiate;

Question 4

Transcriptional factors are important in the synthesis of particular proteins.
Describe how. (2)

Answer 4

1. Bind to DNA/gene;
2. At specific region/base sequence/promoter sequence;
3. Stimulate transcription / prevents transcription / turn on
   gene / turn off gene;

Question 5

The siRNA-protein complex attaches to an mRNA molecule coding for a particular
protein (step 2). Explain what causes the siRNA to attach only to one sort of mRNA
molecule. (1)

Answer 5

Has complementary base sequence;

Question 6

Describe and explain how expression of the target gene is affected by siRNA. (2)

Answer 6

1. No longer able to make specific protein / cannot make
   whole protein / mRNA cannot be translated;
2. Because mRNA has been cut into pieces;

Question 7

Scientists have suggested that siRNA may be useful in treating some diseases.
Suggest why siRNA may be useful in treating disease. (2)

Answer 7

1. Some diseases are genetic / caused by mutations;
2. siRNA will stop product of this gene / the protein being
   produced / stops translation;

Question 8

This siRNA would only affect gene expression in cells infected with HIV.
Suggest two reasons why (4)

Answer 8

Only infected cells have HIV protein
on surface;
So carrier only attaches to/specific to
these cells/siRNA can only enter
these cells;
OR
siRNA (base sequence)
complementary/specific to one
mRNA;
Only infected cells contain mRNA of
HIV/this gene/ stops translation of
this gene/only binds to this mRNA
/destroys this mRNA;

Question 9

Define totipotent cell

Answer 9

Cell that can mature into any body cell.

Question 10

Why do differentiated cells produce different proteins? (2)

Answer 10

Different cells have different genes expressed

Different genes code for different amino acids

Question 11

How can genes be prevented from expressing themselves? (2)

Answer 11

Preventing transcription - no mRNA formed

Preventing translation - mRNA broken down before can be translated

Question 12

Animals:

Totipotent cells? except?
Define stem cells
What 2 types and where found?

Plants:
Totipotent cells?
Importance?

Answer 12

Hardly any, stem

Stem cells = undifferentiated cells, that constantly replace themselves by dividing

Adult stem cells - bone marrow
Embryonic stem cells - embryo

Many

Can be cloned using in vitro

Question 13

Define transcriptional factor

Answer 13

Protein/molecule that moves from cytoplasm to DNA
binds to specific gene
stimulates/prevents mRNA production/transcription

Question 14

Oestrogen:

What effect does it have?

Explain how (4)

Why can it easily diffuse across the cell membrane?

Answer 14

stimulates transcription

1. Oestrogen binds to TF receptor.
2. Receptor changes shape
3. Inhibitor molecule released so TF DNA binding site exposed.
4. TF binds to gene, (RNA polymerase stimulated), transcription stimulated.

Lipid-soluble

Question 15

siRNA:

What effect does it have?

Explain how (3)

Give 2 uses

Answer 15

inhibits translation

1. mRNA cut into pieces by enzyme
2. Cannot make specific/whole protein
3. mRNA cannot be translated;

Can treat genetic diseases
Identify role of genes (by inhibiting we see effect)