Signalling and Regulation of Gene Expression

Question 1

What is signal transduction?

Answer 1

A process by which a signalling induces a biochemical change within target cell.

Question 2

Why is signalling important?

Answer 2

Found in multicellular organisms in which it is essential for intercellular communication.

Question 3

What are the four ways in which cells communicate?

Answer 3

1. Chemical Messengers (ligand that binds to protein receptors).
2. Through Gap Junctions (cells touch and communicate through channel).
3. Cell Surface Proteins (Ligand on surface of signalling cell docks into receptor of target cell).
4. Electrical Impulse (Along a nerve, the synapse).

Question 4

What are some responses to signalling in target cells?

Answer 4

1. Change in metabolism.
2. Regulation of cell division.
3. Changes to gene expression.
4. Programmed cell death.

Question 5

What would the change in metabolism affect?

Answer 5

May induce glycogen breakdown in cytoplasm of muscle cells in response to noradrenalin, releasing glucose units for energy production.

Question 6

What are the details of the regulation of cell division?

Answer 6

Cell-cell interactions that ensure division occurs in synch, and stops dividing when necessary to enter rest state.
Example: Growth Factor, a polypeptide specific for certain cell types stimulating cells to grow.

Question 7

What are the details of changes in gene expression?

Answer 7

May lead to permanent changes in structure and function of target cell-DIFFERENTIATION.

Question 8

What are the details of programmed cell death?

Answer 8

Target cell shuts down and dies so it can be carried away.

Question 9

What are some of the responses to signalling in target cells?

Answer 9

Individual signalling processes may be INTEGRATED, to regulate complex biological programs.

Question 10

List two biological programs?

Answer 10

1. Induction of an immune response-antigen interacts with lymphoid cell and stimulates a series of cell-cell messages that will produce antibody to the original antigen.
2. Control of development-egg to adult cell life.

Question 11

What are some general considerations of the signalling process: Ligands?

Answer 11

Signalling ligands are polypeptides:

• GF
• hormones
• cytokines
• small polar molecules

Question 12

What is unique about these ligands?

Answer 12

They cannot cross the target cell membrane, therefore they must act from outside.

Question 13

What are the exceptions of passing the cell membrane?

Answer 13

There are fat-soluble ligands (steroid hormones) that can enter the cell via passive diffusion, reaching the cytoplasm and nucleus.

Question 14

What are SEVEN main considerations of the signalling process?

Answer 14

1. The presence of the ligand at the cell surface must be sensed.
2. The primary event must be transmitted across the membrane to its inner surface.
3. Biochemical event.
4. Amplification.
5. Nuclear Translocation.
6. Transcription.
7. Expression.

Question 15

Which part of the receptor does the ligand bind to?

Answer 15

The extracellular domain.

Question 16

What does it mean when a cell is unresponsive to a signalling molecule?

Answer 16

Cannot or does not synthesize the required receptor.

Question 17

How may we ensure that the ligand is transmitted across the membrane to the inner surface?

Answer 17

The existence of a transmembrane domain of the receptor as well as a cytoplasmic domain. Through dimerization, the cytoplasmic side will create a new structure that will have new biochemical properties.

Question 18

What is step three of the signalling process?

Answer 18

Enzyme catalyzed reaction initiating a chain of events. The enzymes are usually protein kinases.

Question 19

What is step four in the signalling process?

Answer 19

Phosphorylation of another enzyme, creating a cascade, and may create a large change in the metabolic state of the cell.

Question 20

What is step five of the signalling process?

Answer 20

Nuclear translation in which the ligand may be modified biochemically in order to move into the nucleus and cross the nuclear membrane.

Question 21

What is step six of the signalling process?

Answer 21

Transcription factors are turned on in order to regulate gene expression.

Question 22

What does the activation of transcription factors involve?

Answer 22

1. Covalent modification of transcription factor or inhibitor that stores the inactive form.
2. Translocation of factor from cytoplasm to nucleus.
3. Ligand binding.

Question 23

What is the function of the transcription factor?

Answer 23

Recognize gene that is to be activated, change structure of chromatin exposing DNA so that RNA polymerase II can access target genes.

Question 24

What is the seventh step of the signalling process?

Answer 24

Expression of gene and effects of these expression changes.

1. Proliferation
2. Differentiation
3. Migration
4. Apoptosis

Question 25

How were nerve growth factor and epidermal growth factor discovered?

Answer 25

GF added to stimulate tissue growth, demonstrated their effects, and then were isolated.

Question 26

How did discovery of components of signalling pathways come to be?

Answer 26

1. Discovery of oncogenes.

2. Discovery of genes involved in embryonic development.