Intro To Signaling

Question 1

Why is signaling important?

Answer 1

Cells must be able to sense stimuli, integrate diverse inputs, and produce an appropriate biological response.

Question 2

Outline P2 of cell signalling.

Answer 2

Energy conversion. Cells must respond to signals to survive, adapt etc. External signals from the environment(e.g. light, sound, touch) is converted to nerve and chemical signals ATP/GTP.

Question 3

Outline P3 of cell signalling and give an example.

Answer 3

The same signalling molecular can induce varying responses in different target cells. Binding to one type of receptor can cause a multitude of effects in the target cell(e.g. alters cell shape, metabolism, gene expression). The intracellular relay system and the intracellular targets at which it acts vary from one type of specialized cell to another, so that different types of cells respond to the same signal in different ways.

For example, when a heart muscle cell is exposed to acetylcholine, its rate of firing decreases. Whereas, in skeletal muscles, acetylcholine binds to a different receptor protein(which?), causing the muscle cell to contract. Thus the extracellular signal molecule alone is not the message: the information conveyed by the signal depends on how the target cell receives and interprets the signal.

Question 4

Outline P4 of cell signalling, ensure to include as much detail as possible + illustration of beneficial.

Answer 4

Signalling cascades have several crucial functions:

1. They transform or transduce the signal into a molecular form suitable for passing the signal along or stimulating a response.
2. They relay the signal from the point in the cell at which it is received to the point at which the response is produced.
3. In many cases, signaling cascades amplify the signal received, making it stronger so that a few extracellular signal molecules are enough to evoke a large intracellular response.
4. Signal cascades also distribute the signal so as to influence several processes in parallel: at any step in the pathway, the signal may diverge and be relayed to a number of different intracellular targets, creating branches in the information and evoking complex reactions.
5. Each step in the signal cascade is open to modulation by other factors, so that the effects of the signals may be tailored to the conditions prevailing within or outside the cell.

Question 5

Outline P5 of cell signalling.

Answer 5

Signalling alters cell activity with difference time scales of effects. Essentially, many extracellular signals activate intracellular signaling pathways to change the behaviour of the target cell. A cell-surface receptor protein activates one or more intracellular signalling pathways, each mediated by a series of intracellular siganling molecules, which can be proteins or small messenger molecules. Signalling molecules eventually interact with specific effector proteins, altering them to change the behaviour of the cell in various ways.

(For examples altered cell excitability is done in the short term while gene expression in medium term and altered cell shape in long term.)

Question 6

Outline P6 of cell signalling.

Answer 6

Small stimulus (e.g. low cytokine concentrations or low expression of their receptor, but this still induces a large response) - Think of why!(look at P4)

Question 7

Outline P1 of cell signalling.

Answer 7

Cells respond to multiple signals. The receptor then performs the primary transaction step: it receives an external signal and generates a new intracellular signal in response. The message is passed from one intracellular signaling molecule to another, each generating the next signaling molecule in line, until a metabolic enzyme is activated for example. the final outcome is called the response of the cell. The typically responses are divide, survive, die, differentiate.

Question 8

Define trophic factors, nitrogen is factors, and growth factors.

Answer 8

• Trophic factors an death signals; The helper molecules that allow a neuron to develop and maintain connections with its neighborsare called trophic factors. These small proteins work through their receptors on the surface of the nerve cells.
• Mitogenic factors; A mitogen isa small bioactive protein or peptide that induces a cell to begin cell division, or enhances the rate of division (mitosis). Mitogenesis is the induction (triggering) of mitosis, typically via a mitogen.
• Growth factors, trophic factors, morphogens; Morphogens are secreted growth factorsthat direct cell fate decisions during embryonic development.

Question 9

Draw/discuss the 4 signalling modes.

Answer 9

Endocrine;
Neuronal;
Paracrine;
Contact;

Question 10

Illustrate/explain a general overview of cell signalling.

Answer 10

Generally speaking, cell signalling follow this mechanism:

A transmitter or ligand(e.g. glutamate) binds to the cell-surface receptor of a target cell. This causes an allosteric change inducing an alteration in structure and function. This then links into an adaptor protein(e.g. in g-protein coupled pathway this would be a trimeric g-protein) which may recruit 2nd messengers(e.g. Ca2+) to relay the signal into effector proteins which may then, depending on the signal to instruction, appropriate a biological output(e.g. gene expression, altered metabolism, etc…)

Question 11

List the major cell signalling pathways.

Answer 11

Ion-gated (Ionotropic)
G-protein coupled receptors (Metabotropic)
Enzyme-linked (Metabotropic)

Protein Deg.
Wnt/beta-catenin
NFkB

Protein cleavage
Notched/Delta