16 - cell signalling

Question 1

why does cell signalling happen?

Answer 1

to keep things running smoothly (homeostasis)

to respond to changes:
- development
- repair
- immune response

Question 2

how do cells keep things running smoothly through cell signalling?

Answer 2

external messages and internal messages.

Question 3

what ligands are involved in external messages?

Answer 3

• hormones
• neurotransmitters
• growth factors & mitogens
• cytokines
• membrane bound proteins

Question 4

what is a receptor?

Answer 4

• most on cell surface
• can be intracellular
• sensitive & specific
• > 1500 human genes for receptors

Question 5

how does external massages to other cells through endocrine happen?

Answer 5

• glands secrete hormones
• distant targets
• slow, prolonged

Question 6

what are the major endocrine glands, in males?

Answer 6

• pituitary gland
• thyroid gland
• adrenal gland
• testis

Question 7

what are the major endocrine glands, in females?

Answer 7

• pineal gland
• thymus
• pancreas
• ovary

Question 8

what are paracrine external messages?

Answer 8

• cell-to-cell activation of receptors
• local targets
  -faster

Question 9

what are Autocrine external messages?

Answer 9

• self activation of receptors
• targets on same cell/type
• faster

Question 10

what are contact dependant external messages?

Answer 10

• direct cell-to-cell activation of receptors
• target can be distant
• speed depends on distance.

Question 11

what are neuronal external messages?

Answer 11

• cell-to-cell activation of receptors
  -very local targets
• very fast

Question 12

what are gap junction external messages?

Answer 12

• direct transmission of signal
• extremely local targets
• very fast

Question 13

how can different cells respond in different ways to the same chemical signal?

Answer 13

• same ligand acting at different types of receptor (e.g. acetylcholine contracts skeletal muscle but decreases the contraction of the heart)
• signal acts at the same receptor but internal machinery in the cell coupling receptor to effect is different.

Question 14

local mediators and messengers must generally be rapidly destroyed, retrieved or immobilised. this role is managed by specific enzymes or uptake systems.

give two examples?

Answer 14

1. histamine - released by mast cells, destroyed by enzymes in eosinophils.
2. growth factor activity can be controlled by association of growth factors with the ECM.

Question 15

what are the three classes of cell surface receptors?

Answer 15

1. ion-channel linked
2. enzyme linked
3. G-protein linked

they generate responses in different ways.

Question 16

explain ion-channel linked receptors.

Answer 16

• signal binding opens pore in receptor
• ions flow through the pore, down an electrochemical gradient.
• key in excitable cells such as nerves & muscles
• can trigger nerve impulse, or stop one from occurring.

Question 17

explain enzyme linked receptors.

Answer 17

• signal binding –> enzyme activity on portion of receptor inside cell.
• enzyme –> target proteins, usually activating them. the enzyme and target are often both kinases.
• found in all cell types.

Question 18

explain G-protein linked receptors

Answer 18

• hundreds of types
• diverse ligands
• 7-transmembrane arrangement.

1. signal binding causes activation of a GTP-binding protein
2. activated G-protein diffuses & activates target protein/enzyme
3. second messengers are generated, e.g. IP3 or cAMP, which produce a response.

Question 19

what are the four outputs of cell signals?

Answer 19

1. altered gene expression
2. altered enzyme activity
3. altered metabolism
4. generate action potential