Lecture 4

Question 1

Physiological signals include:

Answer 1

• electrical signals: changes in the membrane potential of a cell
• chemical signals: molecules secreted by cells into ECF, bind to specific receptor on (usually) or in target cells

Question 2

Communication methods between cells (local)

Answer 2

1. Gap junction
2. Contact-dependent
3. Autocrine
4. Paracrine

Question 3

Communication methods between cells (long distance)

Answer 3

1. Neuronal
2. Endocrine

Question 4

Gap junctions

Answer 4

Enable communication between cytoplasms of adjacent cells

Question 5

Contact-dependent signals

Answer 5

Contact-dependent signals require interactions between membrane molecules on two cells

Question 6

Autocrine signals

Answer 6

Act on the same cell that secreted them

Question 7

Paracrine cell

Answer 7

Are secreted by one cell and diffuse to adjacent cells

Question 8

Example of long distance communication (endocrine)

Answer 8

Hormones are secreted by endocrine glands or cells into the blood. Only target cells with receptors for the hormone will responds to the signal.

For example insulin is secreted from the pancreatic b cells and binds to the insulin receptor on the target cell enabling glucose to enter these cell

Question 9

Example of long distance communication (neurotransmitters)

Answer 9

Neurotransmitters are secreted by neurons that diffuse across a small gap to the target cell

Example acetylcholine is a neurotransmitter that can be used to elicit skeletal muscle contraction

Question 10

What is a hormone that is released by neural tissue not endocrine tissue called

Answer 10

Neurohormone (oxytocin)

Question 11

Long distance communication (neurohormones)

Answer 11

Neurohormones are chemicals that are released by neurons into the blood for action at distant targets

Example: oxytocin Is released by neurons into the blood target uterine smooth muscle (if there is a receptor) and stimulates contractions during labour.

Question 12

Steroid hormones are ….

Answer 12

Hydrophobic

Question 13

Intracellular signal receptors

Answer 13

In cytosol (steroid hormone —->hydrophobic)

Question 14

Cell membrane receptor

Answer 14

Extracellular signal molecule binds to a cell membrane receptor
In the plasma membrane (insulin—-> hydrophilic)

Question 15

Receptor-enzyme

Answer 15

Ligand binding to a enzyme receptor activates intracellular enzymes

Example: insulin receptor acts as an enzyme, it phosphorylates stuff and the result inside the cell is glucose party

Question 16

Integrin receptor

Answer 16

Ligand binding to a integrin receptor alters the cytoskeleton

Question 17

What do we call signal transduction when it is sensitive

Answer 17

Signal amplification (volume control)

Question 18

When a signal transduction is tightly regulated this means

Answer 18

Cascade —> when one turns on the next

Question 19

G protein stands for

Answer 19

Guanosine nucleotide-binding protein

Question 20

GPCRs stand for

Answer 20

G protein coupled receptors

Question 21

GPCR:

Answer 21

Ligand binds with a receptor that is physically coupled with a guanosine nucleotide- binding (G) protein

1/3 of all pharmaceutical drugs target GPCRs
Largest family of cell surface receptors
Bind to and activate G proteins

Question 22

When G proteins are activated they may:

Answer 22

• directly alter ion channels
• alter activity of another enzyme

Question 23

2 main enzymes modified by GPCR activation are

Answer 23

1. Adenylate Cyclase (AC)
2. Phospholipase C

Question 24

GPCR and AC

Answer 24

Once ligand binds to receptor and activates G protein…
1. GS (a flavour of G protein) stimulates Adenylate cyclase
2. AC trigger production on CAMP
3. cAMP binds to and activates protein kinase A (PKA)
4. Phosphorylates protein and we receive cell response

GI —> another flavour of G protein, inhibits AC

Question 25

GPCR and PLC

Answer 25

1. Ligand binds to receptor and activates GQ ( a flavour of G proteins)
2. GQ activates phospholipase C (PLC) an amplifier enzyme
3. PLC converts membrane phospholipids into DAG which stays in the membrane and IP3 that diffuses in the cytoplasm
4. DAG activates PKC which phosphorylates proteins —> giving cellular response
5. IP3 causes release of Ca2+ from the endoplasmic reticum to increase intracellular concentration of Ca2+
6. The increased Ca2+ and altered protein function leads to cellular response