Receptors and their signal transduction

Question 1

What are the functions of receptors?

Answer 1

• they need to recognize the mediator
• recognize ligands (molecules that bind to receptors)
• the target cell must revoke a biological response

Question 2

What is contact dependent intercellular communication?

Answer 2

the cell communication is dependent on contact

→ the cells must make contact in order for cell communication to occurr

Question 3

What is a paracrine mediator?

Answer 3

molecules that are released from one type of cell and act locally on a different type of target cell

Question 4

What is synaptic intercellular communication?

Answer 4

neurons trasnsmit electrical signals along their axons and release neurotrasmitters at synapses that affect the function of other neurons or cells that are distant from the neuron cell body

Question 5

What is endocrine intercellular communication?

Answer 5

hormones that are secreted into the blood and spread in the body

example: hormone

Question 6

What is autocrine secretion?

Answer 6

release of a molecule that affects the same cell or other cells of the same type

Question 7

What are the types of intercellular communication?

Answer 7

• gap junctions
• autocrine mediator
• paracrine
• contact dependent communication
• synaptic -endocrine

Question 8

What are the conditions of a receptor in regards to the ligand bonding?

Answer 8

• the binding of ligand to the receptor has to be reversible
• can be saturated
• the receptor has to be specific, however the specificity is not absolute

Question 9

What are the two types of intracellular signaling proteins that act as molecular switches?

Answer 9

1. signaling by phosphorylation
2. signaling by GTP- binding protein

Question 10

Describe the mechanism of signaling by phosphorylation.

Answer 10

• activated by the addition of a phosphate group
• inactivated by the removal of the phosphate
• The phosphate is added covalently to the signaling protein by a protein kinase

Question 11

Describe the mechanism of signaling by GTP-binding-proteins.

Answer 11

• activated by the addition of a phosphate group
• inactivated by the removal of the phosphate
• A signaling protein is induced to exchange its bound GDP for GTP

Question 12

What are the two types of signaling molecules?

Answer 12

• plasma membrane receptors
• intracellular receptors

Question 13

How do signaling molecules work?

Answer 13

• they directly bind to their cognate receptors located in the plasma membrane
• when ligand is bound they regulate gene transcription

Question 14

What is another possible means for the path of a signal molecules?

Answer 14

• bind to carrier proteins in blood and diffuse across the plasma membrane
• they bind to cognate so-called nuclear receptors in the cytosol or nucleus
• when ligand is bound, they regulate gene transcription

Question 15

What is the general mechanism of how cells communicate?

Answer 15

1. A ligand binds to a receptor which may be located in the plasma membrane, cytosol, or nucleus.
2. This binding activates intracellular signaling proteins
3. These proteins interact with and regulate the activity of one or more target proteins to change cellular function.

Question 16

What do signaling moleculares regulate?

Answer 16

• cell growth
• cell division
• differentiate and influence cellular metabolism
• cytoskeletal-associated events (cell shape, division, migration, and cell to cell matrix adhesion)

Question 17

How do signal molecules modulate the intercellular ion composition?

Answer 17

they regulate the activity of ion channels and transport proteins

Question 18

What are examples of plasma membrane receptors?

Answer 18

1. G protein-coupled receptors
2. Ion channel receptors
3. Receptors with enzyme activity
4. Enzyme activity-linked receptors

Question 19

What is the structure of G protein coupled 7TM receptors ?

Answer 19

• 7 transmembrane proteins
• with alpha beta and gamma subunit

Question 20

How is adenyl cyclase activated?

Answer 20

• stimulatory ligands bind to stimulatory receptors which activates the Gs at the alpha subunit

Question 21

How is adenyl cyclase inhibited?

Answer 21

inhibited by G_i

Question 22

What are the effects of G_i/o family proteins?

Answer 22

1. inhibition of adenyl cyclase
2. inhibition of Ca2+ channels
3. activation of K+ channels
4. activation of phospholipase A2

Question 23

Cyclooxygenase is blocked by…?

Answer 23

aspirin

Question 24

What happens in phototransduction?

Answer 24

1. A photon interacts with the receptor and activates the G protein transducer
2. The alpha t activates phosphodiesterase (PDE), and hydrolyzes cGMP

→ lowers the intracellular concentrations of cGMP and therefore closes the cGMP-activated channels

Question 25

What is an example of procaine signaling?

Answer 25

the release of ACh at the neuromuscular junction

Question 26

What are the two possible functions of ligand gated ion channel receptors?

Answer 26

- excitatory receptor - inhibitory receptor

Question 27

What are the ligands of an excitatory receptor?

Answer 27

1. Acetylcholine 2. Glutamate 3. Serotonin (5HT3 receptor) **\* specificity Na+/K+\*** 4. Glutamate (but different specificity **Na+/K+ and Ca2+**)

Question 28

What are the receptors for the excitatory inhibitor **acetylcholine**?

Answer 28

nicotinic

Question 29

What are the receptors for the excitatory inhibitor **glutamate** and what are they specific for?

Answer 29

- AMPA, Kainate (Na+/K+) - NMDA receptor (Na+/K+ and Ca2+)

Question 30

What are the receptors for the excitatory inhibitor **Serotonin**?

Answer 30

5HT3 receptor

Question 31

What are the ligands of inhibitory receptors?

Answer 31

1. γ-Aminobutyric acid, GABA (type A) 2. Glycine **\*specificity Cl-\***

Question 32

What is Kd and what does it define?

Answer 32

- Kd is the dissociation constant - inversely proportional to affinity - tells us the range that receptor can function

Question 33

What is the equation of K_d? And what does K_d equal to at 50% binding?

Answer 33

**K_d = [R] • [L] / [RL]** K_d= [L]

Question 34

What does the max tell us?

Answer 34

How many receptors are in the system

Question 35

What does EC50 tell us?

Answer 35

Defines the **potency** (inversely proportional)

Question 36

What is the difference between EC50 and K_d?

Answer 36

**K_d** is used in regards to **binding** **EC50** is used in regards to a **biological response**

Question 37

What does an **agonist** do?

Answer 37

evokes a biological response

Question 38

What's and **antagonist?** And what are the two types?

Answer 38

a ligand that **does not** evoke a biological response

Question 39

How can we "turn off and turn on" proteins?

Answer 39

- phosphorylation - GTP binding

Question 40

What does **GEF** do?

Answer 40

**phosporylatation** of GDP which in turn **activates** the G protein

Question 41

What does **GAP** do?

Answer 41

**dephosporylatation** of GDP which in turn **inactives** the G protein

Question 42

What happens when **G_s proteins** are activate ? And what are they activated by?

Answer 42

1. adenyl cyclase is activated 2. adenyl cyclase converts ATP → cAMP 3. **protein kinase A** is activated which phosphorylates target proteins * Activated by:* beta-adrenergic, ACTH-r

Question 43

What is the function of phosphodiesterase?

Answer 43

an enzyme that breaks down **cAMP → 51 AMP** ## Footnote *inhibitor:* caffeine

Question 44

What does the G_i/o protein do in regards to cAMP formation?

Answer 44

inhibits

Question 45

What are **gap junctions?**

Answer 45

- allow intracellular signaling molecules to diffuse from **cytoplasm** of one cell to **adjacent cell** - also allow cells to be electrically coupled