Molecular and cell base physiology part 3

Question 1

Major types of cell surface receptors

Answer 1

1. ligand gated ion channel receptors
2. g-protein coupled receptors
3. enzyme coupled receptors (RtK, Cytokine)
4. Integrins
5. Toll-like receptors

Question 2

Types of cell surface receptors

Answer 2

1. ligand gated ion channels (cholinergic nicotinic receptors)
2. g-protien coupled receptors (alpha beta adenoreceptors)
3. enzyme-linked receptors (insulin)

Question 3

what is the name for g-protein coupled receptors related to neurotransmitters?

Answer 3

metabotropic receptors

Question 4

G proteins are what type of membrane protein?

Answer 4

integral membrane protein

Question 5

how many polypeptide chains do g-proteins have?

Answer 5

a single polypeptide chain

Question 6

Does the g protein coupled receptor go through the membrane?

Answer 6

yes it passes in and out of the membrane multiple times

Question 7

what does the g protein couple receptor bind to?

Answer 7

it binds to a particular type of G protein

Question 8

What types of signals do g protein coupled receptors mediate?

Answer 8

They mediate most responses to signals from outside the cell as well as signals from other cells

Question 9

What types of signals do g protein coupled receptors mediate specifically? (examples)

Answer 9

Hormones neurotransmitters and local mediators

Question 10

What is the simple intracellular signaling molecule?

Answer 10

1. Extracellular signaling molecule (first messenger)
2. Receptor Protein on cell membrane
3. Intracellular signaling proteins
4. Effector Proteins

Question 11

What occurs in an intracellular signaling pathway?

Answer 11

• A ligand bind to a membrane receptor which activates intracellular signaling pathways.
• Intracellular signaling proteins process the signal and distribute it to different intracellular targets (effector proteins)

Question 12

What are examples of effector proteins?

Answer 12

Transcription regulator
Ion channels
Metabolic enzyme
Cytoskeleton proteins

Question 13

What are the receptor locations?

Answer 13

1. Cell Surface
   
   • hydrophilic signaling molecules
2. Intracellularly
   
   • Cytoplasm
   • Nucleus
     - hydrophobic molecules

Question 14

How many subunits are associated with the G protein?

Answer 14

3 subunits(a, B, Y)

Question 15

What are G proteins?

Answer 15

Membrane associated tri-meric protein that relays the signal to the interior of the cell

Question 16

Where do G proteins bind?

Answer 16

To the cytoplasmic section of the GPCR

Question 17

G proteins are what type of switches?

Answer 17

Molecular “on/off” switch

Question 18

What is the alpha subunit of the G protein? What is bound to the alpha subunit in the inactive state?

Answer 18

It is a GTPase;

GDP is bound to the alpha subunit in the inactive state

Question 19

What is the result of activation of the G protein?

Answer 19

• Beta/gamma or B/Y dissociates from the a subunit.
• alpha subunit exchanges GDP for GTP
• Both GTP/alpha and B/Y interact with targets
• eventually the GTPase (alpha subunit) hydrolyzes GTP back to GDP

Question 20

Do G proteins only regulate the activity of enzymes? If not what else do they do?

Answer 20

No they also:
1. G proteins can directly activate or inactivate ion channels in the cell membrane by altering “ion permeability”or “electrical excitability”

Question 21

Are G proteins important in medicine? Why?

Answer 21

Yes, because half of drugs work through GPCRs or their activated pathways

Question 22

True or False: One signal can activate only one GPCR

Answer 22

False One signal can activate MANY different GPCRs

Question 23

How is the message sent from the receptor to inside the cell?

Answer 23

Second messengers.

This is why the ligand is called the first messenger. Because there is another that transmits the signal inside the cell.

Question 24

What are second messengers?

Answer 24

Second messengers are intracellular signaling molecules generated in LARGE amounts in response to receptor activation

Question 25

Are there many second messenger systems or only a few?

Answer 25

ONly a few second messenger systems

Question 26

What are the most important second messengers?

Answer 26

1. Diacylglycerol (DAG)
2. Cyclic Adenosine Monophosphate (cAMP)
3. Inositol 1,4, 5-Triphosphate (IP3)
4. Calcium (Ca 2+)

CAMP, IP3, CA 2+ : water soluble molecules; Located in the cytosol

Question 27

How does cAMP become cAMP(lol)? What turns what into cAMP?

Answer 27

Phosphodiesterase turns Adenylyl Cyclase into cAMP

Question 28

How is cAMP formed? And how does it act as a second messenger?

Answer 28

1. An extracellular molecule binds to GPCR which activates the G protein. Specifically the alpha subunit with GTP attached
2. Activated alpha subunit goes on to activate Adenylyl cyclase.
3. Activated Adenylyl cyclase leads to an increase in cAMP
4. THe increase in cAMP activates pKA in the cytosol and the release of its catalytic subunits.
5. The catalytic subunits of PKA move to the nucleus where it phosphorylates CREB gene regulator protein
6. Once phosphorylated, CREB binds to co-activator CBP
7. CREB binding to coactivator CBP stimulates gene transcription

-this can stimulate anything from hormone synthesis in endocrine cells to the production of proteins required for long term memory

Question 29

How do intracellular proteins work?

Answer 29

1. Lipophillic signals are carried by proteins in the blood to their target cell
2. They then diffuse through the plasma membrane of target cells
3. They then bind to intracellular receptors that are transcription regulators.

Question 30

Why can lipophillic molecules diffuse through the cell membrane on their own?

Answer 30

Because they are SMALL, and HYDROPHOBIC

Question 31

What are some examples of intracellular signaling molecules?

Answer 31

Steroid hormones, thyroid hormones, retinoids, and vitamin D

Question 32

What two functions do intracellular receptors have?

Answer 32

1. Receptor

2. Effector proteins of the signal

Question 33

Intracellular signaling molecules alter the ability of the intracellular receptor and make it able to control the transcription of specific genes: True or False

Answer 33

True

Question 34

What drug examples use intracellular receptors as a target?

Answer 34

1. Fibrate drugs: decrease blood lipids

2. Glitazones: used to treat type 2 diabetes and decrease lipids and inflammation