second messanger pathways

Question 1

What is the Second Messenger Pathway, and how does it function?

Answer 1

is initiated when the first messenger binds to a G-protein-coupled receptor (GPCR), which activates a G-protein.
The G-protein then interacts with an effector protein, causing the production of intracellular messengers (second messengers). These second messengers activate protein kinases, leading to phosphorylation and a cellular response.

Question 2

What are G-protein-coupled receptors (GPCRs)?

Answer 2

GPCRs are receptors that, when bound by a first messenger, activate G-proteins (composed of α, β, and γ subunits). G-proteins function as intermediates that alter the activity of nearby membrane proteins, which are typically effector proteins involved in the production of second messengers.

Question 3

What is the role of second messengers in cell signaling?

Answer 3

Second messengers are small molecules that relay signals from the activated receptor to target proteins inside the cell. They help transmit and amplify the signal, eventually leading to the desired cellular response, such as changes in metabolism, enzyme activity, or ion channel opening.

Question 4

What are some examples of second messengers, and what are their roles?

Answer 4

Ca2+
IP3
DAG
cAMP
cGMP
1. Ca2+: Binds to calmodulin and other proteins to alter enzyme activity, trigger exocytosis, muscle contraction, cytoskeletal movement, and channel opening.
2. IP3: Releases Ca2+ from intracellular stores, affecting enzyme activity, exocytosis, muscle contraction, and cytoskeletal movement.
3.DAG: Activates protein kinase C (PKC), which phosphorylates target proteins.
4. cAMP: Activates protein kinase A (PKA) and binds to ion channels, leading to protein phosphorylation and altered channel activity.
5. cGMP: Activates protein kinase G (PKG) and binds to ion channels, leading to phosphorylation and changes in channel opening.

Question 5

What are some examples of effector proteins linked to G-proteins?

Answer 5

1. adenyl cyclase (which produces cAMP),
2. guanylyl cyclase (which produces cGMP)
   3.phospholipase C (which generates IP3 and DAG).
   These effector proteins produce second messengers that mediate the cellular response.

Question 6

what does the activatiohn of G-proteins cause

Answer 6

1. open ion channels
2. alter enzyme activity

Question 7

Adenulyl cyclase- cAMP by the GPCR describe the steps

Answer 7

1. signal molecule binds to G proteins-linked receptor which activate the G protein
2. G protein turns on adenyl cyclase (amplifier enzyme)
3. adenyl cyclase convert ATP to cyclic adenosine monophosphate (cAMP)
4. protein kinase A phosphorylate other proeins leading to cellular response

Question 8

what can activating the cAMP pathway lead to

Answer 8

1.Modify heart rate
2.Formation of female hormones in ovaries
3.Break down stored glucose in liver
4.Control H2O conservation in kidneys
5.Perception of sweet taste in taste buds

depends on cellular location and cell type

Question 9

Gyanyl cyclase - cGMP pathway

Answer 9

1. signal molecule binds to G protein linked receptor which activates G protein
2. G protein turns on guanyl cyclase- amplifier enz
   3, guanyl cyclase converts GTP to cyclic guanosine monophosphate (cGMP)
3. protein kinase G phosphorylates other proteins leading to celluular response

Question 10

how is the gyanyl cyclase- cGMP pathway activated and inhibited

Answer 10

activated- low calciu,
inhib- high calacum ion

Question 11

guanyl cyclase cGMP functions

Answer 11

1.Drive adaptive/developmental changes
2.Causes relaxation (smooth muscle tissue)
3. increasein cGMP contributes to excessive neuron excitability and locomotor activity
4.Stimulate presynaptic glutamate release

Question 12

phospholipase C pathway

Answer 12

1. signal molecule activate receptor and associated G protein
2. G protein activate phospholipase C (PL-C) an amplifier enz
   3.PL-C convert membrane phospholipids into diacylglyferol (DAG) and inositol triphosphate (ip3)
3. DAG activate protein kinase C (PK-C)
4. IP3 causes release of Ca drom organelles

Question 13

What happens to the G-protein after a second messenger response is completed?

Answer 13

the alpha (α) subunit of the G-protein cleaves off a phosphate group, converting GTP to GDP. This inactivates the G-protein, helping to terminate the signaling process.

Question 14

How are second messengers like cAMP and cGMP removed after the response?

Answer 14

degraded by phosphodiesterases, enzymes that break them down to stop their activity and help end the signal transduction pathway.

Question 15

What role do protein phosphatases play in signal termination?

Answer 15

remove the phosphate groups added to proteins by protein kinases, thereby shutting off the signal transduction pathway. Unlike protein kinases, which are activated by signals, protein phosphatases are always active.

Question 16

How do neurotransmitters function through second messenger systems?

Answer 16

seratonin, They change the conformation of chemically gated receptor channels, altering membrane permeability and ion fluxes across the synaptic membrane. These are referred to as “slow” synapses, as opposed to “fast” synapses where neurotransmitters act directly on ion channels.

Question 17

What happens to the first messenger after it initiates the response?

Answer 17

he first messenger (such as a hormone or neurotransmitter) can be degraded by the liver or excreted in the urine. In some cases, both the first messenger and its receptor are removed from the cell surface through receptor-mediated endocytosis.

Question 18

Why do cells respond differently to the same second messenger signal?

Answer 18

The variability in response depends on the specialization of the target cells, not the signaling mechanism itself. Different cell types are equipped with different proteins and pathways that interpret the signal in distinct ways, leading to various outcomes.

Question 19

How important are second messenger systems in drug treatments?

Answer 19

Second messenger systems, particularly those involving G-protein-coupled receptors (GPCRs), are vital targets for drugs. About half of all prescribed drugs act on GPCRs, helping to treat conditions like high blood pressure, congestive heart failure, asthma, and allergic reactions by modulating these signaling pathways.

Question 20

hy are second messenger systems particularly important for water-soluble hormones

Answer 20

ater-soluble hormones cannot easily cross the lipid bilayer of the cell membrane, so they rely on second messenger systems to relay their signals inside the target cells. This allows them to trigger cellular responses without needing to enter the cell.

Question 21

What is the difference between “fast” and “slow” synapses?

Answer 21

“Fast” synapses involve neurotransmitters that directly change the conformation of ion channels, causing immediate effects on membrane permeability and ion flux. In contrast, “slow” synapses, which involve second messenger systems, mediate their effects indirectly and typically result in slower, prolonged responses.

Question 22

ow does receptor-mediated endocytosis help terminate a signal?

Answer 22

In receptor-mediated endocytosis, both the first messenger and its receptor are internalized by the cell, effectively removing them from the cell surface and preventing further signaling. This helps to ensure the signal is properly terminated.

Question 23

describe receptor mediated endocytosis via the 2nd messanger oathway

Answer 23

1. substances attach to membrane receptors
2. membrane pockets inwards
3. pocket pinches off as endocytotic vesicle containing target molecule