week 6- cell signalling

Question 1

what do signal molecules bind to

Answer 1

receptors

Question 2

what are the 4 main types of intracellular signalling

Answer 2

Contact-dependent, paracrine/autocrine, synaptic, and endocrine signaling

Question 3

What is contact-dependent signaling?

Answer 3

It requires cells to be in direct membrane-membrane contact for a signal molecule to bind to a receptor on a target cell.

Question 4

What is paracrine signaling?

Answer 4

It depends on local mediators released into the extracellular space, acting on neighboring cells.

Question 5

What is autocrine signaling?

Answer 5

A form of paracrine signaling where the signaling cell and the target cell are the same

Question 6

What is synaptic signaling?

Answer 6

Neurons transmit signals electrically along their axons and release neurotransmitters at synapses, often far from the cell body.

Question 7

What is endocrine signaling?

Answer 7

it depends on endocrine cells that secrete hormones into the bloodstream for distribution throughout the body.

Question 8

Where are receptors located?

Answer 8

On the cell surface or intracellularly.

Question 9

What type of signal molecules bind to cell surface receptors?

Answer 9

Hydrophilic signal molecules that cannot pass through the cellular membrane.

Question 10

What type of signal molecules bind to intracellular receptors?

Answer 10

Small, hydrophobic signal molecules that can diffuse through the plasma membrane.

Question 11

Can the same signal cause different responses in different cell types?

Answer 11

yes

Question 12

What are the three major classes of cell-surface receptors?

Answer 12

Ion channel-coupled receptors, G-protein-coupled receptors, and enzyme-coupled receptors.

Question 13

What are ion channel-coupled receptors involved in?

Answer 13

Rapid signaling between neurons and electrically excitable target cells.

Question 14

How do G-protein-coupled receptors (GPCRs) function?

Answer 14

By forming an activated receptor and G-protein complex that further activates associated enzymes.

Question 15

How do enzyme-coupled receptors work?

Answer 15

They often rely on dimerization and interaction of cytoplasmic domains to relay signals.

Question 16

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

Answer 16

protein kinases and GTP-binding proteins.

Question 16

How do GTP-binding proteins function as molecular switches?

Answer 16

They exchange GDP for GTP to activate, then hydrolyze GTP to GDP to inactivate.

Question 17

How does signaling by phosphorylation work?

Answer 17

A protein kinase adds a phosphate to the signaling protein, activating it, and a phosphatase removes it.

Question 18

What are the roles of GTPase-activating proteins (GAPs) and guanine nucleotide exchange factors (GEFs)?

Answer 18

GAPs inactivate GTPases by hydrolyzing GTP, while GEFs activate them by facilitating the exchange of GDP for GTP.

Question 19

What is often required for an appropriate cellular response?

Answer 19

High specificity and processing through intermediaries or second messengers.

Question 20

What are some properties of signaling pathways that can vary?

Answer 20

Response timing, sensitivity and amplification, dynamic range and adaptation, persistence, signal processing, and integration.

Question 21

What happens when two signals are needed for a cellular response?

Answer 21

Each signal activates different pathways that converge to fully activate a protein only when both signals are present.

Question 22

What are positive and negative feedback loops?

Answer 22

Positive feedback amplifies signals, while negative feedback inhibits them.

Question 23

What is the largest family of cell-surface receptors?

Answer 23

G-protein-coupled receptors (GPCRs)

Question 24

what is the structure of GPCRs?

Answer 24

They are 7-pass transmembrane proteins.

Question 25

What are some signals GPCRs respond to?

Answer 25

Hormones, neurotransmitters, local mediators, light photons, amino acids, and fatty acids.

Question 26

How is a G-protein activated?

Answer 26

Binding of a molecule to a GPCR causes conformational changes, promoting GDP dissociation and GTP binding.

Question 27

What are the subunits of G-proteins?

Answer 27

A: Alpha (⍺), beta (β), and gamma (𝛾) subunits.

Question 28

What happens when the G⍺ subunit is GTP-bound?

Answer 28

It activates downstream signaling molecules.

Question 29

: What is an example of a GPCR signaling response?

Answer 29

Acetylcholine-induced responses, such as decreasing heart pacemaker cell firing or promoting salivary secretion.

Question 30

What does adenylyl cyclase catalyze?

Answer 30

The synthesis of cyclic AMP (cAMP) from ATP.

Question 31

How does cAMP activate PKA?

Answer 31

By binding to the regulatory subunits, causing them to dissociate and activating the catalytic subunits.

Question 32

What are the two types of PKAs?

Answer 32

Type 1 in the cytosol and Type 2 bound to membranes or microtubules

Question 33

How does activated PKA affect gene transcription?

Answer 33

It phosphorylates the transcription factor CREB, which recruits CBP to stimulate transcription.

Question 34

How do GPCRs regulate ion channels in vision?

Answer 34

Through phototransduction involving rhodopsin, a GPCR linked to retinal.

Question 35

What happens when light is detected by rhodopsin in photoreceptors?

Answer 35

It causes a conformational change, activating transducin and leading to the closure of cGMP-gated Na+ channels.

Question 36

How is the light signal switched off in photoreceptors?

Answer 36

Rhodopsin kinase phosphorylates rhodopsin, arrestin binds it, and RGS protein hydrolyzes GTP on transducin.

Question 37

What is the general structure of RTKs?

Answer 37

Variable extracellular domain, single transmembrane domain, and variable intracellular tyrosine kinase domain.

Question 38

What activates RTKs?

Answer 38

The binding of a signal molecule causes dimerization and phosphorylation of tyrosine residues

Question 39

What are SH domains in RTK signaling?

Answer 39

SH2 and SH3 domains in RTK-binding proteins that recognize phosphorylated tyrosines and bind to other proteins.

Question 40

What is the role of Ras GTPases in RTK signaling?

Answer 40

They are recruited to active RTKs and activate intracellular signaling cascades.

Question 41

How is Ras activated by RTKs?

Answer 41

RTK binds Grb2, which binds Sos, a GEF that activates Ras by exchanging GDP for

Question 42

What is required for RTK activation following the binding of the signal molecule?

Answer 42

Receptor dimerization and phosphorylation.

Question 43

What are SH2 and SH3 domains in RTK-binding proteins?

Answer 43

SH2 domains bind activated phospho-tyrosines on the receptor, and SH3 domains bind domains on other intracellular proteins

Question 44

What is the Ras superfamily of GTPases involved in?

Answer 44

Relaying signals from RTKs and various cellular processes such as cell movement, intracellular traffic, and nuclear transport.

Question 45

What are the steps for Ras activation by RTKs?

Answer 45

1. Activated RTK binds SH2 domain of Grb2.
2. Grb2 binds a GEF (e.g., Sos) via its SH3 domain.
3. Sos activates Ras by exchanging GDP for GTP.

Question 46

What mechanisms ensure short-lived activation of Ras-GTPases?

Answer 46

Phosphatases remove phosphates from tyrosine residues, and Ras-GAPs hydrolyze GTP to GDP.

Question 47

How do TGFβ receptors activate Smads?

Answer 47

The receptor complex phosphorylates receptor-activated Smads (R-Smad), which then bind co-Smad to form a trimeric Smad complex.

Question 48

What does Ran GTPase control?

Answer 48

Nuclear transport

Question 49

What triggers receptor dimerization in RTKs?

Answer 49

The binding of a signal molecule to the extracellular domain of the RTK.