Chedy - theme 5

Question 1

Three components of cell communication through signal receptors:

Answer 1

Extracellular signals, cell receptors, a cellular response.

Question 2

Kinds of cell signalling receptors:

Answer 2

Voltage-gated ion channels, ligand-gated channel receptors, seven transmembrane receptors, enzyme-linked receptors, nuclear transcription factors.

Question 3

Voltage-gated ion channels:

Answer 3

Multimeric membrane-bound proteins that act through synaptic signalling on excitable cells. They respond to voltage changes in membrane potential, opening channels through the membrane for ion passage. Na+ or K+ moves to create electrical charges.

Question 4

Ligand-gated ion channels:

Answer 4

Multimeric membrane-bound proteins that undergo conformational change upon ligand binding. They are controlled by peptide/hormone neurotransmitters. They open channels for ion passage (Na+ and K+) for a short time before the ligand dissociates.

Question 5

Three stages of signal transduction:

Answer 5

Reception, transduction, response.

Question 6

Mechanism by which signalling molecules trigger cellular response:

Answer 6

If the molecule binds to the recognition site of the receptor, it can trigger or block a response. The signal is relayed inside the cell by protein kinases.

Question 7

Phosphorylation cascade:

Answer 7

Each protein kinase catalyzes the phosphorylation of another in the cascade until it reaches the target protein that brings about the cellular response.

Question 8

Amplification:

Answer 8

The magnitude of the signal increases at each step in the phosphorylation cascade. One activated enzyme activates hundreds of others in the next step. As a result, a small number of signalling molecules can produce a full internal response.

Question 9

Seven transmembrane receptors:

Answer 9

(Also termed G protein-coupled receptor.) Cross the cell membrane 7 times and are associated with regulatory proteins.

Question 10

Molecular configuration of seven transmembrane receptors:

Answer 10

A glycosylated amino-terminal domain outside the cell contains the signal binding site. Transmembrane domains are hydrophobic alpha helices. Regulator recognition sequences are inside the cell. Ligand binds to receptors to activate a G protein, which activates an enzymatic effector. Effector causes synthesis of small molecules (second messengers).

Question 11

Molecular homeostasis: (4)

Answer 11

Set point: normal value for ligand
Sensor: the receptor
Integrator: G proteins
Effector: adenylyl cyclase (cAMP generation)

Question 12

Second messengers:

Answer 12

Result of seven transmembrane receptor activity. They are signals from the receptor to the cytoplasm that trigger a cascade. These include: cAMP, cGMP, IP3, DAG, calcium ions, and more.

Question 13

Sub-classes of G proteins:

Answer 13

G-alpha: associated with effector enzyme adenylyl cyclase, which catalyzes ATP into cAMP, which catalyzes PKA.
G-alpha i/o: inhibits adenylyl cyclase.
G-alpha q/11: associated with PLCbeta, which uses PIP2 to synthesize IP3 and DAG.

Question 14

Given the subclasses of G proteins, what are the two main signal pathways involving seven transmembrane receptors?

Answer 14

Stimulation and inhibition of cAMP; phosphatidylinositol (pip) signalling pathway

Question 15

Ligands of seven transmembrane receptors:

Answer 15

Can be pretty much anything. Hormones, neurotransmitters, light-sensitive compounds, odours, pheromones.

Question 16

Same key, different locks principle:

Answer 16

Chemical messengers can have multiple unrelated effects, at the same time or different times. Response is determined by receptor.

Question 17

Enzyme-linked receptors:

Answer 17

Single transmembrane receptors. Extracellular ligand-binding causes intracellular enzyme activity (kinase).

Question 18

Nuclear transcription factors: intracellular

Answer 18

Receptors located in cytosol or nucleus that regulate gene activity.

Question 19

Steroid hormone-receptor complex: you know this! this is estrogen!!!

Answer 19

Steroid hormone binds to inactive receptor. The now active complex enters the nucleus and tells the cell to transcribe a gene. This activity can spread to other cells by gap junctions.