Overview of Signaling

Question 1

Intracellular communication facilitates what?

Answer 1

signal transduction

Question 2

What are the components of signal transduction?

Answer 2

*First messenger (Ligand)
*Receptor
*Amplifier enzymes
*Second messenger
*Amplification cascade (kinases)

Question 3

Why must cells communicate with their envionments?

Answer 3

to maintain homeostasis (constant internal environment in response to environmental changes)

Question 3

What ends the signal transduction process?

Answer 3

The effect

Question 4

What are the types of cellular communication?

Answer 4

1. Direct cell-to-cell communication
2. Local cell-to-cell communciation
3. Long distance cell-to-cell communication

Question 5

What is direct cell-to-cell communication? How are messages conveyed?

Answer 5

Direct cytoplasmic connection
Via gap junctions

Question 6

What is local cell-to-cell communication?

Answer 6

Signalling between cells using autocrine or paracrine signalling

Question 7

What is signal amplification?

Answer 7

A single signal is amplified into many intracellular molecules

Question 8

What are the different long distance cell-to-cell communication

Answer 8

1. neurotransmitters
2. neurohormones
3. hormones

Question 9

Explain activation of the signal pathway

Answer 9

• First messenger (Ligand)
• Receptor
• Second messenger
• Amplification cascade (kinases)
• Effect

Question 10

What are some downstream effects/cell responses

Answer 10

*Structural effects
*Ion changes
*Metabolic effects
*Membrane changes
*Gene expression
*Cell growth (proliferation)
*Programmed cell death (apoptosis)

Question 11

What is an agonist?

Answer 11

Activates a receptor

Question 12

What is an antagonist?

Answer 12

Blocks receptor activity

Question 13

What is a ligand?

Answer 13

primary molecule that activates a receptor

Question 14

What is the implication of lipophilic ligands?

Answer 14

Direct diffusion into cell
Intracellular binding to receptor (i.e.hormones)

Question 15

What is the implication of lipophobic ligands?

Answer 15

Transported into cell
Extracellular binding to receptor

Question 16

Discuss receptors in the cytosol

Answer 16

*hormone binding triggers dissociation of chaperone, heat shock proteins (HSP)
*dimerizationand translocationto the nucleus
*binds to a specific sequence of DNA known as a hormone response element (HRE)
*nuclear receptor DNA complexin turn recruitsother proteins
*transcriptionof downstream DNA into mRNA
*translatedinto protein
*results in a change in cell function.

Question 17

Discuss receptors in the nucelus

Answer 17

Steroid receptors are dimers of zinc-finger proteins that reside within the nucleus (except for the glucocorticoid receptor which resides in the cytosol until it binds its ligand).

Question 18

What are the ligands of nucleus receptors

Answer 18

• glucocorticoids (ie. cortisol)
• mineralocorticoids (ie. aldosterone)
• sex hormones (ie. estradiol; progesterone; testosterone)

Question 19

What are the mechanisms of receptors in the nucleus?

Answer 19

• steroid binds its receptor
• steroid-receptor-complex…
• releases the histone deacetylases(HDACs) and recruits histone acetylases(HATs) relieving chromosome repression;
• binds to a specific DNA sequence (the Steroid Response Element, SRE) in the promoters of genes it will turn on.

Question 20

What are 4 different types of membrane-bound receptors?

Answer 20

1. ligand-gated channels (ligand binding opens or closes the channel)
2. receptor-enzyme (ligand binding activates an intracellular enzyme)
3. G protein-coupled receptor (ligand binding opens an ion channel or alters enzyme activity)
4. Integrin (ligand binding to integrin receptors alters tha cytoskeleton)