Week 9/10: Cell communication

Question 1

what is signal transduction

Answer 1

conversion of a signal from one physical or chemical form to another

e.g a signal molecule binds to a receptor and ends with a response

Question 2

what is the general flow of information during cell signaling

Answer 2

1. receptor-ligand binding
2. Signal transduction (via the second messenger)
3. Cellular response
4. Change in gene expression (mitochondria)

Question 3

how are extracellular signaling molecules released

Answer 3

by exocytosis or diffusion

Question 4

what is a receptor

Answer 4

a specific protein capable of binding to the signal molecule

Question 5

Are receptors transmembrane

Answer 5

most are

Question 6

what begins the intracellular signalling pathway

Answer 6

activation of a receptor

Question 7

what do intracellular signalling proteins do?

Answer 7

• distribute the signal to different parts of the cell

- form different signalling pathways

Question 8

what does a target protein do?

Answer 8

• effector

- causes the cellular response or changes the cell behavior

Question 9

What are the types of cell signaling

Answer 9

chemical: endocrine, paracrine
electrical: nervous, cell-cell contact

Question 10

what is endocrine signaling

Answer 10

• signal molecules are hormones
• secreted by endocrine cells
• carried through the bloodstream to act on target cells at distant body sites
• bind receptors on target cells
• long-distance communication = slow

Question 11

what is an example of endocrine hormones

Answer 11

cortisol, adrenaline

Question 12

what is paracrine signalling

Answer 12

• signal molecules are local mediators
• secreted by neighbouring cells
• diffuse through extracellular fluid
• short distance (fast)
• autocrine: responds to signalling molecules produced themselves

Question 13

Example of paracrine local mediators

Answer 13

nitric oxide, histamine, growth factors

Question 14

neuronal signalling

Answer 14

• long distance
• quick and specific
• Electrical impulses travel down an axon & are converted to a chemical signal (neurotransmitter) which acts on the target cell

Question 15

Direct cell-cell contact

Answer 15

• no molecule released
• direct contact
• fast
  eg. embryonic development

Question 16

gap junctions

Answer 16

are protein channels made up of connexin

• direct flow of signal to neighbouring cell: electrical ions, signal chemicals (eg. cAMP)

Question 17

CAMs

Answer 17

need direct surface contact

Question 18

what are the types of extracellular signal molecules

Answer 18

• large hydrophobic molecules

- small hydrophobic molecules

Question 19

large hydrophobic molecules

Answer 19

Rely on cell-surface receptors to relay their message across the membrane

e.g. adrenaline, insulin, glucagon, adenosine, opiates, histamine, TGF-β

Question 20

Small hydrophobic molecules

Answer 20

Pass through the lipid bilayer

Once inside cell activate intracellular enzymes or bind to intracellular receptors
e.g. steroid hormones, nitric oxide

Question 21

Steroid Hormones

Answer 21

Nuclear receptor can be in cytosol or nucleus

Once activated it alters transcription in nucleus

Some hormone receptors are bound to DNA already

Question 22

molecular switches

Answer 22

Activation is achieved by either phosphorylation or GTP binding = molecular switches

Question 23

phosphorylation molecular switch

Answer 23

is a key way of activating or inactivating a protein

Question 24

protein kinase

Answer 24

enzyme that adds phosphate groups to proteins

Question 25

protein phosphatase

Answer 25

enzyme that removes phosphate

Question 26

GTP - binding molecular switch

Answer 26

Switch between active & inactive depends on binding of GTP or GDP

Intrinsic GTPase activity – shut
themselves down by GTP
hydrolysis

e.g. G proteins

Question 27

what are the 3 cell surface receptors

Answer 27

1. ion-channel coupled
2. G-protein coupled
3. enzyme - coupled

Question 28

ion channel coupled receptors

Answer 28

nervous system
Convert chemical signals into electrical signals

Binding of a neurotransmitter alters the shape of the receptor allowing it to open or close

Ions specific to the channel move in or out of the cell based on their electrochemical gradient
e.g. Na+, K+, Ca2+ or Cl-

Question 29

G-protein coupled receptors

Answer 29

Many hundreds of GPCRs known in humans

Diverse family of receptors

Many of the drugs we use today act at these receptors

All GPCRs possess a similar structure
- Seven-membrane spanning protein domains

Question 30

cholera

Answer 30

Toxin continually activates G protein and adenylate cyclase in the gut cells resulting in abnormally high amounts of cAMP

Causes unregulated secretion of electrolytes (Cl, Na+, K+, bicarbonate) & massive outflow of water (“rice water” stools)

Question 31

Rapid signalling

Answer 31

cyclic amp response

Question 32

slow signalling

Answer 32

involves gene regulation

Question 33

Enzyme coupled receptors

Answer 33

respond to signals that regulate cell growth, proliferation, differentiation & survival, as well as rapid reconfigurations of cytoskeleton etc.

Question 34

what are enzyme coupled receptors

Answer 34

transmembrane proteins

Question 35

what is the largest class of enzyme coupled receptors

Answer 35

receptor tyrosine kinase