Cellular Communication (social cells)

Question 1

How can ligands be released into EC space?

Answer 1

• exocytosis
• diffusion
• expressed on cell surface

Question 2

2x types of communication

Answer 2

-SHORT DISTANCE
- LONG DISTANCE

Question 3

Types of short distance communication

Answer 3

• contact-dependent; eg. immune response
• autocrine signalling; proteins, RNAs etc. SELF
• paracrine signalling “ BESIDE

Question 4

Types of long-distance communication

Answer 4

-synaptic; neurotransmitters
- endocrine; hormones

Question 5

ENDOCRINE SIGNALLING

Answer 5

• long distance
• ligands are hormones
• lipophilic
• very specific targeting

Question 6

PARACRINE SIGNALLING

Answer 6

short distance
- vast range of ligands; eg. growth factors, gases
- conc. of ligand is low and can be controlled with enzymes, ECM, antagonists and inhibitors

Question 7

AUTOCRINE SIGNALLING

Answer 7

• cell signals to itself
• ligands include cytokines, growth factors and hormones

Question 8

CONTACT-DEPENDENT SIGNALLING

Answer 8

THREE FORMS;
- membrane proteins interact on each cell
- membrane proteins interact with part of extracellular matrix
- junctions link cells allowing small molecules to pass

Question 9

SYNAPTIC SIGNALLING

Answer 9

• rapid long-distance signalling
• very specific
• electrical impulses converted to chemical signal

Question 10

How does extracellular signal convert into intracellular response?

Answer 10

• most ligands bind to receptors
• ligand-receptor interaction causes a conformational change in the receptor
• ## need to express correct receptor; competent cell

Question 11

Four types of receptors

Answer 11

• Ion-channel coupled receptors; (ionotropic receptors)
• G-protein-coupled receptors; metabotropic transmission
• Enzyme-coupled reactors (eg. RTKs)
• Nuclear receptors

Question 12

Glucose ion pump

Answer 12

• coupled with sodium uptake
• co-transporter

Question 13

Calcium ion pump

Answer 13

• cytosolic conc. needs to be kept low
• uses ATP
• sodium

Question 14

four types of ion channels

Answer 14

• ligand-gated
• voltage-gated
• leak channels
• stretch-activated

Question 15

LIGAND GATED CHANNELS

Answer 15

• ligand binds to receptor
• opens the channel
• ions ( Na+, K+, Cl-) move through

Question 16

VOLTAGE GATED CHANNELS

Answer 16

• resting potential of membrane; channel is closed
• depolarisation; gate opens

Question 17

Resting membrane potential

Answer 17

• not the same as action potential
• the potential across the membrane where there is no AP being propagated

Question 18

G protein-coupled receptors structure

Answer 18

• Belong to one of 3 families A, B or C
• 7 transmembrane helix structures

Question 19

G proteins

Answer 19

• have 3 subunits; alpha, beta and gamma
• at rest; exists as a trimer where GDP is bound to the alpha subunit
• g-protein is tethered to the cell membrane by the alpha and gamma subunit

Question 20

GPCR activation & inactivation

Answer 20

• Ligand binds to the GPCR @ ligand binding site
• causes a conformational change in the receptor
• causes a conformational change in the G protein
• GDP dissociates and is replaced by intracellular GTP
• alpha-GTP and beta-gamma complexes dissociate from receptor
• GTP is hydrolysed to GDP by GTPase

Question 21

Types of G protein

Answer 21

G alpha (s)
G alpha (i)
G alpha (o)
G alpha (q)

Question 22

Roles of G alpha (s) and G alpha (i)

Answer 22

Stimulation and inhibition of adenyl cyclase
-which converts ATP to cyclic AMP
cAMP activates kinases

Question 23

Role of G alpha (q)

Answer 23

Stimulate phospholipase C
- involved in the release of intracellular Ca2+

Question 24

Enzyme-linked receptors

Answer 24

• a major role in growth & cell division, immune response
• main types; RTKs, receptor serine/threonine kinases
  or cytokine receptors
• structure; large extracellular binding domain, connected by single membrane spanning alpha-helix to intracellular domain

Question 25

Kinase-linked receptor activation & inactivation

Answer 25

• ligand binds to the receptor leads to dimerisation
• association between 2 intracellular domains creates active kinase enzyme
• tyrosine residues are phosphorylated
• these residues act as docking sites for other intracellular relay proteins
• cascade leads to biological effect
• terminated by tyrosine phosphatases

Question 26

Classes of nuclear receptor by action mechanism

Answer 26

Class I; binds to ligand in the cytoplasm, form homodimers
Class II; in nucleus, form heterodimers

Question 27

Receptor homeostasis

Answer 27

• Autologous; the conc. of the receptor can increase or decrease upon activation
• Heterologous; the conc. of the receptor can change upon activation of other nuclear receptors