cell communication

Question 1

why is cell signalling needed

Answer 1

• maintain homeostasis, controls health

Question 2

stages of the main principles of cell signalling

Answer 2

1. release of a ligand
2. ligand delivery and binding to specific receptor
3. receptor activation
4. further relay of signal by intracellular response
5. activation of target proteins and cellular response
6. termination of signal

Question 3

paracrine signalling

Answer 3

• signalling to communicate to cells that are nearby
• proteins are cleaved to make them soluble
• when soluble they can move from cells to act on nearby cells
• nerve cells: synaptic signalling, can signal with cells far away

Question 4

endocrine signalling

Answer 4

• communicate with cells all over the body through the use of blood vessels
• use of circulatory system
• used by signalling molecules e.g. hormones

Question 5

contact dependent signalling

Answer 5

• direct communication with cells in close proximity
• signalling proteins not released but can act on ligand when bound to membrane and bonds with receptor of adjacent cell

Question 6

autocrine signalling

Answer 6

• cells express ligand and receptor to self-stimulate
• allows cells to be self-dependent for signals to stimulate their own survival and proliferation

Question 7

how are signalling receptors relayed

Answer 7

• g protein coupled receptors
• enzyme coupled receptors

Question 8

how does the g protein coupled receptor work

Answer 8

• binding domain > allows conformational change and bonding to G proteins > G protein active enzymes to produce 2nd messenger > 2nd messenger signal
• cells respond to a stimulus to undergo contraction or change shape

Question 9

how do enzyme coupled receptors work

Answer 9

• enzymatic domain > conformational change, phosphorylation and activation > activated receptors recruit other adaptor proteins to relay other signalling kinases

Question 10

what are protein kinases

Answer 10

• class of enzymes that phosphorylate other proteins
• they differ based on the type of amino acid
• add a phosphate group

Question 11

GTP binding controlling signalling

Answer 11

• OFF when GTP proteins are inactivated when GDP is bound
• ON when removal of GDP and binding of GTP activates GTP proteins
• G proteins are GTPases

Question 12

phosphorylation controlling signalling

Answer 12

• addition of a phosphate group from ATP to amino acids by protein kinases
• either activate of inactivate a protein
• dephosphorylation by phosphatases removes it

Question 13

what are GPCR’s

Answer 13

• largest class of cell-surface signalling receptors
• used for many signals
• ligand binding to a GPCR activates it and allows it to bind to G proteins to further relay the signal
• types: muscarinic receptor, opioid receptor, chemokine receptor

Question 14

what are the 3 types of G proteins

Answer 14

• Gs (stimulate adenylyl cyclase)
• Gi (inhibits adenylyl cyclase)
• Gq (activates phospholipase)

Question 15

stages of cell signalling

Answer 15

1. in resting cell the Gs protein in inactive. alpha subunit is bound to GDP
2. when ligand binds to gene proteins - activates the receptor GPCR
3. this allows the G protein to bind via alpha subunit
4. GPCR activates alpha subunits by displacing GDP for GTP
5. active alpha dissociates and binds to adenylyl cyclase to activate it
6. adenylyl cyclase makes cAMP using ATP - increases cAMP concentration
7. cAMP is second messenger - used to activate protein kinase A
8. this activates glycogen phosphorylase which breaks down glycogen to glucose
9. increase glucose form Krebs cycle

Question 16

what is the function of GPCR signalling

Answer 16

• control acid secretion by gastric cells
• regulates water movement in intestinal cells

Question 17

what does protein kinase A (PKA) do

Answer 17

• PKA activates transcription factors
• phosphorylates other proteins on amino acids and activates the protein
  0 glucose breakdown, gastric acid production, water secretion

Question 18

stages of signalling through Gq proteins

Answer 18

1. Gq Cleves phospholipids
2. ligands binds to Gq
3. phospholipase C
4. crease 2 secondary messengers
5. IP3 travels to ER
6. DAG stays attached to PM
7. calcium released and binds to PKC
8. allows PKC to bind to DAG to be attached to the PM
9. can cause polymerisation of actin