Cell communication and cell signalling

Question 1

List different forms of cell communication (5)

Answer 1

Short distance/local:
1)DIRECT contact ( gap junctions)
2)paracrine system (surrounding tissue and cells)
3) autocrine system (denoting or relating to a cell-produced substance that has an effect on the cell by which it is secreted.)
4)neuronal communication
LONG DISTANCE :
5)Endocrine system= hormones !

Question 2

Describe the mechanism of G-protein coupled receptors
use the adrenaline as an example with cAMP
(6)

Answer 2

1) GPCR crosses the membrane 7 times
At rest the G protein is an ALPHA, BETA, GAMMA unit with a GDP attached to it
2) The GPCR gets activated via LIGAND and this causes a conformational change in the G-Protein :
GDP DETACHES
and GTP ATTACHES = ACTIVATED
there are 2 units: Alpha GTP unit / beta gamma unit (they can both go on and cause a response in the proteins)
3) the ACTIVATED alpha unit can now bind to Adenyl cyclase which makes ATP–>cAMP ( secondary messenger )
4)cAMP binds to a protein kinase (which catalyses the transfer of phosphate groups)
5) The catalytic portion of the protein kinase are phosphorylated via ATP, they can now pass on the phosphate group and cause an effect in the cell ie:
6)Phosophorylase enzyme can now break glycogen into glucose !

Question 3

what’s a secondary messenger (2)

Answer 3

A messenger which causes the effect in the cell ( in the cell)

Question 4

identify how RTK (Receptor Tyrosine Kinase) functions and the role of tyrosine phosphorylation
(5)

Answer 4

1) receptor Tyrosine Kinase proteins are inactive MONOMERS
2) the ligand binds to receptor site
3) This forms a DIMER which is UNACTIVATED
4) To form an activated Dimer 6ATP—>6ADP and this phosphorylated DIMER = ACTIVATED RECEPTOR TYROSINE KINASE ( RTK)
5) THIS CAN cause cellular response !

Question 5

name some other forms of cell signalling

explain the smaller ones (5)

Answer 5

1) G-proteins -GPCR
2) RTK
3) ION channels-receptors for extracellular ligands ie: acetylcholine , glycine and GABA (ca2+ for control of hypertension
4) Steroid Hormones signal via CYTOSOLIC RECEPTors (receptor on the inside cytoplasm area )- the transcription factor is a nuclear receptor in the cytosol of the cell , when the cortisol binds = conformational change , enters nucleus , binds to regulatory region of the gene –> TRANSCRIPTION occurs
5) NO - Nitrous Oxide triggers the rapid smooth muscle relaxation , the target is cGMP which causes vasodilation

Question 6

what’s the paracrine system ?
autocrine system ?
what’s the endocrine system ?
(3)

Answer 6

PARACRINE-cells in close proximity cause response in nearby cells ( vesicles of transmitters and ligands )
AUTOCRINE- cell releases ligand/chemical messenger which can send signal BACK TO SAME CELL
ENDOCRINE - chemical messenger has to travel long distances via blood stream to cause effect in another cell ie : insulin , hormones released from pituitary gland .