Cell Signalling

Question 1

Signalling cells

Answer 1

Produce a signal that is detected by target cells

Question 2

Targeted cells

Answer 2

Recognise the signal because they possess receptor proteins that recognise and respond specifically to the signal molecule

Question 3

Signal transduction

Answer 3

Begins when the receptor protein on a target cell receive an incoming extracellular signal and converts it to an intracellular signal that alters cell behaviour

Question 4

Endocrine system

Answer 4

Hormones secreted by an endocrine cell are released and travel through the bloodstream to affect other cells that are located far away from the hormone producing cells

Question 5

Paracrine system

Answer 5

Signals released locally and affect neighbouring cells - do not enter bloodstream, diffuse locally through the extracellular fluid

Question 6

Neuronal system

Answer 6

Nerve cells can deliver messages over long distances —> signal is transmitted very quickly along axons to neighbouring and remote target cells via electrical signals

Question 7

Intracellular receptors

Answer 7

Small, hydrophobic signal molecules diffuse across the cell membrane and bind to receptors inside the cell - e.g. steroid hormone

Question 8

Need for signal transduction

Answer 8

To regulate metabolic pathways

Question 9

Intracellular signalling proteins

Answer 9

Act as molecular switches which switch from an inactive to an active state when they receive a signal

Question 10

Signalling by protein phosphorylation

Answer 10

Molecules activated by phosphorylation by kinase enzymes and inactivated by dephosphorylation by phosphatase enzymes

Question 11

Serine/threonine kinases

Answer 11

Phosphorylation proteins on serine and threonine

Question 12

Tyrosine kinases

Answer 12

Phosphorylation proteins on tyrosine residues

Question 13

Signalling by GTP-binding proteins

Answer 13

G-proteins are activated by the binding of GTP

Have intrinsic GTPase ability to hydrolyse GTP into GDP inactivating the G-protein

Question 14

Enzyme-coupled receptors

Answer 14

Act as enzymes inside the cell to activate a variety of intracellular signalling pathways

Question 15

G-protein coupled receptors

Answer 15

Activate membrane-bound trimeric GTP-binding proteins which then activate an enzyme on the plasma membrane initiating a cascade of cellular effects

Question 16

G-protein coupled receptor structure

Answer 16

A single polypeptide chain which spans the plasma membrane seven times

Consist of 3 subunits Alpha, beta and gamma

Question 17

Alpha Subunit

Answer 17

Turned off when GDP is bound, when signalling molecule binds the alpha subunits affinity for GDP decreases allowing GTP to be exchanged

Question 18

Adenyl cyclise pathway

Answer 18

Activated G-protein switches on adenyl cyclise —> leading to an increase in cyclic AMP inside the cell
cAMP is a small molecule which diffuses freely in the cytoplasm and activates the protein kinase A
pkA phosphorylates a variety of downstream targets —> enzyme which mediates the breakdown of glycogen to glucose in skeletal muscle

Question 19

Adrenaline

Answer 19

Hormone which mediates the production of ATP —> only affects cells which possess a receptor, in skeletal muscles and fat cells by producing fatty acids from triacylglycerols as fuel for the production of ATP

Question 20

Phospholipase C pathway

Answer 20

When phospholipase C is activated, two small second messenger molecules (IP3 and DAG) are produced
IP3 diffuses through the cytoplasm and triggers the release of calcium from the endoplasmic reticulum by binding to and opening calcium channels on ER membrane
Induces a sudden increase in concentration of calcium inside the cell
Calcium and DAG will activate the protein kinase C (PkC) that in turn phosphorylates a number of target proteins

Question 21

Enzyme coupled receptors respond to

Answer 21

growth factors that control cell proliferation, cell survival and differentiation of target cells

Question 22

Intracellular signalling transduction by RTK

Answer 22

The binding of a signalling molecule to the RTKs causes two molecules to come together in the membrane forming a dimer
The dimer formation activates the kinase function with the result that each receptor phosphorylates the other
The phosphorylates RTK serves as a binding site for a number of intracellular signalling molecules that can in turn activate other proteins forming a cascade of intracellular signalling molecules

Question 23

RAS

Answer 23

Intracellular signalling molecule activated by RTK

Functions as the alpha subunit of a g-protein

Question 24

RAS pathway

Answer 24

Binding of the signalling molecule to the RTK leads to the binding of adaptor molecules to the activated receptor that in turn induces RAS to release GDP and bind GTP
RAS has an intrinsic GTPase ability so after a delay switches itself off by hydrolysing GTP

Question 25

Activation of RAS

Answer 25

Promotes activation of a phosphorylation cascade in which a series of protein kinases phosphorylates each other in sequence This relay system that transfers the signal from the plasma membrane into the nucleus includes three kinases known as Mitogen activated protein (MAP) kinases RAs activates the MAP kinase kinase kinase -> activates MAP kinase kinase -> activates MAP kinase -> phosphorylates a number of downstream signalling molecules leading mainly to changes in gene transcription of target molecules that will cause cell proliferation

Question 26

Ras inactivated in cells

Answer 26

Cells become unable to respond to ligand molecules signalling cell proliferation

Question 27

Ras permanently active in cells

Answer 27

Cells continue to proliferate as if they were always activated by the presence of an extracellular mitogen