cell signalling

Question 1

are membrane receptors most hydrophilic/phobic

Answer 1

hydrophilic

Question 2

what does signal transduction pathways do

Answer 2

form a cascade

Question 3

3 methods of cell communication

Answer 3

gap junctions, contact-dependent signals, diffusible chemical signals

Question 4

method of cell communication

Answer 4

GP: direct cytoplasmic connections

Contact: interaction between membrane

diffusible: Autocrine signals act on same cell that secreted them, Paracrine signals are secreted by one cell and diffuse to adjacent cells

Question 5

describe the paracrine and autocrine signalling process

Answer 5

derived from individual cells , act locally, diffuse through interstitial fluid

Question 5

3 types of diffusible chemical signalling and the difference between them

Answer 5

Paracrine: Paracrine agent targets from local cell to local target cell
Autocrine: Autocrine agent targets local cell
Endocrine: from local cell to hormones to remote target cell

Question 6

what happens to the signalling molecule in paracrine and autocrine signalling

Answer 6

either enzymatically destroyed or taken up by local
target cells → minimal entry into bloodstream

Question 7

can Paracrine secretions act as autocrine

Answer 7

yes, e.g. act back on the secretory
cell

Question 8

examples of paracrine and autocrine signalling

Answer 8

Metabolic hyperaemia
Platelet plug formation

Question 9

describe Metabolic hyperaemia

Answer 9

Endothelium secretes
vasodilators (e.g. nitric
oxide) in response to
increased metabolism

Dilation of local
arterioles
↑ local blood flow

Question 10

describe Platelet plug formation

Answer 10

Activated platelets
release agonists (e.g.
ADP, thromboxane A2)
Paracrine and
autocrine
Recruits more platelets
and amplifies platelet
activation

Question 11

describe Endocrine signalling process

Answer 11

Hormones synthesised and secreted by
endocrine cells (glands) → extracellular fluid
→ blood → distributed throughout body i.e.
distant targets

Question 12

how is the secretion triggered during endocrine signalling

Answer 12

a variety of signals:
* Changing levels of blood constituent
* Regulated by blood levels of another
hormone
* Regulated by activity of nerves

Question 13

conditions needed for cells to respond to endocrine signalling to happen

Answer 13

Only cells with specific receptor for
specific hormone can respond

Question 14

why must Receptors must bind hormones very
effectively

Answer 14

they must have a high
affinity for the specific hormone because of dilution in bloodstream,
[hormone]blood are very low (10-9
mol/l)

Question 15

how big is the synaptic gap and how fast do signals get transmitted

Answer 15

Signals transmitted within milliseconds

~20 nm gap

Question 16

what do electrical signals in nerves cause

Answer 16

Electrical signals (action potentials) in nerve
cause release of chemical (neurotransmitter) at
synapse → target cell

Question 17

Name 2 types of neuronal signalling

Answer 17

neurotransmitter e.g. Ach, GABA

neurohormones e.g. adrenaline/noradrenaline

Question 18

define signal transduction

Answer 18

converts one form of signal into a different form
e.g. signal molecules –> response

Question 19

what are the different types of cell membrane receptors

Answer 19

receptor channels, G protein coupled, receptor enzymes, integrin

Question 19

describe intracellular receptors, what type of molecules binds to it

Answer 19

Some signalling molecules are lipid soluble
* Move through the plasma membrane by simple diffusion
* These therefore bind to intracellular receptors in the cytosol (e.g. nitric
oxide) or in the nucleus (e.g. oestrogen

Question 20

what are receptor-enzymes also known as and give an example

Answer 20

enzyme-linked
receptors
* Receptors with intrinsic enzyme activity e.g. insulin receptors
* Bound to an enzyme e.g. cytokine receptors

Question 20

what are integrin receptors

Answer 20

Receptors that interact with the cytoskeleton
involved in:
* Cell movement
* Cell adhesion
* Platelet aggregation

Question 20

what are the different types of receptors

Answer 20

cell membrane receptors, intracellular, sensory

Question 20

what types of molecules binds to cell surface receptors

Answer 20

Hydrophilic signalling molecules bind to receptors on the cell surface

Question 21

what are receptor channels also known as and provide an example

Answer 21

ionic receptors e.g. nicotinic acetylcholine receptors

Question 21

what are G protein coupled receptors also known as and give an example

Answer 21

metabotropic receptors e.g. adrenergic receptors

Question 21

what is the simplest and quickest receptor pathway

Answer 21

ionotropic receptors

Question 21

provide the process to which ionotropic receptors function

Answer 21

Binding of agonist to receptor → channel opening → change in membrane potential

Question 22

what is the largest family of receptors

Answer 22

G protein-coupled receptors

Question 23

what is G- protein - coupled receptor bound to

Answer 23

intracellular GTP-binding regulatory protein (G protein

Question 24

how many subunits does GPCRs have

Answer 24

G proteins have α, β and γ subunits (heterotrimeric)

Question 25

what happens to a GPCR when the signalling molecule binds

Answer 25

he GPCR exchanges exchange guanosine diphosphate (GDP) for guanosine triphosphate (GTP) G protein disassociates from the receptor into α and βγ subunits * Subunits can now interact with ion channels, 2nd messengers

Question 26

example of GPCR

Answer 26

opening of ligand-gated K+ channels leading to hyperpolarisation

Question 27

talk through the 5 steps of the GPCR-adenylyl cyclase pathway

Answer 27

- G protein activates adenylyl cyclase * Adenylyl cyclase converts ATP to cyclic AMP and pyrophosphate * 2nd messenger cAMP activates protein kinase A * Protein kinase A phosphorylates target proteins and changes their activity

Question 28

how much is the amplification from the GPCR-adenylyl cyclase pathway

Answer 28

1 signalling molecule → 102 cAMP → 104 phosphorylated protein → 106 products

Question 29

describe the GPCR-phospholipase C pathway

Answer 29

G protein activates phospholipase C (PLC) * PLC converts the membrane phospholipid phosphatidylinositol bisphosphate (PIP2) into 2nd messengers: * Diacylglycerol (DAG) * Inositol trisphosphate (IP3) * DAG activates protein kinase C * IP3 releases Ca2+ from stores in the endoplasmic reticulum which also activates protein kinase C * Protein kinase C phosphorylates target proteins and changes their activity

Question 30

how to differentiate between adenylyl cyclase and phospholipase C pathway

Answer 30

A denylyl cyclase → A TP → c A MP → protein kinase A Phospholipase C → DAG → protein kinase C IP3 → Ca2+ all A go together and all C

Question 31

what are receptors with intrinsic enzyme activity

Answer 31

protein kinases

Question 32

describe the enzyme receptor pathway

Answer 32

Binding of signalling molecule receptor → conformational change → enzyme activation → autophosphorylation → phosphorylation (activation) of other proteins (e.g. enzymes) * e.g. tyrosine kinase receptors

Question 33

name two molecules that use intracellular receptors

Answer 33

steroid hormones and NO

Question 34

when do steroid hormones is used in intracellular receptor signalling

Answer 34

Receptor is often a transcription factor that regulates transcription in the nucleus

Question 35

describe how NO is used in intracellular receptor signalling

Answer 35

- Binds to soluble guanylyl cyclase in the cytosol * Generates cGMP as 2nd messenger that regulates cell activity

Question 36

name a secondary messenger

Answer 36

Calcium

Question 37

name the sources of calcium

Answer 37

- Release from internal stores via IP3- or Ca2+-stimulated release Ca2+ from endoplasmic reticulum - Extracellular via Ca2+ channels

Question 38

name the effects of calcium

Answer 38

* Directly affects target protein (e.g. PKC) * Binds to calmodulin which affects protein (e.g. Ca2+- calmodulin dependent kinase - CamKinase) * Works via some other Ca2+ binding protein (e.g. troponin)

Question 39

summarise Ionotropic receptors, G protein-coupled receptors, GPCR signalling pathways, Ca2+

Answer 39

* Ionotropic receptors are the simplest receptors and signalling through these is rapid * G protein-coupled receptors (GPCRs) are more complex * Know your GPCR signalling pathways! * Ca2+ is an important intracellular messenger