Cell signalling 1

Question 1

cell signalling basic concept

Answer 1

Chemical signal released by one cell recognised by another
Involves receptor tat recognises signal in specific manner
Allows recipient cell to make a response

Question 2

Why is cell signalling important

Answer 2

• coordination of cell behaviour
• single cell organisms use signalling to identify and interact with cell of correct mating type in sexual reproduction
• Multicellular organisms depend on cell signalling for correct development, tissue maintenance and homeostasis

Question 3

Importance of cell signalling in development

Answer 3

Some cellular decisions during development of a multicellular organism are influenced by signalling.

Question 4

what does mis-regulation of cell signalling in development lead to

Answer 4

cancer

Question 5

Insulin signalling

Answer 5

insulin signals to tissues (adipose, muscle, liver) promoting storage of energy reserves
Secreted in response to incr blood glucose levels and AAs
Failure of pancreatic B cells (insufficient insulin production) or response of peripheral tissues (insulin sensitivity) leads to diabetes

Question 6

4 types cell signalling

Answer 6

endocrine, paracrine, neuronal and contact-dependent

Question 7

Lateral inhibition mediated by the delta-notch signalling system

Answer 7

during development in parts of the nervous system 2 specialised cell types (neurons and support cells) are formed in a organised manner through contact mediated cell signalling involving Delta (signal) and notch (receptor)
Notch receptor can change expression of genes inside the cell

Question 8

Delta notch signalling more detail

Answer 8

Unspecified cells are equivalent, each cell signaling to its neighbours to maintain low levels of neurogenin (promotes low levels of delta expression)

Some cells will express by chance higher levels of delta. Signals to surrounding cells to prevent neurogenin expression and i) stops them from differentiating as neurones and ii) reduces their expression of delta

Neurogenin levels incr in cells not receiving delta signal - allows expression of factors eg Neuro D, that initiate neuronal differentiation

Question 9

What is the range of delta signal limited by

Answer 9

its attachment to the cell surface

Question 10

What other mechanisms could be used to ensure local signals don’t act too far from their origin?

Answer 10

Mechanisms in certain parts of a tissue which breakdown the signal
Signal gets stuck in ECM

Question 11

What other mechanisms could be used to ensure local signals don’t act too far from their origin?

Answer 11

rapid degradation
Binding to inhibitory proteins
Binding to the ECM

Question 12

Response to a signal is

Answer 12

cell type specific eg Ach brings out a different response in heart muscle, salivary glands and skeletal muscle
On cardiac and salivary gland cells the receptor is a GPCR, whereas on skeletal muscle its a ligand-gated ion channel

Question 13

Response to a signal is

Answer 13

cell type specific eg Ach brings out a different response in heart muscle, salivary glands and skeletal muscle
On cardiac and salivary gland cells the receptor is a GPCR, whereas on skeletal muscle its a ligand-gated ion channel

Question 14

Changes in cell behaviour may results from

Answer 14

integration of many signals

Question 15

signal-receptor interaction starts

Answer 15

chain of molecular changes inside the cell eg changes in the cytoplasm (altered metabolism or cytoskeleton) and nucleus (altered gene expression)

Question 16

Intracellular signalling pathway/molecular relay can allow

Answer 16

1. Modulation of the signalling pathway, eg cross-talk with other signalling pathways
2. amplification of the pathway
3. Distribution of the signal to all parts of the cell

relay is from receptor on CSM to eg nucleus, and often involves an en\yme

Question 17

cell surface receptors

Answer 17

eg GPCRs

, enzyme linked receptors

Question 18

Intracelllular receptors

Answer 18

act directly as TFs eg steroid and thyroid hormone receptors

or enzymes directly activated by the signal molecule (can cross CSM) eg guanyl cyclase activated by NO

Question 19

steroid and thyroid hormones

Answer 19

small, hydrophobic signal molecules that interact with intracellular receptors
The hormone-receptor complex acts directly as a TF to regulate expression of specific genes

Question 20

NO

Answer 20

dissolved gas
acts as a signal
Relax blood vessels to treat angina by relaxing muscle around BVs

Question 21

Nitric oxide signalling: why is it short lived

Answer 21

rapid and short lived
NO reacts readily with oxygen to form nitrates /nitrites
Half life of 5-10s
ensures local actions

Question 22

Nitric oxide signalling how does it work

Answer 22

triggering of signalling system begins with release of nt from a nerve terminal which is making contact with the BV endothelial cells
Stimulates production of nitric oxide from arginine in the cell. NO can diffuse across into smooth muscle cells where it acts on its targets- its receptor is guanylyl cyclase (an enzyme), which makes smooth muscle relax and dilates blood vessel

Question 23

Actions of NO and viagra

Answer 23

Target enzyme for NO, guanylyl cyclase, converts GTP to cGMP
Incr cGMP levels cause smooth muscle relaxation

Signalling reversed when cGMP converted to 5’ GMP linear form by cGMP phosphodiesterase

Viagra inhibits the PDE5 phosphodiesterase and prevents cGMP breakdowm in BVs of the erectile tissue, resulting in sustained/longer signalling response.

shows importance of signal reversal mechanisms and signalling pathways as drug targets

Question 24

endocrine signalling

Answer 24

Signal produced by gland/endocrine cell. Hormone goes into bloodstream and receptors for that hormone are on the target cells
Long distance, prolonged process

Question 25

Paracrine signalling

Answer 25

Signal produce by a cell, signal only travels a short distance- acts on cells in same tissue or adjacent tissue
short term

Question 26

Neuronal signalling

Answer 26

involves 1 cell releasing neurotransmitters that are released across the synapse and detected by receptors on the target cell
Rapid

Question 27

contact dependent signalling

Answer 27

only communicating to immediate neighbours
Display a signal on the cell surface and have a receptor on the target cell next to it
Signal-receptor interaction is between adjacent cells

Question 28

What do delta notch signalling allow

Answer 28

cells to be sorted into at least 2 different types eg nerve and epithelial

Question 29

Where is testosterone (hormone) released from

Answer 29

leydig cells

Question 30

Androgen insensitivity syndrome

Answer 30

XY individuals who would develop male characteristics but lack receptors for testosterone and develop female characteristics