Lecture 3

Question 1

How do we ensure the right pathway is activated by signal molecules?

Answer 1

• direct contact - this is so the touch the specific cell physically
• selective receptor expression - which is when the cell only responds to the right signal as the receptor only fits for a specific signals
• degradation/reuptake of signal molecule - so if the signal molecule travels to far it will break down before accidentally activating something else

Question 2

Juxtacrine

Answer 2

• requires direct cell-cell contact, or receptor with a signal molecule that is membrane bound (not released)
• may be mediated by gap junctions
• composed of proteins called connexins
• allow ions and small molecules to move
between cells
• bi-directional
• provide electrical and chemical coupling between cells
• Allow very rapid communication between groups of cells e.g. cardiac muscle cells

Question 3

Autocrine

Answer 3

• Signalling between nearby cells of the same type
• Release and reception of signal molecule
• Can coordinate activity between a group of similar cells
• Specificity achieved by selective receptor expression and rapid degradation of signal molecule

Question 4

Paracrine

Answer 4

• Local signalling between different cell types
• Requires release and reception of signal molecule
• e.g endothelial cells communicate with nearby vascular smooth muscle via release of nitric oxide
• Specificity achieved by selective receptor expression and rapid degradation of signal molecule

Question 5

Neuronal signal

Answer 5

• Signal molecules are neurotransmitters
• Released from neurons and specialised
highly localized synaptic sites
• Cause rapid and often short-lasting effects
• Specificity achieved by precise contacts and rapid removal of neurotransmitter to prevent diffusion

Question 6

Endocrine signal pathway

Answer 6

• Usually involves signalling between distant cells
• Signals are called hormones, and are carried in the blood
• Produced from endocrine glands, tissues and isolated cells
• Many types of hormones e.g. steroids, modified amino acids, peptides
• Specificity achieved by selective receptor expression

Question 7

Neuroendocine

Answer 7

• Neurotransmitters released from neurons into blood
• e.g. hypothalamic neurons project to posterior pituitary to control hormone (ADH and oxytocin) release into the systemic circulation
• e.g. neuroendocrine cells in adrenal medulla release catecholamines into the blood in response to stress

Question 8

Signal molecules - ligands - water soluble

Answer 8

• Can be stored in vesicles within cell
• Rapid release via exocytosis
• Can travel in blood without a carrier
• Cannot enter target cell
• message transduced via cell surface receptor
• fast acting

Question 9

Signal molecules - ligands - lipid soluble

Answer 9

• Cannot be stored in vesicles within cell
• Slow response- made on demand
• Travels in blood with carrier protein
• may be longer lasting
• Can enter target cells by crossing
membrane
• Acts on intracellular receptors
• Often to directly regulate gene expression

Question 10

Signal receptor - intracellular

Answer 10

• Receptor protein located inside cell (Nucleus, Cytoplasm)
• Ligands need to be lipid soluble
• Usually alter gene expression

Question 11

Signal receptors - extracellular

Answer 11

• Ion channels
• G-protein coupled receptors
• Enzyme-linked receptors (cytokine receptors)
• Change membrane conductance
• Alter protein activity
• regulate cellular events