AH Biology: Unit 1 Communication Within Multicellular Organisms
Jan 20, 2016
AH Biology: Unit 1
Communication Within Multicellular Organisms
Communication within multicellular organisms
- General principles.
- Hydrophobic signals and control of transcription.
- Hydrophilic signals and transduction.
In animals communication is mediated by nervous transmission and hormonal secretion.
Nervous communication
Hormonal communication
Nature of signal Electrical impulses and extracellular signalling molecules
Extracellular signalling molecules
Transmission of signal
Along the axons of neurons
Through the bloodstream
Target cells Any cells with connections to neurons (effectors)
Almost any cells in the body
Time for response to occur
Faster Slower
Duration of response
Transient Longer lasting
Extent of response Localised Widespread
Coordination is important for homeostasis
Coordination allows integrated homeostatic responses to be made.
Monitoring centres
Controlled system
Error- correcting mechanisms
Set point values
Disturbances
Error signal
Coordinated responses
Coordination of responses allows animals to cope with physiological stress, eg a human
doing exercise...
Exercise
• Cardiovascular challenge
• Ventilatory challenge
• Metabolic challenge
• Thermoregulatory challenge
• Osmoregulatory challenge
Extracellular signalling
Signalling cells
Specific signalling molecules released as a result of a change in internal state
Signalling molecules carried to target cells
Target cellsArrival of signalling molecules at target cells is linked to a change in the internal state of the cells (cell response)
Extracellular signalling
Signalling cells
Specific signalling molecules released as a result of a change in internal state
Signalling molecules carried to target cells
Target cells (may also act as signalling cells)Arrival of signalling molecules at target cells is linked to a change in the internal state of the cells (cell response)
Different cell types produce specific signalling molecules.
Spatial organisation of signalling molecules
Hormones
Neurotransmitters
Animal pheromones
Eukaryotic cell: 50 μm
Distance: 1 nm 1 μm 1 mm 1 m 1 km
How does a target cell ‘know’ that it should respond to a specific signal?
Cells can only detect and respond to signals if they possess a specific receptor.
InsulinAdrenaline
Insulin receptor protein
Adrenaline receptor protein
Different cell types may show a specific tissue response to the same signal.
Beta-receptor
Adrenaline Beta-receptor
Adrenaline
Cell in mammalian salivary gland
Cell in mammalian liver
Amylase release stimulated Glycogen breakdown stimulated
Hydrophobic signals and control of transcription
Action of hydrophobic signalling molecules
Altered rate of gene transcription
Altered rate of protein synthesis (long-lasting effects)Intracellular
receptor protein
Hormone
Hydrophobic signalling molecules can bind to nuclear receptors to regulate gene
transcription.
Animation of regulation of transcription.
Steroid hormones are hydrophobic signalling molecules.
Animation of mechanism of steroid hormone action.
The steroid hormone receptor proteins are transcription factors.
Hormone-binding site
DNA-binding site exposed
Inhibitory protein complex
Inactive transcription factor
Active transcription factor
Steroid hormone
Thyroxine is a hydrophobic hormone that regulates the metabolic rate.
Why is thyroxine not classified as a carbohydrate, lipid or protein?
Thyroxine is released from the thyroid gland.
Thyroxine absent
Transcription of Na+/K+ ATPase gene inhibited
Thyroid receptor protein bound to DNA
Action of thyroxine
Transcription of Na+/K+ATPase gene
Synthesis of Na+/K+
ATPase
Receptor proteinundergoes conformational change
Thyroxine
Transcription of Na+/K+ATPase gene
Synthesis of Na+/K+ ATPase
More Na+/K+ATPases in cell membrane
Increased metabolic rate
ATP degraded faster
Insertion into membrane
Hydrophilic signals and transduction
Hydrophilic ligands
- Molecules that bind to sites on target proteins (receptors) at the surface of cells to trigger signal transduction.
- Ligand binding triggers the receptor protein to undergo a conformational change.
Hydrophilic signal
Reception + transduction
Amplification
Second messenger
Internal regulator
Tissue-specific effectors
Cell responses
Action of hydrophilic signalling molecules
Receptor protein
Hormone (ligand)
Signal transduction
Cell responses(short-lasting effects)
Peptide hormones are short chains of amino acids.
• ADH
• Insulin
Neurotransmitters are chemical signals released from nerve endings that alter the activity
of target cells.
Animation of action of acetylcholine.
Location of receptors
Axon
Synapse
Neurotransmitter substance
Hydrophilic signal transduction 2: receptors with kinase activity
Part of receptor that binds insulin (alpha-subunit)
Part of receptor with kinase activity (beta-subunit)
Hydrophilic signal transduction 1: G-protein cascade
Animation of G-protein activation.
Signal Signal
Stimulatory G-protein
Inhibitory G-protein
Adenylate cyclase enzyme
cAMP (second messenger)
Protein kinase A
Membrane channels + pumps, microtubules, histones, specific enzymes
Animation of protein kinase activity triggered by adrenaline and tyrosine kinase activity.
2. Kinase enzyme phosphorylates itself(autophosphorylation)
1. Insulin binds to receptor
P
P
P
P
P
3. Receptor phosphorylates insulin receptor substrate (IRS-1)
4. Phosphorylated IRS-1 acts on effectors to trigger cell responses
Insulin regulates the glucose concentration of the blood
Beta-cells in pancreas release more insulin
Insulin transported in blood
ADH acts on adipose, liver and muscle cells
More glucose is taken up by cellsBlood glucose concentration falls
Blood glucose concentration at set point
Blood glucose concentration rises
Change detected
Action of insulin on fat and muscle cells
Animation of insulin action.
GLUT4
GLUT4 recruitment is also induced by exercise.
Diabetes mellitus
• A disease caused by defects in the insulin signalling system.
• Two types of diabetes mellitus are recognised.
• What are the general symptoms of diabetes mellitus?
Type 1: Insulin-dependent diabetes
Type 2: Non-insulin-dependent diabetes
Cause Destruction of beta-cells in pancreas by immune system
Exact cause unknownObesity is a risk factor
Usual age of onset
Childhood Adulthood
Nature of defect
Pancreas does not produce any insulin
Target cells develop insulin resistanceLoss of receptor function
Treatment Daily insulin injections and management of diet to control blood glucose concentration
Eat less sugar and saturated fatRegular exerciseMedication to lower blood glucose concentration
Global prevalence of diabetes mellitus
Numbers are millions!
Review of diabetes mellitus
- Animation of insulin production and type 1 diabetes mellitus.
- Basic animation of type 2 diabetes mellitus.
- Animation of type 2 diabetes mellitus.
Terrestrial vertebrates require mechanisms for conserving water
Thank goodness I can make ADH!
ADH regulates the body’s water balance
Pituitary gland releases more ADH
ADH transported in blood
ADH acts on kidney collecting ducts
More water reabsorbed into bloodLess urine madeBlood water concentration falls
Blood water concentration at set point
Blood water concentration rises
Change detected
Mechanism of action of ADH
Lumen of collecting duct
BloodCollecting duct cell
1. ADH
2. ADH receptor
3. Activation of protein kinase A
5. Fusion of vesicles containing AQP2 water channel proteins
H2O
4. Protein phosphorylation
Aquaporins are protein channels that allow efficient transmembrane movement of water.
Animation of water movement through an aquaporin channel.
Diabetes insipidus
• Disease in which the water conservation mechanism of the kidneys fails.
• What could the nature of the failure be?
• What would the symptoms of diabetes insipidus be?
The two types of diabetes insipidus
• Central diabetes insipidus: insufficient ADH is produced.
• Nephrogenic diabetes insipidus: cells in the lining of the collecting duct are unable to respond to ADH.
Possible causes of diabetes insipidus
Lumen of collecting duct
BloodCollecting duct cell
ADH
ADH receptor
Protein kinase A
AQP2
Phosphorylated target proteins
Symptoms of diabetes insipidus
- Excessive thirst.
- Production of large quantities of dilute urine (‘insipidus’ = lacks flavour).
Overview of the action of ADH