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Coordination in animals is produced through nervous transmission and hormonal secretion.
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AH BIOLOGY
COMMUNICATION W
ITHIN MULTI
CELLULAR ORGANISM
S
COMMUNICATION WITHIN MULTICELLULAR ORGANISMS
This topic will look at 3 areas•Coordination•Hydrophobic signals and control of transcription.•Hydrophilic signals and transduction.
Coordination in animals is produced through nervous transmission and hormonal secretion.
Comparing the 2 systemselectrical impulse and extracellularextracellular signalling signalling molecules moleculesalong neuron axons bloodstream
cells with connections almost any cells into neurons (effectors) the body
faster slowertransient longer lastinglocalised widespread
Nature of signal
Transmission of signalsTarget cells
Time for responseDuration of responseExtent of response
Coordination is important for homeostasis.
What is homeostasis?
What are the main features of homeostatic control?•Controlled system•Monitoring centre•Mechanisms of correction•Set point re-established
Coordination allows humans to cope with physiological challenges
ExerciseWhat challenges does it bring?
•Cardiovascular•Ventilatory•Metabolic•Thermoregulatory•Osmoregulatory
EXTRACELLULAR SIGNALLINGSignalling cellsSpecific 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)
Feedback response may cause original cells to stop producing signalling molecules
Different cell types produce specific signalling molecules.
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.
Insulin
Insulin receptor protein
Adrenaline
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 THE CONTROL OF TRANSCRIPTION
HYDROPHILIC SIGNALS AND TRANSDUCTION
What are hydrophobic signals and how are they involved in the control of transcription?
• Hydrophobic signals can pass through membranes so their receptor molecules can be within the nucleus.
• They can directly influence the transcription of genes.
• They include the thyroid hormone thyroxine and steroid hormones
General action of hydrophobic signalling molecules
Altered rate of gene transcription
Altered rate of protein synthesis (long-lasting effects)
Intracellular receptor protein
Hormone
Thyroxine is a hydrophobic hormone that regulates the metabolic rate.
Thyroxine is released from the thyroid gland.
Thyroxine absent
Transcription of Na+/K+ ATPase gene inhibited
Thyroid receptor protein bound to DNA
Thyroxine present
Transcription of Na+/K+ATPase gene
Synthesis of Na+/K+
ATPase
Receptor proteinundergoes conformational change
Thyroxine
More Na+/K+ATPases in cell membrane
Increased metabolic rate
ATP degraded faster
Transcription of Na+/K+ATPase gene
Synthesis of Na+/K+
ATPase
Insertion into membrane
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 complexInactive transcription factor
Active transcription factor
Steroid hormone
HYDROPHOBIC SIGNALLING MOLECULES CAN BIND TO NUCLEAR RECEPTORS TO REGULATE GENE TRANSCRIPTION.
Animation of regulation of transcription.
What are hydrophilic signals and how are they involved in the transduction of messages?
• Hydrophilic signals need receptor molecules on the cell surface.
• Transmembrane receptors change conformation (shape)when the ligand (messenger) binds to outside of the cell.
• The signal molecule does not enter the cell.• The signal is transduced (passed) across the cell
membrane.• This often involves cascades of G-proteins or
phosphorylation by kinase enzymes.
General action of hydrophilic signalling molecules
Receptor protein
Hormone (ligand)
Signal transduction
Cell responses(short-lasting effects)
Examples include the peptide hormones ADH and insulin. These are made from short chains of amino acids.
ADH Insulin
Insulin regulates the glucose concentration of the bloodBeta-cells in pancreas release more insulin
Insulin transported in blood
Insulin 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
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
Action of insulin on fat and muscle cells
Animation of insulin action.
Exercise triggers recruitment of GLUT 4
GLUT 4
An illness related to blood glucose is Diabetes Mellitus
• A disease caused by defects in the insulinsignalling system.
• Two types of diabetes mellitus are recognised.Type 1 and Type 2
• What are the general symptoms of diabetes mellitus?
Type 1 – Insulin dependant diabetes
Type 2 – Non-insulinDependant diabetes
Cause Destruction of beta cellsin pancreas by immune system
Exact cause unknownObesity is a risk factor
Usual age of onset Childhood Adulthood
Pancreas does notproduce any insulin
Target cells developInsulin resistance. Lossof receptor function
Nature of defect
Treatment Daily insulin injections and management of dietto control glu. Conc.
Eat less sugar and saturated fat.Regular exercise.Medication to lowerBlood glu. Conc.
Global prevalence of diabetes mellitus
Numbers are millions!
Terrestrial vertebrates require mechanisms for conserving water
Thank goodness I can make ADH!
ADH regulates the body’s water balancePituitary gland releases more ADH
ADH transported in blood
ADH acts on kidney collecting ducts
More water reabsorbed into bloodLess urine madeBlood water concentration rises
Blood water concentration at set point
Blood water concentration falls
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.
Aquaporins
An illness related to ADH Diabetes insipidus
• Disease in which the water conservation mechanism of the kidneys fails.
• How could the system fail to work?
• What might the symptoms of diabetes insipidus be?
Symptoms of diabetes insipidus• Excessive thirst.
• Production of large quantities of dilute urine (‘insipidus’ = lacks flavour).
The two types of diabetes insipidus
• Central diabetes insipidus: insufficient ADH is produced.
• Nephrogenic diabetes insipidus: cells in the lining of the collecting duct areunable to respond to ADH.
POSSIBLE CAUSES OF DIABETES INSIPIDUS
Lumen of collecting duct
BloodCollecting duct cell
No ADH
ADH receptor insensitive to ADH
Protein kinase A
AQP2
Phosphorylated target proteins
Summary of ADH action
•ADH binds to receptor in collecting ducts.
•Recruitment of channel protein aquaporin 2 (AQP 2)
•Water moves through aquaporins in membrane
•Water is reabsorbed into blood
•No ADH or insensitive receptor proteins leads to diabetes insipidus