AH BIOLOGY 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 systems electrical impulse andextracellular extracellular signallingsignallingmolecules along neuron axonsbloodstream cells with connectionsalmost any cells in to neurons (effectors)the body fasterslower transientlonger lasting localisedwidespread Nature of signal Transmission of signals Target cells Time for response Duration of response Extent 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 Exercise What challenges does it bring? Cardiovascular Ventilatory Metabolic Thermoregulatory Osmoregulatory

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 Arrival 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 AdrenalineBeta- receptor Adrenaline Cell in mammalian salivary gland Cell in mammalian liver Amylase release stimulatedGlycogen 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 protein undergoes 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. AnimationAnimation 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

HYDROPHOBIC SIGNALLING MOLECULES CAN BIND TO NUCLEAR RECEPTORS TO REGULATE GENE TRANSCRIPTION. AnimationAnimation 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. ADHInsulin

Insulin regulates the glucose concentration of the blood Beta-cells in pancreas release more insulin Insulin transported in blood Insulin acts on adipose, liver and muscle cells More glucose is taken up by cells Blood 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 AnimationAnimation 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 insulin signalling 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-insulin Dependant diabetes Cause Destruction of beta cells in pancreas by immune system Exact cause unknown Obesity is a risk factor Usual age of onsetChildhood Adulthood Pancreas does not produce any insulin Target cells develop Insulin resistance. Loss of receptor function Nature of defect TreatmentDaily insulin injections and management of diet to control glu. Conc. Eat less sugar and saturated fat. Regular exercise. Medication to lower Blood 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 balance Pituitary gland releases more ADH ADH transported in blood ADH acts on kidney collecting ducts More water reabsorbed into blood Less urine made Blood 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 H2OH2O 4. Protein phosphorylation

Aquaporins are protein channels that allow efficient transmembrane movement of water. AnimationAnimation 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 are unable 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