ah biology communication within multicellular organisms

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