Transcript PPT 8 Communication within multicell. orgs.

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 and
extracellular signalling
molecules
along neuron axons
extracellular
signalling
molecules
bloodstream
cells with connections
to neurons (effectors)
almost any cells in
the body
Time for response
faster
slower
Duration of response
transient
longer lasting
Extent of response
localised
widespread
Nature of signal
Transmission of
signals
Target cells
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.
Adrenaline
Adrenaline
receptor
protein
Insulin
Insulin
receptor
protein
Different cell types may show a specific tissue
response to the same signal.
Betareceptor
Adrenaline Betareceptor
Adrenaline
Amylase release stimulated Glycogen breakdown
stimulated
Cell in mammalian
salivary gland
Cell in mammalian liver
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
Hormone
Intracellular
receptor protein
Altered rate of protein
synthesis (long-lasting
effects)
Altered rate of gene
transcription
Thyroxine is a
hydrophobic hormone
that regulates the
metabolic rate.
Thyroxine is
released from the
thyroid gland.
Thyroxine absent
Thyroid receptor
protein bound to DNA
Transcription of Na+/K+
ATPase gene inhibited
Thyroxine present
Receptor protein
undergoes
conformational
change
Thyroxine
Synthesis of Na+/K+
ATPase
Transcription of
Na+/K+ATPase gene
More Na+/K+ATPases
in cell membrane
Insertion into
membrane
ATP degraded
faster
Increased
metabolic rate
Synthesis of Na+/K+
ATPase
Transcription of
Na+/K+ATPase gene
Steroid hormones are hydrophobic signalling molecules.
Animation of mechanism of steroid
hormone action.
The steroid hormone receptor proteins are transcription factors.
Inactive
transcription
factor
Inhibitory protein complex
Hormone-binding
site
Steroid
hormone
Active
transcription
factor
DNA-binding site
exposed
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
Hormone (ligand)
Receptor protein
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 blood
Beta-cells in
pancreas
release more
insulin
Insulin
transported in
blood
Insulin acts on
adipose, liver and
muscle cells
Change
detected
Blood glucose
concentration
rises
Blood glucose
concentration
at set point
More glucose is
taken up by cells
Blood glucose
concentration falls
1. Insulin binds to
receptor
2. Kinase enzyme
phosphorylates itself
(autophosphorylation)
3. Receptor
phosphorylates
insulin receptor
substrate (IRS-1)
P
P
P
P
4. Phosphorylated IRS-1
acts on effectors to trigger
cell responses
P
Action of insulin on fat and muscle cells
GLUT 4
Animation of insulin action.
Exercise triggers recruitment of 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
Cause
Destruction of beta cells
in pancreas by immune
system
Usual age of onset Childhood
Nature of defect
Pancreas does not
produce any insulin
Treatment
Daily insulin injections
and management of diet
to control glu. Conc.
Type 2 – Non-insulin
Dependant diabetes
Exact cause unknown
Obesity is a risk factor
Adulthood
Target cells develop
Insulin resistance. Loss
of receptor function
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
Change
detected
Blood water
concentration
falls
Blood water
concentration
at set point
ADH acts on
kidney collecting
ducts
More water
reabsorbed into blood
Less urine made
Blood water
concentration rises
MECHANISM OF ACTION OF ADH
Lumen of
collecting
duct
Collecting duct
cell
Blood
2. ADH receptor
H2O
1. ADH
5. Fusion of
vesicles
containing
AQP2 water
channel
proteins
4. Protein
phosphorylation
3. Activation of
protein kinase A
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 are
unable to respond to ADH.
POSSIBLE CAUSES OF DIABETES INSIPIDUS
Lumen of
collecting
duct
Collecting duct
cell
Blood
ADH receptor
insensitive to ADH
AQP2
No ADH
Phosphorylated
target proteins
Protein kinase A
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