Transcript 01-Homeostasis Cell Communication and - kyoussef-mci

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Homeostasis
 homeostasis – constant physiological adjustments of
the body in response to external environment
changes
 also known as dynamic equilibrium
What happens to your body when you exercise?
Exercise and Homeostasis
 body temperature
increases
 evaporation of sweat to
cool off
 O2 levels being used up  heart rate increases to
increase blood flow (to get
O2 levels back up)
 increased cellular
metabolism
 pancreas signals breaking
down of biomolecules to
get energy needed to
exercise
Homeostatic Control System
1.
Receptor – organs that detect changes or sense
when conditions are not within “normal” range
2.
Control Centre – organs which process
information it receives from the receptor and send
signals to another part of the body
3.
Effector – coordinating centre sends signals to an
organ / tissue which will normalize the original
organ
dynamic equilibrium
Response
No heat
produced
Analogy
Heater
turned
off
Room
temperature
decreases
Too
hot
Set
point
Too
cold
Set
point
Set point
Control center:
thermostat
Room
temperature
increases
dynamic equilibrium
Heater
turned
on
Response
Heat
produced
Feedback Systems
 negative feedback system - buildup of the end product of
the system shuts the system off
blood pressure drops
blood pressure
rises
brain
nerve pathway
heart rate
increases
arteries
constrict
 The response counteracts further change in the same direction
Feedback Systems
 positive feedback (feed-forward) system - a change in
some variable that triggers mechanisms that amplify the
change
Decrease in
progesterone
increased
contractions
Oxytocin released
Uterus
(contractions)
hypothalamus
Baby creates pressure
on cervix
How are external signals
converted to responses in the cell?
 Cells in a multi-cellular organism communicate via
chemical messengers
 Local and long-distance signaling
Local Signaling
 Animal and plant cells
 Have cell junctions that directly connect the cytoplasm
of adjacent cells Plasma membranes
Gap junctions
between animal cells
Plasmodesmata
between plant cells
Figure 11.3 (a) Cell junctions. Both animals and plants have cell junctions that allow molecules
to pass readily between adjacent cells without crossing plasma membranes.
Cell-cell recognition
Specificity!
Figure 11.3 (b) Cell-cell recognition. Two cells in an animal may communicate by interaction
between molecules protruding from their surfaces.
 In other cases, animal cells
 Communicate using local regulators
Local signaling
Target cell
Electrical signal
along nerve cell
triggers release of
neurotransmitter
Neurotransmitter
diffuses across
synapse
Secretory
vesicle
Local regulator
diffuses through
extracellular fluid
Figure 11.4 A B
(a) Paracrine signaling. A secreting cell acts
on nearby target cells by discharging
molecules of a local regulator (a growth
factor, for example) into the extracellular
fluid.
Target cell
is stimulated
(b) Synaptic signaling. A nerve cell
releases neurotransmitter molecules
into a synapse, stimulating the
target cell.
Long-distance signaling
Long-distance signaling
Endocrine cell
 Both plants and
Blood
vessel
animals use
hormones
Hormone travels
in bloodstream
to target cells
Target
cell
Figure 11.4 C
(c) Hormonal signaling. Specialized
endocrine cells secrete hormones
into body fluids, often the blood.
Hormones may reach virtually all
body cells.
How are external signals
converted to responses in the cell?
 Three stages of cell signaling
EXTRACELLULAR
FLUID
1 Reception
CYTOPLASM
Plasma membrane
2 Transduction
3 Response
Receptor
Activation
of cellular
response
Relay molecules in a signal transduction pathway
Signal
molecule
Figure 11.5
Step 1: Reception
 The binding between signal
molecule (ligand) and receptor is
highly specific
 A conformational change in a
receptor is often the initial
transduction of the signal
 Can have intracellular and
membrane receptors
Intracellular Receptors
 Are proteins found within
cytoplasmic or nucleus
 Signal molecules that
bind are small or
hydrophobic
Hormone
EXTRACELLULAR
(testosterone) FLUID
1 The steroid
hormone testosterone
passes through the
plasma membrane.
Plasma
membrane
Receptor
protein
Hormonereceptor
complex
2 Testosterone binds
to a receptor protein
in the cytoplasm,
activating it.
3 The hormone-
 can readily cross the
plasma membrane
DNA
receptor complex
enters the nucleus
and binds to specific
genes.
mRNA
4 The bound protein
NUCLEUS
stimulates the
transcription of
the gene into mRNA.
New protein
5 The mRNA is
Figure 11.6
CYTOPLASM
translated into a
specific protein.
Membrane Receptors
 There are three main types of membrane receptors
 G-protein-linked
 Tyrosine kinases
 Ion channel
G-protein-linked receptors
Seven α
helices
Signal-binding site
Yeast mating factors, epinephrine,
many hormones and
neurotransmitters
Segment that
interacts with
G proteins
G-protein-linked
Receptor
Plasma Membrane
Activated
Receptor
Signal molecule
GDP
CYTOPLASM
G-protein
(inactive)
Enzyme
GDP
GTP
active
Activated
enzyme
GTP
GDP
Pi
Figure 11.7
Cellular response
Inctivate
enzyme
Receptor Tyrosine Kinases
Important in cell growth and reproduction!
e.g.
growth
factor
Signal-binding sitea
Signal
molecule
Signal
molecule
Helix in the
Membrane
Tyr
Tyrosines
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Receptor tyrosine
kinase proteins
(inactive monomers)
CYTOPLASM
Tyr
Dimer
Activated
relay proteins
Figure 11.7
Tyr
P Tyr
P Tyr
Tyr P
Tyr P
Tyr
P Tyr
Tyr P
Tyr
Tyr
Tyr
Tyr
6
ATP
Activated tyrosinekinase regions
(unphosphorylated
dimer)
6 ADP
Fully activated receptor
tyrosine-kinase
(phosphorylated
dimer)
P Tyr
P Tyr
P Tyr
Tyr P
Tyr P
Tyr P
Inactive
relay proteins
Cellular
response 1
Cellular
response 2
Ion Channel
Receptors
Signal
molecule
(ligand)
Gate
closed
Ions
Ligand-gated
ion channel receptor
 E.g. ligand-gated ion
channels
Plasma
Membrane
Gate open
 Region acts like a gate
 E.g. Sodium and Calcium
channels important in the
nervous system
Cellular
response
Gate close
Figure 11.7
Step 2: Transduction
 Multistep pathways
 Can amplify a signal
 Provide more opportunities for coordination and
regulation
Signal Transduction Pathway
At each step in a pathway the signal is transduced into a different form,
commonly a conformational change in a protein
Signal molecule
Receptor
Activated relay
molecule
Inactive
protein kinase
1
1 A relay molecule
activates protein kinase 1.
2 Active protein kinase 1
transfers a phosphate from ATP
to an inactive molecule of
protein kinase 2, thus activating
this second kinase.
Active
protein
kinase
1
Inactive
protein kinase
2
ATP
Pi
5 Enzymes called protein
phosphatases (PP)
catalyze the removal of
the phosphate groups
from the proteins,
making them inactive
and available for reuse.
PP
Inactive
protein kinase
3
3 Active protein kinase 2
then catalyzes the phosphorylation (and activation) of
protein kinase 3.
P
Active
protein
kinase
2
ADP
ATP
ADP
Pi
Active
protein
kinase
3
PP
Inactive
protein
P
4 Finally, active protein
kinase 3 phosphorylates a
protein (pink) that brings
about the cell’s response to
the signal.
ATP
ADP
Pi
PP
P
Active
protein
Cellular
response
Second Messangers
 Are small, nonprotein, water-soluble molecules or
ions
 Cyclic AMP (cAMP)
 Is made from ATP
NH2
N
N
O
O
O
N
N
–
O P O P O P O Ch2
O
O
O
Figure 11.9
N
N
O
Pyrophosphate
P Pi
O
CH2
Phoshodiesterase
O
OH
Cyclic AMP
N
N
O
HO P O CH2
O
O
P
O
N
N
N
N
Adenylyl cyclase
O
OH OH
ATP
NH2
NH2
O
H2O
OH OH
AMP
 Many G-proteins
 Trigger the formation of cAMP, which then acts as a
second messenger in cellular pathways
First messenger
(signal molecule
such as epinephrine)
G protein
G-protein-linked
receptor
Adenylyl
cyclase
GTP
ATP
cAMP
Protein
kinase A
Cellular responses
Figure 11.10
Reception
Binding of epinephrine to G-protein-linked receptor (1 molecule)
Step 3: Response
Transduction
Inactive G protein
 Each protein in a
signaling pathway
Active G protein (102 molecules)
Inactive adenylyl cyclase
Active adenylyl cyclase (102)
 Amplifies the signal by
activating multiple copies
of the next component in
the pathway
 In the cytoplasm
 Signaling pathways
regulate a variety of
cellular activities
ATP
Cyclic AMP (104)
Inactive protein kinase A
Active protein kinase A (104)
Inactive phosphorylase kinase
Active phosphorylase kinase (105)
Inactive glycogen phosphorylase
Active glycogen phosphorylase (106)
Response
Glycogen
Glucose-1-phosphate
(108 molecules)
 Other pathways
 Regulate genes by activating transcription factors that
turn genes on or off
Growth factor
Reception
Receptor
Phosphorylation
cascade
Transduction
CYTOPLASM
Inactive
transcription Active
factor
transcription
factor
P
Response
DNA
Gene
Figure 11.14
NUCLEUS
mRNA
Thermoregulation
 Process by which animals maintain an internal
temperature within a tolerable range.
 Critical to survival because biochemical and
physiological processes are sensitive to changes in
temperature.
 Enzymatic reactions
 Properties of membranes
Modes of Heat Exchange
Radiation is the emission of electromagnetic
waves by all objects warmer than absolute
zero. Radiation can transfer heat between
objects that are not in direct contact, as when
a lizard absorbs heat radiating from the sun.
Evaporation is the removal of heat from the surface of a
liquid that is losing some of its molecules as gas.
Evaporation of water from a lizard’s moist surfaces that
are exposed to the environment has a strong cooling effect.
Convection is the transfer of heat by the
Conduction is the direct transfer of thermal motion (heat)
movement of air or liquid past a surface,
as when a breeze contributes to heat loss
from a lizard’s dry skin, or blood moves
heat from the body core to the extremities.
between molecules of objects in direct contact with each
other, as when a lizard sits on a hot rock.
Balancing Heat Loss and Gain
1. Insulation
2. Circulatory Adaptations
3. Cooling by Evaporative Heat Loss
4. Adjusting Metabolic Heat Production
Insulation
 Feathers, hair or fat layers
 Reduces the flow of heat between an animal and its
environment
 Lowers the energy cost of keeping warm
 In mammals, the insulating material is associated
with the integumentary system (skin, hair and
nails)
Hair
Epidermis
Sweat
pore
Muscle
Dermis
Nerve
Sweat
gland
Hypodermis
Adipose tissue
Blood vessels
Oil gland
 Most land animals and birds react to cold by raising
their fur or feathers
 Traps a thicker layer of air
 Increasing its insulating power (the more still air = the
better!)
Goosebumps
 Raise hair on our body
 Inherited from our furry
ancestors
 We rely more on a layer
of fat just beneath the
skin
Circulatory Adaptations
 We can alter the amount of blood (and hence heat)
flowing between the body core and the skin.
Vasodilation
Muscles in superficial blood
vessels relax
Increases the diameter of
vessels = more blood
Increases heat transfer,
warming the skin
Vasoconstriction
 Muscles in superficial blood vessels contract
 Smaller diameter of blood vessels = less blood
 Reduces heat transfer, preventing heat loss
 Keeps blood (and heat) in interior of body where it is
needed
Evaporative Heat Loss
 When environmental temperatures are above body
temperature we
 Sweat, pant, bathe, spread saliva over body surfaces
 Heat is carried away with water molecules as they
change into a gas
Adjusting Metabolic Heat Production
 Shivering and Moving - Heat
production is increased by muscle
activity
 Non-shivering Thermogenesis
(NST) - Certain hormones can
cause mitochondria to increase their
metabolic activity and produce heat
 Brown Fat – Specialized tissue for
rapid heat production (has higher
conc’n of mitochondria)
What regulates our temperature?
 Hypothalamus - contains a group of nerve cells
that function as a thermostat
Increased body
temperature (such
as when exercising
or in hot
surroundings)
Body temperature
decreases;
thermostat
shuts off cooling
mechanisms.
Cold Response
Homeostasis:
Internal body temperature
of approximately 36–38°C
Body temperature
increases;
thermostat
shuts off warming
mechanisms.
Decreased body
temperature
Vasoconstriction, diverting
blood from skin to deeper tissues
and reducing heat loss
from skin surface.
Skeletal muscles
rapidly contract,
causing shivering,
which generates
heat.
Thermostat in
hypothalamus
activates
warming
mechanisms.
Heat Response
Thermostat in
hypothalamus
activates cooling
mechanisms.
Sweat glands secrete
sweat that evaporates,
cooling the body.
Vasodilation,
Blood vessels
relax and fill
with warm blood;
heat radiates from
skin surface.
Increased body
temperature
Homeostasis:
Internal body temperature
of approximately 36–38°C
Body temperature
decreases;
thermostat
shuts off cooling
mechanisms.
Extreme Cold
Why does your body allow you to get frost bite?
Why is hypothermia such a concern?
Classwork/Homework
 Section 7.1 – Pg. 337 #1-5, 7-9
 Section 7.2 – Pg. 341 # 1-9,11