Homeostasis
stability of the internal environment and the mechanisms that maintain the stability
Dynamic Equilibrium
maintained where the rate of loss balances out with the rate of gain
Feedback Mechanisms
evolved to help maintain homeostasis in organisms
(+) Feedback Mechanisms
the output (or product) of a system intensifies the response
(+) Feedback Mechanisms Examples
child birth, fruit ripening
(-) Feedback Mechanisms
the output (or product) of a system causes a counter response to return a set point
(-) Feedback Mechanisms Examples
body temperature, water concentration, blood sugar regulation
Receptor
sensory organ that receives the stimulus
Stimulus
an action that evokes a response
Effector
an organ that does the response
Response
the effect, caused by the stimulus
Mistake in a Feedback Loop
homeostasis is thrown off
Mistake in a Feedback Loop Example
Type 1 Diabetes
Catalysts
substances that speed up the reactions without being permanently altered
Enzymes
biological catalysts are proteins
Regulate Metabolism
cells can control the amount of an enzyme
Feedback Inhibition
output of a process is used as an input to control the behavior of the overall process itself
Activity of Enzyme
can be regulated
Chemical Inhibitors
can bind to enzymes and slow reaction rates
Environmental Conditions
play a role in enzyme function
Passive Transport
requiring no extra energy as molecules move down the gradient
Active Transport
requiring extra energy to move molecules against the gradient
Simple Diffusion
the spreading of molecules across the membrane until equilibrium is reached
Transport Protein
acts to help facilitate the diffusion of molecules that couldn't pass through the cells' membrane
Can't Pass Through The Cell Membrane
large and polar molecules
Channel
allows molecules through
Carries
binds to substances to carry across the cell membrane
Osmosis
the simple diffusion of water across the cell membrane
Water
moves from areas of high concentration to areas of low concentration
Low Solute
high concentration
High Solute
low concentration
Hyper Tonic Solutions ^
water is lower than the cells cytoplasm
Water Out of Cells
cell shrivels
Hypo Tonic Solutions v
water is higher than the cells cytoplasm
Water Into a Cell
cell swells
Isotonic Solutions ^ v
identical water to cells cytoplasm
Molecular Pumps
when a cell uses energy to pump molecules across the membrane
Protein Channel
moves molecules across the membrane
Endocytosis
moves particles into the cell
Exocytosis
export materials out of the cell
Cell Signalling
allows cells to process information from their environment and communicate to other cells
Ligands
molecules that bind to other molecules for signalling
Signal Transduction Pathway
signal -> message transduced -> desired response
Autocrine Signals
self"; affect the same cell that releases them
Paracrine Signals
diffuse to nearby cells
Juxtacrine Signals
require direct contact between the signalling cell and the receiving cell
Hormones (Endocrine Signalling)
signal travels to distant cells
Receptors
protein where the signal is received on the target cell
Intracellular Receptors
located inside a cell
Intracellular Receptors (Ligands?)
ligands are small and nonpolar
Membrane Receptors (Ligands?)
ligands are large and polar
Noncolvent
not strong
Inhibitors
can block the normal ligands to prevent communication
Transduction
the passing along the signal until the desired response is reached
Changing the Shape
passing along the message
Phosphorylation
addition of phosphate groups (by kinases)
Dephosphorylation
removal of phosphate groups (by phosphatases)
Second Messenger
a molecule that serves as an intermediate between the receptor and the cascade of responses after
Key for Regulation?
second messenger
Opening of Ion Channels
changing the balance of ion concentration inside and outside of cell
Alternations in Gene Expression
genes may be switched on (unregulated) or off (regulated)
Response Example
alternation of enzyme activities