Transcript Cell Transport - pdecandia.com

CELLS AND THEIR
ENVIRONMENT
Types of cell transport
I.
Passive transport
Movement of molecules of a solute from areas of
high to low concentration without the use of energy
Types of Passive Transport
1.
diffusion:
- movement of molecules of a solute from areas of
high to low concentration (down a concentration
gradient) until equilibrium is reached
- equilibrium: steady state where equal numbers of
molecules move in each direction
- concentration gradient: differences in concentration
of a substance across a space
animation
Diffusion through gated ion channels
•
ion channel: transport protein that
span the thickness of the membrane
with a polar pore through which ions can
pass
- influenced by ions charge – the more
negative the charge, more likely to
move out and vice versa
- some gates always open
- ions can’t move through non polar
interior of lipid bilayer
- allows ion to move thru membrane
without touching non polar lipid interior
- form of passive transport: ions move
down concentration gradient
- some gates stimulated by :
electrical charge
stretching of membrane
binding of specific molecules
2. Osmosis
movement of water from areas of high to low concentration until
equilibrium is reached
- direction of movement depends on
CONCENTRATION OF WATER
on either side of the concentration
gradient
animation
Types of osmotic solutions
- hyptonic
- hypertonic
- isotonic
- indicates relative
concentration of two
solutions being
compared
Osmotic pressure
force caused by osmosis
Results of water transport
in and out of cells:
Animal Cells
Hypertonic: crenation
Hypotonic: cytolysis
Plant cells
Hypertonic: plasmolysis
Hypotonic: turgor pressure
Plant cell adaptations:
Cell wall: limits amount
of water into cell
Contractile vacuole:
rhythmically pumps
water out of cell
(unicellular org.)
Osmosis interactive animation
animation
3. facilitated diffusion
- movement of a substance from areas of
high to low concentration with the aid of
a carrier protein (driven by diffusion)
-
type of passive transport
ex: glucose or amino acids into a
RBC
Steps of Facilitated Diffusion
1.
carrier protein binds a specific molecule on one side of membrane
2.
change in shape of carrier protein exposes one molecule to other
3.
carrier protein shields the molecule from interior of lipid bilayer
4.
molecule is released from carrier protein which goes back to
original shape
II. Active transport
• movement of substances through a membrane against (up) a
concentration gradient
• requires energy (from ATP)
2 types active transport
1. membrane pumps
- involves carrier proteins which act as pumps
- ions in lower concentration bind to carrier protein and
are released to areas of higher concentration (Ca+,
K+, Na+, others)
Sodium Potassium Pump
1.
three Na+ INSIDE cell bind to Na/K pump
(phosphate group is broken off ATP and binds to pump to give pump
energy)
2.
pump changes shape and transports three Na across cell membrane
and releases them OUTSIDE cell
Sodium Potassium Pump
3.
pump now exposed on the surface of cell so two K+ which are on
OUTSIDE bind to pump (phosphate group released changing
shape of pump)
4. pump again exposed to inside of cell so two K+ are transported
across membrane and are released INSIDE cell
http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/
ion_pump/ionpump.html
- this process creates and electrical gradient across
cell membrane
Outside + + + + + + + + + + + + + + + + + +
membrane
Inside
( like + and - terminals on battery)
___________________________
--------------- ----------
Why important:
- animal cells must have higher concentration of Na OUTSIDE
cell, and higher concentration K inside cell in order to
function properly (nerve impulse conduction)
- prevents accumulation of Na+ inside cell which would cause
water to move in and expand or burst cell
2. endocytosis/exocytosis
Endocytosis
process where cells engulf substances too large to enter by
passing through membrane
Types
- phagocytosis: cells engulf solid particles too large to pass
thru membrane
- pinocytosis: cells engulf liquid substances
Exocytosis
process of removing large substances out of cell
(opposite mechanism of endocytosis)
Ex: cells manufacture proteins –
vesicles fuse with cell membrane and dump contents out of
cell
- removal of cell debris, bacteria/viruses, old organelles
animation
Cellular communication
• Cells must communicate with each other to coordinate your growth,
metabolism, and other activities
Ex: hormones – made in one part of the body and carried to
other parts where they perform their function
• Involves signal molecules that are bound by receptor proteins on
receiving cells
Receptor protein: membrane protein (embedded in lipid
layer) that binds to a specific signal
molecule
- enables cell to respond to signal molecule
• Function: changes receiving cell’s activity
Results of cell communication
1. enables specific ions to cross cell membrane
- by changing permeability in receiving cell ion
channels open allowing specific molecules to pass
Ex: this type receptor protein found in nervous system
2. causes formation of a second messenger
- amplifies signal of first messenger
(original signal molecule)
- results: activates enzyme, changes permeability
of membrane opening ion channels
3. speeds up chemical reactions inside cell
- receptor protein acts as enzyme
- may activate other enzymes located inside cell or
membrane
Ex: some drugs affect binding of signal
molecules to receptor proteins
- heroin
- beta blockers
CELL COMMUNICATION
SIGNAL TRANSDUCTION
Signal transduction video
HIV and Receptor Proteins
- initially HIV will only affect macrophages because a
second receptor protein is needed to bring it into cell
- lympohcytes lack this second receptor protein
- as HIV grows and spreads to other macrophages, it
undergoes genetic changes and no longer needs second
protein receptor
- will then attack to lymphocytes (WBC, immune)
eventually will destroy body’s lymphocytes and ultimately
cause death because body can no
longer fight off infections
Study for the test !!!!