Download Cell boundaries

Cell boundaries
Objectives:
1. Describe the functions of the cell
membrane and cell wall.
2. Describe the process that occurs during
diffusion.
3. Discuss how osmosis is a form of
diffusion.
4. Explain the processes of facilitated
diffusion and active transport.
5. Differentiate between endocytosis and
exoctyosis.
Cell membrane (plasma membrane)
 Lipid bilayer = double layer sheets of
phospholipids
 Phosphate group (PO4-3) attached to a
diglyceride
 Hydrophilic head on the outside and
hydrophobic tails on inside
 Hydrophobic tails no association with
water or charged molecules; lipid
soluble molecules, oxygen gas
molecules and carbon dioxide molecules
do pass across the membrane
 Regulates what enters and leaves the cell
while providing protection and support
to the cell
 Membrane proteins – channel proteins
create a channel to allow water, ions to
move across lipid membrane
 Carrier proteins bind and transport
solutes across plasma membrane
may(active transport) or may not need
(facilitated diffusion) ATP
CELL WALLS
 Plants, fungi, algae, and most
prokaryotes
 Provide support and protection
 Allows water, oxygen, carbon dioxide,
other substances to pass across
 Cellulose = fibers of carbohydrate and
protein, cell walls of plants
DIFFUSION
 Cytoplasm = solution of dissolved
solutes in water
 Concentration = amount of solute in a
given volume of water
 Example: 12 grams NaCL in 3 Liters
water  concentration = 4g/L
 Solute particles and water molecules
always moving
 Particles move until at equilibrium
 DIFFUSION = movement of solute
molecules from areas of high
concentration to areas of low
concentration until equilibrium is met
 NO ENERGY REQUIRED
OSMOSIS
 The diffusion of water across cell
membranes
 ISOTONIC = concentration of water and
solute molecules is equal on both sides
of cell membrane : water in equals
water out
 HYPERTONIC = High concentration of
solute molecules than water molecules :
water moves out of cell to achieve
equilibrium – cell shrinks, dies
 HYPOTONIC = lower concentration of
solute molecules than water molecules :
water moves into cell to achieve
equilibrium – cell bursts
 Water will move in the direction of the
concentration gradient
FACILITATED DIFFUSION
 Works with the
concentration gradient
 Simile: you skiing
downhill
 Cell membrane proteins
act as carriers for SPECIFIC
molecules: same principle
as enzyme-substrate
complex
 Binding of molecule to
protein changes the shape
of the protein allowing the
molecule to enter into
cytoplasm
 Cofactors present in
protein transport (just like
in enzyme-substrate
complex)ex: hormones
 facilitated diffusion
 Does not require E
 Works with the
concentration gradient
 Example: RBCcell
membrane
protein(GLUT1)glucose
 cytoplasm
 Glucose can’t diffuse
unless
 Aquaporins: H2O channel
proteins in both plants and
animal cells – facilitate the
MASSIVE amounts of H2O
whereas the polarity of
H2O causes the slow
movement of H2O across
the hydrophobic tails of
membrane
ACTIVE TRANSPORT
 Movement AGAINST
concentration gradient
 Simile: you “skiing”
uphill to retrieve your
“lost”ski
 Requires ENERGY(ATP)
 Transport proteins =
PUMPS
o Small molecules
and ions (Ca+2, Na+,
K+)
o Change in protein
shape – pumps ions
or molecules
AGAINST the
concentration
gradient
o ****Na+/K+ pump
for nerve impulse
o ATPase is the
protein responsible
for Na+/K+ pump –
carries 3Na+ out and
2K+ into cell for each
ATP-> ADP conversion
 Endocytosis
o Large molecules or
clumps of molecules
requires MOVEMENT
of portions of cell
membrane to engulf
molecules
o Infolding – creates
pockets in membrane
o Pinching off of
pocket  vacuole
cytoplasm
o 2 forms of
endocytosis
 Phagocytosisengulf solids
particles
 Very typical of
amoebas
 WBC destroy
bacteria via
phagocytosis
 Requires ENERGY
o Pinocytosis- engulf
liquids
 Same process as
phagocytosis
o EXOCYTOSIS –
reverse of
endocytosis
o Example:
contractile vacuole in
paramecium(protist)