Download plasma membrane - Citrus College

PLASMA MEMBRANE
Plasma Membrane
•
•
•
•
Boundary that separates the living cell from
it’s non-living surroundings.
Phospholipid bilayer
Amphipathic - having both:
hydrophilic heads
hydrophobic tails
Phospholipid
~8 nm thick
Plasma Membrane - cont.
• Controls traffic into and out of the cell with
phospholipids and transport proteins.
• Selectively permeable
Transport protein
Selective Permeability
• The property of biological membranes
which allows some substances to cross more
easily than others.
Fluid Mosaic
• 1972 - Singer and Nicolson called the
membrane a “Fluid Mosaic Model”.
• Mosaic: different proteins embedded in
the phospholipids.
• Fluid:
proteins and phospholipids can
move freely in the membrane.
Fluid Mosaic - cont.
• Components of a phospholipid bilayer.
1.
2.
3.
4.
5.
6.
phospholipids
proteins - enzymes, receptors, transport.
glycolipids
glycoproteins
carbohydrates
cholesterol
Transport Proteins
• Transports molecules or ions across
biological membranes
• 3 types of transport proteins:
proteins
1. uniport
2. symport
3. antiport
Uniport Transport Protein
• Carries a single solute across the membrane.
extracellular
fluid
intracellular
fluid
Symport Transport Protein
• Translocate 2 different solutes simultaneously
in same direction.
extracellular
fluid
intracellular
fluid
Antiport Transport Protein
• Exchanges 2 solutes by transporting them in
opposite directions.
directions
extracellular
fluid
intracellular
fluid
Diffusion
• The net movement of a substance (molecules)
down a concentration gradient from an area of
high concentration to an area of low
concentration.
concentration
• passive transport: NO energy is expended.
• facilitated diffusion: type of passive transport
which uses transport proteins.
Osmosis
• The movement of water across selectively
permeable membranes.
membranes
• The water moves from a high concentration
to low concentration.
concentration
Question:
What’s in a Solution?
Answer:
• solute +
solvent →
• NaCl
H20
+
→
solution
saltwater
Hypertonic
• A solution with a greater solute
concentration compared to another solution.
solution
3% NaCl
97% H2O
Red Blood Cell
solution
5% NaCl
95% H2O
Hypotonic
• A solution with a lower solute concentration
compared to another solution.
solution
3% Na
97% H2O
Red Blood Cell
solution
1% Na
99% H2O
Isotonic
• A solution with an equal solute concentration
compared to another solution.
solution
3% Na
97% H2O
Red Blood Cell
solution
3% Na
97% H2O
Movement of H2O
• Water will “ALWAYS” diffuses down a
concentration gradient from a HYPOTONIC
solution to a HYPERTONIC solution.
solution
“ALWAYS REMEMBER”
• HYPOTONIC →
HYPERTONIC
Animal Cells
• Animal cells placed into a hypotonic solution
will HEMOLYSIS (EXPLODE).
• Animal cells placed into a hypertonic solution
will CRENATE (SHRIVEL).
Hemolysis
Crenation
Red
Blood
Cells
Plant Cells
• Firmness or tension (vacuole full) that is found
in plant cells (cell wall) that are in a hypotonic
environment is called TURGID.
• This process is called TURGOR PRESSURE.
Water
Cell
Wall
Water
Central
Vacuole
Water
Plant Cells
• When the plasma membrane pulls away from
the cell wall (vacuole empty) in a hypertonic
environment (loss of water) is called
PLASMOLYSIS.
PLASMOLYSIS
Water
Water
plasma membrane
Cell
Wall
Water
Active Transport
• The movement of molecules (small or large)
across the plasma membrane in which energy
(ATP) is required.
required
• Examples:
1.
2.
3.
Sodium (Na) - Potassium (K) Pump
Exocytosis
Endocytosis
Sodium-Potassium Pump
• The mechanism that uses energy (active transport)
released from splitting ATP to transport Sodium
(Na+) out of and Potassium (K+) into cells.
extracellular
fluid
intracellular
fluid
K+
K+
Na+
Na+
Question:
• How are large molecules transported into
and out of the plasma membranes?
Answer:
• Exocytosis and Endocytosis
Exocytosis
• Cell secretes macromolecules (proteins and
other biochemicals) out of cell.
• Part of the Endomembrane System: the
fusion of transport vesicles with plasma
membrane.
Endocytosis
• The energy requiring movement of particles
(foreign or natural) into the cell.
• 3 types of endocytosis:
A. Phagocytosis
B. Pinocytosis
C. Receptor-mediated endocytosis
A. Phagocytosis
• Cell eating: cells engulf particles with
pseudopodia and pinches off a food
vacuole.
Bacteria
• Two examples:
1. White Blood Cell
2. Amoeba
Food
Vacuole
White Blood Cell
B. Pinocytosis
• Cell drinking: droplets of extracellular fluid
are absorbed into the cell by small vesicles.
vesicles
• Example:
1. Fungi
Hyphae
Food Particles
C. Receptor-Mediated Endocytosis
• Importing specific macromolecules (hormones)
into the cell by the inward budding of vesicles
formed from coated pits (receptors).
Liver Cell
Hormones
Receptors