Membranes and Transport
Cells!
Smallest cell: Mycoplasma (0.2 μm)
Largest cell: Ostrich egg (45 cm)
Giant amoeba: Chaos chaos (1000
μm)
Most between 5 and 50 μm
Cells!
Three basic structures common to
all cells:
Membrane
Cytoplasm
Ribosome
Cell Membrane
Regulates material movement into
and out of cell
Helps protect and support
Fluid Mosaic Model of cell
Fluid Mosaic Membrane
Phospholipid bilayer
Individual molecules:
Phospholipids
Lipids can be saturated or
unsaturated
Fluid Mosaic Membrane
Stuck to surface of bilayer, but can
move between surfaces
Form channels to allow free (or
mostly free) movement of
molecules
Act as pumps to force materials
from one side of membrane to the
other
Fluid Mosaic Membrane
Carbohydrates
Attached to lipids, proteins, or both
Signaling and identification
molecules
E.G. MHC
Movement of Materials
All cells exist in a liquid
environment
Most organisms use blood or some
similar fluid
Blood has similar solute
concentration and osmotic pressure
to cells
Movement of Materials
Concentrations in cells
Hypertonic
More solutes in water than cell
Hypotonic
More solutes in cell than water
Isotonic
Equal concentration in cells/water
Types of Movement
Passive transport: Movement that
does not require energy
Cannot work against concentration
gradient
Active transport: Movement that
does require energy
Can work against concentration
Diffusion
Molecules move from high
concentration to low concentration
No energy required
Will continue until isotonicity is
reached
Permeable, impermeable,
selectively permeable
Facilitated Diffusion
Passive
Carrier proteins move molecules
across the membrane without use
of energy
Used for molecules that don’t easily
pass through membrane
E.X.: Red blood cells have glucose
transport protein
Facilitated Diffusion
Specific, quick
Aquaporin: transport water
Osmotic pressure has to be
maintained, since cells have high
concentrations of sugars, proteins,
etc
Active Transport
Requires energy to move materials
against a concentration gradient
Two types: Molecular transport and
bulk transport
Molecular Transport
Molecular transport
Move individual macromolecules
All cells transport at least a few
things in this way
Bulk Transport
Need large amounts of specific
molecules
Can bring then in all at once
Endocytosis
Engulfing materials in pockets of
cell membrane
Phagocytosis: solid particles
Pinocytosis: liquids
Exocytosis
Sending materials out of cells
Contractile vacuole: attaches to
membrane to send large amounts
of water out of cell