Download Movements Through Cell Membranes

Movements Through Cell Membranes
3.3
Rima Smadi
Cell Membrane
 Plasma membrane
 Contains the cell’s content
 Regulates movement of substances in and out of the cell
 Communication
 Selectively permeable membrane
 Phospholipids bilayer
Cell Membrane
Movement
 Passive Mechanism: Does not requires energy
 Diffusion
 Facilitated Diffusion
 Osmosis
 Filtration
 Active Mechanism: Requires energy
 Active transport
 Endocytosis
 Exocytosis
Diffusion
 Process by which molecules or ions scatter or spread
spontaneously from regions where they are in higher
concentrations toward regions where they are in lower a
concentration gradient.
 Equilibrium: uniformly distributed, concentration no longer
changes.
 Diffusion only occurs if:
 Membrane is permeable to the substance
 A concentration gradient exists.
Facilitated Diffusion
 Diffusion of substances that cannot pass through the lipid
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bilayer, need help from membrane proteins.
High to low concentration
Water insoluble substances (ions,) cannot pass through the
inner hydrophobic part of the membrane.
Glucose and amino acids are water soluble, but are too large
to pass through.
Substance attaches to carrier protein, the protein changes
shape to allow the substance to pass through. Then it returns
to its original shape. For example, Insulin helps open the
carrier proteins (change their shape) to let cells take in
glucose.
Osmosis
 Diffusion but only with water molecules.
 High to low concentration.
 In a solution:
 Solute: what is dissolved. (ex. Sugar)
 Solvent: what is doing the dissolving. (ex. Water)
 When solute cannot diffuse, then the solvent diffuse to the
area of higher solute concentration.
 Osmotic pressure: the ability of osmosis to generate enough
pressure to lift a volume of water.
 Water diffuses to an area of higher osmotic pressure.
Osmosis
 Isotonic: any solution that has the same osmotic pressure
as body fluids.
 Hypertonic: solutions with a higher osmotic pressure
than body fluids.
If cell is in this solution, water moves out of cell (shrinks).
 Hypotonic: solution with lower osmotic pressure than
body fluids.
If cell is in this solution, water moves into the cell (swell
up).
Filtration
 Forces molecules through membrane.
 Hydrostatic pressure: created by the weight of due to gravity,
forces water molecules through to the other side.
 Occurs in blood vesicles from the pumping of the heart and
in kidneys to cleanse the blood.
 Edema: condition in which excessive water is built up in
tissue, because of failed filtration.
Active Transport
 Process that moves particles through membranes from low to high
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concentration.
Equilibrium is never reached.
Uses specific carrier proteins in the membrane also called pumps.
Uses energy in the form of ATP (Adenosine triphophate)
40% of cell’s energy is used in active transport.
Carrier molecules: proteins with binding sites that combine with
substances and transport them.
Release of energy changes the shape of the protein and transports
the substance.
Molecules include: sugar, amino acids, sodium, potassium,
calcium, and hydrogen ions.
Endocytosis and Exocytose
 Use energy to move substances in and out without having to
cross the membrane.
 Endocytosis: large substances that can’t enter a cell by any of
the previous processes are taken within a vesicle formed
from a section of the cell membrane.
 Exocytosis: a substance that is stored in a vesicle is secreted
by merging the vesicle with the cell membrane and releasing
the substance.
Endocytosis
 Endocytosis happens in 3 ways:
 Pinocytosis: (cell drinking) droplets of liquid are taken in by membrane
when it indents. The open ends seal off, producing a small vesicle . The
vesicle’s membrane then breaks down and the substance is released into
the cytoplasm.
 Phagocytosis : (cell eating) same as pinocytosis but cell takes in solids.
The substance usually attaches to receptors on the membrane then it
indents, and detaches to become a vesicle. Lysosomes attach to the
newly formed vesicle and break down the content. Ex. White blood cells
(phagocytes) that take in solids like bacteria or harmful chemicals
 Receptor-mediated endocytosis: moves very specific kinds of particles
into the cell. Where proteins from within the cell become receptors on
the membrane waiting for specific molecules outside the cell (ligands).