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The Plasma Membrane
Chapter 5
(pgs 99-110)
Plasma Membrane
Plasma membrane is a loose, lipid
structure
Fluid-mosaic model
Functions of the Plasma Membrane
Isolates the outside of the cell from the
environment
Controls what enters and leaves the cell
therefore, it’s a semi-permeable membrane
Selective as to what enters the cell and the
direction molecules travel
Plasma Membrane is made up of:
Phospholipid bilayer
two-layers of phospholipids
fluid in nature
hydrophobic and other small
molecules can pass through
Contains proteins
structural support, signaling
or communication, recognition,
passage or transport
2 types:
Integral = span the membrane
Peripheral = on surface
Plasma Membrane is made up of:
Contains cholesterol
between phospholipid molecules
used for “patching” so small
molecules can’t get through
helps keep optimum fliudity
Glycocalyx
short branched carbohydrate
extensions coming off of
proteins
used as binding sites for
signaling molecules
General Movement of Molecules
1. Diffusion: movement from high concentration
to lower concentration
Ex. Glass of water and you add red dye
Occurs with odors; occurs in plants
Movement of Molecules
1. Diffusion: movement from high concentration
to lower concentration
Ex. Glass of water and you add red dye
Occurs with odors; occurs in plants
2. Osmosis: movement of water across a semipermeable membrane from low concentration
to high concentration
Yes, it is going against gravity!
Ex. When a plant wilts; why preservatives are put
into food products; how the fluid part of blood is
put back into your blood vessels
Osmosis
1. Hypertonic solution: greater concentration of
solutes (ex. salts) outside the cell than inside
the cell
So water moves out of the cell and the cell shrinks
Ex. Egg in syrup
2. Isotonic solution: solute concentration inside
and outside the cell are equal
Ex. Egg
3. Hypotonic solution: greater concentration of
solutes inside the cell than outside the cell
So water moves into the cell and the cell expands
Ex. Egg in vinegar
Movement of Small Molecules in Cells
1. Passive transport
A. Simple diffusion: diffuses through a
membrane from high concentration to low
concentration; no energy required
Ex. How oxygen and carbon dioxide get
into and out of our cells
“Smelly balloons”
demo!
Movement of Small Molecules in Cells
1. Passive transport
A. Simple diffusion: diffuses through a
membrane from high concentration to low
concentration
Ex. How oxygen and carbon dioxide get into and
out of our cells
B. Facilitated diffusion: movement from
high concentration to low concentration
through a membrane with the help of a
protein; no energy required
Example of facilitated diffusion
Low Concentration
Molecules randomly move
through the integral protein
Molecules move from an
area of high concentration to
an area of low concentration
High Concentration
Example of facilitated diffusion
Molecules randomly move
through an integral protein
Molecules move from an
area of high concentration to
an area of low concentration
(Animation by Jim Sullivan)
Example of facilitated diffusion
Low Concentration
Peripheral proteins don’t extend
through the membrane
Proteins bind and drag the
molecules through the lipid
bilayer and releases the
molecules on the opposite side
High Concentration
Example of facilitated diffusion
Peripheral proteins don’t extend
through the membrane
Proteins bind and drag the
molecules through the lipid
bilayer and releases the
molecules on the opposite side
(Animation by Jim Sullivan)
Movement of Small Molecules in Cells
1. Passive transport
A. Simple diffusion
B. Facilitated diffusion
2. Active transport:
movement through a transport protein
movement against a concentration gradient
requires energy = ATP
Low
Ex. Storage of glucose
in the liver
Ex. Sodium-potassium pump
Conc.
High
Conc.
Movement of Large Molecules in Cells
1. Exocytosis: movement out of a cell through the
formation of a vesicle
Ex. proteins; the release of digestive enzymes;
mucus
Movement of Large Molecules in Cells
1. Exocytosis: movement out of a cell through the
formation of a vesicle
Ex. Proteins; digestive enzymes; mucus
2. Endocytosis: movement into a cell
Types of Endocytosis
1. Pinocytosis:
“cell-drinking” because its bringing into the
cell fluids with materials suspended in it
Ex. Movement of blood
Types of Endocytosis
3. Phagocytosis:
“cell-eating” because it brings into the cell
large materials
Ex. Bacteria; cell debris
Types of Endocytosis
2. Receptor-mediated endocytosis:
specialized cell surface receptors bind to
molecules and pulls it into the cell
Ex. Transport of iron
Plant cells:
Cell wall: maintains structure;
protection from environment;
limits water absorption
Central vacuole: storage of
nutrients; gets rid of waste
products; maintains pH;
enzymes for digestion;
contains pigments
Plastids: storages nutrients;
contains pigments; needed for
photosynthesis (chloroplast)
Amyloplast: makes starch
Do not contain lysosomes…in
animals only!!!