Honors Biology
LIPIDS & CELL MEMBRANES
RECALL: MACROMOLECULES

BIG biological
molecules

Made of smaller
parts
 Monomers

Carbon-based
(organic)
Carbohydrates
 Nucleic acids
 Proteins
 Lipids

LIPIDS

Monomer?
Glycerol head
 Fatty acid tail


Used for:
Long term energy storage
 Insulation
 Major component of
membranes
 Signaling molecules and
hormones


Examples:


Fats, oils, waxes
Found in:

All the good tasting foods
CELL MEMBRANES
CELLULAR BIOLOGY REVIEW
All cells have cell membranes
 Some cells (eukaryotes) have membranes
surrounding organelles

 Example:

nucleus
All cells need to import and export molecules in
order to function properly and maintain
homeostasis
CELL MEMBRANE FUNCTION: HOMEOSTASIS!
1.
2.
3.
4.
Regulate passage of nutrients, wastes, gases, and water into
and out of cell
Selectively permeable – “picky” about what passes
Separate cell from the environment
Allow cells to communicate with other cells via receptors on
the surface
CELL MEMBRANE: FLUID MOSAIC MODEL
STRUCTURE OF THE CELL MEMBRANE

Made of phospholipid bilayer
 Phosphate
(hydrophilic) “head”
 Lipid (hydrophobic) “tail”
Phospholipid bilayer
STRUCTURE OF THE CELL MEMBRANE

Channel protein
 Allow
large molecules to pass through
Protein channels
STRUCTURE OF THE CELL MEMBRANE

Receptor Protein
 Receives
messages from outside the cell
 Cell communication
is key
for homeostasis!
Receptor
Protein
STRUCTURE OF THE CELL MEMBRANE

Cholesterol
 Lipids
that prevent freezing
 Helps membrane remain fluid (flexible) Cholesterol
CELL TRANSPORT: A QUICK REVIEW
 All
cells exist in a liquid environment.
 The cell membrane must keep the cell’s
internal environment constant.
(homeostasis)
 The cell membrane regulates the
movement of molecules in and out of the
cell.
 Insulin maintains homeostasis
https://www.youtube.com/watch?v=OlHez8gwMgw
PASSIVE CELL TRANSPORT
 Passive
transport—the movement of
materials across the cell membrane
without the use of energy
TYPES OF PASSIVE TRANSPORT
Diffusion—the movement of molecules from an
area of high concentration to an area of low
concentration.
 Substances will move toward the area where it
is less concentrated until it is evenly
distributed.
 Equilibrium—When the concentration of a
substance on both sides of the cell membrane
is the same.

DIFFUSION
 The
concentration
gradient is the direction
particles move in order
to reach equilibrium.
The concentration
gradient is always from
high concentrations to
low concentrations.
CONCENTRATION GRADIENT
FACILITATED DIFFUSION
Facilitated diffusion—When molecules are too
large,channel proteins embedded in the cell
membrane facilitate, or help, the diffusion of
specific materials across the cell membrane.
 There are hundreds of different channel
proteins that allow specific substances across
the cell membrane.

Ex: Channel proteins help glucose molecules move
into a cell - they are too big to fit in between the
lipid bilayer
OSMOSIS
Osmosis—The
diffusion of water
through a selectively permeable
membrane.
Water
will move across the
membrane until equilibrium is
reached.
ISOTONIC SOLUTIONS
Isotonic solution—When the concentrations of
water and dissolved material (solute) are the
same on both sides of the membrane.
 Equilibrium has been reached in an isotonic
solution.
 Water will continue to move in both directions
across the membrane but there is no net
movement of water.

HYPERTONIC SOLUTIONS
 Hypertonic
solution—”above
strength” When there is a greater
amount of solute outside of the cell
than inside the cell.
 Water will move out of the cell until
equilibrium is reached.
 Plasmolysis—cell shrinkage due to
water loss
HYPERTONIC SOLUTION DIAGRAM
HYPOTONIC SOLUTIONS
Hypotonic solution—”below strength”
When
there is less solute outside the cell than inside
the cell.
 Water will move into the cell until equilibrium is
reached.
 This can cause an animal cell to swell or even
burst if it is placed in fresh water.
 Plant cells have cell walls, so are not as
vulnerable to bursting.

THE EFFECTS OF OSMOSIS ON CELLS
ACTIVE CELL TRANSPORT

Active transport—the movement of materials
across the cell membrane against the
concentration gradient. Active transport
requires energy.
TYPES OF ACTIVE TRANSPORT
Remember, active transport requires energy. It
involves moving molecules against the
concentration gradient.
 Movement of molecules from low to high
concentrations requires energy.
 2 types of active transport:

 Molecular
(small molecules)
 Bulk (larger molecules or clumps of molecules)
MOLECULAR ACTIVE TRANSPORT
Small molecules and ions are carried across
the cell membrane by protein pumps.
 Much of the cell’s energy is used transporting
molecules from low concentrations to high
concentration.
 This allows cells to concentrate substances in a
particular location and to transport materials
against the concentration gradient.

BULK ACTIVE TRANSPORT: ENDOCYTOSIS

Endocytosis—”into the cell” When a cell takes
in large molecules, clumps of food, or other
cells. The cell membrane folds in on itself,
forming a pocket.
 Phagocytosis—when
a cell takes in food or other
cells
 Pinocytosis—when a cell takes in a large amount of
water by pinching its cell membrane off into
vacuoles
BULK ACTIVE TRANSPORT: EXOCYTOSIS
Exocytosis—”out
of the cell”
When cells release large amounts
of material. The membrane of the
vacuole fuses with the cell
membrane, forcing material out of
the cell.
TYPES OF ACTIVE TRANSPORT DIAGRAM