Download Wednesday, September 20, 2006

Target VII
Identify and describe the functions of the
component structures of the plasma
membrane: phospholipid, integral protein,
peripheral protein, cholesterol, hydrophilic
head (polar), hydrophobic tails (nonpolar), glycolipids, and glycoproteins.
The Cell Membrane
• Composed of macromolecules: phospholipids,
proteins, and carbohydrates
• Is selectively permeable . . .
• Phospholipid bilayer is amphipathic
– Hydrophobic hydrocarbon tails
– Hydrophilic phosphate heads
• Structure and movement of cell membrane is
described as the FLUID MOSAIC MODEL
I. FLUIDITY of Membrane
A. Lipids and proteins move laterally within the membrane
B. Fluidity depends upon a variety of factors:
1. Type of hydrocarbon tails
2. Temperature
3. Presence of cholesterol
4. Composition of lipids and proteins within the
membrane (dynamic)
5. Whether membrane components are attached to ECM
or cytoskeleton
I. FLUIDITY of Membrane
C. Proper functioning of membrane depends upon
membrane fluidity
D. Fluidity can be altered by changing composition and
quantity of proteins and/or lipids within membrane
-->Adaptations of plants and smaller vertebrates to
cold temperatures in winter
II. Mosaic:assortment of various proteins w/in membrane
A. PROTEINS determine function(s) of membrane
1. Integral Proteins
*transmembrane protein
*describe the domain (portion) of the protein that
is embedded within the membrane
2. Peripheral Proteins
*If inside cell, held in place by cytoskeleton
*If outside cell, held in place by Extracellular
matrix (ECM)
3. One protein may have multiple functions OR
several different proteins are required in a
membrane to accomplish cellular tasks
Hydrophobic/philic Domains
II. Mosaic:assortment of various proteins w/in membrane
B. Carbohydrates are located on the exterior surface of
plasma membrane
1. Cells communicate with and recognize each other
by the types of CHO on their exterior plasma
membrane surface (ex: A, B, O blood types)
2. Oligosaccharides may be bound to lipids or
proteins (oligo- = Few; ~15 monosaccharides)
a. Glycolipid
b. Glycoprotein
Target VIII
Use representations, models, and/or data
to analyze situations in which molecules
move passively by diffusion, osmosis, or
facilitated diffusion.
III. Movement Across Membranes
A. Membrane is selectively permeable
1. What does selectively permeable mean?
2. Name examples of molecules that CAN pass thru cell
membrane… WHY can they pass thru?
3. Name examples of molecules that CANNOT pass thru
c.m WHY can’t they?
B. Functions of membrane proteins
1. Transport: water, ions, glucose
2. Enzyme Activity: cellular respiration, photosynthesis
3. Signal Transduction: bind protein hormone
4. Intercellular joining: tight &/or gap junctions, desmsomes
5. Cell to Cell Recognition: glycoproteins
6. Attach cell to ECM and/or cytoskeleton
C. All transport proteins must be ________, because….
Membrane Protein Functions
IV. Passive Transport
A. Movement of molecules down concentration gradient; from
high [ ] to low [ ]
B. Membrane must be permeable for molecules to diffuse
C. Once equilibrium is reached, NET molecular movement is
EQUAL both into and out of cell
**molecules DO NOT stop moving**
D. Diffusion HAPPENS (no energy required!)
E. Diffusion of one type of molecule occurs independent of
another molecule if they’re both permeable; direction of
diffusion for each molecule depends upon [ ] of a particular
molecule across membrane
F. Can be: Diffusion, Facilitated Diffusion, Osmosis
V. Facilitated Diffusion
A. ‘Help’ polar and charged molecules across membrane
thru transport (integral) proteins
1. Recall transport proteins are specific to molecules
they move (like enzyme/substrate specificity)
2. Transport proteins can be saturated therefore, they
have a maximum rate of moving stuff due to limited
# of proteins within membrane
3. Transport proteins can be inhibited
4. ‘Catalyze’ physical movement of stuff that would not
be able to cross membrane
B. Molecules move down concentration gradient
C. AQUAPORINS: transport protein for water
D. GATED CHANNELS: stimulus (electrical or chemical),
cause opening & closing
--> stimulus causes change of protein shape
V. Facilitated Diffusion
E. Examples of gated channels:
 Ligand-gated
 Voltage-gated
 Mechanically-gated
VI. Osmosis (a type of passive transport)
A. Movement of WATER from high [water] to low [water]
B. Water follows solutes… water moves from area of low
[solute] to area of high [solutes]
C. Direction of water movement depends upon [ ] of water and
solutes across a membrane between a cell and solution
(environment)
D. Osmosis and Cells
Animal Cell
Plant Cell
Plant & Animal Cell Osmosis Review
A. hypotonic solution
-->low [solute] in solution compared to cell
animal cell: lysed L
plant cell: turgid J
B. HYPERTONIC solution:
-->high [solute] in solutionn compared to cell
animal cell: crenate L
plant cell: plasmolysed L
C. ISOTONIC solution: =[solute] in solution & cell
animal cell: normal J
plant cell: flaccid K
Osmosis
VI. Osmosis
Water balance for Osmoregulators
1. In cells WITHOUT cell walls (animals, protists)
•MUST control amount of water entering and leaving cell
if not in an environment that is isotonic to cell =
osmoregulate
•Osmoregulators use ENERGY to maintain internal
osmotic balance different from the surrounding
environment
•example: Paramecium contractile vacuole
-->The pond in which the Paramecium lives is ______
to the cell, so water moves ______ and cell has to use
energy to pump water ______ the cell
Paramecium Contractile
Vacuole
VI. Osmosis
Water balance for Osmoregulators
2. In cells WITH cell walls (plants, fungi, bacteria)
•Cells prefer to be in a HYPOTONIC solution
because water enters cells and pressure of extra
water in vacuole pushes against cell walls.
•The water pressure in the vacuole is exterted onto
and by nearby cells which makes cells TURGID very firm so plant structures (stems, leaves) stand
upright :)
•In isotonic solution cells lack adequate ‘push’ from
water in nearby cells…FLACCID-plants wilt, droop:|
•In hypertonic solution, cell wall NOT an advantage,
cell shrinks and plasma membrane pulls away from
cell wall…PLASMOLYSIS - lethal to cell :(
Target IX
Use representations, models, and/or data
to analyze situations in which molecules
move actively to establish concentration
gradients across a membrane or move
large molecules into or out of a cell
(endocytosis and exocytosis).
Co-Transport
VII. CO-TRANSPORT
(active transport)
SYMPORT (Active, Indirect) ANTIPORT (Active, Direct)
Hyperlink to Animation
How do macromolecules enter
or exit cells?
How do large quantities of
substances enter or exit cells?
There are FOUR ways!
IIX. EXOCYTOSIS
A. Secrete large molecules out of cell
B. Cellular vesicles fuse with plasma membrane
C. Process of fusion repairs / replaces cell membrane
D. Process deposits proteins from inside surface of
vessicle membrane to outer surface of cell membrane
b/c vesicle turned inside out as it becomes part of
plasma membrane
E. Therefore, exocytosis ensures the plasma membrane
will display its characteristic CELL SURFACE proteins
which dictate membrane function
IX. ENDOCYTOSIS
A. Phagocytosis: cell eating
More animations
B. Pinocytosis: cell drinking
Another animation of pinocytosis
X. Receptor Mediated Endocytosis
-->Intake of specific molecules, regardless of their
concentration, due to specificity and affinity of ligand
(binding molecule) to it’s ligand-receptor protein on cell
surface
-->Example Animation: Cholesterol Metabolism
X. Receptor-Mediated Endocytosis