Transcript Chapter 7 - Madeira City Schools

Chapter 7
I. MEMBRANE STRUCTURE AND FUNCTION
A. Membranes organize the chemical activities of cells by allowing
things in and out
1. The plasma membrane exhibits selective permeability--screen
B. Phospholipids
1. Form a bilayer in water.
a. Why they are selectively permeable.
b. Nonpolar molecules
c. Polar molecules
2. Amphipathic molecule
a. the head (glycerol and phosphate) is polar
or hydrophilic.
b. the tail (the fatty acids) are nonpolar
or hydrophobic
C. Read about how Fluid mosaic model
was developed (pg. 126)
C. The fluid mosaic model.
1. Mosaic…
2. Fluid…
a. Refers to the way the lipids and proteins behave in a membrane.
b. Molecules are not bonded together, so are free to shift.
c. Must remain "fluid" for membranes to function.
3. Some proteins are attached to the cytoskeleton and fibers in the extracellular
matrix.
4. Most of the phospholipids have kinked tails…
5. Also contains cholesterol…
a. keeps the membrane from solidifying
b. keeps the membrane from being total liquid
6. Glycoproteins…protein with attached sugar on outside of
membrane.
Glycolipid…lipid with attached sugar on outside of membrane.
Fibronectin
Collagen
Integrin
Hibernation animals increase
cholesterol production
D. Proteins give the membrane function
1. Made in the rough ER
2. Functions of proteins in the membranes
a. Transport
b. Enzymatic activity
c. Signal Transduction (Receptor sites for signals)
d. Intercellular Joining
e. Cell-cell recognition
f. Attachment to cytoskeleton and extracellular matrix
3. Types of membrane proteins
a. Integral - inserted into the lipid bilayer.
b. Peripheral - not embedded in the lipid bilayer, but are
attached to the membrane surface.
How do the integral proteins stick to the membrane?
D. Proteins give the membrane function
1. Made in the rough ER
2. Functions of proteins in the membranes
a. Transport
b. Enzymatic activity
c. Signal Transduction (Receptor sites for signals)
d. Intercellular Joining
e. Cell-cell recognition
f. Attachment to cytoskeleton and extracellular matrix
3. Types of membrane proteins
a. Integral - inserted into the lipid bilayer.
b. Peripheral - not embedded in the lipid bilayer, but are
attached to the membrane surface.
How do the integral proteins stick to the membrane?
By the solubility of their amino acids.
Hydrophilic
Amino Acids
Hydrophobic
Amino Acids
Hydrophilic
Amino Acids
E. Membranes are Bifacial (meaning, there is an inside and outside face)
1. The lipid composition of the two layers is different.
2. The proteins have specific orientations
3. Carbohydrates are found only on the outer surface
a. Branched oligosaccharides form glycolipids and
glycoproteins on external surface.
b. Function - recognition of "self" vs "other”.
Question: On which side of a
vesicle membrane are the
carbohydrates?
Question: How do materials get across a membrane
Answer:
First, there are two problems.
1. The lipid bilayer is hydrophobic. Hydrophilic materials
don’t cross easily.
2. Large molecules don’t cross easily. Too big to get
through membrane.
So…. There are two mechanisms
1. Passive transport (diffusion, osmosis, facilitated
diffusion)
2. Active transport (carrier mediated, endocytosis,
exocytosis)
F. Transport proteins
1. Hydrophilic substances can avoid contact with the lipid
bilayer by passing through these proteins.
2. “Channel Proteins”
a. Aquaporins
3. “Carrier Proteins”
4. These proteins are specific in what they transport.
a. glucose carrier protein is so specific that fructose can’t
even flow through.
5. What determines the direction substances flow?
G. Diffusion: passive transport across a membrane
1. Definition
a. lungs
b. water
2. Passive transport
3. Concentration gradient…
a. 2 or more
substances move
independently of
each other.
b. Solute/Solvent
c. Concentration
4. Equilibrium
5. Factors that Effect Diffusion
a. Concentration
b. Temperature
c. Particle size
d. Mixing
H. Osmosis: passive transport of water
1. Definition
2. Tonicity: the ability of a solution to cause a cell to
gain or lose water
a. Hypertonic
b. Hypotonic
c. Isotonic
3. Aquaporins
a. newly found channels for osmosis
GFP labeled
Aquaporins
I. Osmoregulation
1. Definition
2. Animal cell versus Plant cell (why different?)
a. Flaccid
b. Turgid
c. shriveled and death
J. Facilitated Diffusion (carrier proteins and channel proteins)
1. Two types of channel proteins
a. open hydrophilic channels
b. gated channels (ion channels)
2. If protein not present…
3. Passive transport
4. Rate of diffusion
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
K. Active Transport
1. Definition
2. Against the
concentration gradient.
3. Steps: (see picture)
4. Examples:
a. Na+- K+ pump
b. Electrogenic or H+
pumps (CR & Ps)
c. Cotransport-Movement of H+ that allows
other materials to be
transported into the cell as
the H+ diffuses back across
the cell membrane.
Example - Sucrose transport

QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Cotransport
A “pump” that is powered by ATP builds up a concentration gradient that is
then used by another carrier protein to transport something else. The
energy for the second transport is from the flow of the first substance
down its concentration gradient.
L. Exocytosis and Endocytosis
1. Exo means outside
2. Kytos means cell
3. Exocytosis
4. Endo means inside
5. Endocytosis
Three types:
a. Phagocytosis
b. Pinocytosis
c. Receptor-mediated
endocytosis
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
M. Bad membranes can cause more cholesterol to be in blood.
1. Our liver removes excess cholesterol from our blood.
a. receptor-mediated endocytosis
2. People with high cholesterol either do not have receptors
or have low amounts of protein receptors on the
membrane of liver cells.