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 liquid6. Glycoproteins…protein with attached sugar on outside of membrane. Glycolipid…lipid with attached sugar on outside of membrane.

Collagen

Fibronectin

Integrin

Hibernation animals increase cholesterol production

D. Proteins give the membrane function1. Made in the rough ER2. 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 matrix3. 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 function1. Made in the rough ER2. 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 matrix3. 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?

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)

Question: How do materials get across a membrane

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

GFP labeled Aquaporins

3. Aquaporins

a. newly found channels for osmosis

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

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K. Active Transport

1. Definition

2. Against the concentration gradient.

3. Steps: (see picture)

4. Examples:a. Na+- K+ pumpb. 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

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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

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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.