1) Name the major molecules that make up the cell membrane. How thick is the membrane?

2) How does the fluid mosaic model proposed by Singer & Nicholson (1972) compare with the Daveson & Danielli (1935) model?

3) Briefly explain how the membrane remains fluidic in lower temperatures?

4) What did the freeze fracture process and electron microscope reveal about the membrane?

5) How does cholesterol act as a “buffer” for the membrane? How does a hypotonic solution differ from a hypertonic solution?

5) What are the three forms of endocytosis? Explain how they are different.

Amphipathic Lipids~ hydrophobic & hydrophilic regions

Singer-Nicholson:

fluid mosaic modelproposed in 1972

(Current model)

The Phospholipid Bilayer

Figure 5.11B

Hydrophilicheads

Hydrophobictails

Water

Water

The heads face outward and the tails face inward In water, phospholipids form a stable bilayer

Approx. 10 nm thickPhospholipid Bilayer

-Amphipathic molecules-Saturated and Unsaturated lipids

Proteins: integral &* peripheralCholesterol

-acts as a buffer-increases membrane integrity-increases fluidity

Membranes organize the chemical reactions making up metabolism

Cytoplasm

Figure 5.10

They control the flow of substances into and out of a cell Membranes are selectively permeable

**Small, Nonpolar molecules easily pass through the membrane: O2, CO2, H2O, Hormones, Steroids

**Large, Charged do not pass through easily and must be

helped in. These molecules would include:

C6H12O6 , Proteins, and Ions

Membranes regulate chemical reactions and can hold teams of enzymes that function in metabolism

Phospholipids are the main structural components of membranes

They each have a hydrophilic head and two hydrophobic tails

Head

Hydrophobic tail

Hydrophilic head

Phospholipids~ membrane fluidity

Cholesterol~ membrane stabilization

“Mosaic” Structure~

Integral proteins~ transmembrane proteins

Peripheral proteins~ surface of membrane

Membrane carbohydrates ~ cell to cell recognition; oligosaccharides (cell markers); glycolipids; glycoproteins

David Frye & Micheal Edin (1970)

To function properly: Lipids must be in a state of optimal fluidity Too much fluidity weakens the membrane

-not enough cholesterol-too many unsaturated phospholipids

Also, the membrane cannot be too rigid because transport through the membrane is inhibited

Temperature changes can severely effect the membrane. HOW?

Proteins: Six Major Functions Observed- Pg. 128

A

B

C,D

FG

G

See Pgs. 204-210 (Ch. 11- Cell Communication)

Begins w/ signaling molecule called a Ligand Ligands-examples are hormones & proteins

Involves several proteins: Receptor (1st messenger) binds w/the ligand Protein Kinases: an enzyme that transfers

phosphate groups from ATP to a protein (uses ATP & moves phosphates)

G proteins & Adenylyl cyclase Cyclic AMP: 2nd messengers

• Lateral Transfer of Information Across the Membrane

Figure 5.13

Ligand

Receptor

Enzymatic Rxns

G Protein

Adenylyl Cyclase

2nd messenger cAMP

In passive transport, substances diffuse through membranes without work by the cell They spread from

areas of high concentration to areas of lower concentration

EQUILIBRIUMMolecule of dye

Figure 5.14A & B

Membrane

EQUILIBRIUM

Diffusion~ tendency of molecules to move from

areas of high concentration to areas of low. Concentration gradient

Passive transport~ diffusion of a substance across a biological membrane

Osmosis~ the diffusion of water across a selectively permeable membrane

Osmosis is the passive transport of water

• In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration

Hypotonicsolution

Figure 5.15

Solutemolecule

HYPOTONIC SOLUTION

Hypertonic solution

Selectivelypermeablemembrane

HYPERTONIC SOLUTION

Selectivelypermeablemembrane

NET FLOW OF WATER

Solute molecule with cluster of water molecules

Water molecule

Two Models of Facilitated Diffusion

Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution The control of water balance

(osmoregulation) is essential for organismsISOTONIC SOLUTION

Figure 5.16

HYPOTONIC SOLUTION

HYPERTONIC SOLUTION

(1) Normal

(4) Flaccid

(2) Lysing

(5) Turgid

(3) Shriveled

(6) Shriveled

ANIMALCELL

PLANTCELL

Plasmamembrane

Osmosis and Animal Cells

CRENATION WILL LYSENO CHANGE

OSMOSIS AND ANIMAL CELLS

The role of contractile vacuole in protists

HYPERTONIC SOLUTION= PLASMOLYSIS

HYPOTONIC SOLUTION= NORMAL TURGOR PRESSURE

OSMOSIS IN PLANT CELLS (Elodea)

Plasmolyzed cells

Active Transport (Pg. 135)

• Active transport in two solutes across a membrane

Figure 5.18

Transportprotein

1

FLUIDOUTSIDECELL

Firstsolute

First solute, inside cell, binds to protein

Phosphorylated transport protein

2 ATP transfers phosphate to protein

3 Protein releases solute outside cell

4 Second solute binds to protein

Second solute

5 Phosphate detaches from protein

6 Protein releases second solute into cell

Utilizes ATP and a protein

Moves substances against the concentration gradient

(Low to High)

Typical example is: Na/K pump(Observed in nerve

cells)

Membrane potential: a charge difference across the membrane

Most commonly seen in nerve cells (sodium & potassium pump) – see pg 135

Achieved through actively pumping ions on one side of the membrane. (Na+ and K+)

All cells have a potential with a slight negative charge on the inside a positive charge on the outside. Why???

Transport proteins Facilitated diffusion~

passage of molecules and ions with transport proteins across a membrane down the concentration gradient

Active transport~ movement of a substance against its concentration gradient with the help of cellular energy

1) Name the major molecules that make up the cell membrane. How thick is the membrane?

2) How does the fluid mosaic model proposed by Singer & Nicholson (1972) compare with the Daveson & Danielli (1935) model?

3) Briefly explain how the membrane remains fluidic in lower temperatures?

4) What did the freeze fracture process and electron microscope reveal about the membrane?

5) How does cholesterol act as a “buffer” for the membrane? How does a hypotonic solution differ from a hypertonic solution?

5) What are the three forms of endocytosis? Explain how they are different.

1) What did the freeze fracture process and electron microscope reveal about the membrane?

2) How is diffusion different from facilitative diffusion?

3) Name some factors that can affect diffusion rates of molecules.

4) Name the ions used to show how active transport works in a the cell membrane. What role does ATP play during this process?

5) What is the charge range difference across the membrane? Which side is positive and which side is negative?

Osmoregulation~ control of water balance

Hypertonic~ higher concentration of solutes

Hypotonic~ lower concentration of solutes

Isotonic~ equal concentrations of solutes

Cells with Walls: Turgid (very firm) Flaccid (limp) Plasmolysis~ plasma

membrane pulls away from cell wall

Endocytosis~ import of macromolecules by forming new vesicles with the plasma membrane

•phagocytosis•pinocytosis•receptor-mediated

Exocytosis~ secretion of macromolecules by the fusion of vesicles with the plasma membrane

To move large molecules or particles through a membrane a vesicle may fuse with the membrane and expel

its contents

Figure 5.19A

FLUID OUTSIDE CELL

CYTOPLASM

or the membrane may fold inward, trapping material from the outside (endocytosis)

Figure 5.19B

ENDOCYTOSIS

Three Types of Endocytosis

Three kinds of endocytosis

Figure 5.19C

Pseudopod of amoeba

Food being ingested

Plasma membrane

Material bound to receptor proteins

PIT

Cytoplasm

EXAMPLES OF ENDOCYTOSIS

Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors

Figure 5.20

LDL PARTICLEPhospholipid outer layer

Protein

Cholesterol

Plasma membraneCYTOPLASM

Receptor protein

Vesicle

CHOLESTEROL

The plasma membrane of an animal cell

Fibers of the extracellular matrix

Figure 5.12

Glycoprotein Carbohydrate (of glycoprotein)

Microfilaments of the cytoskeleton

Phospholipid

Cholesterol

Proteins

CYTOPLASM

Glycolipid

1) What did the freeze fracture process and electron microscope reveal about the membrane?

2) How is diffusion different from facilitative diffusion?

3) Name some factors that can affect diffusion rates of molecules.

4) Name the ions used to show how active transport works in a the cell membrane. What role does ATP play during this process?

5) What is the charge range difference across the membrane? Which side is positive and which side is negative?

6) Name the three types of endocytosis observed in cells. (pg. 138)

Introductory Questions #41) Name the major molecules that make up the cell

membrane. How thick is the membrane? 2) How does the fluid mosaic model proposed by Singer &

Nicholson (1972) compare with the Daveson & Danielli (1935) model?

3) Briefly explain how the membrane remains fluidic in lower temperatures?

4) What did the freeze fracture process and electron microscope reveal about the membrane?

5) How does cholesterol act as a “buffer” for the membrane? How does a hypotonic solution differ from a hypertonic solution?

5) What are the three forms of endocytosis? Explain how they are different.