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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.
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Amphipathic Lipids~ hydrophobic & hydrophilic regions
Singer-Nicholson:
fluid mosaic modelproposed in 1972
(Current model)
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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
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Approx. 10 nm thickPhospholipid Bilayer
-Amphipathic molecules-Saturated and Unsaturated lipids
Proteins: integral &* peripheralCholesterol
-acts as a buffer-increases membrane integrity-increases fluidity
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Membranes organize the chemical reactions making up metabolism
Cytoplasm
Figure 5.10
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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
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Phospholipids are the main structural components of membranes
They each have a hydrophilic head and two hydrophobic tails
Head
Hydrophobic tail
Hydrophilic head
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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
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David Frye & Micheal Edin (1970)
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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?
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Proteins: Six Major Functions Observed- Pg. 128
A
B
C,D
FG
G
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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
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• Lateral Transfer of Information Across the Membrane
Figure 5.13
Ligand
Receptor
Enzymatic Rxns
G Protein
Adenylyl Cyclase
2nd messenger cAMP
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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
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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
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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
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Two Models of Facilitated Diffusion
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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
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Osmosis and Animal Cells
CRENATION WILL LYSENO CHANGE
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OSMOSIS AND ANIMAL CELLS
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The role of contractile vacuole in protists
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HYPERTONIC SOLUTION= PLASMOLYSIS
HYPOTONIC SOLUTION= NORMAL TURGOR PRESSURE
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OSMOSIS IN PLANT CELLS (Elodea)
Plasmolyzed cells
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Active Transport (Pg. 135)
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• 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
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Utilizes ATP and a protein
Moves substances against the concentration gradient
(Low to High)
Typical example is: Na/K pump(Observed in nerve
cells)
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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???
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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
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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.
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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?
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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
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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
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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
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or the membrane may fold inward, trapping material from the outside (endocytosis)
Figure 5.19B
ENDOCYTOSIS
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Three Types of Endocytosis
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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
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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
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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
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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)
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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.