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AP BIO Chapter 7 - Membrane Structure and Function
Cell (plasma) Membrane
Cells need an inside and an outside
Separate cell from its environment
cell membrane is the boundary
Lipids of Cell Membrane
Membrance is made of phospholipids
phospholipid bilayer
Phospholipid Bilayer
What molecules can get through directly?
fats and other lipids can slip directly through the phospholipid cell membrane
Membrane Proteins
Proteins determine most of the membrane’s specific functions
cell membrane and organelle membranes each have unique collections of proteins
Membrane Proteins:
peripheral proteins = loosely bound to surface of membrane
integral proteins = penetrate into lipid bilayer, often completely spanning the membrane = transmembrane proteins
Membrane Protein Types (you do need to know all)
Channel Proteins - wide open passage
Ion channels - gated (opening and closing the space)
Aquaporins - water only, kidney and plant root only
Carrier Protiens - change shape
Transport Proteins - require ATP
Recognition Proteins - glycoproteins
Adhesion Proteins - anchors
Receptor Proteins - hormones
Membrane Carbohydrates
Play a key role in cell-cell recognition
Ability of a cell to distinguish neighboring cells from another
important in organ & tissue development
basis for rejection of foreign cells by immune system
Cholesterol
Provides stability in animal cells
replaced with sterols in plant cells
Getting Through A Cell Membrane
Passive Transport
No energy needed
move down concentration gradient
Non-polar molecules, CO2 and O2
Active Transport
Movement against concentration gradient (low → high)
requires ATP
Diffusion
2nd Law of Thermodynamics
Universe tends towards disorder
Diffusion
movement from high → low concentration
Diffusion of 2 solutes
Each substance diffuses down its own concentration gradient, independent of concentration gradients of other substances
The Special case of water
Osmosis
Movement of water across cell membrance
Concentration of Water
Direction of osmosis is determined by comparing total solute concentrations
Hypertonic - more solute, less water
Hypotonic - less solute, more water
Isotonic - equal solute, equal water
WATER MOVES FROM HYPOTONIC TO HYPERTONIC
Managing Water Balance
Cell survival depends on balancing water uptake and loss
Hypotonicity
animal cell in hypotonic solution will gain water, swell & possibly burst (cytolysis)
Paramecisum vs. Pond Water
Paramecium is hypertonic
H20 continually enters cells
to solve problem, specialized organelle, contractile vacuole
pumps H20 out of cell = ATP
plant cell
turgid (turgor pressure)
cell wall
Hypertonicity
animal cell in hypertonic solution will lose water, shrivel and possibly die
salt water organisms are hypotonic compared to their environment
they have to take up water and pump out salt
plant cells
plasmolysis
Water Potential (ψ)
Water moves from a place of greater water potential to a place of lesser water potential (net.)
As the concentration of a solute increases in a solution, the water potential will decrease accordingly.
Water Potential and Solute Potential
Ψ = Ψp(pressure) + Ψs(solute)
The unit is (-)BARS
Note: the water potential will be equal to the solute potential of a solution in an open container since pressure would be zero
Ψs = -iCRT
i= ionization constant (sucrose = 1.0)
C = molar concentration
R = 0.0831 liter bars/mole K
T = temp in Kelvin (273+C)
Facilitated Diffusion
Move from HIGH to LOW concentration through protein channel
passive transport
no energy needed
facilitated = with help (from proteins)
Gated Channels
Some channel proteins open only in presence of stimulus (signal)
stimulus usually different from transported molecule
ex: ion-gated channels
when neurotransmitters bind to a specific gated channels on a nuearon, these channels open = allow Na+ ions to enter nerve cell
ex: voltage-gated channels
change in electrical charge across nerve cell membrane opens Na+ & K+ channels
Active Transport
Cells may need molecules to move against concentration situation
need to pump against concentration
protein pump
requires energy
ATP
How about large molecules?
Moving large molecules into & out of cell requires ATP!
through vesicles & vacuoles
endocytosis
phagocytosis = “cellular eating”
pinocytosis = “cellular drinking”
receptor-mediated
endocytosis
exocytosis
AP BIO Chapter 7 - Membrane Structure and Function
Cell (plasma) Membrane
Cells need an inside and an outside
Separate cell from its environment
cell membrane is the boundary
Lipids of Cell Membrane
Membrance is made of phospholipids
phospholipid bilayer
Phospholipid Bilayer
What molecules can get through directly?
fats and other lipids can slip directly through the phospholipid cell membrane
Membrane Proteins
Proteins determine most of the membrane’s specific functions
cell membrane and organelle membranes each have unique collections of proteins
Membrane Proteins:
peripheral proteins = loosely bound to surface of membrane
integral proteins = penetrate into lipid bilayer, often completely spanning the membrane = transmembrane proteins
Membrane Protein Types (you do need to know all)
Channel Proteins - wide open passage
Ion channels - gated (opening and closing the space)
Aquaporins - water only, kidney and plant root only
Carrier Protiens - change shape
Transport Proteins - require ATP
Recognition Proteins - glycoproteins
Adhesion Proteins - anchors
Receptor Proteins - hormones
Membrane Carbohydrates
Play a key role in cell-cell recognition
Ability of a cell to distinguish neighboring cells from another
important in organ & tissue development
basis for rejection of foreign cells by immune system
Cholesterol
Provides stability in animal cells
replaced with sterols in plant cells
Getting Through A Cell Membrane
Passive Transport
No energy needed
move down concentration gradient
Non-polar molecules, CO2 and O2
Active Transport
Movement against concentration gradient (low → high)
requires ATP
Diffusion
2nd Law of Thermodynamics
Universe tends towards disorder
Diffusion
movement from high → low concentration
Diffusion of 2 solutes
Each substance diffuses down its own concentration gradient, independent of concentration gradients of other substances
The Special case of water
Osmosis
Movement of water across cell membrance
Concentration of Water
Direction of osmosis is determined by comparing total solute concentrations
Hypertonic - more solute, less water
Hypotonic - less solute, more water
Isotonic - equal solute, equal water
WATER MOVES FROM HYPOTONIC TO HYPERTONIC
Managing Water Balance
Cell survival depends on balancing water uptake and loss
Hypotonicity
animal cell in hypotonic solution will gain water, swell & possibly burst (cytolysis)
Paramecisum vs. Pond Water
Paramecium is hypertonic
H20 continually enters cells
to solve problem, specialized organelle, contractile vacuole
pumps H20 out of cell = ATP
plant cell
turgid (turgor pressure)
cell wall
Hypertonicity
animal cell in hypertonic solution will lose water, shrivel and possibly die
salt water organisms are hypotonic compared to their environment
they have to take up water and pump out salt
plant cells
plasmolysis
Water Potential (ψ)
Water moves from a place of greater water potential to a place of lesser water potential (net.)
As the concentration of a solute increases in a solution, the water potential will decrease accordingly.
Water Potential and Solute Potential
Ψ = Ψp(pressure) + Ψs(solute)
The unit is (-)BARS
Note: the water potential will be equal to the solute potential of a solution in an open container since pressure would be zero
Ψs = -iCRT
i= ionization constant (sucrose = 1.0)
C = molar concentration
R = 0.0831 liter bars/mole K
T = temp in Kelvin (273+C)
Facilitated Diffusion
Move from HIGH to LOW concentration through protein channel
passive transport
no energy needed
facilitated = with help (from proteins)
Gated Channels
Some channel proteins open only in presence of stimulus (signal)
stimulus usually different from transported molecule
ex: ion-gated channels
when neurotransmitters bind to a specific gated channels on a nuearon, these channels open = allow Na+ ions to enter nerve cell
ex: voltage-gated channels
change in electrical charge across nerve cell membrane opens Na+ & K+ channels
Active Transport
Cells may need molecules to move against concentration situation
need to pump against concentration
protein pump
requires energy
ATP
How about large molecules?
Moving large molecules into & out of cell requires ATP!
through vesicles & vacuoles
endocytosis
phagocytosis = “cellular eating”
pinocytosis = “cellular drinking”
receptor-mediated
endocytosis
exocytosis