ap biology the cell membrane *very thin (7.5-10 nm) *elastic *semipermeable * dynamic *lipid bilayer...
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AP Biology
The Cell Membrane *Very thin (7.5-10 nm) *Elastic *Semipermeable
* Dynamic *lipid bilayer *Made of phospholipids, proteins, CHO& otherlipids *amphipathic
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Phospholipids
Fatty acid
PhosphateFlexibility & selective permeability Fatty acid tails
hydrophobic Phosphate group head
hydrophilic Arranged as a bilayer
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Phospholipid bilayer
polarhydrophilic
heads
nonpolarhydrophobic
tails
polarhydrophilic
heads
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Protein:
*Hydrophilic & hydrophobic
*Integral & peripheral Cholesterol: permeability & toughness CHO: recognition sites & attach cells
togetherGlycoprotein Glycolipid
Peripheralprotein
Cholesterol
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Functions of membrane proteins 1- structural ptns 2- passive channels: ungated & gated(voltage / ligand) 3- carriers for facilitated diffusion 4- carriers for active transport (uniport /symport/ antiport) 5- receptors: number & sensitivity change 6- enzymes 7- identity ptns 8-intercellular connections: a. binding j: tight & desmosomes
b. gap j 9- cell adhesion molecules 10- fixation of cytoskeleton
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Many Functions of Membrane Proteins
Outside
Plasmamembrane
InsideTransporter Cell surface
receptorEnzymeactivity
Cell surface identity marker
Attachment to thecytoskeleton
Cell adhesion
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Membrane carbohydrates Play a key role in cell-cell recognition
ability of a cell to distinguish one cell from another antigens
important in organ & tissue development
basis for rejection of foreign cells by immune system
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Movement across the Cell Membrane
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Diffusion All molecules are in constant motion
Diffusion movement from high low concentration
Diffusion movement from high low concentration
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Facilitated Diffusion Diffusion through protein channels
channels move specific molecules across cell membrane
no energy neededopen channel = fast transport
facilitated = with help
high
low
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Facilitated Diffusion
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Active Transport
“The Doorman”“The Doorman”
conformational change
Against concentration gradient Needs carrier protein Energy is needed
ATP
low
high
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Active transport Many models & mechanisms
ATP ATP
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Active transport
1ry active:
*eg Na+/K+ pump
*α &β subunits
*α subunit contains 2 binding sites for K+ on the outside & 3 binding sites for Na+ on the inside & an ATP binding site
*β subunit has ATPase activity.
2ry active:
*eg Glucose transport 2ry to active transport of Na
1st Na pumped out ….creates concentration gradient… Na & glucose bind a carrier…transports them to inside
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Getting through cell membranePassive Transport
Simple diffusion diffusion of nonpolar, hydrophobic molecules
lipids high low concentration gradient
Facilitated transport diffusion of polar, hydrophilic molecules through a protein channel
high low concentration gradient
Active transport diffusion against concentration gradient
low high uses a protein pump requires ATP
Vesicular transportATP
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Transport summary
simplediffusion
facilitateddiffusion
activetransport
ATP
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How about large molecules? Moving large molecules into & out of cell
through vesicles & vacuoles endocytosis
phagocytosis = “cellular eating” pinocytosis = “cellular drinking”
exocytosis
exocytosis
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Endocytosis
phagocytosis
pinocytosis
receptor-mediated endocytosis
fuse with lysosome for digestion
non-specificprocess
triggered bymolecular signal
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Osmosis is diffusion of water Diffusion of water from
high concentration of water to low concentration of water across a
semi-permeable membrane
The pressure necessary to stop solvent mol movements= osmotic pressure
The numbers of particles per unit volume of fluid Measured in mmHg Osmole osmolarity osmolality
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The osmolarity of ICF=that ECF=300 mosmol 280 mosmol is due to Na, Cl & HCO3 20 mosmol is due to protein Tonicity: is the osmolality of a solution relative to
the plasma Plasma proteins of blood is called oncotic
pressure. It is important for capillary circulation ®ulation of ECF
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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
hypotonic hypertonic
water
net movement of water
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Donnan effect The protein anions inside the cells are
non diffusible hinder the diffusion of diffusible cations
More osmotically active particles inside the cell
The cell tends to swell But the Na+/ K+ pump prevents cell
rupture
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Any Questions??