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Advanced BiologyAdvanced Biology
MembranesMembranes
Animal Animal CellCell
The plasma membraneThe plasma membraneIs the boundary that separates the living cell Is the boundary that separates the living cell from its nonliving surroundingsfrom its nonliving surroundings
It allows some substances to cross it more easily It allows some substances to cross it more easily than othersthan others
Membrane CompositionMembrane Composition
LipidsLipids PhospholipidsPhospholipids CholesterolCholesterol
ProteinsProteins TransportTransport SignalingSignaling StructuralStructural
PhospholipidsPhospholipids
The non-polar region The non-polar region forms a barrier from forms a barrier from the surrounding waterthe surrounding water
Polar Head Group
Non-polar Tail
8.1
Membrane ProteinsMembrane Proteins
8.2
Membrane ProteinsMembrane Proteins
8.2
Membrane Membrane FluidityFluidity
Both lipids and Both lipids and proteins can move proteins can move within a membranewithin a membrane
8.3
Enzymatic activityEnzymatic activity
Signal transductionSignal transduction
TransportTransport
ATP
Enzymes
Signal
Receptor
Functions of Functions of Membrane Membrane
ProteinsProteins
8.4
Functions of Functions of Membrane Membrane
ProteinsProteins
Cell-cell Cell-cell recognitionrecognition
Intercellular joiningIntercellular joining
Attachment to the Attachment to the cytoskeleton and cytoskeleton and extracellular matrixextracellular matrix
Glycoprotein
8.4
Membrane Membrane proteins and proteins and lipidslipids
Are synthesized Are synthesized in the ER and in the ER and Golgi apparatusGolgi apparatus
ER
Transmembraneglycoproteins
Secretoryprotein
Glycolipid
Golgiapparatus
Vesicle
Transmembraneglycoprotein
Membrane glycolipid
Plasma membrane:Cytoplasmic face
Extracellular face
Secretedprotein
4
1
2
3
The Permeability of the Lipid The Permeability of the Lipid BilayerBilayer
The membrane regulates transport of all The membrane regulates transport of all molecules in and out of the cellmolecules in and out of the cell Nutrients - amino acids, sugars, lipids Nutrients - amino acids, sugars, lipids Wastes Wastes Oxygen and carbon dioxideOxygen and carbon dioxide Ions - Na , K , Ca , ClIons - Na , K , Ca , Cl Many othersMany others
+ + +2 -
8.5
Two Types of Molecules to Two Types of Molecules to RegulateRegulate
Hydrophobic moleculesHydrophobic molecules Are lipid soluble and can pass through the Are lipid soluble and can pass through the
membrane rapidlymembrane rapidly
Hydrophilic (polar) moleculesHydrophilic (polar) molecules Do not cross the membrane rapidly without Do not cross the membrane rapidly without
the aid of transport proteinsthe aid of transport proteins
DiffusionDiffusion
Is the tendency for Is the tendency for molecules of any molecules of any substance to substance to spread out evenly spread out evenly into the available into the available spacespace
Molecules move Molecules move from areas of high from areas of high concentration to concentration to areas of low areas of low concentrationconcentration
8.6
TonicityTonicityIsotonic Isotonic Same concentration on both sides of a membraneSame concentration on both sides of a membrane
HypertonicHypertonic Higher concentrationHigher concentration
HypotonicHypotonic Lower concentrationLower concentration
8.7
OsmosisOsmosis
Is the movement Is the movement of water across a of water across a semi-permeable semi-permeable membranemembrane
Is caused by an Is caused by an imbalanced imbalanced concentration of concentration of dissolved dissolved substancessubstances
8.8/8.9
Passive and active transport comparedPassive and active transport comparedPassive transport Substances diffuse down their concentration gradients, crossing a membrane with no energy input required. The rate of diffusion can be greatly increased by transport proteins in the membrane.
Diffusion Hydrophobicmolecules can diffuse through the lipid bilayer.
Facilitated diffusion Many hydrophilic substances diffuse through membranes with the assistance of transport proteins,either channel or carrier proteins.
ATP
Active transport Some transport proteins act as pumps, moving substances across a membrane against their concentration gradients. Energy for this work is usually supplied by ATP.
1 2
3
One type of active One type of active transport systemtransport system
Maintains an Maintains an imbalance in of imbalance in of sodium and sodium and potassium inside potassium inside and outside the celland outside the cell
The Na -K The Na -K PumpPump
++
8.10
Membrane Potential and SignalingMembrane Potential and Signaling
1.1. The Na/K Pump creates a concentration The Na/K Pump creates a concentration difference across the cell membranedifference across the cell membrane
2.2. If a Na channel is then opened, Na is will If a Na channel is then opened, Na is will rush into the cellrush into the cell
3.3. This creates an electrical potential This creates an electrical potential measured in millivolts (mV)measured in millivolts (mV)
4.4. This potential is called an action potential This potential is called an action potential an is the basis for nerve impulsesan is the basis for nerve impulses
8.10
8.10
Bulk TransportBulk Transport
Exocytosis (exit)Exocytosis (exit) Transport vesicles migrate to the plasma Transport vesicles migrate to the plasma
membrane, fuse with it, and membrane, fuse with it, and releaserelease their their contentscontents
Endocytosis (enter)Endocytosis (enter) The cell The cell takes intakes in macromolecules by forming macromolecules by forming
new vesicles from the plasma membranenew vesicles from the plasma membrane
8.11
Three types of endocytosisThree types of endocytosis
8.11