membranes structure and function. membrane structure phospholipid bi-layer phospholipid bi-layer...
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Membrane StructureMembrane Structure
Phospholipid Bi-layerPhospholipid Bi-layer Contains Different Types of ProteinsContains Different Types of Proteins
– Channel proteinsChannel proteins– Protein Pumps proteinsProtein Pumps proteins– Adhesion proteinsAdhesion proteins– Cell-to-Cell Communication proteinsCell-to-Cell Communication proteins– Hormone Receptor proteinsHormone Receptor proteins– Immobilized EnzymesImmobilized Enzymes
Fluid Mosaic ModelFluid Mosaic Model
Phospholipid Bi-layerPhospholipid Bi-layer
ContainsContains GlycoproteinsGlycoproteins Integral ProteinsIntegral Proteins Peripheral ProteinsPeripheral Proteins CholesterolCholesterol
Channel proteinsChannel proteins
Integral protein: embedded across bi-layerIntegral protein: embedded across bi-layer Allows for movement of molecules across Allows for movement of molecules across
cell membranecell membrane
Protein PumpsProtein Pumps
Integral proteinIntegral protein Transports molecules across membranes Transports molecules across membranes
by changing shapeby changing shape
Adhesion proteinsAdhesion proteins
Connects internal Connects internal cytoskeleton to cytoskeleton to external points of external points of attachmentattachment
Secures cells of Secures cells of multi-cellular multi-cellular organisms in placeorganisms in place
Cell-to-Cell Communication Cell-to-Cell Communication proteinsproteins
Cells within the Cells within the same organism use same organism use membrane proteins membrane proteins to recognize each to recognize each otherother
Often use Often use glycoproteinsglycoproteins
Major importance Major importance to immune systemto immune system
Hormone Receptor proteinsHormone Receptor proteins
Hormones bind to Hormones bind to cell surface proteinscell surface proteins
Initiates a series of Initiates a series of reactions within cellreactions within cell
Results in cellular Results in cellular response such gene response such gene expression (making expression (making more or less of a more or less of a protein)protein)
Immobilized EnzymesImmobilized Enzymes
Many enzymes used by cells are Many enzymes used by cells are embedded within membranesembedded within membranes
Useful in keeping certain Useful in keeping certain reactions in specific parts of the reactions in specific parts of the cellcell
Membrane FunctionMembrane Function
Boundary Separates Two EnvironmentsBoundary Separates Two Environments Selectively PermeableSelectively Permeable Passive TransportPassive Transport
– Simple DiffusionSimple Diffusion– Facilitated DiffusionFacilitated Diffusion
Active TransportActive Transport– Protein PumpsProtein Pumps
Endocytosis / ExocytosisEndocytosis / Exocytosis
Selectively PermeableSelectively Permeable
Membranes and their proteins allow Membranes and their proteins allow only certain molecules to crossonly certain molecules to cross
Diffusion: movement of a substance Diffusion: movement of a substance from an area of high concentration to from an area of high concentration to low concentrationlow concentration
Osmosis: movement of water from Osmosis: movement of water from an area of low solute concentration an area of low solute concentration to highto high
Passive TransportPassive Transport
The movement of a molecule across a The movement of a molecule across a membrane from high to low membrane from high to low concentrationconcentration
Molecules move with the concentration Molecules move with the concentration gradientgradient
Simple DiffusionSimple Diffusion– No proteins neededNo proteins needed
Facilitated DiffusionFacilitated Diffusion– Membrane proteins requiredMembrane proteins required
Simple DiffusionSimple Diffusion
Small, uncharged Small, uncharged molecules can molecules can move directly move directly across membraneacross membrane
Includes gases Includes gases (CO(CO2 2 and 0and 022 ) and ) and waterwater
Facilitated DiffusionFacilitated Diffusion Uses either protein channels or Uses either protein channels or
transporters (change shape)transporters (change shape)
ChannelChannel TransporterTransporter
Active TransportActive Transport
Movement of molecules across a Movement of molecules across a membrane from low concentrations membrane from low concentrations to highto high
Molecules move against the Molecules move against the concentration gradientconcentration gradient
Requires a protein transporter Requires a protein transporter (pump) and energy supplied by ATP(pump) and energy supplied by ATP
Ex. sodium/potassium pumpEx. sodium/potassium pump
EndocytosisEndocytosis
Cell membrane surrounds and Cell membrane surrounds and engulfs food particle or extra-cellular engulfs food particle or extra-cellular fluidfluid
Results in vesicle inside cellResults in vesicle inside cell Phagocytosis: engulfing large Phagocytosis: engulfing large
particles like bacteriaparticles like bacteria Pinocytosis: engulfing extra-cellular Pinocytosis: engulfing extra-cellular
fluid and whatever it might containfluid and whatever it might contain
ExocytosisExocytosis
Opposite of endocytosisOpposite of endocytosis Vesicle containing secretory proteins Vesicle containing secretory proteins
or wastes joins with plasma or wastes joins with plasma membranemembrane
Molecules inside vesicle are then Molecules inside vesicle are then released outside of the cellreleased outside of the cell
Review QuestionsReview Questions
Name 5 types of membrane proteins Name 5 types of membrane proteins and describe their functionsand describe their functions
What is the most significant difference What is the most significant difference between passive and active transport?between passive and active transport?
Why are transport proteins necessary Why are transport proteins necessary in facilitated diffusion?in facilitated diffusion?
Why does active transport require Why does active transport require energy?energy?
ProblemsProblems
#1#1
The internal cell The internal cell concentration of concentration of sucrose is 1M, the sucrose is 1M, the external external concentration is .1M, concentration is .1M, how might a cell how might a cell raise the internal raise the internal concentration to 2M concentration to 2M without using a without using a metabolic pathway?metabolic pathway?
#2#2
What might What might happen if a cell happen if a cell continually continually secreted enzymes, secreted enzymes, but never but never participated in participated in endocytosis?endocytosis?