Membrane Chapter 7 Cell membrane Cell Membrane n
Membrane Chapter 7
Cell membrane
Cell Membrane n n Plasma membrane Selective permeability Surrounds all living cells 2 molecules thick.
Plasma Membrane n n n Interacts with environment Exchanges information Manages movement in & out of cell
Fluid mosaic model n n Revised in 1972 by Singer & Nicolson Globular proteins imbedded in the membrane Not surrounding the lipid layer Proteins “float” in the membrane like boats in a pond.
Plasma membrane n n n Lipid membrane (phospholipids) Protein passageways Allow water-soluble substances to pass
Membrane Structure n n n 1. Phospholipid layer 2. Cholesterol 3. Transmembrane proteins 4. Interior protein network 5. Cell surface markers
Membrane structure
Triglycerides n n Water insoluble Non-polar
Phospholipid n n n Glycerol (3 carbon alcohol) 2 fatty acids Phosphate attached to 3 rd carbon
Phospholipid bilayer n n n Orients polar head toward water molecules Non-polar tail away from water. Non-polar barrier to water soluble molecules
Phospholipid bilayer n n Hydrophobic interactions hold membrane together Phospholipids & unanchored proteins move freely within the membrane
Cholesterol n n n Located between lipids Increases or decreases fluidity Depends on temperature.
Cholesterol
Structures of membrane proteins n n n 1. Peripheral proteins Attached to the surface membrane 2. Integral proteins Extend through the membrane Transmembrane proteins Partway
Structures of membrane proteins n n Non-polar section of protein Contact with the non-polar interior (hydrophobic) Polar section of the protein Extends out of membrane
Transmembrane proteins n 1. Single-pass anchors 2. Multiple-pass channels and carriers 3. Pores n Aquaporins n n
Functions of membrane proteins n n n 1. Transport Allow specific substances to enter or leave 2. Enzymes Carry out reactions on interior surface 3. Cell surface receptors Sensitive to chemical messages
Functions of membrane proteins n n n n 4. Cell surface identity markers Cell recognition between cells Glycoproteins 5. Cell adhesion proteins Proteins stick to each other Temporary or more permanently 6. Attachments to the cytoskeleton
Membrane Proteins
Membrane structure
Membrane formation n n Proteins & lipids made in ER Processed in Gogi apparatus Vesicles Fuse with membrane Correct orientation
Movement across the membrane n n n 1. Passive transport 2. Active transport 3. Bulk transport
Passive transport n n n Diffusion High concentration to areas of lower concentration Concentrations are the same in all regions
Passive transport n n n Two conditions determine the direction of the flow of ions 1. Relative concentration of the ion on each side of the membrane 2. The voltage across the membrane
Figure 7. 10 Molecules of dye Membrane (cross section) WATER Net diffusion Equilibrium (a) Diffusion of one solute Net diffusion Equilibrium (b) Diffusion of two solutes
Osmosis n n Net movement of water across a membrane Moves towards an area of lower water concentration Or higher solute concentration Passive transport of water
Osmosis n n Osmoregulation: Control of water balance
Osmosis n n n n Hyperosmostic Solution with higher concentration of solute Has less water Hypoosmostic Solution with the lower concentration of solute Has more water Isosmostic Solutions have equal concentration of solutes
Solutions n n Solute Substance being dissolved Solvent Substance doing the dissolving
Solutions n n n Hypertonic: Solution with higher concentration of solute Hypotonic: Solution with lower concentration of solute Isotonic Solutions with equal solute concentrations
Figure 7. 12 Hypotonic Isotonic (a) Animal cell H 2 O Lysed H 2 O Shriveled Normal Cell wall H 2 O Plasma membrane H 2 O (b) Plant cell Plasma membrane H 2 O Hypertonic Turgid (normal) Flaccid Plasmolyzed
Facilitated diffusion n n Carriers transport Ions, aa or sugars across the membrane Specific for type of solute Moves from high concentration to low The carrier facilitates the process
Examples n n RBC diffusion of the bicarbonate ion RBC diffusion of glucose
Facilitated diffusion n n n 1. It is specific 2. It is passive 3. It saturate Carriers are saturated Transport rate cannot increase Despite the concentration gradient
Active transport n n n Movement of substances against or up the concentration gradient Low concentration to high Requires energy. Requires the use of ATP. Cell takes up substances into cytoplasm that are already hypertonic to the extracellular fluid.
Sodium-potassium pump n n Protein transports Na and K ions across the membrane. Every cycle transports 3 Na ions out Exchange for 2 K ions into the cell Against concentration gradients.
Coupled transport n n n Molecule moves up its concentration gradient Uses the drive from another substance moving down its concentration gradient. Na ions and glucose
Fig. 7 -19 – + ATP – H+ H+ + Proton pump H+ H+ – H+ + – + Sucrose-H+ cotransporter H+ H+ Diffusion of H+ H+ Sucrose – – + + Sucrose
Bulk transport n n n Endocytosis Membrane envelops food particles 1. Phagocytosis 2. Pinocytosis 3. Receptor-mediated endocytosis
Bulk transport n n n Phagocytosis: The cell engulfs particles Pinocytosis: The cell engulfs liquid Receptor-mediated: Transported molecules bind specific receptors in the plasma membrane
Figure 7. 19 Phagocytosis Pinocytosis Receptor-Mediated Endocytosis EXTRACELLULAR FLUID Solutes Pseudopodium Plasma membrane Coat protein “Food” or other particle Food vacuole CYTOPLASM Coated pit Coated vesicle Receptor
Phagocytosis
Pinocytosis
Receptor-mediated
Exocytosis n n n The reverse of endocytosis Discharge of materials from the cell Secretion of many hormones, neurotransmitters, digestive enzymes and other substances
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