1. Cell membrane characteristics and transport mechanisms

2. Plasma Membrane  Physical barrier - separates intracellular fluids from extracellular fluids  Helps in maintaining homeostasis  Plays a dynamic role in cellular activity – selectively permeable

3. Fluid Mosaic Model  Double bilayer of phospholipids  Phospholipids have hydrophobic tails and hydrophilic heads CH 2 CH 3 CH 2 CH CH 2 CH 3 CH 2 CH 3 CH3CH3 N + O O O–O– P O CH2CH2 CHCH CH2CH2 C O C O O O Phosphate group Hydrophilic head Hydrophobic tails

4. The plasma membrane includes proteins  The functions of the plasma membrane include:  Isolation  Regulation of exchange with the environment  Sensitivity to the environment  Structural support

5. The plasma membrane includes proteins  The proteins in the plasma membrane includes:  Anchoring proteins  Recognition proteins (immune system)  Receptors  Carrier proteins  channels

6. Structures on the plasma membrane surfaces Microvilli, Cilia, Stereocilia Specialized junctions

7. Features of Apical Surface of Epithelium - Microvilli  Projections that increase surface area  Folding of the plasma membrane http://cellbio.utmb.edu/microanatomy/epithelia/epith_lec.htm

8. Features of Apical Surface of Epithelium - Cilia  These structures are designed for motility.  Epithelia that need to move substances across their surface (like mucous in the air passages) have cilia.  Each cilium or flagellum has a basal body located at its base.  Basal bodies anchor the cilia or flagella and are thought to be responsible for their formation.  They look like centrioles and are believed to be derived from them

9.  Flagella: (ex) spermatoza  Extra long cilia  Moves cell http://www.lbl.gov/Science-Articles/Archive/sabl/2006/Jul/02.html

10. Cell junctions – 3 groups  Tight junction  designed to restrict the movement of material between the cells they link  Gap junction  create cytoplasmatic communication bridges between cells  Anchoring junction  attach cells to one another or to extracellular matrix

11. Tight Junctions  An intercellular junction between cells in which the outer layers of the cell membranes fuse,  reducing the ability of larger molecules and water to pass between the cells.  Tight junctions prevent the free movement of molecules between cells in the intestine and allow the intestinal cell to control absorption

12. Gap junctions  Example – intercalated discs in the heart, electrical synapses

13. Cell transport mechanisms - How things enter and leave the cell

14. 2 groups of movement  Passive transport – no energy is needed  Diffusion  Carrier-mediated  Active transport – requires ATTP  Pumps  Vesicular transport

15. Passive transport  All molecules in the body are in constant motion regardless of the presence of a membrane (kinetic energy)  Motion stops only at absolute zero  By international agreement, it is defined as 0K on the Kelvin scale, −273.15°C on the Celsius scale and −459.67°F on the Fahrenheit scale  When a membrane is present the movement in a certain direction can be limited or changed  A molecule will move in a certain direction until collide with another molecule. When this happens, the direction of the movement will change

16. Diffusion  Depends on a concentration gradient. (What is a concentration? A concentration gradient?)  The driving force is kinetic energy and it is influenced by:  Molecule size – the smaller the faster  Temperature – the warmer the faster

17. Diffusion  The movement of molecules will happen in ALL directions  What is usually important is the net rate of diffusion in a certain direction  The net movement will be from high to low concentration until equilibrium is reached  At equilibrium, the net movement is equal in all directions

18. Membrane permeability  Membrane can be:  Freely permeable (this does not apply to plasma membrane) – allows passage of all substances  Selectively permeable – permits passage of some materials and prevents passage of others  Impermeable – cells can be impermeable to specific substances, but no living cell has a completely impermeable membrane

19. Diffusion through cell membrane  Diffusion is divided into 2 types:  1. Simple diffusion – the movement of particles through the membrane with no assistance  Nonpolar / lipid-soluble substances that diffuse directly through the lipid bilayer  Gases readily diffuse through lipid bilayer. (Ex. movement of oxygen inside cells and CO 2 outside)  Diffusion of water and other lipid-insoluble molecules happens via protein channels  The channels are highly selective as a result of the diameter, shape, charge and chemical bonds

20. Diffusion through cell membrane  2. facilitated diffusion - Assisted by carrier protein  Materials are bound to specific proteins and move through water-filled protein channels (big polar molecules; ex. – glucose)  The facilitated diffusion rate depends on the rate in which the carrier protein molecule can undergo changes that allow passage  Carrier Proteins  Are integral transmembrane proteins  Show specificity for certain polar molecules  Their number will influence the amount that can be transferred through the membrane

21. Osmosis  Osmosis is a simple diffusion of water.  It occurs through a selectively permeable membrane  Occurs when the concentration of a water is different on opposite sides of a membrane

22. Osmosis – osmolality, osmolarity and osmotic pressure  Osmolality (molecular weight) - One osmole is 1 gram molecular weight  Osmolarity (concentration) - One osmole in one liter  Osmotic pressure – defined by the concentration of solute particles in a solution  Is defined by the number of particles, not their size or nature  Each particle in a solution, regardless of its mass, exerts the same pressure against the membrane

23. Effects of Solutions of Varying Tonicity  Tonicity – description of how the solution affects a cell  Isotonic – solutions with the same solute concentration as that of the cytosol  Hypertonic – solutions having greater solute concentration than that of the cytosol  Hypotonic – solutions having lesser solute concentration than that of the cytosol

24. Passive Membrane Transport: Filtration  The passage of water and solutes through a membrane by hydrostatic pressure  Pressure gradient pushes solute-containing fluid from a higher-pressure area to a lower-pressure area  Depending on the size of the membrane pores  only solutes of a certain size may pass through it.

25. Transport that uses ATP  A movement that can be against concentration gradient  Uses ATP to move solutes across a membrane  Two types:  Active transport - use of carrier proteins  Vesicular transport

26. Types of Active Transport  2 types according to the source of energy used for the transport  Primary active transport  The energy for the transport derived directly from a high energy molecule – ATP  The hydrolysis of ATP causes phosphorylation of a transport protein that in turn changes its shape.  That change “promotes” the passage of materials (ex. Sodium-potassium pump)

27. Types of Active Transport  Secondary active transports – one ATP-powered pump can drive secondary transport of other solutes.  The energy is derived from the energy stored in creating the concentration gradient  This concentration difference was created by the primary active transport that used ATP  Secondary transport, like the primary, depends on carrier proteins, but without the need of energy

28. Active transport  Symport system – two substances are moved across a membrane in the same direction  Antiport system – two substances are moved across a membrane in opposite directions (Na/K)

29. Vesicular Transport  Transport of large particles and macromolecules across plasma membrane using vesicles and ATP  Endocytosis – enables large particles and macromolecules to enter the cell. Few types:  Receptor-mediated endocytosis – selective process that depends on the binding of extracellular material to a specific receptor  This binding initiates the endocytosis  Phagocytosis – “cell eating”; endocytosis of solid objects  pseudopods engulf solids and bring them into the cell’s interior  Happens in specialized cells  Pinocytosis – “cell drinking”; endocytosis of liquids.  This is not a selective process and does not involve receptor

30. Vesicular Transport  Exocytosis – moves substance from the cell interior to the extracellular space  Transcytosis – moving substances into, across, and then out of a cell  Vesicular trafficking – moving substances from one area in the cell to another

31. Passive Membrane Transport – Review ProcessEnergy SourceExample Simple diffusionKinetic energy Movement of O 2 through membrane Facilitated diffusion Kinetic energy Movement of glucose into cells OsmosisKinetic energy Movement of H 2 O in & out of cells Filtration Hydrostatic pressure Formation of kidney filtrate

32. Active Membrane Transport – Review ProcessEnergy SourceExample Active transport of solutesATP Movement of ions across membranes ExocytosisATPNeurotransmitter secretion EndocytosisATP White blood cell phagocytosis