![Passive transport includes
Diffusion
Tendency of molecules of any substance to spread out
into the available space. Substances will diffuse
DOWN their concentration gradient.
Osmosis
The diffusion of water molecules across a selectively
permeable membrane.
Hypertonic = solution with higher [conc.] of solutes
Hypotonic = solution with lower [conc.] of solutes
Isotonic = solutions are equal in solute concentration
Facilitative Diffusion
Transport proteins are helping molecules to cross
membrane, but still diffusion (lowering overall free
energy) thus doesn’t require energy from cell.](https://image.slidesharecdn.com/lecture3-membranestructureandfunction-230227132758-0c0329fb/85/Cell-Membrane-Structure-and-Function-ppt-22-320.jpg)
Cell Membrane Structure and Function.ppt
- 1. Plasma Membrane Structure and Function By Dr. Huma Jawed Ph.D Pharmacology
- 2. Membrane Structure and Function Cells must contain a cell membrane, cytoplasm and genetic material. The cell membrane is the EDGE, “boundary of life”, while the cytoplasm is the site of all the reactions of life and the genetic material is the information required for life. SELECTIVELY PERMEABLE means that the cell membrane allows some substances across more easily than others… some it helps and some it inhibits or rejects all together.
- 3. Molecules need to move across membranes in cells Image modiified from: http://www.accessexcellence.org/AB/GG/importProt.html IN food carbohydrates sugars, proteins amino acids lipids salts, O2, H2O OUT waste ammonia salts CO2 H2O products
- 4. Membrane Structure Development of models as a scientific process Models include Overton – proposed lipid base Langmuir (phospholipids) – made membrane Gorter and Grendel (two layers) Davson and Danielli (sandwich image, protein outside) Singer and Nicolson = Fluid Mosaic Model Required electron microscopy 1972
- 5. MEMBRANE MODELS 1915: Scientists analyzed isolated red blood cell membranes, found them made up of proteins and lipids 10 years later: E. Gorter and F. Grendel reasoned membranes are made of a phospholipid bilayer 1935: Hugh Davson and James Danielli proposed membrane was a “sandwich” of proteins and phospholipid bilayer with proteins on outside of phopholipids DAVSON-DANIELLI MODEL
- 6. FLUID MOSAIC MODEL 1972- S.J. Singer and G. Nicolson propose membrane is a “mosaic” of proteins and phospholipids that are constantly moving and changing Animation from: http://www.sp.uconn.edu/~terry/images/anim/fluidmem.gif
- 8. Membrane Structure Phospholipids – phosphate and fatty acid tails Hydrophilic phosphates Hydrophobic fatty acid tails Two layers With tails together Protein Embedded throughout - integral Some just surface – peripheral Motility Phospholipid
- 11. Idea of Fluidity Cholesterol molecules prevent membrane from becoming ‘crispy’ Proteins ‘bob’ along surface Proteins are anchored by fibers in the cytoskeleton Phospholipids can even flip flop Merging of membranes.
- 13. Membrane Proteins Proteins determine most of membrane’s specific functions cell membrane & organelle membranes each have unique collections of proteins Membrane proteins: peripheral proteins = loosely bound to surface of membrane integral proteins = penetrate into lipid bilayer, often completely spanning the membrane = transmembrane protein
- 14. Membrane Carbohydrates Attached to proteins (glycoproteins) or lipids (glycolipids) Play a key role in cell-cell recognition ability of a cell to distinguish neighboring cells from another important in organ & tissue development basis for rejection of foreign cells by immune system
- 15. Membrane Lipids
- 16. Membranes provide a variety of cell functions
- 17. Other organelles The cell membrane is continuous with other membranes in the cell Endoplasmic reticulum (ER) starts/ends at cell membrane ER makes cell membrane & it is turned inside out as the new cell membrane flows out of the ER
- 18. Traffic Across the Membrane Small particles and ions move in both directions; sugars, amino acids, CO2, NH4 and O2. Also Na+, K+, Ca+2 and Cl- Hydrophobic molecules ( like CO2) can dissolve in lipid layer Hydrophilic core of cell membrane impedes movement of ions and polar molecules that are hydrophilic. Proteins built into membrane facilitate the process
- 20. Transport Proteins Span the Cell membrane Function as a channel Some also physically move passengers Specificity of fit allows for membrane selectivity.
- 21. Passive Transport Molecules have intrinsic kinetic energy They are in constant motion. Cytoplasm, extracellular fluid and cell membrane vary in concentrations and pressure gradients. Concentration refers to the overall POPULATION of molecules as well as the RATIO in that location compared to another. DYNAMIC EQUILIBRIUM
- 22. Passive transport includes Diffusion Tendency of molecules of any substance to spread out into the available space. Substances will diffuse DOWN their concentration gradient. Osmosis The diffusion of water molecules across a selectively permeable membrane. Hypertonic = solution with higher [conc.] of solutes Hypotonic = solution with lower [conc.] of solutes Isotonic = solutions are equal in solute concentration Facilitative Diffusion Transport proteins are helping molecules to cross membrane, but still diffusion (lowering overall free energy) thus doesn’t require energy from cell.
- 23. 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
- 24. Facilitated Diffusion Carrier Proteins Grab molecule, undergo conformational change, flip to other side Channel Proteins Create passageway for substances to pass through May be gated or not: open in response to chemical or electrical signals
- 25. Active Transport Movement of solutes, UP their concentration gradient, with the help of transport proteins in a CM. Requires cell to expend energy / do work. Solute becomes more concentrated or “stock- piled” in a particular area. Example is Sodium-Potassium Pump. (Na-K)
- 27. Electrogenic Pumps In addition to moving ions, some active transport pump also generate electric current and/ ATP. An enzyme called ATP synthase is built into the membrane and ADP is phosphorylated as a result of ions (often H+) passing through the membrane. Examples are found in the Electron Transport Chains of respiration (inner mitochondrial membrane) and photosynthesis (chloroplasts thylakoid membrane)
- 28. Endocytosis phagocytosis pinocytosis receptor-mediated endocytosis “Cell eating” large molecules; whole cells “Cell drinking” Fluids; Small molecules triggered by ligand signal
- 29. EXOCYTOSIS • Active transport (requires ATP) • Uses vesicles • Releases substances to outside INSULIN being released by pancreas cells using exocytosis