Ch 5: Membrane Dynamics - bloodhounds Incorporated

Ch 5: Membrane Dynamics - bloodhounds Incorporated

Membrane Dynamics Cell membrane structures and functions Membranes form fluid body compartments Membranes as barriers and gatekeepers

How products move across membranes i.e., methods of transport Distribution of water and solutes in cells & the body Chemical and electrical imbalances Membrane permeability and changes

Microscopic Observation of Cells 2 Electron Micrograph 3

Cell organelles 4 The Cell Membrane Fluid Mosaic Model

Phospholipids Integral Proteins Peripheral Proteins Glycocalyx Glycoproteins

MHC Glycolipids Cholesterol 6

Membrane Structure 7 Thickness ~ 8nm Cell Membrane Structure: Fluid Mosaic Mod

PLs Cholesterol Proteins: peripheral (associated) or integral Integral Membrane Proteins 9

Membrane Bound Receptors 10 http://www.youtube.com/ watch?v=Qqsf_UJcfBc Passive Transport

= Diffusion (Def?) 3 types: 1. Simple diffusion 2. Facilitated diffusion (= mediated transport)

3. Osmosis Active Transport Always protein-mediated 3 types:

Co-transport Vesicular transport Receptor mediated transport Diffusion Process (Passive) Uses energy of concentration

gradient Net movement until state of equilibrium is reached (no more conc. gradient) Direct correlation to temperature Indirect correlation to molecule size Lipophilic molecules can diffuse

through the phospholipid bilayer Diffusion through Membranes Oxygen, carbon dioxide, fatty acids, and steroid hormones are examples of nonpolar molecules that diffuse rapidly through the lipid portions of membranes. Remember that lipophilic (lipid-loving) substances move through easily.

Polar molecules and hydrophilic (water-loving) do not diffuse readily through the membranes. 14 Simple Diffusion Simple Diffusion

Open and Closed Ion Channels 17 http://www.youtube.com/ watch? v=s0p1ztrbXPY&feature=r elated

Facilitated Diffusion Some molecules are too polar or too large to pass through the lipid bilayer. Carrier proteins change shape after the molecules bind then envelopes the

molecule and releases it The binding site is moved from one side of the membrane to the other by a change in the confirmation of the carrier protein.

http://highered.mcgrawhill.com/sites/ 0072495855/ student_view0/chapter2/ animation__how_facilitate d_diffusion_works.html Osmosis The net diffusion of water across a

membrane Through channel proteins called aquaporins 21 Tonicity Physiological term describing how cell volume changes if cell placed in the

solution Always comparative. Has no units. Isotonic soln = No change in cell Hypertonic soln = cell shrinks Hypotonic = cell expands Depends not just on osmolarity but on nature of solutes and permeability of

membrane Red Blood Cells in Isotonic and Hypotonic Solutions 24 Tonic solutions

Isotonic, hypotonic, and hypertonic solutions: Isotonic solutions have the same concentration of nonpenetrating solutes as normal extracellular fluid. Hypotonic solutions have a lower concentration of nonpenetrating solutes as normal extracellular fluid. Hypertonic solutions have a higher concentration of nonpenetrating solutes as normal extracellular fluid.

26 Active Transport Movement from low conc. to high conc. ATP needed Creates state of disequilibrium

1o (direct) active transport ATPases or pumps Uniport and Antiport 2o (indirect) active transport Symport and antiport

Na+/K+ ATPase 28 Primary Active-Transporters The Na+/K+-ATPase primary active transporter is found in every cell and helps establish and maintain the

membrane potential of the cell. In addition to the Na+/K+-ATPase transporter, the major primary active-transport proteins found in most cells are: (1) Ca2+-ATPase (2) H+-ATPase (3) H+/K+-ATPase 29

http://www.youtube.com/watch? v=9CBoBewdS3U&feature=related http://www.youtube.com/watch? v=STzOiRqzzL4&NR=1 Secondary Active Transport

32 Cotransport Symport Molecules are carried in same

direction Examples: Glucose and Na+ Antiport Molecules are carried in opposite

direction Examples: Na+/K+ pump Vesicular Transport Movement of macromolecules across cell membrane: 1. Phagocytosis (specialized cells

only) Macrophage or Phagocytes 2. Pinocytosis Cell drinking 3. Receptor mediated endocytosis

Down Regulation 4. Exocytosis http://www.youtube.com/ watch?v=KiLJl3NwmpU http://www.youtube.com/watch?

v=4gLtk8Yc1Zc&feature=related Endocytosis & Exocytosis 37 Endocytosis Movement of molecules into the cell via

vesicles. There are three general types of endocytosis that may occur in a cell: 1. Phagocytosis 2. Pinocytosis 3. Receptor-mediated endocytosis 38

Phagocytosis Phagocytosis Requires energy Cell engulfs particle into vesicle via pseudopodia formation E.g.: some WBCs engulfs bacteria

Vesicles formed are much larger than those formed by endocytosis Phagosome fuses with lysosomes ? Pinocytosis Receptor Mediated Endocytosis

No. 1 uptake method in most cells Receptors and substance is internalized into a coated pit-clathrin Down Regulation

Exocytosis Intracellular vesicle fuses with membrane Requires energy (ATP) and Ca2+ Examples: large lipophobic molecule secretion; receptor insertion; waste removal Clinical Case Study

A 22-year-old woman was competing in her first marathon. She was in good health, but was completely inexperienced in long-distance runs. In the hour before the race, she drank two 20-ounce bottles of water in anticipation of the water loss she expected to experience due to perspiration during the race. The race took place on an unseasonably cool day in April. As she ran, she took a drink at each water station. At the 20-mile mark she was feeling extremely fatigued and her leg muscles began cramping. Thinking she was losing too much fluid, she drank

additional water. At 23 miles she began to feel confused and disoriented and developed a headache. She finished yet another bottle of water even though she was not thirsty. Twenty minutes later, she collapsed, lost consciousness, and was taken to a local hospital. Her blood Na + levels had decreased to 115 mM and she was diagnosed with exerciseassociated hyponatremia. What was the effect of excessive water consumption on the osmolarity of this womans extracellular fluids? How would this affect ion gradients and cell volumes in areas such as her brain and skeletal muscles?

45

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