Cell Membrane & Homeostasis

1. Cell Membrane & Homeostasis

2. DEFINITIONS: • Diffusion: movement of molecules from region of high concentration to low concentration • Diffusion Gradient: the concentration spectrum (difference) of solute molecules from high concentration to low concentration. • Osmosis: diffusion of water molecules across a membrane from high water amounts (low solute) to low water amounts (high solute).

3. DEFINITIONS: • Cell membranes are completely permeable to water. • The environment the cell is exposed to can have a dramatic effect on the cell. • Solute: a dissolved molecule in water. • Eg. Sodium chloride dissolved in water makes a saline solution. The sodium chloride is the solute. The water is the solvent.

4. DEFINITIONS: • Common cell solutes include salts, sugars, some minerals (iron ions and calcium ions) and protons (electrons from acids). • CONCENTRATION: amount of solute per unit volume of solution. Concentration can be expressed in mass/volume (g/100ml - percentage), ppm (parts per million), and moles/volume (molarity). The greater the mass or moles per unit volume, the more concentrated the solution.

5. 3 Osmotic Solution Terms

6. Isotonic • Same concentration of solute surrounding a cell as inside the cell. • When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. • The fluid that surrounds the body cells is said to be “isotonic”.

7. Hypertonic • The surrounding solutioncontains a higher concentration of solute relative to the cell. • When a cell is placed in a hypertonic solution, the water diffuses out of the cell attempting to match the solute concentration outside of it, causing the cell to shrivel. • The fluid surrounding the body cell is said to be “hypertonic”.

8. Hypotonic • The surrounding solution contains a lower concentration of solute relative to the cell (e.g. the cell's cytoplasm). • When a cell is placed in a hypotonic solution, the water diffuses into the cell in an attempt to dilute the solutes inside the cell, causing the cell to swell and possibly explode in animal cells. • Plant cells have a strong cell wall that prevents explosions. • Plant cell central vacuoles will fill to maximum and push against the cell wall – this is called high turgor pressure.

9. CELL MEMBRANE FUNCTION and STRUCTURE • The CELL MEMBRANE is chiefly responsible for maintaining homeostasis inside a living cell using different methods to transport molecules in and out of the cell. • Too much water can burst the cell • Too many wastes can poison the cell • The cell cannot tolerate any great variations in ion conditions. osmosis animation

10. Jobs of the cell membrane • Isolate the cytoplasm from the external environment • Regulate the exchange of substances (gases and ions) • Communicate with other cells • Identification (proteins and carbohydrates on its surface)

11. http://www.goldiesroom.org/AP%20Biology/AP%20Lecture%20Notes%20pdf/LN014--Ch05--Cell%20Transport.pdfhttp://www.goldiesroom.org/AP%20Biology/AP%20Lecture%20Notes%20pdf/LN014--Ch05--Cell%20Transport.pdf

12. http://www.goldiesroom.org/AP%20Biology/AP%20Lecture%20Notes%20pdf/LN014--Ch05--Cell%20Transport.pdfhttp://www.goldiesroom.org/AP%20Biology/AP%20Lecture%20Notes%20pdf/LN014--Ch05--Cell%20Transport.pdf

13. DESCRIPTION • The fluid mosaic model (S.J Singer) selectively-permeable: allows some substances in all the time, some only when needed, excludes others, allows one-way flow of some. • Fluid portion is a double layer of phospholipids, called the phospholipid bilayer. • large transport proteins, oligoproteins and oligosaccharides aid in transport • energy is required from the cell • aid in communication as well as identification

14. Phospholipid bilayer • Phospholipids contain a hydrophilic head and a non-polar hydrophobic tail • Hydrogen bonds form between the phospholipid “bilayer” and the watery environment inside and outside of the cell. • Hydrophobic (water fearing) interactions force the “tails" to face inward. • Phospholipids are not bonded to each other, which makes the double layer fluid.

15. Cholesterol embedded in the membrane makes it stronger and less fluid.

16. http://www.goldiesroom.org/AP%20Biology/AP%20Lecture%20Notes%20pdf/LN014--Ch05--Cell%20Transport.pdfhttp://www.goldiesroom.org/AP%20Biology/AP%20Lecture%20Notes%20pdf/LN014--Ch05--Cell%20Transport.pdf

19. The different components of a plasma membrane are integral proteins, peripheral proteins, glycoproteins, phospholipids, glycolipids, and in some cases cholesterol, and lipoproteins. • Construction of the Cell Membrane - Learning Activity • detailed cell membrane animation

20. Proteins Embedded in Membrane Serve Different Functions • Transport Proteins • regulate movement of substance • Channel Proteins • form small openings for molecules to diffuse through like water • Carrier Proteins • binding site on protein surface "grabs" certain molecules and pulls them into the cell animation

21. Gated Channels • similar to carrier proteins, not always "open"—eg. Bind and pull in calcium ions when needed. This requires cell energy—active transport.

22. Receptor Proteins • molecular triggers that set off cell responses (such as release of hormones or opening of channel proteins) e.g. The junction between nerve cells requires the transmission of neurotransmitters between synaptic gaps—these chemicals bind onto receptor proteins.

23. Recognition Proteins - ID tags, to identify cells to the body's immune system (called antigens)

24. TRANSPORT MECHANISMS • PASSIVE TRANSPORT • ACTIVE TRANSPORT • ENDOCYTOSIS • EXOCYTOSIS

25. Weeee!!! high low This is gonna be hard work!! high low Types of Cellular Transport • Passive Transport cell doesn’t use energy • Diffusion • Facilitated Diffusion • Osmosis • Active Transport cell does use energy • Protein Pumps • Endocytosis • Exocytosis • Animations of Active & Passive Transport

26. 1. Passive Transport (p. 198) • Simple Diffusion - water, oxygen and other molecules move from areas of high concentration to areas of low concentration, down aconcentration gradient. • Note – Osmosis is the diffusion of water Diffusion animation Passive Transport Animation

27. 1. Passive Transport (cont’d) • Facilitation Diffusion - diffusion that is enabled by proteins (channel or carrier proteins) which bind onto required molecules so that they flow into the cell. Animation: How Facilitated Diffusion Works

29. Contractiles Vacuoles are found in freshwater microorganisms - they pump out excess water. Recall: • Turgor pressure occurs in plants cells as their central water vacuoles fill with water.

30. Factors Affecting Rate of Diffusion

31. 1. Size • small molecules can slip through phospholipids bilayer easier than large molecules • very large molecules may not be able to diffuse at all

32. 2. Concentration • the greater the concentration gradient (bigger range) the quicker a material diffuses (makes the molecules want to move faster) – think of a crowded room

33. 3. Temperature • In general as temperature increases – molecules move faster which translates into faster diffusion

34. 4. Polarity of molecules • Water-soluble (polar) molecules will not easily move through the membrane because they are stopped by the middle water-insoluble (nonpolar) layer

35. 5. Surface Area • As a cell’s size increases its volume increases much quicker than it’s surface area. • If you double individual lengths (1 cm to 2 cm) the surface areas increases 4 times, and the volume increases 8 times. • If cell size is doubled, it would require 8 times more nutrients and have 8 times s much waste. SA only increases by a factor of 4 – not enough surface area through which nutrients and wastes could move. • Cell would either starve or be poisoned (waste products) • Cells divide before they come too large to function.

36. 2. Active Transport (p. 199) • Involves moving molecules "uphill" against the concentration gradient, which requires energy. • Uses carrier protein molecules as receptors. • One may transport calcium ions another glucose molecules. • There are hundreds of these types of protein molecules. *Each one changes shape to accommodate a specific molecule.

37. 2. Active Transport (cont’d) • Their activity can be stopped from transporting molecules with inhibitors (unfortunately, these are usually poisons) which: • either destroy the membrane protein • or just plug it up (e.g. for your neurons – tetanus & botulinum-B secrete a poison that suppress the Na/K pump) • active transport animation http://www.biology4kids.com/files/cell2_activetran.html

38. Sodium-Potassium Pump • Pumps out 3 sodium atoms for ever 2 potassium atoms taken in against gradient in the cell. ATP and the Na/K Pump Animation: How the Sodium Potassium Pump Works

39. The H+/K+ ATPase • The parietal cells of your stomach (lining) use this pump to secrete gastric juice. • These cells transport hydrogen ions (H+) from a concentration of about 4 x 10-8 M within the cell to a concentration of about 0.15 M in the gastric juice (giving it a pH close to 2). • Recall: pH – power of the H+ ion • Small wonder that parietal cells are stuffed with mitochondria and use huge amounts of energy as they carry out this three-million fold concentration of protons.

40. The H+/K+ ATPase

41. Ca2+ ATPases • In resting skeletal muscle, there is a much higher concentration of calcium ions (Ca2+) in the sarcoplasmic reticulum (__) than in the cytosol (_________). • Activation of the _______ fiber allows some of this Ca2+ to pass by fascilitated diffusion into the cytosol where it triggers contraction. After contraction, this Ca2+ is pumped back into the sarcoplasmic reticulum. This is done by a Ca2+ ATPase that uses the energy from each molecule of ATP to pump 2 Ca2+ ions.

42. Exocytosis • Moves large, complex molecules such as proteins out of the cell membrane. • Large molecules, food, or fluid droplets are packaged in membrane-bound sacs called vesicles.

43. Endocytosis • Endocytosis moves large particles (huge molecules or molecular conglomerates) into a cell. • endo & exocystosis animations

44. Phagocytosis • Phagocytosis is another type of endocytosis used for massive transport.Cell membrane extends out forming pseudopods (fingerlike projections) that surround the particle. • Membrane pouch encloses the material & pinches off inside the cell making a vesicle. • Vesicle can fuse with lysosomes(digestive organelles) or release their contents in the cytoplasm Animation: Phagocytosis HowStuffWorks "Phagocytosis"

45. Used by ameba to feed & white blood cells to kill bacteria.Known as “killer cells"

46. Pinocytosis is another type of endocytosis • Cell membrane surrounds fluid droplets • Fluids taken into membrane-bound vesicle • Known as “cell drinking”

47. Exocytosis is used to remove large products from the cell such as wastes, mucus, & cell products such as hormones and antibodies. • Exocytosis is the process used by our memory cells (white blood cells that produce antibodies to fight infection). • It is also used by our gland cells to secrete hormones when needed.

48. phagocytosis • animation

49. In Summary Essential Biochemistry - Membrane Transport

50. Transport of Materials Across a Membrane Transport Flowchart Active Passive Ion Pump Simple Diffusion Endocytosis Exocytosis Osmosis Facilitated Diffusion Pinocytosis Phagocytosis