The Cellular Level of Organization

1. The Cellular Level of Organization Chapter 1 Section 1: Parts of a Cell

2. Typical Structures Found in a Cell

3. Plasma Membrane • forms a cell’s flexible outer surface • separates inside from outside • acts as a selective barrier that regulates what gets in or out of cell • plays key role in communication with other cells

4. Plasma MembraneFluid Mosaic Model • resembles an ever-moving sea of fluid lipids that has large proteins bobbing along throughout the lipids

5. Fluid Mosaic Model of Plasma Membrane • membrane proteins either float around like icebergs or are anchored at specific locations

6. The Lipid Bilayer • basic structure of plasma membrane • made of 2 back-to-back layers using 3 types of lipids • asymmetric

7. Lipid Bilayer1st Lipid • Phospholipids • 75% of lipid membrane • lipids with phosphate groups

8. Lipid Bilayer2nd Lipid 2. Cholesterol • 20% of lipid membrane • a steroid • makes bilayer less fluid • weakly amphipathic (-OH group on 1 end can form H-bonds)

9. Lipid Bilayer3rd Lipid • Glycolipids • ~5% of membrane lipids • lipid with attached carbohydrate group • stick out into extracellular space

10. Phospholipids are Amphipathic

12. PhospholipidBilayer

13. “like likes like” • hydro: water • philic: loving • phobic: hating • Polar molecules hydrophilic • Nonpolar molecules hydrophobic

14. Arrangement of Membrane Proteins • Integral Membrane Proteins • embedded in membrane • most are transmembrane: protrude both into cytosol & ECF • amphipathic • Peripheral Protein • loosely ass’c with polar heads of membrane lipids or with integral proteins • inner or outer surface of membrane

15. Membrane Proteins

16. Glycoproteins • proteins with carbohydrate groups attached to the ends that protrude into ECF • these carbohydrate groups are oligosaccharides (few-sugars): straight or branched chains of 2 – 60 monosaccharides

17. Glycoproteins

18. Glycocalyx • carbohydrate portions of glycolipids + glycoproteins = glycocalyx • acts like name tag for cells to recognize each other

19. Glycocalyx • enables cells to adhere to each other • protects some cells from being digested by enzymes in ECF

20. Types & Functions of Membrane Proteins: Integral Proteins • ION CHANNELS • are holes or pores thru which specific ions flow in or out of cell • most are very selective • Examples: K+ ion channels

21. Types of Integral Membrane Proteins 2. TRANSPORTERS • selectively move a polar substance (like water) across the plasma membrane • water transporters called aquaporins • Example: aquaporin

22. Types of Integral Membrane Proteins • RECEPTORS • serve as cellular recognition sites • recognizes & binds specific type of molecule • the specific molecule that binds to a receptor protein is called a ligand

23. Receptor Proteins

24. Types of Integral Membrane Proteins 4. ENZYMES • catalyze specific chemical reactions at inside or outside cell

25. Types of Integral Membrane Proteins 5. LINKERS • integral proteins anchor proteins in the plasma membranes of neighboring cells or to protein filaments inside & outside the cell

26. Cell-Identity Markers • glycoproteins or glycolipids • Example: ABO blood type markers

27. Selective Permeability • some substances can easily pass thru, others not at all • lipid-bilayernonpolar so • permeable to small nonpolar substances • impermeable to polar substances • Water is an exception • is polar • small amts cross plasma membrane

28. Gradients Across the Plasma Membrane • selective permeability across plasma membrane maintains different concentrations of certain substances on either side of plasma membrane • concentration gradient: a difference in the concentration of a chemical from 1 place to another

30. Gradients across the Plasma Membrane • because several of the substances kept in different concentrations on either side of membrane have (+) or (-) charges there is an electrical gradient across the membrane • typically, inside surface of membrane is slightly (-) & outside surface of membrane is slightly (+)

31. Gradients across thePlasma Membrane • a difference in charge across membrane is called: membrane potential

32. just like a battery where there is separation of charge used as source of energy so too a membrane potential can be thought of as potential energy for cell to move substances in or out of cell

33. The combined influence of the concentration gradient & membrane potential on movement of a particular ion is referred to as its electrochemical gradient

34. Chapter 3 Section 2Transport Across the Plasma Membrane

35. Essential Question • What is the main difference between primary & secondary active transport mechanisms?

36. Kinetic Energy Transport • diffusion is a passive process in which the random mixing of particles in a solution occurs because of the particle’s kinetic energy • solute: dissolved substances • solvent: liquid that does dissolving

37. Diffusion • solutes move down their concentration gradient until they are evenly distributed

38. Diffusion • solute particles continue to move due to their kinetic energy • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

39. Factors that Influence Rate of Diffusion acrossPlasma Membrane • Steepness of Concentration Gradient • greater the difference between 2 sides, higher rate of diffusion • steepness of electrochemical gradient determines rate of diffusion

40. Factors that Influencethe Rate of Diffusion acrossPlasma Memebrane 2. Temperature • higher temperature  higher KE of particles  faster it diffuses • all diffusion processes go faster when person has a fever

41. Factors that Influence Rate of Diffusion acrossPlasma Membrane 3. Mass of the Solute Diffusing • larger masses diffuse slower than smaller masses

42. Factors that Influence Rate of Diffusion acrossPlasma Membrane 4. Surface Area • larger membrane surface area, faster the diffusion rate

43. Factors that Influence Rate of Diffusion acrossPlasma Memebrane 5. Diffusion Distance • greater distance over which diffusion must occur, the longer it takes • plasma membranes very thin so diffusion is rapid, processes that thicken that space (autoimmune disease) slow down rate

44. What Diffuses Across Plasma Membrane • nonpolar, hydrophobic, small molecules: • O2 & CO2 gases • Lipids (fatty acids, steroids) • fat-soluble vitamins: • A, D, E, K

45. Facilitated Diffusion • diffusion through an integral membrane protein from side with higher concentration to side with lower concentration

46. Facilitated Diffusion

47. Facilitated Diffusion • transporters very specific • passive process (no nrg output by cell) • # of transporters limited so there is an upper limit to the amount that can cross membrane: called a transport maximum or Tmax • once all transporters occupied the diffusion rate cannot increase

49. Facilitated Diffusion • http://programs.northlandcollege.edu/biology/Biology1111/animations/passive3.swf

50. Gated Channels when part of the channel protein acts as a “plug” or “gate” changing shape to open pore & in another shape to close it