1. Membrane Chapter 7

2. Cell membrane

4. Cell Membrane Plasma membrane Selective permeability
Surrounds all living cells
2 molecules thick.

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6. Plasma Membrane Interacts with environment Exchanges information
Manages the movement in and out of the cell

7. Fluid mosaic model Revised in 1972 by Singer & Nicolson
Globular proteins imbedded in the membrane
Not surrounding the lipid layer
Proteins “float” in the membrane like boats in a pond.

8. Plasma membrane Lipid membrane (phospholipids) Protein passageways
Allow water-soluble substances to pass

9. Membrane Structure 1. Phospholipid layer 2. Cholesterol
3. Transmembrane proteins
4. Interior protein network
5. Cell surface markers

10. Membrane structure

11. Triglycerides
Water insoluble
Non-polar

12. Phospholipid Glycerol (3 carbon alcohol) 2 fatty acids
Phosphate attached to 3rd carbon

15. Phospholipid bilayer Orients polar head toward water molecules
Non-polar tail away from water.
Non-polar barrier to water soluble molecules

16. Phospholipid bilayer Hydrophobic interactions hold membrane together
Phospholipids & unanchored proteins move freely within the membrane

18. Cholesterol Cholesterol between lipids Increases or decreases fluidity
Depends on temperature.

19. Cholesterol

20. Structures of membrane proteins
1. Peripheral proteins
Attached to the surface membrane
2. Integral proteins
Extend through the membrane
Transmembrane proteins
Partway

21. Structures of membrane proteins
Non-polar section of protein
Contact with the non-polar interior (hydrophobic)
Polar section of the protein
Extends out of membrane

22. Transmembrane proteins
1. Single-pass anchors
2. Multiple-pass channels and carriers
3. Pores
Aquaporins

26. Functions of membrane proteins
1. Transport
Allow specific substances to enter or leave
2. Enzymes
Carry out reactions on interior surface
3. Cell surface receptors
Sensitive to chemical messages

27. Functions of membrane proteins
4. Cell surface identity markers
Cell recognition between cells
Glycoproteins
5. Cell adhesion proteins
Proteins stick to each other
Temporary or more permanently
6. Attachments to the cytoskeleton

28. Membrane Proteins

29. Membrane structure

30. Membrane formation Proteins & lipids made in ER
Processed in Gogi apparatus
Vesicles
Fuse with membrane
Correct orientation

31. Movement across the membrane
1. Passive transport
2. Bulk transport
3. Active transport

32. Passive transport Diffusion
High concentration to areas of lower concentration
Concentrations are the same in all regions

33. Passive transport
Two conditions determine the direction of the flow of ions
1. Relative concentration of the ion on each side of the membrane
2. The voltage across the membrane

34. Diffusion

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36. Osmosis Net movement of water across a membrane
Moves towards an area of higher solute concentration
Or lower water concentration
Passive transport of water

37. Osmosis
Osmoregulation:
Control of water balance

38. Osmosis Hyperosmostic Solution with higher concentration of solute
Has less water
Hypoosmostic
Solution with the lower concentration of solute
Has more water
Isosmostic
Solutions have equal concentration of solutes

39. Solutions Solute Substance being dissolved Solvent
Common solutes in the cell or cell’s cytoplasm?
Solvent
Substance doing the dissolving
What is the most common solvent in the cell?

40. Solutions Hypertonic: Solution with higher concentration of solute
Hypotonic:
Solution with lower concentration of solute
Isotonic
Solutions with equal solute concentrations

43. Facilitated diffusion
Carriers transport
Ions, aa or sugars across the membrane
Specific for type of solute
Moves from high concentration to low
The carrier facilitates the process

45. Examples
RBC diffusion of the bicarbonate ion
RBC diffusion of glucose

46. Facilitated diffusion
1. It is specific
2. It is passive
3. It saturate
Carriers are saturated
Transport rate cannot increase
Despite the concentration gradient

47. Bulk transport Endocytosis Membrane envelops food particles
1. Phagocytosis
2. Pinocytosis
3. Receptor-mediated endocytosis

48. Bulk transport Phagocytosis: The cell engulfs particles Pinocytosis:
The cell engulfs liquid
Receptor-mediated:
Transported molecules bind specific receptors in the plasma membrane

49. Phagocytosis

50. Pinocytosis

51. Receptor-mediated

52. Exocytosis The reverse of endocytosis
Discharge of materials from the cell
Secretion of many hormones, neurotransmitters, digestive enzymes and other substances

53. Active transport
Movement of substances against or up the concentration gradient
Low concentration to high
Requires energy.
Requires the use of ATP.
Cell takes up substances into cytoplasm that are already hypertonic to the extracellular fluid.

54. Sodium-potassium pump
Protein transports Na and K ions across the membrane.
Every cycle transports 3 Na ions out
Exchange for 2 K ions into the cell
Against concentration gradients.

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57. Coupled transport Molecule moves up its concentration gradient
Uses the drive from another substance moving down its concentration gradient.
Na ions and glucose

58. – + H+ ATP H+ – + H+ H+ – + H+ H+ – + H+ H+ – + – + Diffusion of H+
Fig. 7-19 – + H+
ATP H+ – +
Proton pump H+ H+ – + H+ H+ – + H+
Diffusion
of H+
Sucrose-H+
cotransporter
Figure 7.19 Cotransport: active transport driven by a concentration gradient H+ –
Sucrose + – +
Sucrose