Membrane Structure

1
Chapter 8

• Membrane Structure
• and Function

2
Plasma Membrane Early Models

• 1895 Overton - lipid in memb.
• 1917 Langmuir - one layer of phospholipids
• 1925 Gorter and Grendel - bilayer arrangement
• 1935 Danielli and Davidson - phospholipids
  between two layers of protein

3
Fluid Mosaic Model

• 1972 Singer and Nicolson
• the membrane is a mosaic of numerous protein
  molecules (mlc) bobbing in a fluid bilayer of
  phospholipids

4
Membranes

• 7-8 nm few molecules thick
• bifacial
• distinct interiors and exteriors
• those with different functions have different
  chemical composition

5
Phospholipid Molecule

• Amphipathic
• hydrophilic region
• head phosphate glycerol
• polar
• hydrophobic region
• tails 2 f.a.
• nonpolar

6
Membrane Fluidity

• Unsaturated f.a. fluidity
• cholesterol in membranes
• at high temp fluidity
• at low temp fluidity
• movement of phospholipids
• frequent lateral
• rare flip-flop
• mouse experiment

7
Selective Permeability of Membranes

• Theoretically, the phospholipid bilayer should be
  
• Permeable
• nonpolar
• Impermeable
• polar

8
Selective Permeability of Membranes cont.

• Actually
• permeable
• nonpolar
• small polar
• (water, carbon dioxide)
• contains transport proteins

9
Membranes

• every membrane has its unique collection of
  proteins
• plasma membrane (RBC),
• organelle (mitochondria)
• protein types determine the function

10
Membrane Proteins

• Integral - embedded
• unilateral
• transmembrane
• peripheral - surface

11
Membrane Composition

• Lipids
• phospholipid molecules
• cholesterol
• glycolipids on surface

12
Membrane Composition cont.

• Proteins
• integral
• peripheral

13
Membrane Composition cont.

• Carbohydrates, attached
• exterior only

14
Ways Cell Membranes Interact w/ Environment

• 1. Water Passage
• 2. Bulk Passage
• 3. Selective transport
• 4. Reception of information
• 5. Expression of cell identity
• 6. Physical connections

15
1. Water Passage

• simple diffusion
• solid, liquid, gas
• rate of diffusion
• conc of substances,
• MW of substance,
• temperature

16
Osmosis

• isotonic solution
• equal solute conc
• no net water movement
• 0.85
• 0.85

17
Isotonic Solution

• Animal cell
• normal

• Plant cell
• flaccid, wilt

18
Osmosis

• hypertonic solution
• higher solute conc in solution
• water mostly leaves cell
• 0.85
• 10

19
Hypertonic Solution

• Animal cell
• shriveled

• Plant cell
• plasmolyzed

20
Osmosis

• hypotonic solution
• lower solute conc in solution
• water mostly enters cell
• 0.85
• 0

21
Hypotonic Solution

• Animal cell
• lyzed

• Plant cell
• turgid (normal) (turgor pressure)

22
Erythrocytes

• Erythrocytes 0.85 NaCl
• isotonic soln 0.85 NaCl
• normal, biconcave discs
• hypertonic soln gt0.85 NaCl
• crenate
• hypotonic soln (lt0.85 NaCl)
• hemolyze

23
Osmosis cont.

• osmoregulation
• control of water balance
• osmotic pressure (OP)
• take in water
• osmometer
• hydrostatic pressure (HP)
• take out water
• equilibrium OP HP

24
Ways Cell Membranes Interact w/ Environment

• 1. Water Passage
• 2. Bulk Passage
• 3. Selective transport
• 4. Reception of information
• 5. Expression of cell identity
• 6. Physical connections

25
2. Bulk Passageeuk. only

• Passage of large material
• endocytosis
• engulfing
• exocytosis
• exporting

26
Endocytosis

• Nonspecific
• phagocytosis
• cell eating
• pinocytosis
• cell drinking

27
Exocytosis

• Secretion
• excretion

28
Ways Cell Membranes Interact w/ Environment

• 1. Water Passage
• 2. Bulk Passage
• 3. Selective Transport
• 4. Reception of information
• 5. Expression of cell identity
• 6. Physical connections

29
3. Selective Transport

• phospholipid mlc allow
• nonpolar mlc
• O, lipids, hydrocarbons
• small polar mlc
• H2O , CO2

30
Selective Transport cont.

• transport proteins allow
• ions
• Ca, Na, H, Cl-
• large polar mlc
• sugars
• a.a. and proteins

31
Transport Proteins

• uniport
• symport
• antiport

32
Selective Transport Mechanisms

• facilitated diffusion
• active transport

33
Facilitated Diffusion

• passive, w/ conc. gradient
• requires transport protein, specific
• Cl-
  
  

34
Active Transport

• active, against conc. gradient
• requires transport proteins, specific
• glucose

35
Sodium-Potassium Pumpexample of active transport

• Na
• K

36
Cotransport

• Couple f. diffusion with the transport of other
  solutes against their conc. gradients
• Na -- solute
• Na
• K

37
Proton Pumpexample of active transport

• H

38
Cotransport

• H
• H -- solute

39
Ways Cell Membranes Interact w/ Environment

• 1. Water Passage
• 2. Bulk Passage
• 3. Selective transport
• 4. Reception of information
• 5. Expression of cell identity
• 6. Physical connections

40
4. Reception of Information

• receptor
• transmembrane protein
• conveys information
• ligand
• target molecule

41
Receptor-mediated endocytosis

• specific
• enables cell to acquire bulk quantities of
  specific substances

42
Ways Cell Membranes Interact w/ Environment

• 1. Water Passage
• 2. Bulk Passage
• 3. Selective transport
• 4. Reception of information
• 5. Expression of cell identity
• 6. Physical connections

43
5. Cell Identity

• Every cell has a unique set of antigens (Ag)
• cell surface markers

44
Cell Identity cont.

• Ag vary from
• species to species
• individual to individual
• cell to cell of same person
• membrane to membrane of the same cell

45
Major Histocompatibility Complex (MHC)

• A collection of tolerable molecules (Ag)
• self-recognition markers

46
Tissue-recognition markers

• Identify a cell as belonging to a specific tissue
  group
• connective, muscle, nervous, epithelial
• recognition in forming embryonic tissues

47
Ways Cell Membranes Interact w/ Environment

• 1. Water Passage
• 2. Bulk Passage
• 3. Selective transport
• 4. Reception of information
• 5. Expression of cell identity
• 6. Physical connections

48
6. Physical Connections Intercellular junctions

• Plant cells
• plasmodesmata (pl)

49
Physical Connections cont.

• Animal cells
• desmosomes (anchoring junc)
• tight (organizing) junctions
• gap (communicating) junctions

50
Chapter 8

• The END

51
Graft Types

• Autograft
• Isograft
• Allograft
• Xenograft