Homework

1
Homework

• Read Chapter 7
• Chapter 5 today
• Test 1 Week of 13-17

2
Chapter 7 Membrane Structure and Function
3
Plasma Membrane

• The membrane at the boundary of every cell.
• Functions as a selective barrier for the passage
  of materials in and out of cells.

4
Membrane Composition

• phospholipids
• Proteins
• Question How are the
  materials arranged?

5
Phosphophospholipid Bilayer

• Phospholipids
• Hydrophilic heads
• Hydrophobic tails

6
Membrane Models
7
Davson-Danielli Model 1935

• phospholipid bilayer.
• Proteins coat the surfaces.
• Sometimes called the sandwich model.

8
Evidence

• Biochemical work.
• TEM pictures show the membrane as a double line.

9
(No Transcript)
10
Problems

• Not all membranes in a cell were the same.
• How could the proteins stay in place?
• Result - the model was questioned and tested by
  scientific process.

11
Fluid Mosaic Model 1972

• New model to fit the new evidence with membranes.
• Example of Science as a
  Process.

12
Fluid Mosaic Model

• Refers to the way the phospholipids and proteins
  behave in a membrane.

13
Fluid

• Refers to the phospholipid bilayer.
• Molecules are not bonded together, so are free to
  shift.
• Must remain "fluid" for membranes to function.

14
Ways to keep the membrane fluid

• phospholipid changes or shifts
• Cold hardening of plants (shift to
  unsaturated fatty acids).
• Hibernating animals (Cholesterol increase).

15
(No Transcript)
16
Mosaic

• Proteins float in a sea of phospholipids.
• Proteins form a collage or mosaic pattern that
  shifts over time.

17
Evidence

• TEM pictures of fractured membranes.
• Cell fusion studies.
• Tagging of membrane proteins by antibodies.

18
(No Transcript)
19
(No Transcript)
20
Protein Function in Membranes

• Transport.
• Enzymatic activity.
• Receptor sites for signals.
• Cell adhesion.
• Cell-cell recognition.
• Attachment to the cytoskeleton.

21
(No Transcript)
22
(No Transcript)
23
Types of Membrane Proteins

• Integral - inserted into the phospholipid
  bilayer.
• Peripheral - not embedded in the phospholipid
  bilayer, but are attached to the membrane
  surface.

24
(No Transcript)
25
Question?

• How do the integral proteins stick to the
  membrane?
• By the solubility of their amino acids.

26
Hydrophilic Amino Acids
Hydrophobic Amino Acids
Hydrophilic Amino Acids
27
Membranes are Bifacial

• The phospholipid composition of the two layers is
  different.
• The proteins have specific orientations.
• Carbohydrates are found only on the outer surface.

28
Carbohydrates
29
Membrane Carbohydrates

• Branched oligosaccharides form glycophospholipids
  and glycoproteins on external surface.
• Function - recognition of "self" vs "other.

30
Question

• How do materials get across a cell's membrane?

31
Problems

• phospholipid bilayer is hydrophobic. Hydrophilic
  materials don't cross easily.
• Large molecules don't cross easily. Too big to
  get through the membrane.

32
Mechanisms

• 1. Passive Transport
• 2. Active Transport

33
Passive Transport

• Movement across membranes that does NOT require
  cellular energy.

34
Types of Passive Transport

• 1. Diffusion
• 2. Osmosis
• 3. Facilitated Diffusion

35
Diffusion

• The net movement of atoms, ions or molecules down
  a concentration gradient.
• Movement is from High Low

36
(No Transcript)
37
Equilibrium

• When the concentration is equal on both sides.
• There is no net movement of materials.

38
Factors that Effect Diffusion

• 1. Concentration
• 2. Temperature
• 3. Pressure
• 4. Particle size
• 5. Mixing

39
Osmosis

• Diffusion of water.
• Water moving from an area if its high
  concentration to an area of its low
  concentration.
• No cell energy is used.

40
Tonicity

• The concentration of water relative to a cell.
• 1. Isotonic (same)
• 2. Hypotonic (below)
• 3. Hypertonic (above)

41
(No Transcript)
42
Isotonic

• Isosmotic solution.
• Cell and water are equal in solute concentration.
• No net movement of water in or out of the cell.
• No change in cell size.

43
Hypotonic

• Hypoosmotic solution
• Cell's water is lower than the outside water
  (more solutes).
• Water moves into the cell.
• Cell swells, may burst or the cell is turgid.

44
Hypertonic

• Hyperosmotic solution
• Cell's water is higher than the outside water
  (less solutes)
• Water moves out of the cell.
• Cell shrinks or plasmolysis occurs.

45
Problems in tonicity

• Common to AP exams
• Usually depend on being able to define high and
  low water or solute concentrations.
• U-tube problems

46
Facilitated Diffusion

• Transport protein that helps materials through
  the cell membrane.
• Doesn't require energy (ATP).
• Works on a downhill concentration gradient.

47
(No Transcript)
48
Aquaporins

• Newly found channels for osmosis.

GFP labeled Aquaporins
49
Active Transport

• Movement across membranes that DOES require
  cellular energy.

50
A.P. BIOLOGY

• Susan IASMH

51
Homework

• Read Chapter 7, 44
• Test 1 Week of 13-17
• No Lab Broadcast Thursday
• Chapter 7 Fri. 9/17
• Chapter 44 Wed. 9/22

52
Self-Study Chapters

• Additional chapters that you are expected to read
  and complete homework on your own time.
• Overlap in-class chapters.
• Expands what we can cover.

53
Types of Active Transport

• 1. Carrier-Mediated
• 2. Endocytosis
• 3. Exocytosis

54
Carrier-Mediated Transport

• General term for the active transport of
  materials into cells AGAINST the concentration
  gradient.
• Movement is low high

55
Examples

• 1. Na- K pump
• 2. Electrogenic or H pumps
• 3. Cotransport

56
(No Transcript)
57
Na- K pump

• Moves Na ions out of cells while moving K ions
  in.

58
Electrogenic or H pumps

• Also called Proton pumps.
• Create voltages across membranes for other cell
  processes.
• Used by plants, fungi and bacteria.

59
(No Transcript)
60
Cotransport

• Movement of H that allows other materials to be
  transported into the cell as the H diffuses back
  across the cell membrane.
• Example - Sucrose transport

61
(No Transcript)
62
Exocytosis

• Moves bulk material out of cells.
• Example - secretion of enzymes.

63
Endocytosis

• Moves bulk materials into cells.
• Several types known.

64
Types

• 1. Pinocytosis - liquids
• 2. Phagocytosis - solids
• 3. Receptor Mediated - uses receptors to "catch"
  specific kinds of molecules.

65
Carbohydrates
66
Forming vesicles
67
(No Transcript)
68
Summary

• Know membrane structure.
• Be able to discuss the various methods by which
  cells move materials through membranes.
• Be able to solve problems in osmosis.