Lifes Border:

1

• 5
• Lifes Border
• The Plasma Membrane

2

• I. Introduction (Sections 5.1 and 5.2)
• A. Importance of the plasma membrane (seen in
  malfunctioning transport in cystic fibrosis)
• B. Overview of major functions
• 1. Regulates what goes into and out of a cell.
• 2. Communication with other cells

3

• II. Four Components of the Plasma Membrane
  (Section 5.3)
• A. Phospholipid Bilayer
• 1. Phospholipidstwo fatty-acid chains and a
  polar phosphate group attached to glycerol
  Figure 5.1a

4

• 2. Arrangement of phospholipids in water (two
  layers, heads pointed out, tails pointed in)
  Figure 5.1b

5

• 3. Permeability of bilayerlipid center is a
  barrier to passage of large hydrophilic
  molecules, but it allows nonpolar, hydrophobic
  molecules to pass. (Interactive Activity 1)

6

• B. Cholesterol (prevents passage of some small
  molecules and adds fluidity) Figure 5.2

7

• C. Proteinsintegral (span entire membrane) and
  peripheral (lie on either side) with diverse
  range of functions Figure 5.2
• 1. Structural supportattach to cytoskeleton
• Recognitionhelps immune system determine self
  from foreign (thats why we reject transplants
• 3. Communicationreceptors and binding sites
  (Interactive Activity 2)
• 4. Transportallow molecules to pass

8

• D. Glycocalyx Figure 5.2sugar components
  protruding from lipids and proteins, functions
• 1. Binding sites for proteins in communication,
  and recognition
• 2. Lubricate cells
• 3. Stick cells down

9

• III. Moving Materials In and Out Diffusion and
  Gradients (Section 5.4)
• A. Random Movement and Diffusion Figures 5.3 and
  5.4
• 1. Diffusion movement of molecules from region
  of higher to lower concentration
• 2. Concentration gradient difference between
  the highest and lowest concentration of a solute,
  like bike coasting downhill, the tendency is for
  molecules to travel from high to low
  concentration.

Diffusion
Random Movement
10

• B. Diffusion through Membranes

11

• C. Permeability verses semi-permeability
• D. Osmosis net movement of water across a
  semi-permeable membrane from an area of lower
  solute concentration to higher solute
  concentration Figure 5.5 animation
• E. Importance of osmosis to membrane function in
  animals (drinking sea water) and plants (turgid
  pressure) Figure 5.6

12
OSMOSIS
13
Hypertonic Solution More water inside cell than
outside
Plasmolysis
Plasmolysis
Cells shrink and die
14
Iso-osmotic Solution same concentration of
water inside and outside cell
Animal cell
Plant cell
No net gain or loss of water
15
Hypotonic Solution more water outside cell than
inside
Cytolysis cell swells and bursts
Builds up turgor pressure cell becomes stiff,
keeping plant upright
16

• IV. Two Main Types of Transport across Cell
  Membranes (Section 5.5)
• A. Passive Transport
• 1. Simple diffusion (water, gases, fat-soluble)
  membrane is permeable, so they travel down
  concentration gradient and enter without energy
  output by cell Figure 5.7a

17
2. Facilitated diffusion (larger polar
molecules) membrane is impermeable, so even if
they want to travel down the concentration
gradient they cant without help from a membrane
channel (transport protein) Figure 5.7b
18

• B. Active TransportIf molecules have to pass
  across the membrane up their concentration
  gradient, they cannot use the energy of
  diffusion, but must expend energy (ATP) Figure
  5.7c

19
Na-K pump Figure 5.8
20
V. Getting the Big Stuff In and Out (Section
5.6) A. Exocytosis Figure 5.9movement of
materials out of the cell by fusion of vesicles
with the plasma membrane (export or removal of
wastes in single-celled organisms)
21
B. EndocytosisInfolding of the plasma membrane
to bring large materials into the cell
Pinocytotic vessicle
22

• 1. Pinocytosis, cell drinkingwater and
  solvents are enclosed in invaginating vesicle,
  used in digestive tract Figure 5.10a

23

• D. Receptor-mediated endocytosismore specific
  with receptor capturing ligand and concentrating
  into an invaginating pit Figure 5.10b

24
E. Phagocytosis, cell eatingHow the human
immune system ingests whole bacteria or
one-celled creatures eat pseudopodia, Figure
5.10c (Interactive Activity 4 5)
25
(No Transcript)