CELL SURFACES

1
CELL SURFACES

• The plasma membrane is the edge of life -- the
  boundary that separates the living cell from its
  nonliving surroundings.

2
Artificial Membranes
3
Original Davson-Danielli model
This is also known as the butter sandwich model.
4
Sidedness of the plasma membrane
5
Fluid Mosaic Model

• Proteins embedded in the phospholipid bilayer
• Hydrophilic parts of proteins phospholipids are
  exposed to water to produce a stable membrane
• Membranes are a mosaic of proteins bobbing in a
  fluid bilayer of phospholipids

6
Current Fluid Mosaic Model
7
Functions of membrane proteins
8
Detailed structure of animal plasma membrane
9
The plasma membrane is
a dynamic living membrane.

• It is not permeable.
• It is not just semi-permeable.
• The plasma membrane is selectively permeable.

10
III. Plant Cell Walls

• A. Primary Cell Walls
• composed of cellulose
• found in ALL plant cells
• are permeable or porous
• external to the cell membrane
• provide a boundary which permit turgor
• found in plant cells which are living

11
III. Plant Cell Walls

• B. Secondary Cell Walls
• composed of lignin
• found in dead plant cells
• are impermeable
• external to the cell membrane but internal to the
  primary cell wall
• found in the cells commonly called wood

12
IV.Cell Connections

• The many cells of an animal or plant are
  integrated into one functional unit.
• Neighboring cells often adhere, interact, and
  communicate through special patches of direct
  physical contact.

13
Plant Cell Connections...

• 1.Middle Lamella- composed of pectin cements
  adjacent plant cell walls together
• 2.Plasmodesmata- cytoplasmic strands between
  adjacent plant cells which permit communication
  between cells

14
Plant cell walls
15
There are 3 animal cells connections

• 1. Desmosomes - hold cells together with
  interwoven protein fibers
• 2. Tight Junctions adjacent cells are fused
  together to prevent leakage
• 3. Gap Junctions - small channels that allow
  macromolecules to pass between adjacent cells

16
Intercellular junctions in animals
17
B. Animal Cells

• Whereas plant cells are cemented together by
  pectins in the middle lamella, animal cells are
  cemented together by hyaluronic acid.

Cement
18
The cell is a living unit greater than the sum of
its parts.

• Organelles do not function in isolation!
• At the cellular level, life emerges from
  complex interactions of a cells parts.