The Living Cell Membrane

1
The Living Cell Membrane
2
What is it?

• The cell membrane is a flexible container for the
  cells cytoplasm and organelles,
• but it is also much more.
• The cell membrane is a semi permeable barrier
  which separates the cells cytoplasm and
  organelles from the external environment.

3
Semi Permeable?

• A semi permeable membrane is a barrier which
  allows only certain molecules to pass through it.
• This way the cell membrane can allow certain
  molecules to enter the cell while keeping others
  out.

4
External Environment Cell
Interior
5
Why is the cell membrane necessary?

• Cells need to both taken in food, or in plants
  the materials to make food, and get rid of waste
  products.
• To avoid absorbing material which would be
  harmful or useless to the cell, or losing
  material which the cell must retain.

6
What is the Cell Membrane made of?

• The cell membrane is made of many many
  phospholipids
• The membrane also contains different kinds of
  proteins between the phospholipids.

7
How is this Phospholipid Membrane Made?

• The membrane has two layers each composed of
  Phospholipids.
• The hydrophilic (water loving) heads of each
  layer point outwards.
• The hydrophobic (water fearing) tails point
  inwards.

8
(No Transcript)
9
Where Do The Proteins Fit In?

• The cell membrane has a number of different types
  of proteins embedded in it.
• Glycoproteins
• Gatekeeper (Porin) Proteins
• Receptor Proteins
• Transport Proteins

10
Glycoproteins

• Glycoproteins carry special sugar molecules which
  help identify the cell to the immune system.
• Glycoproteins differ between species and
  individuals in the same species. (Type A and Type
  B blood for example.)

11
(No Transcript)
12
Gatekeeper (Porin) Proteins

• Gatekeeper proteins can open or close to allow or
  prevent molecules from entering or leaving the
  cell.
• These proteins open channels and allow passive
  transport by diffusion.

13
(No Transcript)
14
Receptor Proteins

• Receptor proteins connect with hormones on the
  cells outer surface
• These proteins can trigger changes in the cell.

15
(No Transcript)
16
Transport Proteins

• Transport proteins move specific molecules into
  or out of the cell
• Transport proteins require ATP (energy) to
  function.

17
(No Transcript)
18
Liposomes

• Liposomes are artificial lipid vesicles.
• Liposomes function like cell membranes, they can
  fuse with a cell membrane and deliver its
  contents into a cell.
• They are used in drug and gene therapy.

19
Diffusion

• Passive Transport

20

• Molecules in a solution or gas move about
  randomly
• This movement is called Brownian Motion
• This causes particles to move from an area of
  high concentration to an area of low
  concentration.
• Concentration is the number of molecules per unit
  of volume
• Can you think of examples of diffusion of a gas?
  How about a solution?

21
Concentration Gradient

• The difference between in the number of molecules
  of a substance between adjoining regions.

22
http//highered.mcgraw-hill.com/sites/0072495855/s
tudent_view0/chapter2/animation__how_diffusion_wor
ks.html
23
Osmosis, what is it?

• Osmosis is the diffusion of water across a
  selectively permeable membrane
• Osmosis is like other diffusion, water molecules
  moves from an area of high concentration to an
  area of low concentration.

24
(No Transcript)
25
Types of Solutions

• Isotonic solution a solution where the
  concentration of solute is equal inside and
  outside the cell.
• Hypotonic a solution where the concentration of
  solute is lower outside the cell than inside.
• Hypertonic a solution where the concentration of
  a solute is higher outside the cell than inside.

26
Equilibrium

• Equilibrium is a condition in which all acting
  influences are balanced and a stable environment
  results.
• Molecules continue to move in an equilibrium
  environment, but there is no net gain or loss of
  molecules.

27
Facilitated Diffusion

• Protein carrier molecules, located on cell
  membranes, can help in passive transport.
• For example glucose diffuses into cells about a
  hundred times faster than other similar sugars.
• Carrier proteins must be specialized to aid the
  diffusion of glucose molecules, but not other
  sugars.