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Plasma Membrane

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THE FLUID MOSAIC MODEL Plasma Membrane What is it? What is it made of? What is its function? About Cell Membranes All cells have a cell membrane Functions: Controls ... – PowerPoint PPT presentation

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Title: Plasma Membrane


1
Plasma Membrane
THE FLUID MOSAIC MODEL
  • What is it?
  • What is it made of?
  • What is its function?

2
Structure of the Cell Membrane
Outside of cell
Carbohydrate chains
Proteins
Lipid Bilayer
Transport Protein
Phospholipids
Inside of cell (cytoplasm)
Animations of membrane structure
Go to Section
3
Membrane structure A membrane is a fluid mosaic
of lipids, proteins and carbohydrate.
A membrane is a fluid mosaic The membrane is a
mosaic of protein molecules bobbing in a fluid
bilayer of phospholipids.
4
Fluid Mosaic Model of the cell membrane
Polar heads love water dissolve.
Membrane movement animation
Non-polar tails hide from water.
Carbohydrate cell markers
Proteins
5
HOW DOES THE MEMBRANE MOVE?
  • A membrane is held in together by weak
    hydrophobic interactions.
  • Most membrane lipids and some proteins can drift
    laterally within the membrane
  • Molecules rarely flip transversely (flip-flop)
    across the membrane, because hydrophilic parts
    would have to cross the membranes hydrophobic
    core.

Fig. 8.4a
6
About Cell Membranes
  • All cells have a cell membrane
  • Functions
  • Controls what enters and exits the cell to
    maintain an internal balance called homeostasis
  • Provides protection and support for the cell

TEM picture of a real cell membrane.
7
About Cell Membranes (continued)
  • Structure of cell membrane
  • Lipid Bilayer -2 layers of phospholipids
  • Phosphate head is polar (water loving)
  • Fatty acid tails non-polar (water fearing)
  • Proteins embedded in membrane

Phospholipid
Lipid Bilayer
8
About Cell Membranes (continued)
  • 4. Cell membranes have pores (holes) in it
  • Selectively permeable Allows some molecules in
    and keeps other molecules out
  • The structure helps it be selective!

Pores
9
Membranes are mosaics of structure and function
  • A membrane is a mosaic of different proteins
    embedded and dispersed in the phospholipid
    bilayer. These proteins vary in both structure
    and function, and they occur in two spatial
    arrangements

1- Integral proteins 2- Peripheral proteins
10
TYPE OF INTEGRAL PROTEINSin the plasma membrane
may provide a variety of.
11
FUNCTIONS OF INTEGRAL PROTEINS Channel Protein
Allow a substance to move across the membrane (EX
all hydrogen ions to flow across membrane of
electron transport chain) Carrier Protein
Selectively interacts with specific molecules or
ions so it can cross membrane (EX Sodium and
Potassium pump) Cell Recognition Protein Called
glycoproteins, allow cell to be recognized by
bodys immune system Receptor Protein
Specifically shaped to a specific molecule (EX
liver stores glucose after insulin binds to cell
receptor) Enzymatic Protein Catalyze specific
reactions (EX ATP metabolism)
12
FUNCTIONS OF PERIPHERAL PROTEINS To provide
structural stability and shape to the plasma
membrane
13
  • What else can we find in this membrane?
  • Cholesterol helps control membrane fluidity by
    making the membrane
  • Less fluid at warm temperatures (e.g. 37 C body
    temperature) by restraining the phospholipid
    movement.
  • More fluid at lower (cool) temperatures by
    preventing close packing of phospholipids.
  • Cells may alter membrane lipid concentration in
    response to changes in temperature

Fig. 8.4c
  • Many cold tolerant plants (e.g. winter wheat)
    increase the unsaturated phospholipid
    concentration in autumn, which prevents the
    plasma membranes from solidifying in winter.

14
  • Lastly, why is fluidity important??
  • Membrane must be fluid to work properly.
    Solidification may result in permeability changes
    and enzyme deactivation.
  • Unsaturated hydrocarbon tails enhance membrane
    fluidity because kinks at the carbon-to-carbon
    double bonds hinder close packing of
    phospholipids.
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