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The Cell Membrane. Ms. Napolitano & Mrs. Haas CP Biology. The Cell Membrane. Thin, flexible barrier that surrounds the cell AKA plasma membrane Selectively permeable – allows some substances to cross more easily than others Usually ~8nm thick. The Phospholipid Bilayer. Fluid Mosaic Model.

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The Cell Membrane

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the cell membrane

The Cell Membrane

Ms. Napolitano & Mrs. Haas

CP Biology

the cell membrane1
The Cell Membrane
  • Thin, flexible barrier that surrounds the cell
  • AKA plasma membrane
  • Selectively permeable – allows some substances to cross more easily than others
  • Usually ~8nm thick
fluid mosaic model
Fluid Mosaic Model
  • Used to describe the structure of the membrane
  • Fluid structure of phospholipids with a mosaic of various proteinsembedded in it
  • Cholesterol helps maintain fluidity
    • Membrane becomes less fluid as temperature increases by restricting movement
    • Membrane becomes more fluid as temperature decreases by maintaining space
membrane proteins
Membrane Proteins
  • Different types of cells contain different types of membrane proteins
  • Integral proteins – embedded into the hydrophobic core of the lipid bilayer
    • May or may not go all the way through the membrane
  • Peripheral proteins – on the bilayer surface



types of membrane proteins 1 of 2
Types of Membrane Proteins(1 of 2)
  • Transport
    • Channel or carrier proteins (hydrophilic tunnels) allow polar molecules and ions to pass through the hydrophobic layer
    • Proteins are specific for the substance they transport
  • Enzymatic
  • Signal Transduction (chemical messages)
    • Receptor proteins transmit information from outside of the cell to inside of the cell
types of membrane proteins 2 of 2
Types of Membrane Proteins(2 of 2)

4. Recognition

  • ID tags – glycolipids or glycoproteins

5. Intercellular Joining

  • Join together adjacent cells

6. Support

  • Attach to cytoskeleton or extracellular matrix for stability
the phospholipid bilayer is in the middle and on the outsides
The phospholipidbilayer is __________ in the middle and __________ on the outsides.
  • Hydrophobic, hydrophilic
  • Hydrophilic, hydrophobic
  • Hydrophobic, hydrophobic
  • Hydrophilic, hydrophilic
what is the function of cholesterol in the cell membrane
What is the function of cholesterol in the cell membrane?
  • Identification
  • Transport
  • Membrane fluidity
  • Recognition
which of the following is not a function of membrane proteins
Which of the following is NOT a function of membrane proteins?
  • Signal transduction
  • Identification
  • Transport
  • Support
passive transport
Passive Transport
  • Passive Transport – the movement across the cell membrane that does not require energy
  • Types:
    • Diffusion
    • Osmosis
    • Facilitated Diffusion
  • Diffusion – the movement of particles from an area of high concentration to an area of low concentration until an equilibrium is reached
    • Transports small, nonpolar molecules such as CO2 and O2
  • Concentration Gradient – the difference in the concentration of a substance across a space
  • Equilibrium – concentration of a substance is equal throughout a space
  • Osmosis – diffusion of free water across a selectively permeable membrane
  • Water diffuses across the cell membrane from the region of low solute concentration to that of a higher solute concentration until it reaches equilibrium
u tube not youtube
U-Tube (not YouTube!)

Which way will water flow?

osmoregulation in cells without cell walls
Osmoregulation in Cells Without Cell Walls
  • Osmoregulation: control of water balance
  • Tonicity: the ability of a solution to cause a cell to gain/lose water
    • Isotonic solution: no net movement of water across the cell membrane
    • Hypertonic solution: more free water inside the cell (cells lose water & shrivel)
    • Hypotonic solution: less free water inside the cell (cells gain water & lyse)
      • Some cells have a contractile vacuole to pump water out of the cell

osmoregulation of cells with cell walls
Osmoregulation of Cells WithCell Walls
  • Plant cells are healthiest in a hypotonic solution
    • Osmotic pressure keeps cell walls turgid (very firm)
  • Plant cells are flaccid (limp) in an isotonic solution
  • In a hypertonic solution, the cell membrane will shrink and pull away from the cell wall
    • AKA plasmolysis (wilting)

facilitated diffusion
Facilitated Diffusion
  • Facilitated Diffusion: passive transport aided by proteins
  • Molecules travel from high  low concentration
  • Transports small, polar molecules
    • Glucose
    • Salts
    • Ions
    • Amino Acids
    • Water (aquaporins)
channel proteins
Channel Proteins
  • Hydrophilic passageways
  • Some are always open for diffusion
  • Rate of movement is determined by the concentration gradient
  • Some ion channels have gates that can be opened by:
    • Cell membrane stretching
    • Change in electrical charge
    • Binding of specific molecules
carrier proteins
Carrier Proteins
  • Specific substance binds to carrier protein
  • Protein changes shape & transports substances across the cell membrane
  • Molecule is released into the cell, and carrier protein returns to its original shape

active transport
Active Transport
  • Uses energy to move solutes AGAINST the concentration gradient
  • Carrier proteins act as “pumps” powered by ATP
  • Examples:
    • Sodium Potassium Pump
    • Proton Pump
    • Cotransport
sodium potassium pump
Sodium Potassium Pump
  • Pumps 3 Na+ out of the cell and 2 K+ into the cell
  • Actively transports both ions against their concentration gradient
  • Powered by ATP
proton pump
Proton Pump
  • Actively transport protons (H+) through the internal membranes of mitochondria & chloroplasts
cotransport coupled transport
Cotransport (Coupled Transport)
  • Cotransport: The transport of one solute indirectly drives the transport of several other solutes (using ATP)
  • Example: As proton pump pumps H+ out, H+ ions diffuse back in pulling sucrose with it
bulk transport
Bulk Transport
  • Substances that are too large to be transported by carrier proteins
  • Example: proteins leaving/entering the cell
  • Uses vesicles
  • Types:
    • Exocytosis
    • Endocytosis
  • Exo= Export (recall exo means outside!!)
  • Vesicles fuse with the cell membrane, releasing the contents outside of the cell
  • Recall endo means inside!!
  • Cell membrane engulfs particles
  • Pinches off to form vesicles inside of the cell