Cell Membranes and Transport

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Cell Membranes and Transport

• B9 - Analyze the structure and function of the
  cell membrane

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Cell Walls

• NB Cell walls are different from cell membranes
• Stiff, non-living
• Made of complex carbohydrates
• Cellulose for plants
• Chitin for fungi
• Chitin-like frame for bacteria
• Used for support and protection
• Very porous entry only controlled by size

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Cell Membranes gate keepers

• 1. Isolate form outside
• 2. Control entry and exit
• 3. Communicate with others
• 4. Bare identification (Im one of you!)

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Which of these statements are true comparing cell
walls with membranes?
Walls Membranes
A Non-living Living
B Plants and bacteria only Animals only
C Control entrance by size only Control entrance by many factors
D Made with cellulose Made with lipids
E Contain pores Contain pores
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Fluid Mosaic Model

• A phospholipid bilayer with proteins scattered
  through it
• fluid because the proteins seem to float
  around the bilayer
• Hydrophilic heads on the outside
• Hydrophobic tails on the inside

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• Hydrophobic layer is a barrier to H2O soluble
  molecules (but makes it less fluid)

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• Cholesterol in the bilayer is even less permeable
  to H2O soluble molecules (but makes it less fluid)

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Protein Mosaic

• Membrane proteins will interact with the
  hydrophobic and hydrophilic layers of the bilayer
• Some proteins will protrude into the cytoplasm,
  some into the extracellular space, others into
  both

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Glycoproteins

• Membrane proteins that have a carbohydrate chain
  attached
• Often seen in proteins that protrude outside the
  cell

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Glycolipids

• Membrane lipids that have a carbohydrate chain
  attached
• Both glycoproteins and glycolipids OFTEN function
  in cell-to-cell communication and/or recognition

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What does the fluid in fluid mosaic model
refer to?

• A. The structure of the cell membrane
• B. The structure of the cell wall
• C. The fact that the membrane is made up mostly
  of water
• D. The fact that the membrane is always changing,
  so it seems to be fluid
• E. The fact that the membrane is made up of
  lipids, and they tend to flow

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What does mosaic mean?

• A. a picture
• B. a lipid
• C. a bunch of different things clumped together
  on a background
• D. a type of protein that lets things into the
  cell
• E. No idea!

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Which of the following is true regarding this
diagram?

• A. 1a and 1b are fatty acids
• B. 3 is a phosphate group
• C. 5 is the hydrophobic end of the molecule
• D. 6 is the hydrophobic end of the molecule
• E. this is a type of lipid

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Which one is a

• 1. Phospholipid
• 2. Glycoprotein
• 3. Cholesterol

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3 major membrane Protein Categories

• 1. Transport proteins
• Regulated, fast method for specific molecules to
  enter and exit
• Channel proteins
• Carrier proteins

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2. Receptor Proteins

• When activated, set off enzymatic sequences
  inside the cell

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3. Recognition Proteins

• identification tags

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Membrane Transport - RATE

• Depends on
• Gradient (concentration, electrical or pressure)
• Size of molecule
• Lipid solubility
• of transporters

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Diffusion

• The random net movement of molecules from an area
  of high concentration to an area of low
  concentration.
• (this is following the concentration gradient)

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Osmosis

• The diffusion of WATER across a selectively
  permeable membrane
• (this is also following the concentration
  gradient and does not require energy)

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Osmotic Effects

• Isotonic solution
• Same solute concentration
• Cell is happy (no net loss or gain of water)

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HYPERtonic solutions

• Solute is greater outside the cell than inside
  the cell
• Cell is not happy
• It will crenate (shrink)

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HYPOtonic solutions

• Solute concentation is less outside the cell than
  inside
• Cell is not happy
• Cell will lyse

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Active transport

• Often against the concentration gradient
• Therefore, REQUIRES ENERGY
• (ATP --gt ADP P)
• Uses transporter proteins

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Endocytosis - 3 types
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PhagocytosisLarge particles
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2. Pinocytosis

• Liquid and
• smaller particles only

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Receptor-mediated Endocytosis

• Uses receptors to bind first to the desired
  molecules, then gathers them together before
  enclosing them in a membrane