Cell Membrane

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Cell Membrane
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Review of phospholipid bilayer
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Monomers of fatty acids are used to build
triacyglycerol (fats) and membrane lipids
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(No Transcript)
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Hydrophobic effect
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A lipid bilayer prevents the diffusion of polar
substances
solutes spontaneously diffuse from a region of
high concentration to a region of low
concentration a lipid bilayer prevents the of
polar substances of the inner
compartment (also prevents the inward diffusion
of polar substances)
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Cell Membrane fluid mosaic model

• Composed of
• Lipids
• double layer
• Proteins
• surface
• embedded proteins
• Act as
• Act as
• Carbohydrates
• Attached to surface on lipids or proteins
• Many act as cards

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Cell Membrane

• The cell membrane is permeable
• Materials may cross the cell membrane in 3
  methods
• through the membrane
• Diffusion (passive transport)
• Openings created via
• Diffusion via channel (e.g. osmosis)
• Diffusion via carrier (facilitated transport)
• Carrier (active transport)
• the cell membrane
• Exocytosis or endocytosis (active transport)

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Cell Membrane is Selectively Permeable
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Transport of Molecules via Diffusion
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Factors effecting diffusion rate

• gradient
• of solute molecule
• of medium (solvent)
• Solubility of molecule (polarity/charge)
• Temperature of
• stream (continuous movement of cytoplasm
  moves molecules around the cell)

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Diffusion across a cell membrane

• Diffusion the of molecules from an area of
  concentration to an area of concentration until
  distributed
• Diffusion is most rapid when there is a
  different in concentration (this is called the
  concentration gradient)
• As the concentration decreases, the rate of
  diffusion
• The rate of diffusion also depends on molecule
  and and the temperature and of
  the .

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Diffusion across a cell membrane
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Osmosis

• Diffusion of H2O across a selectively permeable
  membrane
• Every solution is made up of and the
• Solute the substance being
• Solvent the liquid that the is being
  dissolved within

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Osmosis

• The of water across a cell membrane
  depends on the type of solution (the solute
  of the solution) on both sides of the
  barrier
• The tonicity ( ) of a cell can be classified
  by the following
• Hypotonic a solution with a solute
  concentration (and so more H2O ) compared to the
  other solution.
• Hypertonic The solution that has a
  solute concentration (and so less H2O ) compared
  the other solution
• Isotonic the solutions have H2O concentration

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Cells in Hypertonic Solutions

• In hypertonic solutions, the of solute
  molecules the cell is higher than the
  concentration the cell
• As a result, water out of the cell until
  equilibrium is
• Cells in hypertonic solutions usually because
  the cells activities are by lack of

• Scientific term when RBC shrinks is crenation

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Cells in Hypotonic Solutions

• In a solution, the concentration of solute
  molecules the cell is lower than the
  of solutes inside the cell
• Water will therefore flow into the
  until equilibrium is established
• The flow of water into a cell causes it to

• Scientific term when water enters the RBC is
  hemolysis

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Cells in Isotonic Solutions

• In an isotonic solution, the concentration of
  solutes outside of the cell are
• Water will therefore into and out of the cell
  at equal rates there will be no movement of
  water

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Movement of Water

• WATER WILL ALWAYS FLOW FROM HYPOTONIC TO A
  HYPERTONIC SOLUTION

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increase in vacuole's volume causes the
cell membrane to push against the cell
wall
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Transport of Molecules by Carriers
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Facilitated Transport

• Follows the gradient, so therefore, it is a
  passive transport

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Facilitated Transport

• Doesnt require
• Transports large molecules and charged ions
  since they cannot freely diffuse across the
  hydrophobic cell .
• Carrier protein ( ) molecule in membrane is
  gated
• CP molecule to be
• CP to the molecule being
• CP a conformational change and its gate opens
  and releases molecule to the other side
• moves across the cell membrane in this manner

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Conformational Change in Proteins
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Active Transport

• Requires energy since molecules move against the
  concentration gradient
• Carrier protein molecule in membrane is gated
• CP molecule to be transported
• CP to the molecule being transported
• ATP CP to open its gate to release the molecule
  to the side
• Example pump

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Sodium-Potassium Pump
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Endocytosis and Exocytosis
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Endocytosis

• Is an process and energy
• Other molecules which cant cross the cell
  membrane through protein channels or carriers due
  to their size/type enter the cell via
• During endocytosis, the membrane off the cell
  membrane and smaller vesicle is made, which
  carries the material being transported in
• Two types on endocytosis

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Phagocytosis

• This type of is used by the immune system cells
• Large or bacteria cells are engulfed by cell
  membrane
• Fused with to break the bacteria down

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Pinocytosis

• Other large taken in by the cell
• Also known as

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Exocytosis

• Getting rid of from the cytoplasm
  to the exterior of the cell
• Membrane of the fuses with the
  cell membrane and discharges its

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Whats going on inside the cell?
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How the fluid mosaic model is established
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Fluid Mosaic Model

• helps keep the membrane firm and prevents it
  from beings too fluidy
• and are surface
  identification markers and play a role in
  cell-cell (what kind of
  cell is this? Good or bad?)
• -sugar molecule attached to a phospholipid
• sugar molecule attached to a protein
  embedded in the membrane

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Proteins in the cell membrane
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By the end of this section you should be able to

• Apply knowledge of organic molecules
  phospholipids, proteins, glycoproteins,
  glycolipids, and cholesterol to explain the
  structure and function of the fluid mosaic model
• Identify the hydrophobic and hydrophilic regions
  of the phospholipid bilayer
• Explain why the cell membrane is described and
  selectively permeable
• Describe passive transport processes including
  diffusion, osmosis and facilitated transport
• Explain factors that affect the rate of diffusion
  across a cell membrane (temperature, size of
  molecule, charge of molecule, concentration
  gradient, pressure gradient)
• Predict the effects of hypertonic, isotonic and
  hypotonic environments on osmosis in animal cells
• Describe the active transport process in terms
  of concentration gradients, use of channel or
  carrier proteins, use of energy, types/sizes of
  molecules transported
• Describe active transport processes such as
  endocytosis and exocytosis in terms of use of
  energy, type/size of molecules transported