CELL MEMBRANES and TRANSPORT

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CELL MEMBRANESandTRANSPORT
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The Cell
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Cell membrane

• All living things are surrounded by a membrane.

• A cell membrane is also known as plasma membrane.

• Controls exchange of materials such as nutrients
  and waste between cells and their environment.

• Has other important functions for example to
  enable cells to receive hormones.

• To understand the function of anything in
  biology, you must study the structure first!

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Cell Membranes from Opposing Neurons (TEM
x436,740).

Nerve cell
Gap between cells
cell membrane 7nm wide
Cell membrane
Nerve cell
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Cell membranes are made of PHOSPHOLIPIDs

• HYDROPHILIC heads (water liking)-Attracted to
  the water
• called POLAR
• HYDROPHOBIC tails (water fearing)-Not attracted
  to the water
• called NON-POLAR

A Phospholipid
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A phospholipid

• HYDROPHILIC HEAD
• At the other end of the phospholipid is a
  phosphate group and several double bonded
  oxygens. The atoms at this end of the molecule
  are not shared equally. This end of the molecule
  has a charge and is attracted to water. It is
  POLAR
• HYDROPHOBIC TAILS
• The two long chains coming off of the bottom of
  this molecule are made up of carbon and hydrogen.
  Because both of these elements share their
  electrons evenly these chains have no charge.
  They are NON POLAR. Molecules with no charge are
  not attracted to water as a result water
  molecules tend to push them out of the way as
  they are attracted to each other. This causes
  molecules with no charge not to dissolve in
  water.

3D model of a Phospholipid
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A Phospholipid Bilayer

• Phospholipids can form
• BILAYERS
• -2 layers of phospholipids with
• hydrophobic tails protected inside by the
  hydrophilic heads.
• The PHOSPHOLIPID
• BILAYER is the basic
• structure of membranes.

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Fluid mosaic model

• Cell membranes also contain proteins within the
  phospholipid bilayer.
• This model for the structure of the membrane is
  called the
• FLUID MOSAIC MODEL
• FLUID- because individual phospholipids and
  proteins can move around freely within the layer,
  like its a liquid.
• MOSAIC- because of the pattern produced by the
  scattered protein molecules when the membrane is
  viewed from above.

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Cell Membranes from Opposing Neurons (TEM
x436,740).

Phospholipid Bilayer 7nm wide
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Movement of selected molecules across the cell
membrane
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Methods of Transport Across Membranes

• 1. Diffusion
• 2. Osmosis
• 3. Facilitated Diffusion
• 4. Active Transport

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Methods of Transport Across Membranes

• Diffusion -passive transport - no
• energy expended
• 2. Osmosis - Passive transport of water
  across membrane
• Facilitated Diffusion - Use of proteins to
• carry polar molecules or ions across
• Active Transport- requires energy to
• transport molecules against a
  
• concentration gradient energy is
• in the form of ATP

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Diffusion

• Movement of molecules from an area of high
  concentration to an area of low concentration.
• Movement from one side of a membrane to another,
  un-facilitated

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Diffusion
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Solutions

• Solutions are made of solute and a solvent
• Solvent - the liquid into which the solute is
  poured and dissolved. We will use water as our
  solvent today.
• Solute - substance that is dissolved or put into
  the solvent. Salt and sucrose are solutes.

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Osmosis
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Tonicity is a relative term

• Hypotonic Solution - One solution has a lower
  concentration of solute than another.
• Hypertonic Solution - one solution has a higher
  concentration of solute than another.
• Isotonic Solution - both solutions have same
  concentrations of solute.

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Plant and Animal Cells put into various
solutions
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Types of Transport
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Diffusion Lab

• We are using dialysis tubing as the cell membrane
  - It is selectively permeable
• The solute is either the eosin starch solution or
  the sugar solution
• What is the solvent?

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Membrane Permeability

• Solute is eosin-starch-chloride solution
• Solvent is Water
• Indicator for presence of starch is IKI
• Starch is made of amylose and amylopectin
  amylopectin is insoluble
• Iodine is not very soluble in water, but with KI
  it forms a I3- (triiodine ion) which is soluble.
  
• I3- combines with the amylose and the starch
  molecule turns blue-black.

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Test for Starch
Elmhurst College Website
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Test for Chloride ions

• Indicator for presence of chloride ions is silver
  nitrate, AgNO3
• A white precipitate, AgCl, forms if chloride is
  present.

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Test for Sulfate ions

• Indicator for the presence of sulfate ions is
  Barium chloride, BaCl
• Barium sulfate, BaSO4 - forms a white precipitate
• BaCl NaSO4 ----gt BaSO4 NaCl

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Living Cells

• Fern gametophytes are used to see result of
  putting live cells in solutions of varying
  tonicity

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Osmosis

• We will make an osmometer to see osmosis
• Sugar solution in a dialysis tube is used to
  simulate a cell membrane.
• Various concentrations of solute may be used
  around the room.

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• Moving amoeba