How things get into cells: Principles of diffusion, osmosis, and the nature of biological membranes. - PowerPoint PPT Presentation

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How things get into cells: Principles of diffusion, osmosis, and the nature of biological membranes.

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Title: Cell Physiology Author: DGILMORE Last modified by: D Gilmore Created Date: 9/7/2005 6:50:45 PM Document presentation format: On-screen Show – PowerPoint PPT presentation

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Title: How things get into cells: Principles of diffusion, osmosis, and the nature of biological membranes.


1
How things get into cellsPrinciples of
diffusion, osmosis, and the nature of biological
membranes.
  • Diffusion
  • Movement of substances from an area of high
    concentration to an area of low concentration
  • Depends on 2nd law of thermodynamics
  • Osmosis special case of diffusion of water
  • Biological membranes
  • Lipids barriers proteins channels.

2
  • Movement of molecules depends on
  • 1. Kinetic energy
  • higher temperature more kinetic energy
  • 2. Concentration
  • gradient more of something in one area than
    another
  • Second Law of Thermodynamics all things tend
    toward entropy.
  • If theres more of something in one area, it will
    spread out.

3
Diffusion
  • Passive process
  • Depends on concentration and kinetic energy
  • Does not require energy
  • Moves substances from an area of high
    concentration to an area of low concentration
  • Down a concentration gradient

4
Osmosis a special instance of diffusion
  • The most concentrated form of water is
  • pure water.
  • To make water less concentrated, we dissolve
    substances in it.
  • Concentration of one solution relative to another
  • Isotonic equal concentrations
  • Hypertonic more concentrated
  • Hypotonic less concentrated

5
Tonicity relative concentrations of solutions
  • Isotonic two solutions contain the same amount
    of substance dissolved in them- equal
    concentrations
  • Hypertonic a solution containing a greater
    amount of dissolved substance- more concentrated
  • Hypotonic a solution containing a lesser amount
    of dissolved substance less concentrated
  • Osmosis The movement of water across a
    selectively permeable membrane, down a
    concentration gradient.

6
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8
  • Osmosis special case of the diffusion of water.
  • Movement of water across a semi permeable
    membrane.
  • If the environment is
  • Isotonic No NET flow.
  • Hypertonic Water flows OUT of cell.
  • Hypotonic Water flows IN.

Water flows from where it (the water) is in high
concentration to where it is in low concentration.
9
Osmosis is an important phenomenon in biology
  • Red blood cells must be collected carefully
  • In a hypotonic solution (distilled water), water
    enters the RBCs and explodes them.
  • The action of penicillin depends on it
  • Bacteria are protected by a cell wall. When drugs
    damage the wall, water rushes in and explodes the
    bacterium, killing it.
  • Filtering action of the kidney depends on it
  • Water is drawn back out of urine.

10
The physical law that molecules travel down a
concentration gradient (from a region of high to
low concentration) drives most movement of
molecules in and out of cells.
  • Other movement of molecules and particles e.g.,
    movement against a concentration gradient,
    requires some form of metabolic energy.

11
Entry of particles and molecules attached to the
cell membrane
  • Requires
  • Direct access of cell membrane to outside
  • Cytoskeleton
  • Source of energy

Thus NOT done by cells with cell walls (plants,
fungi, bacteria) or cells without a cytoskeleton
(bacteria).
http//bio.winona.msus.edu/bates/genbio/images/end
ocytosis.gif
12
The type of molecule affects how it gets through
a membrane
  • Small molecules can pass through a membrane
  • Water Gases such as O2 and CO2
  • Lipid molecules can
  • Dissolve in lipid bilayer, pass through membrane
  • Many drugs, vitamins, hormones are lipid soluble
  • Larger, hydrophilic molecules cannot
  • Ions, sugars, amino acids cannot
  • Transport proteins required

13
Transport through membranes
  • Simple diffusion
  • Molecules travel down concentration gradient
  • Membrane is not a barrier to their passage
  • Facilitated diffusion
  • Molecules travel down concentration gradient
  • Cannot pass through lipid bilayer their passage
    is facilitated by protein transporters
  • Active transport
  • Molecules travel against concentration gradient
  • Requires input of metabolic energy (ATP),
    transporter

14
How molecules get through the membrane
http//www.rpi.edu/dept/chem-eng/Biotech-Environ/M
embranes/bauerp/diff.gif
15
Active transport movement of molecules against a
concentration gradient. Requires Energy.
16
Transport into cells a step in the middle of a
process
  • All cells need raw materials
  • For maintaining cells, building new ones
  • All cells need a source of energy
  • For continuing cell functions like movement
  • For building new molecules, new cells
  • Chemical reactions that use or release energy
    Metabolism

17
Food preparation, consumption, digestion (break
down into smaller molecules.)
Small molecules absorbed or transported into
cells.
http//www.nlm.nih.gov/medlineplus/ency/images/enc
y/fullsize/8710.jpg
18
Chemical reactions carried out by enzymes
  • Once inside the cell, molecules are used as raw
    materials or for their energy.
  • The chemical reactions involved are carried out
    by protein molecules called enzymes.
  • Enzymes are the tools of the cell and have
    several important properties.

19
Enzymes are catalysts
  • Catalysts speed up the rate of a chemical
    reaction
  • 2H2 O2 2H2O
  • Reactions must occur quickly in a cell.
  • A catalyst is not used up
  • Enzymes are tools, so think hammer
  • Used over and over to pound nails

20
Enzymes overcome activation energy
Enzymes give an extra push to reactions that
dont require energy to finish. Enzymes are
facilitators they get all the reactants together
on the enzymes surface so they can react.
21
Enzymes are specific
  • There are thousands of different reactions that
    take place in a cell, most of them going on at
    the same time.
  • To speed up each one, there is a different
    enzyme. Each type of enzyme can speed up only 1
    type of chemical reaction.
  • Enzymes are proteins, and their 3D shape is what
    makes them specific. Think wrenches
  • Instructions for making enzymes thus found in the
    DNA

22
The next lecture(s) will discuss how cells take
molecules, break them down and release the energy
in them, and put them back together in the unique
way required by the cells.
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