Water: the environment of life

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Water the environment of life

• Chemical interactions in water solutions
• Water balance in the cell and in the body
• Dissociation and acid base equilibrium

Dr Miroslawa Ferens-Sieczkowska Department of
Chemistry and Immunochemistry Medical University
of Wroclaw
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Part IChemical interactions in water

• Structure and properties of water molecule
• Water as a solvent
• Weak chemical interactions in water solutions
• Hydrophilic and hydrophobic chemical compounds

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Water molecule
Molecular composition of cells...
Water (H2O) 70 Inorganic ions (Na, K, Cl, PO4)
1 Small molecules (aas, sugar,
nucleotides) 5 Macromolecules (protein, n.a.,
etc) 24
The approximate shape and charge distribution of
water.
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Water molecule forms a dipol
Two pairs of free electrons at the oxygen atom
A pair of electrons which makes a covalent bond
is shifted towards oxygen atom
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Water dipols react one with the other
A pair of free electrons of oxygen atom attracts
proton of a partial positive charge, and
simultaneously is shifted towards the attracted
proton. This weak interaction is called a
hydrogen bond.
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Three-dimensional structure of water molecules is
highly ordered by hydrogen bonds
Liquid water
Ice
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Different chemical compounds can react with water
in a different manner
Hydrophilic water loving - dissolve
easily in water Hydrophobic water fearing
nonpolar, dissolve poorly in water
Water is a polar solvent !
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Salts easily dissolve in water
Water dipols elute salt ions from the crystal
salt anion surrounded with water molecules
salt kation surrounded with water molecules
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Hydrophilic molecules

• They are composed of ions or polar molecules that
  attract water molecules though electrical charge
  effects. Water molecules surround each ion or
  polar molecule on the surface of solid substance
  and carry it into solution

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Hydrogen bonds stabilize polar structures in
water solutions
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More examples of hydrogen bonds
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Amino acid side chains have different potential
for hydrogen bond forming
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Three-dimensional structure of macromolecules is
stabilized by hydrogen bonds
In nucleic acids
and in proteins
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Colloidal solutions
Protein macromolecules need special forces to
stabilize their water solubility. Because of
their surface charge protein molecules are able
to attract water dipols. As a consequence, water
forms a hydration envelope round the protein,
which anables repulsion of particular molecules
repulsion
dehydration
attraction and sedimentation
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Hydrophobic molecules

• What kind of chemical structures display
  hydrophobic properties ?

Hydrocarbon chains, linear as well as
branched, aromatic structures, single as well as
condensed rings
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Behaviour of hydrophobic compounds in water
Hydrophobic molecules clump together to
minimalize the area of contact with water
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Amphipatic compounds
Hydrophilic head
Hydrophobic tail
Highly ordered water molecules Form a cage
around the hydrophobic alkyl chain
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Bi-phasic hydrophilic / hydrophobic arrangements
water in liquid oil emulsion
monolayer separating water and oil
micelle
bilayer
Bilayered vesicle (liposom)
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The cellconsists of hydrophobicmembrane
vesicles,separating compartments of different
colloidalsolutions (organelles)
Membrane structure limits and organizes
communication among particular cell compartments
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Part IIWater balance in the cell and in the body

• Diffusion, osmosis osmotic pressure
• Cell compartments and osmotic equilibrium
• Colloids and Gibbs-Donnan equilibrium

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Another weak interactions in water solutions
Van der Waals
Ionic
dipol - dipol

-
Dipol arrangement in the solution
dipol dipol indukowany
dyspersyjne
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Osmosis
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Gibbs-Donnan Equilibria

• Cytosol and the extracellular fluid contain some
  ionic species to which the plasma membrane is
  permeable and others to which the plasma membrane
  is impermeable
• Cytosol has a significant concentration of
  charged, impermeant macromolecules, such as
  proteins and nucleic acids. These are
  predominantly anionic (negatively charged)
• Many intracellular metabolites are also
  impermeant anions
• The presence of impermeant species influences the
  equilibrium distribution of permeant species

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Gibbs-Donnan equilibria
protein anion (10) sodium kation (10)
(20)
protein anion (10)
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How do cells cope with the osmoticconsequences
of Gibbs-Donnan equilibria
Plant cells have a rigid cell wall and develop
turgor pressure Animal cells pump certain
other ions out of the cytosol to compensate The
principal ion that is pumped is Na Poisoning
the Na,K-ATPase causes cells to swell The
Na,K-ATPase is important in regulation of cell
volume
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Features of Gibbs-Donnan equilibria
The side with the fixed anions corresponds to
the cytosol) has Greater concentration of
mobile cations Smaller concentration of mobile
anions Negative membrane potential Greater
osmotic pressure
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Water dissociation, proton concentration and pH
value
H2O H2O ? H3O OH-
Z prawa dzialania mas
H3O ?? OH- Kdys H2O2 10-14
H 10-14/OH-
- log H pH
pH pOH 14
In pure water pH pOH 7
HCl H2O ---gt H3O Cl- pH ?
NH3 H2O ---gt NH4 OH- pH ?
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Acid base balance in the body

• Proper function of cell and organism is possible
  only in very narrow range of pH
• pH change higher than 0,1 Soerensen unit is
  dangerous to health and even life
• There are many control mechanisms for maintaining
  proper acid base balance (buffers)