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Interaction with water isa primary factor in
determining thestructure that is formed
Principle 3 Group 3
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What is Water?
vWater is the predominant chemicalcomponent of living organisms.
vWater has a very simpleatomic structure with twohydrogen atoms bonded to oneoxygen atom.
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What is Water?
The H2O molecule is electrically neutral,with the hydrogen side has a slightpositive charge and the other side of the
molecule with a negative charge.
But the positive and negative charges arenot distributed uniformly. This makes the
extra atom of hydrogen always available to"stick" to another element in order tobalance its energy.
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Water is called a polar moleculebecause it has a positive side and anegative side, called a dipole
moment. Water is a dipole, a molecule with
electrical charge distributedasymmetrically about its structure.
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Has polar nature
unequal sharing of its electrons betweenoxygen and hydrogen in which the former
has larger electronegativity than the latter,resulting in a bent structure.
Positive and negative
charges attract each other, so that the oxygen and
hydrogen atoms form
hydrogen bonds.
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Properties of Water in BiochemicalSense
The chemical properties of water, makethis fluid the primary energizer of allfunctions in the body
Water manufactures hydroelectricenergy at the cell membranes all over thebody, particularly in the neurotransmittersystem.
It also and initially breaks down allelements to their primary constituents forabsorption into the system for further use
for example, proteins to amino acids, starch tosugar, and fats to fatty acids.
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Properties of Water in BiochemicalSense
Water transfers its hydrolytic energyto the elements that the body canuse.
Water is also the adhesive thatbonds cells membranes. It plays anall-encompassing role in energy
metabolism and the physiologicfunctions of the body.
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Biomedical Importance
Its physical properties derive fromwaters dipolar structure andexceptional capacity for forming
hydrogen bonds.
The manner in which water interactswith a solvated biomolecule
influences the structure of each.
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Electrostatic Interactions
shape biomolecular structure
salt bridges between oppositelycharged groups within biomolecules
often facilitate the binding of ions toproteins and nucleic acids
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Van der Waals Forces attractions between transient dipoles
generated by the rapid movement of
electrons on all neutral atoms
Covalent and Non-CovalentBond Covalent bond: strongest force
Non-Covalent bond: lesser magnitude offorce
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Multiple Forces StabilizeBiomolecules
Example: DNA double helix
Covalent bonds (each individual DNAstrand)
Hydrogen bonds (between nucleotidebases)
Van der Waals (between purine and
pyrimidine bases) Charged phosphate groups and polar
ribose sugars are presented to water
Hydrophobic nucleotide bases are buried
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Hydrogen bonds
form when ahydrogen atomcovalently bonds to
a stronglyelectronegativeatom likenitrogen, oxygen
paradoxically strongenough to providestructural stability
but weak enough to
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Example: DNA
the hydrogenbonds betweencomplementary
base pairs arein the middle ofthe double helix
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Hydrophobic and HydrophilicInteractions
Hydrophobic
Nonpolar molecules in aqueous solutionwhich exclude water molecules
The hydrophobic effect can be used toseparate mixtures of proteins based ontheir hydrophobicity.
HydrophilicPossible with polar groups
Can form ionic bonds with water
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Hydrophobic and HydrophilicInteractions
Affect protein shape
Because of the polar or nonpolar natureof the constituent amino acid building
blocks, as well as in carbohydrate andlipid constituents of microorganisms,molecules can assume shapes andorientations that depend on theintracellular/extracellular environment.
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Aggregation of Non-polar Molecules in
Water
Concrete example
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Formation of a micelle from the sodium saltof a long-chain carboxylic acid. The nonpolarhydrocarbon tails of the acid arrangethemselves to avoid contact with water.
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Lipid Bilayer of the
Cells
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Figure 1 : Schematic representation of the variousways that water molecules are implicated in protein
structure and stability.
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The degree of hydration of nucleic acids also plays akey role in their conformation. For example highwater activity favors the B form of DNA and reducedwater activity (or increased ionic strenght) leads to
a transition from the B form to the C and A formsand if se uence ermits to the D and Z DNA forms
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