principle 3

7/31/2019 Principle 3

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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

principle 3

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