BU BI 421 - Lesson 3 The Structure of Water

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The octect rule dictates that there are 4 electron Water is the medium for life Life evolved in water due to the protection it provides from UV light Organisms typically contain 70 90 Water chemical reactions occur in aqueous environments Water is a critical determinant of the structure and function of g Proteins nucleic acids and membrane pairs around an oxygen atom in water cid 15483 cid 15482 B g These electrons are in four Sp orbitals atoms to a central oxygen atom Two of these pairs covalently link two hydrogen The two remaining pairs are nonbonding lone pairs g 8 1 A qq gzq r Dipole Moment water geometry is a distorted tetrahedron The electronegativity a ne oxygen atom induces a net dipole moment Because of the dipole moment as both a hydrogen bond donor and acceptor water can serve Hydrogen Bonds strong bond hydrogen Hydrogen bonds are strong dipole dipole Or charge dipole interactions that arise between a covalently bound hydrogen and lone pair of electrons 1 Weaker hydrogen bond Typically involve 2 electronegative atoms frequently nitrogen and oxygen Hydrogen bonds are strongest when the R 1 1 p p 3 atoms involved are in a line water can serve as an H donor and an H acceptor Hydrogen bonding in water is cooperative cooperative effect Increases donor strength of a hydrogen bond If it concurrently acts as an acceptor for a 2nd hydrogen bond bonded molecules allow for linear bonding patternsEE cid 15482 q k qg a B ioBIFH as IM I qi iEBEM q i cid 15482 a cid 15482 up to 4 H bonds per water molecule give water its High boiling point high melting point and Large surface tension H bonds between neighboring molecules are weak C 20k 1m01 relative to the H O covalent bonds 420 Kj 1m01 H bonds sources unique properties of water function and structure of proteins DNA and Polysaccharides binding of substrates 10 enzymes and hormones 10 receptors Matching of mRNA and tRNA R Carboxyl group 11 C lketonetwater Water as a solvent universal Good solvent for charged and polar substances amino acids and peptides small alcohols carbs Poor solvent for nonpolar substances nonpolar gases aromatic environments aliphatic chains 1 Of relating 10 or being an Organic compound such as an alkane having an open chain structure g H O H Peptide groups H polypeptides I C C 11 7 I R O pi H to R 0 1 hydroxyl group H l alcohol water E H H CHS RIN Cy I c 1 c o N o I H I NH I H z N He C C C I N N 11 1 N CH k Thymine Adenine

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