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Chemical Foundations Presented by Shana Shanto February 9, 2004
Types of Molecular Interactions 1) Covalent • Two atoms share one or more pairs of electrons • Strong • May be Polar or Non-polar 2) Non-covalent • Weak • 4 Major Types 1. Ionic Interactions 2. Hydrogen Bonds 3. Van der waals Interactions 4. Hydrophobic Effect
Ionic Interactions Attraction Between a Cation and an Anion Hydrogen Bonds Attraction between a covalently bonded hydrogen with a partial positive charge and another atom (usually C or N) with a partial negative charge
Van der Waals Interactions Weak attractive force between two atoms in close proximity as a result of transient dipoles in their electron clouds Hydrophobic Interactions Tendency of non-polar hydrophobic molecules or portions of molecules to aggregate in water
Molecular Complementarity • Involves shape, charge, and other factors • Allows molecules to interact tightly • Enzyme-substrate interactions
Biological Macromolecules • Polymers of identical or nearly identical monomers • The 3 most abundant in biological systems are: 1) Proteins 2) Nucleic Acids 3) Polysaccharides
Proteins • Composed of amino acid monomers linked by peptide bonds • Peptide bonds are formed by a dehydration reaction • 19 Amino Acids and 1 Imino Acid (Proline) compose all proteins • Only L amino acids are found in proteins • All amino acids have the same basic structure
Nucleic Acids • Composed of nucleotide monomers • 2 Types: 1) DNA 2) RNA • 2 Types of Bases • Purines have 2 fused rings (Adenine & Guanine) • Pyrimidines have a single ring (Uracil, Thymine, & Cytosine)
Nucleic Acids Continued • Nucleotides are joined by phosphodiester bonds
Polysaccharides • Composed of monosaccharide monomers • Monosaccharides are composed of Carbon and water in a 1:1 ratio • Hexoses and Pentoses are most common • Glucose is an important monosaccharide with 3 forms
Polysaccharides Continued • Monosaccharides join through glycosidic linkages to form polysaccharides
Fatty Acids • Composed of a hydrocarbon chain attached to a carboxyl group • No monomeric subunits • Saturated FA have no carbon-carbon double bonds • Unsaturated FA have at least one double bond • Double bonds create kinks in the chain
Phospholipids • Consist of 2 non-polar long chain fatty acyl chains linked to a polar group including a phosphate • Amphipathic • Building blocks of biological membranes • Phospholipid Bilayer due to hydrophobic effect
Summary/Conclusions • Proteins, nucleic acids, polysaccharides, and lipids play important roles in biological systems • Covalent bonds provide strong linkages within and between these molecules • Non-covalent interactions such as hydrogen bonds are weaker, but are still important because they allow flexibility and are collectively strong • Molecular complementarity allows these molecules to interact with each other and with other molecules and to perform their specific functions, especially in the case of enzymes.