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Carbon and the Molecular Diversity of Life Backbone of Biological Molecules • • Carbon is the backbone to life: • Living organisms are made up of chemicals based on element carbon • Proteins, DNA, carbohydrates are carbon-based Source of biological carbon: • Carbon enters biosphere through action of photosynthetic plants, which uses sun’s energy to convert CO2 into the molecules of life • Molecules are then passed through ecosystem, often through feeding relationships 1 Carbon Bonds • • Molecular structure of carbon: Mass number • 6 total electrons • 4 valence electrons (shell holds 8) Rules of covalent bonding: • Carbon forms covalent bonds with other molecules (H, O, N) • Number of valence electrons indicate how many covalent bonds are formed for a given element (subtract valence e- from number of e- needed to complete shell) Atomic number 12 6 C C Hydrogen Oxygen Nitrogen Valence e- = 1 e- to complete shell = 1 # of bonds = 1 Valence e- = 6 e- to complete shell = 2 # of bonds = 2 Valence e- = 5 e- to complete shell = 3 # of bonds = 3 Distinctive Properties of Organic Molecules • Organic molecules: • Consist mostly of “carbon” and “hydrogen” atoms H H H C H • From where do organic molecules get their distinctive properties? • Molecular diversity – changes in the number of C-H (hydrocarbons) or changes in orientation (isomers) • Functional groups – component of organic molecule 2 Molecular Diversity from Carbon Hydrocarbons • • Hydrocarbons: • Organic molecules consisting only of carbon and hydrogen • Hydrogen atoms attach to carbon wherever electrons are available for covalent bonding Biological significance: • Although rare in living organisms, many of cell’s organic molecules have regions consisting of only C and H (e.g., tails of fat molecules) • Undergo reactions that release a lot of energy (gasoline of cars, fats that fuel animal activity) Why are fats so energy rich? Hydrocarbon tails of fat serve as stored fuel for animal bodies. Molecular Diversity from Carbon Hydrocarbons 3 Molecular Diversity from Carbon Isomers • Isomers: • • Structural isomers: • • One of several organic compounds that have same molecular formula but differ in covalent arrangements of their atoms Geometric isomers: • • Compounds that have same numbers of atoms of same elements but different structures and different properties One of several organic compounds that have same molecular formula but differ in spatial arrangements of atoms around double bond Enantiomers: • Molecules that are mirror images of each other Functional Groups • • Functional groups: • Components of organic molecules that are most commonly involved in chemical reactions • Functional groups often replace one or more hydrogens bonded to carbon skeleton of a hydrocarbon • Functional groups give organic molecules their unique properties Six key functional groups: • Hydroxyl • Carbonyl • Carboxyl • Amino • Sulfhydryl • Phosphate 4 Functional Groups Hydroxyl Potential to form hydrogen bonds Functional Groups Carbonyl 5 Functional Groups Carboxyl Component of amino acids (building blocks of proteins) and fatty acids (building blocks of some lipids) Functional Groups Amino Component of amino acids (building blocks of proteins) 6 Functional Groups Sulfhydryl Disulfide bridges (S – S) Functional Groups Phosphate Component of nucleotides (building blocks of nucleic acids) and component of ATP (important for energy transfer) 7 8