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Chapter 3

BIOL 1107 Chapter Notes - Chapter 3: Stereoisomerism, Triple Bond, Hydrogen Bond

Course Code
BIOL 1107
Thomas Abbot

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3.1 Formation and Modification of Biological Molecules
βž” Organic Molecule: molecule based on carbon
βž” Inorganic Molecule: molecule without carbon in its structure
βž” A few of the smallest carbon-containing molecules that occur as minerals/atmospheric gases (like CO2)
are considered inorganic
βž” 4 major classes of organic molecules are carbohydrates, lipids, proteins, and nucleic acids
βž” Carbon atoms bond covalently to each other and other atoms
βž” Hydrocarbon: molecule consisting of carbon linked only to hydrogen atoms
β—† Simplest is methane (CH4)
β—† Triple bond can only occur in a 2 carbon hydrocarbon, single and double bonds are found in both
linear and ring hydrocarbons
βž” Chemical Evolution: formation of the organic molecules that allowed the first forms of life to originate
β—† Primordial Earth’s atmosphere lacked oxygen and contained hydrogen, methane, ammonia, and
β—† Energy for evolution came from solar energy and natural sources like lightning
βž” Functional Group: small, reactive groups of atoms, each with specific chemical properties
β—† Found in carbs, lipids, proteins, and nucleic acids
β—† Number and arrangement in a molecule determine function of that molecule
β—† Can participate in biological reactions, most common are
● Hydroxyl (-OH)
● Carbonyl (>C=O)
● Carboxyl (-COOH)
● Amino (-NH2)
● Phosphate (-OPO32-)
● Sulfhydryl (-SH)
βž” Isomers: 2 or more molecules that have the same chemical formula but different molecular structures
βž” Stereoisomers: molecules that are mirror images of one another
β—† L isomer (L for laevus = left)
β—† D isomer (D for dexter = right)
βž” Asymmetric Carbon: carbon linked to 4 different atoms/functional groups
β—† Can take either of 2 fixed positions in space with respect to other carbons in the chain
βž” Enzymes tend to fit best to one of the 2 forms of a stereoisomer
β—† Most enzymes that catalyze biochemical reactions involving amino acids recognize the L
β—† Most enzymes that catalyze biochemical reactions involving sugars recognize the D stereoisomer
βž” Structural Isomers: 2 molecules with the same chemical formula but atoms that are connected in
different ways
β—† Ex. glucose and fructose
βž” Dehydration Synthesis Reaction: components of a water molecule are removed during a reaction,
usually as part of the assembly of a larger molecule from smaller subunits
β—† Occurs when sugar molecules combine to form starch
βž” Hydrolysis: components of a water molecule are added to functional groups as molecules are broken
down into smaller subunits

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β—† Breakdown of a protein molecule into amino acids in digestive processes
βž” Polymer: molecule assembled from subunit molecules called monomers into a chain by covalent bonds
β—† Proteins are polymers made of amino acid monomers
βž” Polymerization: process of assembly of a polymer from monomers
βž” Macromolecule: single polymer molecule with mass of 1000 Da or more
β—† Many carbohydrates, proteins, and nucleic acids
β—† Macromolecules interact to form larger functional structures
● ribosome (cellular structure that plays central role in polymerization of amino acids into a
protein chain) consists of RNA and protein macromolecules
3.2 Carbohydrates
βž” Most abundant organic molecules in the world
βž” Major fuel substances, provide energy for cellular activities
β—† Ex. sucrose (common table sugar)
βž” Starch: storage polysaccharide in plants consisting of branched/unbranched chains of glucose subunits
βž” Glycogen: energy providing carbohydrates stored in animal cells
βž” Cellulose: primary constituents of plant cell walls
βž” Carbohydrates contain carbon, hydrogen, and oxygen in a ratio of 1 carbon : 2 hydrogens : 1 oxygen
βž” Monosaccharide: contains 3-7 carbon atoms
β—† Ex. glucose (C6H12O6)
β—† Soluble in water, most have a sweet taste
β—† Those with 3 (trioses), 5 (pentoses), 6 (hexoses) carbons are most common in living organisms
βž” Disaccharide: 2 monosaccharides
β—† Ex. sucrose (glucose + fructose), transported to/from parts of leafy plants
β—† Maltose is present in germinating seeds, major sugar used in brewing industry
β—† Lactose (glucose + galactose) is primary sugar of milk
βž” Polysaccharide: 10+ monosaccharides
β—† Ex. starch, glycogen, cellulose
β—† May be linear/unbranched molecules or may contain branches in which side chains of sugar units
attach to a main chain
β—† Plant starches contain linear forms of amylose and branched forms of amylopectin
β—† Glycogen contains branched amylopectin, can be assembled/disassembled to take up/release
glucose (stored in liver of many animals)
β—† Cellulose (most abundant) contains unbranched glucose monomers bound by beta-linkages
(primary structural fiber of plant cell walls, likened to steel rods)
β—† Chitin is assembled from glucose modified by the addition of nitrogen-containing groups, held
together by beta-linkages
● Main structural fiber in exoskeletons of arthropods such as insects and crabs
βž” Monosaccharides with 4+ carbons can assume a ring form (much more common than linear form)
β—† In 5 or 6 carbon monosaccharides, carbon at the 1 position is asymmetric because its 4 bonds
link to different groups of atoms, allowing them to exist as 2 different stereoisomers
β—† Glucose stereoisomer with -OH pointing below plane is alpha-glucose
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