Important Biological Molecules


  • ·         carbon has the capability to bond with four other atoms
  • ·         when carbon is bonded to four atoms, it is “saturated” and it forms a symmetrical molecule with a tetrahedral shape
  • ·         if the four atoms are the same, the structure is non-polar, since the pull on the shared electron pairs is evenly distributed throughout the molecule, resulting in no over all net pull
  • ·         molecules that contain only carbon and hydrogen atoms are called hydrocarbons
  • ·         all hydrocarbons are symmetrical molecules, and are therefore non-polar
  • ·         sometimes, oxygen, sulfur, phosphorous, as well as many other atoms, can attach to the carbon backbone of a hydrocarbon to form clusters of atoms called functional groups, these are special arrangements of atoms that exist in molecules and give them their character
  • ·         various atoms always form the same number of covalent bonds with adjacent atoms
  • ·         for example, hydrogen can only share one pair of electrons to form one bond with another atom, since hydrogen only has one electron
  • ·         oxygen, for example, usually shares two pairs of electrons, therefore forms two bonds with atoms – either a double bond with one atom, or two single bonds with two separate atoms 


  • ·         macromolecules are polymers, consisting of a large number of repeating subunits and one or more functional groups
  • ·         there are four major classes of macromolecules common to all living systems:
  1. carbohydrates – made of simple sugar subunits
  2. lipids – made of glycerol and fatty acids
  3. proteins – made of amino acids
  4. nucleic acids – made of nucleotides
  • ·         the assembling and disassembling of macromolecules is performed in the same manner for all four types
  • ·         it is important to note that any assembling or disassembling of molecules in living systems, almost always involves specific “helper“ molecules called enzymes – proteins that make the process quicker, often referred to as catalysts – molecules that speed up chemical reactions, but are not used up in the process
  • ·         enzymes “recognize” the covalent bonds that must be created or broken in the reaction


  • ·         when monomer units combine to form large polymer chains, the reaction is typically called a condensation reaction (or dehydration synthesis reaction) – water is formed from the hydrogen of the functional group of one of the monomers, and the hydroxyl (-OH) of the functional group of the other monomer involved in the reaction .this reaction results in a covalent bond between the subunits that possesses an oxygen in the attachment – this is called an ester bond
  • ·         condensation reactions are considered anabolic reactions because they result in the building up of large molecules from smaller monomer units


  • ·         in the breaking down of large molecules into smaller monomer units, known as catabolic reactions, the reverse happens
  • ·         in the presence of water, the ester bond is broken (with the help of enzymes), and water is split into its components, H and OH
  • ·         the H is added to one monomer unit, and the OH is added to the other, at the appropriate location, re-establishing the functional group
  • ·         this reaction is called hydrolysis – “hydro” means water, and “lysis” means to split

·         for an animation of how these two types of reactions work to build macromolecules click on


  • ·         carbohydrates are special molecules that are typified by carbon chains with either aldehyde, or ketone groups, along with a lot of hydroxyl groups attached on the remaining carbons
  • ·         millions of tonnes of carbohydrates are naturally synthesized by photosynthetic organisms (plants and algae)
  • ·         they function as energy sources for living cells, building materials in photosynthetic organisms, and cell surface markers for cell-to-cell identification and communication
  • ·         their components are carbon, hydrogen, and oxygen in the ration 1:2:1
  • ·         therefore, the empirical formula for carbohydrates is (CH2O)n, where n is the number of carbon atoms in the chain
  • ·         the carbohydrates are categorized into three major categories:
    • monosaccharides
    • oligosaccharides
    • polysaccharides
  • ·         carbohydrates that possess the aldehyde group are referred to as aldoses
  • ·         carbohydrates that possess the ketone group are referred to as ketoses
  • ·         typically, saccharides contain the ending “ose”, meaning “sugar”
  • ·         carbohydrates that possess five carbons in their chain are called pentoses
  • ·         carbohydrates that possess six carbons in their chain are called hexoses
  • ·         the simplest kind of sugars are trioses – they possess three carbons in their chain
  • ·         two common pentose sugars are ribose (found in RNA) and ribulose (used in photosynthesis)
  • ·         three common hexoses are glucose (a source of energy for all living cells), galactose (the monomer of the milk sugar lactose), and fructose (the sugar found in fruit)
  • ·         it is important to note that when both pentoses and hexoses dissolve in living systems, they are not stable as chains – instead, they reshuffle, or reconfigure themselves into a much more stable ring system
  • ·         this reconfiguration is called an internal intramolecular reaction
  • ·         the reaction occurs between two functional groups in the same molecule
  • ·         in glucose, for example, it is between the aldehyde group of carbon 1, with the alcohol group of carbon 5
  • ·         in fructose, the ketone group of carbon 2 reacts with the alcohol group of carbon 5 in the chain
  • ·         when the position of the OH group on carbon 1 of the glucose ring lies below the plane of the ring, a-glucose results (pronounced “alpha” glucose)
  • ·         when the position of the OH group on carbon 1 lies above the plane of the ring, b - glucose results (pronounced “beta” glucose)
  • ·         sugars containing two or three simple sugars attached to one another by covalent bonds are called oligosaccharides (disaccharides)
  • ·         the links between the sugars are called glycosidic linkages
  • ·         maltose is found in grains and is used to produce malt liquor and beer
  • ·         sucrose is table sugar, and also the way plants transport the glucose that they make (glucose + fructose) – it is found in large amounts in sugar cane, sugar beets, and maple trees (sap)
  • ·         lactose is the oligosaccharide found in mill (a-glucose + a-galactose)
  • ·         the glycosidic linkage between monosaccharides is characterized by the number of the carbon on each sugar that is involved in the bonding
  • ·         for example, the linkage in maltose is called a 1-4 glycosidic linkage because it forms between the hydroxyl group of carbon 1 on glucose 1 and the hydroxyl group of carbon 4 of the adjacent molecule
  • ·         several hundred to several thousand monosaccharides units will link together to form polysaccharides (complex carbohydrates)
  • ·         some are straight chains (amylose – made of 1-4 glycosidic linkages between a-glucose molecules), and some are branched (amylopectin – a branched a-glucose polymer composed of a main chain of 1-4 linkages, and branched points formed by a- 1-6 glycosidic linkages) 
  • ·         starch is a combination of amylose and amylopectin
  • ·         polysaccharides serve two functions:  energy storage (starch and glycogen) and structural support (chitin and cellulose)
  • ·         a potato, for example, is 20% amylose, and 80% amylopectin
  • ·         with the help of enzymes (amylase, maltase, etc.) animals hydrolyze starches into glucose units then through anabolic activity, condensed them into a energy storage polymer called glycogen – stored in the liverglycogen – a more branched polymer than amylopectin
  • ·         all three polysaccharides are helical in their physical 3-D geometry 
  • ·         the most abundant organic substance on Earth is cellulose – a straight-chain polymer of b-glucose held together by b 1-4 glycosidic linkages 
  • ·         if b-glucose is linked at the 1 and 4 positions of each respective glucose, it causes the inversion of each link
  • ·         this means that cellulose is neither coiled nor branched like other polysaccharides
  • ·         the result is that the hydroxyl groups of adjacent straight chains form numerous H-bonds, making tight bundles called micro fibrils 
  • ·         these micro fibrils intertwine  to form tough, insoluble cellulose fibres that plants utilize to build their cell walls
  • ·         practical uses of these micro fibrils are in wood for lumber and paper and in cotton and linen for clothing
  • ·         humans cannot hydrolyze cellulose because they do not possess the enzymes necessary to break down the b-glucose glycosidic linkages – this means that humans cannot use cellulose as a source of energy
  • ·         however, cows, sheep, and other ruminant animals do possess them, which allows them to use cellulose a food source
  • ·         this doesn’t mean that eating cellulose is a waste of time and energy for humans – in fact, cellulose fibre moves down the digestive tract undigested, scraping the inner walls of the large intestine, stimulating intestinal cells to secrete mucus, which make the feces more lubricated and aids in the elimination of solid waste – eliminating waste and harmful toxins is a vital process in maintaining good health and avoiding cancers and other incurable diseases
  • ·         the hard exoskeleton of insects is extremely important to the survival and success of the entire insect species
  • ·         almost 50% of all the animal species are insects!
  • ·         the exoskeleton of such animals as insects, crabs, lobsters, as well as the cell walls of many fungi, are made of the polysaccharide chitin
  • ·         chitin is a cellulose-like polymer of N-acetylglucosamine– a glucose molecule to which a nitrogen-containing group is attached at the second carbon position
  • ·         next to cellulose, chitin is the second most abundant organic material on earth
  • ·         chitin is also used to make contact lenses and biodegradable stitches used in surgeries that break down on their own