Organic Molecules and Macromolecules

Organic Molecules

• All organic molecules contain carbon
• Carbon's special property comes from having 4 valence electrons, allowing 4 strong covalent bonds with other atoms, including other carbons
• Carbon atoms can form chains, branched chains, and other complex structures

Monomers, Polymers, and Macromolecules

• Four main types of organic macromolecules: carbohydrates, lipids, proteins, and nucleic acids
• Three of these are polymers, large molecules made up of repeating subunits (monomers)

Dehydration Synthesis

• Also known as condensation
• Monomers are joined to form a polymer with the release of water
• This reaction is used to build polymers in the body

Hydrolysis

• Breaking of bonds between monomers by using water
• Used to break polymers down into monomers in the body

Carbohydrates

• Polymers made of monomers called monosaccharides (single sugars)
• Monosaccharides contain carbon, hydrogen, and oxygen in a 1:2:1 ratio
• Classified by the number of carbons (trioses, pentoses, hexoses)
• End in "-ose"
• General formula for monosaccharides is (CH₂O)n
• Common pentoses: ribose and deoxyribose
• Common hexoses: glucose, fructose, and galactose
• Glucose is the most common monosaccharide
• Carbon 1 joins to oxygen on carbon 5 to form a ring structure with 5 carbon and 1 oxygen
• The hydroxyl group on Carbon #1 (the anomeric carbon) may be up (β-glucose) or down (α-glucose)
• Main source of energy in respiration
• Building blocks for larger molecules
  • Glucose is a monomer for starch, glycogen, and cellulose
  • Ribose and deoxyribose make RNA and DNA nucleotides, respectively, and ATP
• Glycosidic bonds are formed between monosaccharides to create disaccharides and polysaccharides

Polysaccharides

• May be composed of several thousand monosaccharides
• Are not sugars
• Important polysaccharides include starch, glycogen, and cellulose
• All are made up of glucose monomers
• Starch is a mixture of amylose (~20%) and amylopectin (~80%)
  • Amylose is composed of α-glucose molecules, linked by α(1→4) glycosidic bonds
  • Amylopectin is also made of α-glucose molecules, but has both α(1→4) and α(1→6) glycosidic bonds
  • This branching structure causes starch to adopt a spiral shape.
• Glycogen is similar to amylopectin but is more branched
• Cellulose is a polymer of β-glucose molecules, linked by β(1→4) glycosidic bonds
• The glucose in the cellulose chain is rotated 180° relative to the next glucose
• Hydrogen bonds form between glucose molecules in adjacent chains, creating microfibrils—strong, tightly cross-linked bundles.

Lipids

• A diverse category of molecules unified by being non-polar or insoluble in water
• Primarily composed of glycerol bonded to fatty acid chains
• Fatty acid chains are long hydrocarbon backbones
  • Saturated fatty acids have no double bonds and are solid at room temperature
  • Unsaturated fatty acids have double bonds and are liquid at room temperature
• Bonds between glycerol and fatty acids are called ester bonds
• Triglycerides (fats and oils) are made up of one glycerol molecule with three fatty acid chains
• Serve as energy reserves and insulate against heat loss
• Phospholipids are made of one glycerol molecule, one phosphate group, and two fatty acid chains
• The phosphate group ("head") is hydrophilic, and the fatty acid "tails" are hydrophobic
• Form phospholipid bilayers, which make up all cell membranes

Proteins

• Monomers are amino acids
• Amino acids have a central carbon bonded to an amine group, a carboxyl group, and a variable R-group (side chain)
• Peptide bonds form between the carboxyl group of one amino acid and the amine group of another (dehydration synthesis/condensation)
• A chain of amino acids is called a polypeptide
• One protein may consist of more than one polypeptide chain
• Four levels of protein structure
  • Primary structure: sequence of amino acids linked by peptide bonds
  • Secondary structure: caused by hydrogen bonding between carbonyl oxygen and amine hydrogen; can form α-helices or β-pleated sheets
  • Tertiary structure: complex 3-D folded shape caused by interactions between R-groups (hydrogen bonds, disulfide bridges, ionic bonds, hydrophobic interactions)
  • Quaternary structure: association between multiple polypeptide chains (or between a polypeptide and a nonprotein component); held together by the same types of bonds as in tertiary structure
• Globular proteins are somewhat spherical; examples include hemoglobin (oxygen-carrying pigment)
• Fibrous proteins form long strands; examples include collagen (structural protein)

Water

• A polar molecule capable of forming hydrogen bonds
• The most important biological molecule due to its properties (solvent, high heat capacity, high latent heat of vaporization)
  • Dissolves ionic and polar substances, allowing reactions to occur in aqueous solutions
  • High specific heat capacity: resists temperature changes, maintaining homeostasis
  • High latent heat of vaporization: allows evaporative cooling (e.g., sweating)

Testing for Biological Macromolecules

• Methods exist to test for the presence of carbohydrates, lipids, and proteins
  • Reducing sugars can be identified using Benedict's test, which exploits the ability of reducing sugars to reduce copper ions from Cu2+ to Cu+
  • Non-reducing sugars are identified by first hydrolyzing the disaccharides into monosaccharides using HCl and then performing the Benedict's test.
  • Starch is identified using iodine test, which leads to a blue-black color change if starch is present
  • Lipids are identified using an emulsion test that depends on the property of lipids to dissolve in ethanol (alcohol) and be insoluble in water.
  • Proteins are detected by the Biuret test, which forms a purple complex with copper ions.

Explore the fascinating world of organic molecules, including the structure and function of monomers, polymers, and macromolecules. Understand key processes like dehydration synthesis and hydrolysis, which are crucial for the formation and breakdown of these compounds. Learn about the four main types of macromolecules that are essential for life.