Chapter 2, part two of two, Molecules of Life 

I.  Organic molecules are those with carbon based structure.

                               ˝
Why Carbon?        -C-    because carbon forms 4 covalent bonds and thus as a "tinker toy" quality and is a versatile building block capable of .
                               ˝      forming many 3-dimensional shapes.

Molecular chains, branches, rings and innumerable three dimensional molecular structures are built of carbon atoms.  The shape of these molecules supports the shape of cellular parts and the cell itself.  Cell shapes and arrangements into tissues and organs determine the shape of the individual organism.

Inorganic molecules contain no carbon chains or rings, ex. O2,  H2O,  CO2

Many inorganic molecules are important for life but the structure of life is largely carbon based.

Almost all organic molecules in nature are formed by living cells.

     So, “organic” does relate to “natural” as in the popular sense of the term "organic gardening."  

The building blocks (monomers) of complex organic molecules are:

  • Simple Sugars (made by plants) – C,H,& O, the simplest ingredients.
  • Fatty Acids - C,H, & O but many O’s removed forming long chains of hydrocarbons (carbon and hydrogen only); made from sugars.
  • Amino Acids - C, H, O, N, & S – we acquire most from the food we eat; ultimately plants are the original manufacturers.
  • Nucleotides - C, H, O, N, P – we acquire from food and the restructuring of the other organic molecules above.

 II.  Carbohydrates – All are sugar-based molecules.

Monosaccharides – simple sugars, ex. The 6-carbon sugar glucose

Disaccharides – two simple sugars bound together, ex. Maltose is a  glucose-glucose molecule

Polysaccharides – many simple sugars bound together, ex. …glucose-glucose-glucose-glucose-glucose-glucose-glucose-etc, etc. may be starch, cellulose, or glycogen depending on the nature of the bonds.

Some Functions of Carbohydrates:

1. Energy source

·        glucose  used directly to produce ATP, the energy currency of cells, via respiration

·        glucose is stored as starch in plants, glycogen in animals (in muscle & liver), lactose in milk

2.  Structural material

·        cellulose - plant cells walls

·        chitin - insect exoskeletons & fungi cell walls

[Cellulose & chitin are indigestible for most organisms but can be digested by bacteria & fungi which are necessary symbionts in the digestive tract of herbivores.]

 II.  Lipids – fatty acids, waxes, and steroids (all hydrophobic)

            A.  Fats and Oils often have fatty acids occurring 3 per molecule = Triglyceride

                        unsaturated fats:  oils [fatty acids have some double bonds between carbons, hence some carbon are bond to only one H]

                        saturated fats: fats(solid)[no double bonds between carbons]

            Some functions of fats and oils:

·        Energy storage - 1 gram of fat has twice the energy as 1 gram of carbohydrate.  Animals store fat under the skin; plants store fats and oils in seeds as long term storage for embryonic plant (in nuts, i.e. large seeds, particularly).

·        Protection & insulation: cushions vital organs (kidney); blubber in whales & seals

B.     Waxes - Ear wax; bees wax; plant cuticle (waxy covering of plants that protects against water loss, i.e. desiccation)

            C.     Steroids - Cholesterol (in cell membranes & used to make the sex hormones);  testosterone & estrogen

            D.     Phospholipids – major component of cell membranes

 

III.  Proteins are made of Amino Acids held together by peptide bonds, covalent bonds that join amino acids.  A polypeptide is simply a protein.  The properties of the protein are determined by the sequence of its amino acids much as the sequence of letters determines different words only there are 20 different amino acids in contrast to the 26 letters of the English alphabet.  The final shape of a protein is a three dimensional and it is this 3-D shape that determines the function.  Globular proteins have crevices that interact with other molecules (hemoglobin has a crevice to hold O2; enzymes have crevices to facilitate and speed up or catalyze chemical reactions.   Fibrous proteins provide for structural strength as keratin (fibers in hair), collagen (fibers in muscle and bone); actin and myosine are fibrous proteins that contract for muscle movement.  Some proteins are hormones, e.g. insulin.  Other proteins are antibodies, protein molecules produced by the immune system that combat foreign invaders (bacteria and viruses). 

            Proteins have the greatest diversity of functional roles: structural support, chemical catalysts, transport, defense, hormones, and motion.

 

IV.  Nucleic Acids are made of nucleotides.  Each nucleotide consists of a sugar, a phosphate group, and a nitrogenous base. DNA, RNA, and ATP are important nucleic acids.