General ---------Biology----------------------------------------------------- ------------------Online-------------------------------- Ch. 5 Macromolecules:carbohydrates, fats, proteins, nucleic acids

The chemical reactions of life animate us.  These chemical reactions produce emergent properties such as muscle movement, cell growth and reproduction, energy storage and utilization, nerve impulse propagation, thought and emotion.

These chemical reactions also produce microscopic structures inside our cells.  These structures (e.g. ribosome's, mitochondria, Golgi bodies, etc.) allow the chemical reactions to be partitioned and arranged in complex sequences.  Each reaction in the sequence is described as a step in a "chemical pathway." Your cells can take in a carbohydrate molecule (starch) and through a series of steps (chemical reactions) convert that starch molecule into a hormone such as estrogen or testosterone.  Such chemical pathways are hundreds of steps long and appear like a road network with lots of intersections, entrance and exit points.  Fig. 6.1, on pg. 88 of your text, illustrates a typical pathway.

Nucleic Acid.  The recipe for all these reactions is stored in your nucleic acid molecules (DNA).  The information in your DNA is unique to you; no one else has the exact same recipe, i.e the exact same genetic code, unless they are an identical twin.

All life on earth, from bacteria to mammals, uses the same genetic code; just like all songs use the same basic notes.  Different songs are produced by different arrangement of these notes and cords.  Likewise, each creature on earth is a unique arrangement of genetic code, producing a symphony of chemical reactions, recognizable and distinct.

The genetic code is arranged in units called genes, and each gene produces a specific protein.  The genes are like songs on a cassette tape.  There are about 30,000 genes in humans, arranged on 23 threads of DNA.  This is like having 23 tapes, containing 30,000 songs.  Each person has two sets of DNA, 23 threads in each set;  one set comes from the mother via her egg, and the other from the father via his sperm.

The genetic code is written with only four variables: A, T, G, C.  This is analogous to having 30,000 songs written with only four notes, or writing 30,000 poems using an alphabet with only four letters. 

Your 30,000 genes produce 30,000 different proteins. 

Protein.    Each proteins has a unique chemical function.  Some are catalysts that act like conductors of a chemical symphony; they cause reactions to occur but are not consumed or transformed by the reaction.  Other proteins are structural, like muscle fibers.  Proteins also function as hormones, antibodies and chemical receptors.  Table 5.1 on page 72 lists eight functions of proteins. 

Fat.  Fats are produced by enzymatic reactions in your body that take the food molecules you eat and rearrange them into fats for long term energy storage, membrane production and certain hormones.

Carbohydrate.  The simplest carbohydrate is a 3-carbon sugar.  This sugar is produced by photosynthesis.  This basic sugar is rearranged by  enzymatic reactions into 5 and 6 carbon sugars, that can be used by the plant for quick energy or made into long carbohydrate polymers for energy storage.  These carbohydrate products can be rearranged by chemical reactions to produce proteins, fats and nucleic acid.   A few carbohydrates serve a structural role, e.g. the wood of plants (cellulose fiber) and the hard outer shells of insects.