Organic Compounds

all living things fall into one of four classes of macromolecules: carbohydrates, lipids, proteins, and nucleic acids

macromolecules are polymers built from monomers

polymer: a long molecule consisting of many similar building blocks
these small building-block molecules are called monomers
three of the four classes of life’s organic molecules are polymers: carbohydrates, proteins, and nucleic acids

storage polysaccharides

chitin is present in plants and consists entirely of glucose monomers
glycogen is present in animals and consists entirely of glucose monomers; it is how animals store sugars
* humans and other vertebrates store glycogen mainly in liver and muscle cells
* perennials: never die—need stored sugars (starch) to build stem and leaves in the Spring, then photosynthesize

structural polysaccharides

chitin is found in the exoskeleton of arthropods (a kind of animals)
* also provides structural support for the cell walls of many fungi
cellulose is a major component of the tough wall of plant cells, also made of glucose monomers
* humans can’t digest cellulose because we lack the enzymes to break the beta linkages between glucose molecules; we can break it down to some extent, but not at the molecular level

the most biologically important lipids are fats, oils, phospholipids, cholesterol, and steroids
lipids are non-polar parts of living things which contain long hydrocarbon tails
* consist of a glycerol head and fatty acid tails
triglycerides consist of a glycerol head and three fatty acid tails
* provide us with the most energy per gram of any substance
fats
  * saturated fats
    * animal fats like butter and grease
    * solidify at room temperature
    * carbons are “saturated” with hydrogen
  * unsaturated fats
    * plant oils like olive oil and peanut oil
    * remain liquid at room temperature
    * have hydrocarbon tails, long chains if C-H that are linked because the carbons are not saturated with hydrogen (C=C)
phospholipids
  * material of all cell membranes
  * phospholipid-glycerol, two fatty acids, and a phosphate group polar heads and non-polar tails
    * polar heads are hydrophilic (have an affinity to water)
    * non-polar tails are hydrophobic (repel water)
steroid: a lipid molecule in which the carbon solution forms four fused rings
cholesterol: an important steroid in animal cell membranes
* can help membranes stay fluid by keeping the phospholipids from packing tightly together
* used to make essential molecules such as hormones, fat-soluble vitamins, and bile acids

functions of lipids/fats

all enzymes are made of protein, but not all proteins are enzymes
protein: a polymer made of amino acid monomers
* there are 20 amino acids; the human body can produce twelve, so we need eight from our diet
proteins have hundreds of functions, here are a few major ones:
  * work as enzymes
  * some are embedded in cell membranes that assist in the transport of substances
  * antibodies of the immune system are proteins
  * serve as hormones (chemical messengers)
  * muscle cells are made of protein and contract
  * structural proteins--collagen, ligaments, tendons
different proteins differ in number and order/arrangement of amino acids
  * amino acids are covalently bonded by peptide bonds
  * a polypeptide is a chain of amino acids with many peptide bonds
    * peptide bonds are connectors—if you have 40 amino acids, you will have 39 peptide bonds (one connecting each to the next)
  * a protein consists of one or more polypeptides
  * the sequence of amino acids determines the shape of a protein; its shape determines its function
denaturation: a process which changes the shape of a protein
* temperature and pH level are the two main causes of denaturation
since the shape of the protein determines its function, the protein can no longer perform its function once it has been denatured

nucleic acid: a polymer made of monomers called nucleotides
* eg. DNA, RNA
nucleotide: a monomer consisting of sugar, a phosphate group, and a nitrogen-containing base

activation energy: the amount of energy that must be absorbed for a chemical reaction to start
catalyst: a substance that decreases the activation energy needed to start a chemical reaction, therefore speeding up the rate of the reaction
enzyme: a catalyst made of protein which is present in living things
  * structure dictates function
  * changes in pH and temperature can affect shape and function
  * high fever/hypothermia denatures enzymes, causing functional problems