Main types of organic molecules

							Main types of organic molecules
•   Carbohydrates
•   Proteins
•   Nucleic acids
•   Lipids
Typical composition of organisms by mass
CARBOHYDRATES
• carbon chain with equal numbers of OH
  and H and a few carbonyl
• general formula "CH2O"
• Includes:
  monosaccharides (simple sugars) and
  polysaccharides (complex carbohydrates)
Monosaccharides
• Simple sugars small chains or ring
  structure, with H, OH, and one =O
• Triose, tetrose, pentose, hexose sugars
  name depends on number of carbons in
  the chain
• Sugars may be aldose or ketose
  depending on whether aldehyde or ketone
The structure and classification of some monosaccharides
Monosaccharides, continued
• Important as fuel for energy metabolism
  (glycolysis, cellular respiration)
• Building blocks (monomers) for
  polysaccharides such as starch, cellulose
• Monosaccharide example: glucose
Glucose
• An aldose hexose C6H12O6
• Primary fuel for cells
• Linear and ring forms (structural isomers)
Polysaccharides
• polymers (chains) of monosaccharides
• condensation reactions link
  monosaccharides
• hydrolysis reactions separate them
Polymers
• Large molecules built from chains of
  smaller molecules (monomers)
• Important polymers include
  – Polysaccharides (polymers of ring-form
    hexose sugars)
  – Proteins (polymers of amino acids
  – Nucleic acids (polymers of nucleotides)
Condensation reactions make polymers
from monomers
Hydrolysis reactions take polymers apart
Example of a condensation (or “dehydration”)
synthesis – the disaccharide maltose formed
from two glucose monomers by 1-4 linkage




 By the way…names for short chains:
 Mono-, di-, tri-, tetra-, penta-, etc. and oligo-
Functions of polysaccharides

1. Fuel storage - small molecules such as
   glucose affect the osmotic concentration
   of body fluids – must be sequestered to
   store in large quantities
2. Structural – long molecules used to
   toughen and support cells and tissues
Glucose storage polysaccharides
• starch in plants and glycogen in animals
• Both are polymers of the glucose isomer
  α-glucose
• Helical filaments, differ in branching
  pattern.
                        Alpha-glucose




α and β glucose are
structural isomers of
glucose
                         Beta-glucose
Storage polysaccharides
Structural polysaccharides
•   Cellulose is a polymer of β-glucose.
    – Plant cell-walls
    – Most abundant (greatest mass quantity) of
      any organic molecule on earth
    – Straight chains cross-linked by hydrogen
      bonds.
The arrangement of cellulose in plant cell walls
Starch and cellulose structures
Starch


Cellulose
Structural polysaccharides, continued

• Chitin
  – cell walls of fungi, exoskeletons of arthropods
  – Tough, resistant to digestion
  – Similar to cellulose but with acetylamino
    attached to each glucose
  – Chitinase - enzyme to break down chitin
    produced by certain microorganisms and
    plants but not animals
                       Cellulose




aminoacetyl

              Chitin
LIPIDS
• Diverse molecules, grouped mainly
  because of hydrophobicity
• Mostly hydrocarbon: few polar functional
  groups
• Types of lipids include fatty acids,
  triglycerides, waxes, phospholipids, and
  steroids
Fatty acids
• Carboxyl group at one end of a long
  hydrocarbon tail




• ionized at physiological pH
 A fatty acid     O
             HO C

The sodium salt of a fatty acid (“soap”)

             O      amphipathic

 Na+         C
         O

    Hydrophilic          Hydrophobic
How Soap works

 Na+     Na+     Na+




 Na+




                  Na+

Na+
Triacylglycerol (fats and oils)
• Three fatty acids joined to glycerol.
• Important energy stores in animals-
  hydrocarbons to be used as metabolic fuel.
• “Fats” are H-saturated, have higher melting
  temperature
• “Oils” are H-unsaturated, so have lower
  melting temperature
Saturated and unsaturated fatty acids
Unsaturated fat
Triacylglycerol synthesis


1. Dehydration linkage of a fatty acid to glycerol
Triacylglycerol synthesis
2. Completed triacylglycerol molecule
Phospholipids
• Two fatty acids plus hydrophilic phosphate
  “head” attached to glycerol
• Amphipathic molecules – ionized,
  hydrophilic “head” and hydrocarbon,
  hydrophobic tails
• important structural functions
The structure of a phospholipid
Phospholipid functions
• Cell membranes – phospholipid bilayer

    Water outside cell




     Water inside cell
Phospholipid functions
• Lung surfactant – interface between air
  and moist surface




• Breakfast cereal additive?
Steroids


• Another class of lipids, but structurally
  unrelated to FA and triglycerides
• Example: cholesterol is a component of
  cell membranes
• also precursor of steroid hormones,
  including androgens and estrogens