BASIC CHEMISTRY, continued...

You can probably see that in bonding with itself, carbon  can form chains of atoms:  C-C-C-C-C-C etc
  The chains also include hydrogen, oxygen, nitrogen, and  often sulfur and phosphorus.

Certain types of carbon chains predominate.
 4 main classes:
  carbohydrates, lipids, proteins, and nucleic  acids.

CARBOHYDRATES:
Carbohydrates contain hydrogen and oxygen in addition to carbon, and generally conform to the molecular
 formula (CH2O) -- Hence the name, 'carbohydrate'.
        E.g. C6H12O6, or glucose, a simple sugar. (What does ‘ose refer to?)
   The number of carbons in sugars generally varies from 3 to 7.

The oxygens and hydrogens are attached to the carbons in certain ways: C-H, and C-OH   (Fig. 2.10)
 The -OH arrangement is called a FUNCTIONAL GROUP.
     It has properties defined by the atoms acting as a unit.
  -OH is called a HYDROXYL GROUP
Alcohols are characterized by hydroxyl groups.
   E.g. methanol, ethanol.

The carbon chains in carbohydrates often exist either as linear chains or as closed rings.
   E.g. glucose, fructose.
Note: the hydroxyl group can occur on different sides of the chain or ring, and that matters.
    E.g. glucose vs. galactose or mannose.
Chains convert spontaneously to rings (Fig. 2.10)
  Rings are the most common form inside the cell.

Simple sugars can join to make even more complex structures. E.g., glucose joins with itself to make amylose (part of starch) or cellulose.

Each sugar unit is called a MONOMER. The product is called a POLYMER.
  Since in this case the monomer is a sugar, it’s called a  MONOSACCHARIDE. The polymer is called a ..........?
 Sucrose is a disaccharide, composed of glucose and fructose. Lactose is also a disaccharide composed of glucose and galactose.

 (Note: when monomers are joined, water is removed, as H and OH.
    Called a DEHYDRATION REACTION.)

Amylose and cellulose are both composed of hundreds or thousands of glucose units.
 BUT, they have very different chemical properties.
      Due to the way the sugars are bonded to each other.
 
Starch is easily hydrated and digested by enzymes in our saliva.
Cellulose doesn’t dissolve well, is very stable, and impossible for most organisms to digest.
Starch is a storage form of carbohydrate that plants mobilize easily when they need sugar.
Cellulose is a structural molecule in cell walls; it’s sugars are not recycled.

What is the basis for this difference?  The kind of bond between glucose monomers in the polysaccharide.

Carbohydrates serve as the main initial repository of  energy in chemical form after it’s harvested from  the sun during photosynthesis.
Plants store carbohydrate principally as starch, e.g. in stems,  roots, seeds.

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LIPIDS

Lipids comprise fats, oils, waxes and related molecules.

Their carbon chains are usually much longer than those  of sugars.
They have more hydrogen atoms, and fewer oxygen  atoms, than sugars.
They contain more energy (as calories) per gram than  carbohydrates.
They are largely insoluble in water, but soluble in other  oily substances like petroleum. I.e., they are
    HYDROPHOBIC (‘water fearing’).
          (What’s the opposite of hydrophobic called?)

Although their carbon chains are longer, lipids comprise  shorter macromolecules than carbohydrates like starch and cellulose.

Fats and Oils
 Consist of 2 main components.
  Glycerol -- a 3 carbon sugar.
   Contains 3 hydroxyl groups, one on each C.
  Fatty Acids
   Long carbon chain with attached carboxyl group.
                (Fig. 2.11)

       Carboxyl group is another functional group. What function does it confer???????

    16 or 18 C’s, but 20 and higher too.
    H’s attached to carbon atoms.
    Mostly single bonds between C’s, but  some double bonds.

 Three fatty acids are attached to one glycerol by ESTER bonds between the carboxyl groups and hydroxyl groups.
                (Dehydration reaction).
    Called TRIGLYCERIDES.
  Lipids are mostly hydrophobic, b/c of the long carbon chains with attached H’s.

There are different kinds of fatty acids.
             C16, C18 etc.
 Number of double bonds between carbons varies.
  If no double bonds, then the fatty acid is said to be SATURATED.
  If one or more double bonds (usually up to 3),  then the fatty acid is UNSATURATED.

For example, a C18 saturated fatty acid is called STEARIC ACID.    (Fig. 2.11)
 One double bond makes OLEIC ACID.
 Two double bonds make LINOLEIC ACID.
 Three double bonds make LINOLENIC ACID.

When fatty acids are saturated, the chains look corrugated.

Due to the way the bonds and carbons are arranged.
  They are said to be all TRANS.
When saturated fatty acids are packed together, they sort of fit together neatly.
This highly ordered  packing lets them solidify easily.
  It takes energy (e.g. HEAT) to liquify them, to disturb this relationship.
   These are called FATS.

But double bonds introduce kinks in the fatty acid chains.
Called the CIS arrangement.
 As a result, closely packed fatty acids aren’t as ordered.
 They don’t solidify as easily. They’re more liquid.
 In other words, it takes less energy to maintain them as liquids. They’re OILS.

 Oils are more common in plants than animals. That’s why we try to eat more vegetable oils.

Fats and oils serve a storage function, for carbon chains and energy.
 That’s why there’s lots of oil in corn grain, soybean   seeds, canola seeds, sunflower seeds, peanut seeds.
  Carbohydrate has an average of 3800 calories per gram.
  Lipids have an average of 9100 calories per gram.

 What accounts for the energy difference?
  There are fewer oxygens in fatty substances.  With oxygen, we say a molecule is OXIDIZED.   That means it’s less energetic.
        It’s electrons are at a lower energy level.
  With fewer oxygens, fatty acids have a higher energy content. They’re more REDUCED.
 Fats are a better energy resource, BUT they are less easily mobilized than carbohydrates.  It takes more enzymatic steps to metabolize    them.

Review of Phospholipids
 A class of lipids with a highly charged, POLAR phosphate group attached to one end of glycerol.
    Phosphate is another functional group.
        It is NEGATIVELY charged.
 Also attached to the other end of the phosphate group is another organic molecule, such as the amino acid serine, or the sugar inositol.
 
The other two hydroxyl groups of glycerol have a fatty acid esterified to them.
  This makes a phospholipid sort of a SPLIT PERSONALITY.
 One end of the molecule is charged, or hydrophilic. The other end with the fatty acid carbon chains is hydrophobic.
     
 This property is quite special, and important. Phospholipids are the principle components of biological membranes, and are responsible
    for membrane properties.   (Fig. 3.7)

Membranes consist of two layers of phospholipids  ‘cemented’ together. The fatty acid chains, being  hydrophobic, interact with each other and face the  middle of the membrane. The hydrophilic phosphate  groups face the aqueous medium to either side of  the membrane. This arrangement is called a lipid BILAYER.
 Proteins are embedded in or traverse these bilayers.
                We'll talk more about phospholipids when we discuss membranes.