BSC 215 Lecture Notes - Lecture 2: Phenylalanine, Uracil, Ribose
8 Jun 2018
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Inorganic Compounds
Inorganic compounds are typically compounds without carbon atoms. H2O, O2, and NaCl
are examples of inorganic compounds.
Water is the most abundant substance in the body. Its abundance is due
partly to its unique chemical properties created by the influence of its
hydrogen bonds. These properties include the following:
• Solvency. Water is an excellent solvent. Ionic substances are soluble in
water (they dissolve) because the poles of the polar water molecules
pull them apart, forming ions. Polar covalent substances are also
water‐soluble because they share the same hydrogen bonding as water
shares with itself. For this reason, polar covalent substances are
called hydrophilic (water loving). Because they lack charged poles,
nonpolar covalent substances do not dissolve in water and are
called hydrophobic (water fearing).
• Cohesion. Because water molecules are held together by hydrogen
bonds, water molecules have a high degree of cohesion, or the ability
to stick together. As a result, water has strong surface tension. This
tension, in turn, gives water strong capillary action, allowing water to
creep up narrow tubing. These qualities contribute to the movement of
water through capillaries.
• Stability. The temperature of water is stable. You must add a relatively
large amount of energy to warm (and boil) it and remove a large
amount of energy to cool (and freeze) it. So, when sweat evaporates
from your forehead, a large amount of heat is taken with it and you
are cooled.
Organic Molecules
Organic compounds are those that have carbon atoms. In living systems, large organic
molecules, called macromolecules, can consist of hundreds or thousands of atoms. Most
macromolecules are polymers, molecules that consist of a single unit (monomer) repeated
many times
Four of carbon's six electrons are available to form bonds with other atoms. Thus, you
will always see four lines connecting a carbon atom to other atoms, each line
representing a pair of shared electrons (one electron from carbon and one from another
atom). Complex molecules can be formed by stringing carbon atoms together in a
straight line or by connecting carbons together to form rings. The presence of nitrogen,
oxygen, and other atoms adds variety to these carbon molecules.
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Four important classes of organic moleculescarbohydrates, lipids, proteins, and
nucleic acidsare discussed in the following sections.
Carbohydrates
Carbohydrates are classified into three groups according to the number of sugar (or
saccharide) molecules present:
• A monosaccharide is the simplest kind of carbohydrate. It is a single sugar
molecule, such as a fructose or glucose (Figure 1). Sugar molecules have the
formula (CH2O) n , where n is any number from 3 to 8. For glucose, n is 6, and its
formula is C6H12O6. The formula for fructose is also C6H12O6, but as you can see
in Figure 1, the placement of the carbon atoms is different. Very small changes in
the position of certain atoms, such as those that distinguish glucose and fructose,
can dramatically change the chemistry of a molecule.
• A disaccharide consists of two linked sugar molecules. Glucose and fructose, for
example, link to form sucrose (see Figure 1).
• A polysaccharide consists of a series of connected monosaccharides. Thus, a
polysaccharide is a polymer because it consists of repeating units of
monosaccharide. Starch is a polysaccharide made up of a thousand or more
glucose molecules and is used in plants for energy storage. A similar
polysaccharide, glycogen, is used in animals for the same purpose.
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Lipids
Lipids are a class of substances that are insoluble in water (and other polar solvents),
but are soluble in nonpolar substances (such as ether or chloroform). There are three
major groups of lipids:
• Triglycerides include fats, oils, and waxes. They consist of three fatty acids
bonded to a glycerol molecule (Figure 2). Fatty acids are hydrocarbons (chains of
covalently bonded carbons and hydrogens) with a carboxyl group (COOH) at
one end of the chain. A saturated fatty acid has a single covalent bond between
each pair of carbon atoms, and each carbon has two hydrogens bonded to it.
You can remember this fact by thinking that each carbon is saturated with
hydrogen. An unsaturated fatty acid occurs when a double covalent bond
replaces a single covalent bond and two hydrogen atoms (Figure 2).
Polyunsaturated fatty acids have many of these double bonds.
• Phospholipids look just like lipids except that one of the fatty acid chains is
replaced by a phosphate (P0 4 3) group (Figure 3). Additional chemical groups
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Document Summary
Inorganic compounds are typically compounds without carbon atoms. H2o, o2, and nacl are examples of inorganic compounds. Water is the most abundant substance in the body. Its abundance is due partly to its unique chemical properties created by the influence of its hydrogen bonds. Ionic substances are soluble in water (they dissolve) because the poles of the polar water molecules pull them apart, forming ions. Polar covalent substances are also water soluble because they share the same hydrogen bonding as water shares with itself. For this reason, polar covalent substances are called hydrophilic (water loving). Because they lack charged poles, nonpolar covalent substances do not dissolve in water and are called hydrophobic (water fearing): cohesion. Because water molecules are held together by hydrogen bonds, water molecules have a high degree of cohesion, or the ability to stick together. As a result, water has strong surface tension.
