PROTEINS
Proteins carry out many functions in the cell: metabolism (enzymes),
molecule transport, and cell structure.
Proteins (polypeptides) are polymers of amino acids. Amino acids
are joined to one another via peptide bonds.
Amino acids are organic molecules which contain a carboxyl group, an
amino group and a side chain (an R group). The R group is unique
to each amino acid. The R group helps determine the unique biochemical
nature of each amino acid. There are 20 amino acids commonly found in all
proteins.
POLYSACCHARIDES
Polysaccharides serve as carbon and energy sources for the cell.
Polysaccharides (carbohydrates) are polymers of sugar (monosaccharide)
subunits. Polysaccharides are formed when a glycosidic bond is formed between
sugar molecules.
Common sugars contain either 5 carbons (i.e., ribose, deoxyribose)
or 6 carbons (i.e., glucose, galactose, fructose).
NUCLEIC ACIDS
Nucleic acids serve as ģinformationī molecules in the cell. DNA
stores the genetic information and RNA transforms it into proteins.
There are two important types of nucleic acids - DNA and RNA.
Nucleic acids are polymers of nucleotides. Nucleotides are joined
together via phosphodiester bonds, creating the sugar-phosphate backbone
from which the nucleotide bases protrude. DNA and RNA contain different
types of nucleotides. The nucleic acid molecule has directionality;
one end is the 5ķ end and the other end is the 3ķ end.
Nucleotides are organic molecules made up of a 5-carbon sugar (either
deoxyribose or ribose), a phosphate group [attached to the 5th (5ķ) carbon
of the sugar], and a nitrogenous base. There are two types of nitrogenous
bases, either purines or pyrimidines.
DNA is a polymer which contains four different deoxyribonucleotides:
Adenine (A) , Guanine (G), Cytosine (C), and Thymine (T). Deoxyribonucleotides
contain deoxyribose as the sugar. Adenine and guanine are purine
bases while cytosine and thymine are pyrimidine bases. In a DNA double
helix, purines and pyrimidines always pair via hydrogen bonds. Specifically,
A and T pair; G and C pair. This pairing is referred to as ģcomplementary
base pairingī.
RNA is a polymer which contains four different ribonucleotides: Adenine
(A) , Guanine (G), Cytosine (C), and Uracil (U). Ribonucleotides
contain ribose as the sugar. RNA is usually a single stranded molecule.
LIPIDS
Phospholipids are one of the main structural components of membranes.
Phospholipids, a specific type of lipid, are composed of long chains
of fatty acids, glycerol and a phosphate group. Phospholipids are
polar; the phosphate group determines the hydrophilic (water-loving) head
and the fatty acid chains determine the hydrophobic (water-fearing) tails.
STRUCTURES
You should be able to recognize (not draw) an amino acid molecule (i.e.,
Figure 2.7), a sugar molecule (i.e., Figure 2.16), a DNA double helix molecule
(i.e., Figures 2.21 or 6.2) and a phospholipid molecule (i.e., Figure 2.24).