DNA, Chromosomes, and Genes


The human genome is composed of 46 chromosomes.  These chromosomes compose our genetic material, our DNA (deoxyribonucleic acid).  DNA is composed of purine and pyrimidine bases, sugars, and phosphate groups.  The structural portion of the DNA molecule is composed of alternating sugars, composed of beta-D-deoxyriboses, and phosphate groups.  Phosphodiester bonds form between the 5 and 3 carbons, respectively, of the deoxyribose sugars.  The bases contain the genetic information and are attached to the 1 carbons of the deoxyriboses.  In DNA, the bases are adenine (A), guanine (G), thymine (T), and cytosine (C).

The bases of two complementary DNA strands form hydrogen bonds (between adenine and thymine and between guanine and cytosine) which give the DNA molecule its characteristic double helical shape.  The base interactions between base pairs can be found here.

Sequences of three bases, called a codon, specify a specific amino acid.  For example, three sequential guanine bases specify the amino acid glycine.  Proteins are formed through the transcription of DNA into RNA (ribonucleic acid) and then through translation of the RNA molecules into proteins.

Proteins are the most abundant macromolecule found in the cells of living organisms.  The human body utilizes slightly less than 100,000 proteins.  Human DNA contains approximately three billion bases that contain the genetic information needed to synthesize the various proteins required for human life.  Four general classes of proteins are the following:

 Structural proteins, which provide physical support; e.g. collagen
 Hormonal proteins, which regulate physiological processes; e.g. insulin
 Respiratory proteins, which transport oxygen; e.g. myoglobin
 Enzymes, which increase the rate of biochemical reactions; e.g. lysozyme

The sequences of the bases in the DNA molecule specifies complementary sequences of RNA nucleotides which in turn specifies the amino acid sequence of a protein.  The segment of chromosomal DNA that directs the synthesis of a single type of protein constitutes a single gene.

For more information about DNA and genetics try the Morgan Genetics Tutorial supported by Rutgers University.

Continue to the next page to learn about The Human Genome Project.

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