The hereditary material in a cell is coded in the sequence
of the heterocyclic amines of DNA. There are normally
46 strands of DNA called chromosomes in human cells. Specific
regions, called genes, on each chromosome contain the
hereditary information which distinguishes individuals from each
other. The genes also contain the coded information required
for the synthesis of proteins and enzymes needed for the normal
functions of the cells. Bacterial cells may have 1000 genes,
while the human cell contains more than a million genes. A single
E. coli (bacteria) chromosome of double helical DNA consists
of 3.4 million base pairs.
Prior to cell division, the DNA material in the original cell
must be duplicated so that after cell division, each new cell
contains the full amount of DNA material. The process of DNA
duplication is usually called replication. The replication
is termed semiconservative since each new cell contains one strand
of original DNA and one newly synthesized strand of DNA. The
original polynucleotide strand of DNA serves as a template to
guide the synthesis of the new complementary polynucleotide of
DNA. A template is a guide that may be used for example, by a
carpenter to cut intricate designs in wood.
The DNA single strand template serves to guide the synthesis
of a complementary strand of DNA. DNA polymerase III is an example
of this process. More explanation in the next panel.
DNA Polymerase III - Chime
in new window
|Quiz: In the green ribbon
form of the enzyme, on the outside there are several series where
the ribbons lie side by side. What protein structure is this?
| On the inside of the "clamp",
what protein structures are visible?
E. coli DNA Polymerase III Beta Subunit The Sliding DNA Clamp
© David Marcey, 1997
Reference: Kong, X-P., Onrust, R., O'Donnell,
M., and J. Kuriyan (1992). Three-Dimensional Structure of the
Beta Subunit of E. coli DNA Polymerase III Holoenzyme: A Sliding
DNA Clamp. Cell 69: 425-437.