sequence complimentary to the original strand. Each double-stranded DNA
molecule contains one original and one new strand. In bacteria, each daughter
receives a chromosome that is identical to the parent’s chromosome.THE CHROMOSOME CONNECTION
Chromosomesare structures that contain DNA. DNAconsists of two long chains
of repeating nucleotides that twist around each other, forming a double helix. A
nucleotidein a DNA chain consists of a nitrogenous base, a phosphate group,
and deoxyribose(pentose sugar).
The two DNA chains are held together by hydrogen bondsbetween their nitro-
genous bases. There are two major types of nitrogenous bases. These are purines
and pyrimidines. There are two types of purine bases: adenine(A) and guanine(G).
There are also two types of pyrimidine bases: cytosine(C) and thymine (T). Purine
and pyrimidine bases are found in both strands of the double helix.
Base pairsare arrangements of nitrogenous bases according to their hydrogen
bonding. Adeninepairs with thymineand cytosinepairs with guanine. Adenine is
said to be complementary to thymine and cytosine is said to be complementary
with guanine. This is known as complementary base pairing and is shown in
Table 7-1.
Genetic information is encoded by the sequence of bases along a strand of
DNA. This information determines how a nucleotide sequence is translated into
an amino acid which is the basis of protein synthesis. The translation of genetic
information from genes to specific proteins occurs in cells.(^122) CHAPTER 7 Microbial Genetics
Messenger Double-Helical Strand
RNA Base DNA Molecule Base
Adenine (A) Thymine (T)
Guanine (G) Cytosine (C)
Cytosine (C) Guanine (G)
Uricil (U) Adenine (A)
Table 7-1. Complementary Messenger RNA
Bases and DNA Bases