Chemistry Reference
In-Depth Information
THE NUCLEIC ACIDS
HUMAN TRAITS; GENETICS
AND EVOLUTION
12
The
nucleic acids
are substances produced by living cells to preserve and
carry hereditary traits of living organisms from one generation to the next;
they store and transmit the genetic information that regulates all the
cell's activities. There are two main classes of nucleic acids:
deoxyribonucleic
acids
(DNA) and
ribonucleic acids
(RNA). DNA carries genetic hereditary
information and controls all cellular functions in most living organisms;
RNA transfers the genetic information encoded in DNA to the site in the cell
where proteins are synthesized and there translates this information into
proteins.
12.1.
DNA AND RNA
Two different types of DNA occur in distinct locations in the living cell:
nuclear DNA
in the cell's nucleus and
mitochondrial DNA
(mt-DNA) in the
mitochondria (see Textbox 50). RNA occurs in several types:
messenger RNA
,
transfer RNA
,
ribosomal RNA
, and others, all in the cytoplasm of the cells (see
Table 85) (Bloomfield et al. 2000).
The chemical composition of
nuclear DNA
, also called
genomic DNA
, is
unique to each organism and different from that of all others. This implies
that nuclear DNA carries, embedded in its structure, the genetic code of
every living organism (together with some proteins, nuclear DNA makes up
the genes and chromosomes that constitute the heredity units in the nuclei
of the cells). When cells divide, DNA preserves and transfers, in its chemi-
cal composition and structure, the characteristics of each living organism
from one generation to another; RNA carries this information from the DNA
in the chromosomes to the cytoplasm, so that specific proteins, characteris-
tic to every organism, needed for life processes can be built by the cells.
