cell’s survival, they dominate different types of traits from the main DNA. These
genes are called plasmids.
Eukaryote mitochondria and chloroplasts (see Fig. 2.3) also contain several
ring-shaped pieces of mini-DNA. In addition to information for the proteins that
form the mitochondria and chloroplasts, this DNA has also been found to carry
information for leaf spots and male sterility, a condition in which pollen is not
formed in flowers. Mitochondria and chloroplasts (for plants) are contained in egg
cells; since only the nucleus is received from the male gamete during fertilization,
DNA for these organelles contained in fertilized eggs and the somatic cells that
develop from them is thought to come entirely from the mother. These
plasmid-determined traits that are passed down from the mother thus do not conform to Mendel’s laws, a phenomenon known as “cytoplasmic inheritance” or
“maternal inheritance.”
2.9 What Is Genetic Information?
So what is this diagram for proteins contained in DNA as genetic information?
Before considering this question, it is first necessary to understand proteins.
Proteins (also known as polypeptides) are polymer compounds formed as water
molecules leave amino acids and peptide bonds form between the acids, linking
them into a chain. The number of amino acids formed is typically greater than 100
(see Figs. 2.12 and 2.13). Varieties include fibrous proteins like the keratin in hair
and the fibroin in silk thread, in which peptides are linked through several S-S or
hydrogen bonds and arrayed regularly in a single direction to form a long chain, and
globular proteins such as enzyme proteins, in which peptide chains are bent and
overlap into a round general form.
Twenty types of amino acids combine to form proteins. While the same amino
acid may repeat several times, the sequence of amino acid combination differs
between proteins. This sequence of amino acids is called the protein’s primary
structure.
In addition to the primary peptide bonds among their amino acids, the unique
shapes of natural proteins are also maintained through secondary ionic, hydrogen,
and S–S bonds between proteins molecules as a result of the many free amino
groups and free carboxyl groups existing within those molecules. Those
three-dimensional structures, however, are often transformed under the influence of
physical actions such as heating, freezing, high pressure, and ultraviolet ray
exposure and by chemical effects from acids, bases, organic solvents, and fibers.
This transformation of structure in natural substances is known as denaturation.
In most cases, denaturation of natural globular proteins results in unfolding,
which causes a sharp increase in the number of active sulfhydryl groups, amino
groups, and carboxyl groups that had not been exposed in the original natural
protein. Secondary bonds then form between these active groups, forming an
insoluble protein. Because the biochemical activity of proteins such as enzymes and
2.8 Plasmids
39
genes are called plasmids.
Eukaryote mitochondria and chloroplasts (see Fig. 2.3) also contain several
ring-shaped pieces of mini-DNA. In addition to information for the proteins that
form the mitochondria and chloroplasts, this DNA has also been found to carry
information for leaf spots and male sterility, a condition in which pollen is not
formed in flowers. Mitochondria and chloroplasts (for plants) are contained in egg
cells; since only the nucleus is received from the male gamete during fertilization,
DNA for these organelles contained in fertilized eggs and the somatic cells that
develop from them is thought to come entirely from the mother. These
plasmid-determined traits that are passed down from the mother thus do not conform to Mendel’s laws, a phenomenon known as “cytoplasmic inheritance” or
“maternal inheritance.”
2.9 What Is Genetic Information?
So what is this diagram for proteins contained in DNA as genetic information?
Before considering this question, it is first necessary to understand proteins.
Proteins (also known as polypeptides) are polymer compounds formed as water
molecules leave amino acids and peptide bonds form between the acids, linking
them into a chain. The number of amino acids formed is typically greater than 100
(see Figs. 2.12 and 2.13). Varieties include fibrous proteins like the keratin in hair
and the fibroin in silk thread, in which peptides are linked through several S-S or
hydrogen bonds and arrayed regularly in a single direction to form a long chain, and
globular proteins such as enzyme proteins, in which peptide chains are bent and
overlap into a round general form.
Twenty types of amino acids combine to form proteins. While the same amino
acid may repeat several times, the sequence of amino acid combination differs
between proteins. This sequence of amino acids is called the protein’s primary
structure.
In addition to the primary peptide bonds among their amino acids, the unique
shapes of natural proteins are also maintained through secondary ionic, hydrogen,
and S–S bonds between proteins molecules as a result of the many free amino
groups and free carboxyl groups existing within those molecules. Those
three-dimensional structures, however, are often transformed under the influence of
physical actions such as heating, freezing, high pressure, and ultraviolet ray
exposure and by chemical effects from acids, bases, organic solvents, and fibers.
This transformation of structure in natural substances is known as denaturation.
In most cases, denaturation of natural globular proteins results in unfolding,
which causes a sharp increase in the number of active sulfhydryl groups, amino
groups, and carboxyl groups that had not been exposed in the original natural
protein. Secondary bonds then form between these active groups, forming an
insoluble protein. Because the biochemical activity of proteins such as enzymes and
2.8 Plasmids
39