H2
In most organisms, the genetic material is a long double-stranded DNA polymer. The sequence of
units (deoxyribonucleotides) of one DNA strand is complementary to the deoxyribonucleotides of the
other strand. The process of DNA synthesis is called replication. A specific order of
deoxyribonucleotides determines the information content of an individual genetic element (gene).
The protein-coding genes (structural genes) are decoded by two successive major cellular processes:
RNA synthesis (transcription) and protein synthesis (translation). First, a messenger RNA (mRNA)
molecule is synthesized from a structural gene using one of the two DNA strands as a template.
Second, an individual mRNA molecule interacts with other components, including ribosomes,
transfer RNAs (tRNAs), and enzymes, to produce a protein molecule. A protein consists of a precise
sequence of amino acids, which is essential for its activity. O
O P
O– O
Structure of DNA 5’
CH 2 Base
DNA is made up of individual units called nucleotides that are linked to O
each other to form long chains. A nucleotide consists of an organic base 4’ 1’
H H Deoxyribose
(base), a five-carbon sugar (pentose), and a phosphate group. The sugar of H H
3’ 2’ H
DNA is 2′-deoxyribose because it does not have a hydroxyl (OH) group on OH
the 2′ carbon; rather, it has a hydroxyl group only on the 3′ carbon of the sugar moiety. mRNA, the
five-carbon sugar ribose has hydroxyl groups at both the 2′ and 3′ carbons of the pentose ring. The
phosphate group and base are attached to the 5′ carbon and 1′
carbon atoms of the sugar moiety. The nucleotide subunits of DNA
are joined by phosphodiester bonds, with the phosphate group of
the 5′ carbon of one nucleotide linked to the 3′ OH group of the
deoxyribose of the adjacent nucleotide. A polynucleotide strand has
a 3′ OH group at one end (the 3′ end) and a 5′ phosphate group at
the other (the 5′ end).
In 1953, James Watson and Francis Crick, using X-ray diffraction
analysis of crystallized DNA, discovered that DNA consists of two long
chains (strands) that form a double-stranded helix. The two
polynucleotide chains of DNA are held together by hydrogen bonds
between the bases of the opposite strands. The A⋅T base pairs are
held together by two hydrogen bonds, and the G⋅C base pairs are
held together by three.
The A⋅T and G⋅C base pairs lies on the inside, and the 5′-to-3′-linked
phosphate and deoxyribose are backbone. The DNA strains run in
opposite direction, 3′-to-5′ direction and 5′-to-3′ direction.
Genetic material has two major functions. It encodes the information
for the production of proteins, and it is reproduced (replicated) with
a high degree of accuracy to pass the encoded information to new
cells. The Watson–Crick model of DNA fully meets these important
requirements. First, because of base complementarity, each
preexisting DNA strand can act as a template for the production of a
new complementary strand.Second, the sequence of nucleotides of a
In most organisms, the genetic material is a long double-stranded DNA polymer. The sequence of
units (deoxyribonucleotides) of one DNA strand is complementary to the deoxyribonucleotides of the
other strand. The process of DNA synthesis is called replication. A specific order of
deoxyribonucleotides determines the information content of an individual genetic element (gene).
The protein-coding genes (structural genes) are decoded by two successive major cellular processes:
RNA synthesis (transcription) and protein synthesis (translation). First, a messenger RNA (mRNA)
molecule is synthesized from a structural gene using one of the two DNA strands as a template.
Second, an individual mRNA molecule interacts with other components, including ribosomes,
transfer RNAs (tRNAs), and enzymes, to produce a protein molecule. A protein consists of a precise
sequence of amino acids, which is essential for its activity. O
O P
O– O
Structure of DNA 5’
CH 2 Base
DNA is made up of individual units called nucleotides that are linked to O
each other to form long chains. A nucleotide consists of an organic base 4’ 1’
H H Deoxyribose
(base), a five-carbon sugar (pentose), and a phosphate group. The sugar of H H
3’ 2’ H
DNA is 2′-deoxyribose because it does not have a hydroxyl (OH) group on OH
the 2′ carbon; rather, it has a hydroxyl group only on the 3′ carbon of the sugar moiety. mRNA, the
five-carbon sugar ribose has hydroxyl groups at both the 2′ and 3′ carbons of the pentose ring. The
phosphate group and base are attached to the 5′ carbon and 1′
carbon atoms of the sugar moiety. The nucleotide subunits of DNA
are joined by phosphodiester bonds, with the phosphate group of
the 5′ carbon of one nucleotide linked to the 3′ OH group of the
deoxyribose of the adjacent nucleotide. A polynucleotide strand has
a 3′ OH group at one end (the 3′ end) and a 5′ phosphate group at
the other (the 5′ end).
In 1953, James Watson and Francis Crick, using X-ray diffraction
analysis of crystallized DNA, discovered that DNA consists of two long
chains (strands) that form a double-stranded helix. The two
polynucleotide chains of DNA are held together by hydrogen bonds
between the bases of the opposite strands. The A⋅T base pairs are
held together by two hydrogen bonds, and the G⋅C base pairs are
held together by three.
The A⋅T and G⋅C base pairs lies on the inside, and the 5′-to-3′-linked
phosphate and deoxyribose are backbone. The DNA strains run in
opposite direction, 3′-to-5′ direction and 5′-to-3′ direction.
Genetic material has two major functions. It encodes the information
for the production of proteins, and it is reproduced (replicated) with
a high degree of accuracy to pass the encoded information to new
cells. The Watson–Crick model of DNA fully meets these important
requirements. First, because of base complementarity, each
preexisting DNA strand can act as a template for the production of a
new complementary strand.Second, the sequence of nucleotides of a
