Nucleic acids
Structure of DNA and RNA
Both DNA and RNA carry information, for instance DNA holds
genetic information, whereas RNA transfers this genetic information from DNA
to ribosomes for protein synthesis. Ribosomes are formed of ribosomal RNA
and proteins. Both deoxyribonucleic and ribonucleic acid are polymers of
nucleotides. Nucleotides consist of pentose which is a 5 carbon sugar, a
nitrogen containing organic base and a phosphate group:
- The components of a DNA nucleotide are deoxyribose sugar, a
phosphate group and one of the nitrogen containing organic bases
adenine, cytosine, guanine or thymine.
- The components of an RNA nucleotide are ribose sugar, a phosphate
group and one of the nitrogen containing organic bases adenine,
cytosine, guanine or uracil.
The pentose sugar, phosphate group and organic base are joined as a result of
a condensation reaction to form a single nucleotide (mononucleotide). Two
mononucleotides can join as a result of a condensation reaction between the
deoxyribose sugar and the phosphate group of the other nucleotide, the bond
is called a phosphodiester bond. They can form a polynucleotide chain.
A DNA molecule is a double helix composed of two polynucleotide strands
joined together by a hydrogen bonds between complementary bases whereas
RNA is a relatively short polynucleotide chain.
Base pairing nitrogen containing organic bases occurs as follows:
Adenine ALWAYS pairs with/ complementary to Thymine
Guanine ALWAYS pairs with/ complementary to Cytosine
A-T and G-C
, DNA is a stable molecule for the following reasons:
- The phosphodiester backbone protects the more chemically reactive
organic bases inside the double helix.
- Hydrogen bond form bridges between the phosphodiester uprights. As
there are three hydrogen bond between guanine and cytosine, rather
than two for adenine and thymine, a higher proportion of C—G pairings
makes DNA more stable. The hydrogen bonds hold the two strands
together.
Structure of DNA and RNA
Both DNA and RNA carry information, for instance DNA holds
genetic information, whereas RNA transfers this genetic information from DNA
to ribosomes for protein synthesis. Ribosomes are formed of ribosomal RNA
and proteins. Both deoxyribonucleic and ribonucleic acid are polymers of
nucleotides. Nucleotides consist of pentose which is a 5 carbon sugar, a
nitrogen containing organic base and a phosphate group:
- The components of a DNA nucleotide are deoxyribose sugar, a
phosphate group and one of the nitrogen containing organic bases
adenine, cytosine, guanine or thymine.
- The components of an RNA nucleotide are ribose sugar, a phosphate
group and one of the nitrogen containing organic bases adenine,
cytosine, guanine or uracil.
The pentose sugar, phosphate group and organic base are joined as a result of
a condensation reaction to form a single nucleotide (mononucleotide). Two
mononucleotides can join as a result of a condensation reaction between the
deoxyribose sugar and the phosphate group of the other nucleotide, the bond
is called a phosphodiester bond. They can form a polynucleotide chain.
A DNA molecule is a double helix composed of two polynucleotide strands
joined together by a hydrogen bonds between complementary bases whereas
RNA is a relatively short polynucleotide chain.
Base pairing nitrogen containing organic bases occurs as follows:
Adenine ALWAYS pairs with/ complementary to Thymine
Guanine ALWAYS pairs with/ complementary to Cytosine
A-T and G-C
, DNA is a stable molecule for the following reasons:
- The phosphodiester backbone protects the more chemically reactive
organic bases inside the double helix.
- Hydrogen bond form bridges between the phosphodiester uprights. As
there are three hydrogen bond between guanine and cytosine, rather
than two for adenine and thymine, a higher proportion of C—G pairings
makes DNA more stable. The hydrogen bonds hold the two strands
together.
