Structure of RNA and DNA
Nucleotide Structure
DNA Structure
Ribonucleic Acid (RNA Structure)
Nucleic acids are a group of the most important molecules of which the best known are ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).
Individual nucleotides are made up of three components.
A nucleotide contains a pentose sugar, a phosphate group and a nitrogen-containing organic base. These are cytosine (C), thymine (T), uracil (U), adenine (A) and guanine (G).
The pentose sugar, phosphate group and organic base are joined, as a result of condensation reactions, to form a mononucleotide.
Two mononucleotides joined forms a dinucleotide. There is a condensation reaction between the deoxyribose
sugar on one nucleotide and the phosphate group of another.
The bond formed between them is called a phosphodiester bond.
The continued linking of mononucleotides in this way forms a long chain known as a polynucleotide.
A nucleotide in RNA contains a pentose sugar, a phosphate group and a nitrogen-containing organic base. These are cytosine (C), uracil (U), adenine (A) and guanine (G).
A nucleotide in RNA contains a pentose sugar, a phosphate group and a nitrogen-containing organic base. These are cytosine (C), thymine (T), adenine (A) and guanine (G).
RNA is a single and short polynucleotide chain.
The pentose sugar is always ribose in RNA.
RNA is involved in transferring genetic information from DNA to the ribosomes, to make proteins.
There are three types of RNA.
mRNA (messenger RNA) carries the DNA code from the nucleus to the ribosome.
tRNA (transfer RNA) carries amino acids across the cytoplasm.
rRNA (ribosomal RNA) makes up the ribosomes.
The chemical stability of RNA is less stable that DNA.
DNA is double stranded and an extremely long chain.
There are two antiparallel DNA strands held together by hydrogen bonding between complementary bases.
The two strands are twisted into a double helix.
The pentose sugars and phosphates link by phosphodiester bonds which is the sugar-phosphate backbone of the DNA double helix.
5' is the end that has a free phosphate group on carbon 5.
"Antiparallel" is when each strand runs in opposite directions from 5' to 3'.
3' is the end that has a free hydroxyl group on carbon 3.
Adenine and Thymine pair up, whilst Guanine and Cytosine pair up.
Structure and Function of DNA
The pentose sugar is always deoxyribose in DNA.
The phosphodiester backbone protects the more chemically reactive organic bases inside the double helix.
Hydrogen bonds link the organic base pairs forming bridges (rungs) between the phosphodiester uprights. As there are three hydrogen bonds between cytosine and guanine, the higher the proportion of C - G pairings. the more stable the DNA molecule.
There are other interactive forces between the base pairs that hold the molecule together.
DNA is a long/large molecule so it can store lots of information.
DNA has a sugar-phosphate backbone and is double stranded so that it is strong, stable and the bases are protected.
DNA is coiled and is a double helix which makes it compact.
DNA has a base sequence which allows information to be stored as it codes for amino acids.
DNA is double stranded so that replication can occur semi-conservatively (the strands can act as templates).
DNA has weak hydrogen bonds for replication.
DNA has many hydrogen bonds for its stability.
DNA was discovered by James Watson and Francis Crick, after previous work carried out by Rosalind Franklin. X-rays were used to understand the physical structure of the DNA molecule.