The structure and function of nucleic acids
Nucleic acids are essential biomacromolecules that carry or contain genetic information. They can be separated primarily into two groups: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Both groups are made up of monomers called nucleotide . The image below shows the general structure of these nucleotides which contain a phosphate group, a pentose sugar and a base. Click on the image to see details of how nucleotides differ between DNA and RNA.
Use this page to revise the following concepts of nucleic acids:
DNA
Structure: DNA is composed of two long chains of nucleotides forming a double helix. The nucleotides within each strand are joined together through covalent (specifically phosphodiester) bonds between the phosphate group of one nucleotide and the carbon atom in position 3 of the deoxyribose sugar of the next nucleotide. The two strands are held together by hydrogen bonds between complementary bases (A = T and C ≡ G). The sugar-phosphate sections of DNA are often referred to as the ‘backbone’ of the DNA structure, while the base pairing is referred to as the ‘rungs’, like those of a rope ladder.
DNA is found in the nucleus of eukaryotic cells in the form of linear chromosomes. The number of chromosomes differ from species to species. Most prokaryotes such as bacteria have a single chromosome.
Function: Chromosomal DNA contains the genetic blueprint for an organism, encoding the instructions necessary for the development, functioning, growth, and reproduction of all living organisms. It plays a crucial role in heredity, the passing down of traits and characteristics from one generation to the next.
Mitochondrial and chloroplast DNA
Structure: The organelles mitochondria and chloroplasts have their own DNA that is separate from the genomic DNA found in the nucleus. Mitochondrial DNA (mtDNA) and chloroplast DNA (cpDNA) are small, circular DNA molecules found within the mitochondria and chloroplast respectively. Unlike genomic DNA, which is linear and organised into pairs of chromosomes in eukaryotes, mtDNA and cpDNA exist in multiple copies within these organelles, as depicted in the image below.
Human mtDNA consists of about 16,500 base pairs and encodes 37 genes essential for mitochondrial function. In photosynthetic organisms such as plants, cpDNA ranges from 120,000 to 170,000 base pairs. This is compared to approximately 3 billion base pairs on the human genome .
Function: Mitochondrial DNA is crucial for the production of proteins involved in the electron transport chain and ATP synthesis, processes central to cellular respiration.
Chloroplast DNA is crucial for the production of proteins involved in photosynthesis . Both also encode ribosomal RNA (rRNA) and transfer RNA (tRNA), which are necessary for protein synthesis.
RNA
RNA molecules are single stranded polymers made up of RNA nucleotide monomers. Although there are a number of types of RNA, the 3 main forms are messenger RNA (mRNA), ribosomal RNA (rRNA) and transfer RNA (tRNA). Each has a different structure and function.
