Deoxyribonucleic and ribonucleic acid are both nucleic acids, which 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, a phosphate group and one of the organic bases adenine, cytosine, guanine or thymine.
Adenine and guanine both have two nitrogen-containing rings and are classified as purine bases.
The components of an RNA nucleotide are ribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or uracil.
Thymine, uracil and cytosine all have a single ring structure and are classified as pyrimidines.
Pyrimidines are smaller than purines as they only contain one nitrogen-containing ring.
Nucleotides join together via phosphodiester bonds formed in condensation reactions.
RNA is single-stranded and comes in multiple different forms, such as mRNA (messenger RNA), tRNA (transfer RNA) and rRNA (ribosomal RNA), which are involved in protein synthesis.
A DNA molecule is a double helix composed of two polynucleotides joined together by hydrogen bonds between complementary bases - there are two hydrogen bonds between adenine and thymine, and three hydrogen bonds between cytosine and guanine.
The genetic code consists of triplets of bases called codons.
Each codon codes for an amino acid.
The amino acids are then joined together by peptide bonds and form a polypeptide chain.
A gene is a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain.
Not all of the genome codes for proteins - the non-coding regions of DNA are called introns and the coding regions are called exons.
The genetic code is non-overlapping, meaning that each triplet is only read once and triplets don't share any bases.
The genetic code is universal, meaning it is the same in all organisms and species.
The genetic code is degenerate, meaning that more than one triplet codes for the same amino acid.
The genetic code reduces the effect of mutations which are changes to the base sequence such as base deletions, insertions or substitutions.
A deletion or insertion is more likely to be harmful because it causes a 'frameshift', in which all codons 'downstream' of the mutation are read differently.
Some mutations which do change the base sequence are harmful, such as the mutation which leads to sickle cell anemia, in which a mutated form of haemoglobin distorts the shape of red blood cells.
The genetic codes contains start and stop codons which either start or stop protein synthesis.
A change in the base sequence of DNA may not affect the amino acid coded for as the new triplet may still code for the same amino acid.