Adenosine triphosphate (ATP): An activated nucleotide composed of adenine, a ribose sugar and three phosphate groups. Acts as the universal energy currency for cells.

Anticodon: A sequence of three bases at the end of a tRNA molecule that determines the specific amino acid carried by the tRNA. Forms hydrogen bonds with the codon in mRNA during translation.

Coding (sense) strand: The strand of DNA with the same base sequence as the mRNA (except T is replaced with U in mRNA).

Codon: A sequence of three bases in mRNA that codes for one amino acid.

Complementary base pairing: Specific base pairing rules in DNA and RNA.

Deoxyribonucleic acid (DNA): The molecule responsible for the storage of genetic information in a cell.

DNA gyrase: Unwinds a specific section of the DNA molecule.

DNA helicase: Unzips a specific section of the DNA molecule by breaking the hydrogen bonds between the two DNA strands.

Gene: A length of DNA that carries the code for the synthesis of one specific polypeptide chains or for other RNA molecules that regulate genes.

Genetic code: A sequence of three bases in DNA codes for a particular amino acid in a polypeptide chain.

Messenger RNA (mRNA): A single stranded polynucleotide formed as a result of the transcription of a gene from the template of the DNA. Carries the information coding for a polypeptide from the nucleus to the ribosomes in the cytoplasm.

Mutation: A change to the sequence of bases in DNA.

Nucleotide: The monomer of nucleic acids consisting of a phosphate group, a pentose sugar and a nitrogen containing organic base.

Phosphodiester bond: Covalent bond joining 3’ carbon atom of one nucleotide to the 5’ carbon of another.

Polynucleotide: Larger polymer molecule made of many nucleotide monomer joined by phosphodiester bonds.

Promoter: DNA sequence at the start of a gene, to which RNA polymerase binds to start transcriptions.

Purine: Nitrogenous base consisting of a double ring structure.

Pyrimidine: Nitrogenous base with a single ring structure.

Reverse transcriptase: An enzyme originally derived from retroviruses. This enzyme catalyses the synthesis of a DNA strand using an RNA molecule as a template.

Ribonucleic acid (RNA): Single stranded polynucleotide that exists in three forms. Each form plays a part in the synthesis of proteins within cells.

Ribosomal RNA (rRNA): Types of RNA molecules found in both small and large subunits of ribosomes.

Ribosomes: Structures composed of two subunits, made from rRNA and proteins, which are the site of protein synthesis.

RNA polymerase: Binds to a specific binding site on the DNA at the start of the gene.

Semi conservative replication: The replication of a DNA molecule where the two strands separate and each strand acts as a template for the synthesis of a new DNA strand according to the complementary base-pairing rule.

Template (antisense) strand: The strand of DNA that acts as the template for transcription and has a complementary base sequence to both the mRNA and the DNA coding strand.

Transcription: The process of formation of an mRNA copy of a section of the template strand of DNA that corresponds to a gene, catalysed by RNA polymerase.

Transcription factor: Protein that binds to a specific DNA sequence to alter the expression of a gene.

Transfer RNA (tRNA): Single RNA polynucleotide chain that carries a specific activated amino acid to the ribosomes during translation to be added to the growing polypeptide chain.

Translation: The production of a polypeptide chain at a ribosome using the sequence of codons in the mRNA to direct the order amino acids are joined together.