amino acid - an organic molecule that has both amino and carboxyl groups; amino acids constitute the monomers (basic units) of proteins.
anticodon - a specific base triplet located on one end of a tRNA molecule that recognises the complementary codon on an mRNA molecule.
A site - the binding site on a ribosome that holds the tRNA carrying the next amino acid to be added to a growing polypeptide chain.
base pair substitution - a type of point mutation; the replacement of one complementary set of nucleotides by another pair.
codon - a three-nucleotide sequence of DNA or mRNA that codes for a specific amino acid or termination signal; the basic unit of the genetic code.
deletion - the mutational loss of a nucleotide from a gene.
deoxyribose - the sugar component of DNA. Deoxyribose has one fewer hydroxyl group than ribose.
DNA ligase - a DNA replication enzyme that catalyzes the formation of covalent bonds between the 3' end of a new DNA fragment and the 5' end of the growing strand.
DNA polymerase - an enzyme that catalyzes the formation of new DNA at a replication fork in the 5' to 3' direction by adding nucleotides to the existing strand.
There are three types of DNA polymerase in prokaryotic cells; polymerase III adds nucleotides to a growing strand in a 5' to 3' direction; polymerase I removes the RNA primer and replaces it with DNA; and polymerase II proof reads DNA for mutations.
double helix - the natural form of DNA, refering to its two complementary neucleotide strands which wind into a spiral shape due to hydrogen bonds.
elongation - the stage in translation where amino acids are added one by one to the first amino acid.
exons - the portion of a eukaryotic gene that is expressed; exons are divided from eachother by introns.
frameshift mutation - a mutation that occurs when the number of nucleotides inserted or deleted is not a multiple of 3; results in incorrect codon grouping.
helicase - an enzyme which promotes the unwinding of the DNA strand.
initiation - the frist stage of translation; mRNA, tRNA with the first amino acid, and the two ribosomal units are brought together
insertion - a mutation where one or more nucleotide pairs is/are added to a gene.
introns - the noncoding regions of a gene. See exons.
lagging strand - the DNA strand which is discontinuously synthesized in direction away from the replication fork.
leading strand - the new complementary DNA strand which is synthesized continuously in the 5' to 3' direction.
missense mutations - the most common type of mutation involving a base-pair substitution within a gene that changes a codon, but the new codon makes sense in that it still codes for an amino acid.
messenger RNA (mRNA) - a type of RNA that is synthesised from DNA in the genetic material. It attaches to ribosomes in the cytoplasm and specifies the structure of a protein.
mutagen - a chemical or other physical agent that interacts with DNA to cause a mutation.
mutations - rare changes in the DNA of genes which eventually lead to genetic diversity.
nonsense mutations - a mutation that changes a codon for an amino acid to one of the three stop codons. This usually results in a shorter nonfunctional protein.
nucleolus - a specialized structure within the nucleus formed by various chromosomes. It is active in the synthesis of ribosomes.
nucleoside - an organic molecule made up of a nitrogenous base attached to a five carbon sugar.
nucleotide - the building block of a nucleic acid; it consists of a five carbon sugar covalently bonded to a nitrogenous base and a phosphate group.
nucleus - the organelle of an eukaryotic cell which contains chromosomes.
origins of replication - the locations on a DNA strand where the strand begins "unzipping".
point mutations - a chromosomal change at some single nucleotide of a gene.
poly-A-tail - a nucleotide complex attached to the 3' end of and mRNA molecule that stops degredation and helps translation.
polysome - a group of several ribosomes attached to the same single mRNA molecule.
primase - a enzyme which adds RNA primer to the beginning of a new strand (one primer on the leading strand and one primer per Okazaki fragment.
primer - a pre-existing DNA strand bound to the template DNA to which nucleotides must be added during DNA synthesis.
promoter - a DNA codon found near the beginning of a gene that tells RNA polymerase where to start transcribing RNA.
P site - the binding site on a ribosomal unit that holds the tRNA carrying a growing polypeptide chain.
replication fork - a Y-shaped point (fork) on a replicating DNA strand where new DNA is being formed by the addition of nucleotides.
ribose - the five carbon sugar component of RNA.
ribosome - a cell organelle produced in the nucleolus. It consists of two subunits and is
ribosomal RNA (rRNA) - forms the structure of ribosomes that coordinate the sequential joining of tRNA molecules to the series of mRNA codons.
RNA polymerase - an enzyme that links the growing chain of ribonucleotides during transcription.
RNA splicing - the removal of noncoding portions of the RNA molecule after its initial sysnthesis.
splicesome - an assembly that interacts with the ends of RNA introns. It cuts out an intron and joins two adjacent exons.
termination - the final stage of protein synthesis. A stop codon in conjunction with a releasing factor signals the ribosome to stop adding amino acids and release the peptide chain.
transcription - the transfer of information from a DNA molecule into an RNA molecule.
transfer RNA (tRNA) - a RNA molecule that interprets mRNA nucleotide codons and picks up the specific amino acids which the mRNA code for.
translation - the conversion of information from a RNA molecule into a polypeptide.
triplet code - a set of three nucleotides that specify the amino acids for polypeptide chains.