Aerobic respiration
Metabolic process in some cells, in which ATP is produced by the oxidation of carbohydrates (respiration) involving oxygen.
Amino acid
A small molecule consisting of carbon, hydrogen, oxygen and an amine group (NH2)—some also contain sulfur. Amino acids join together to form proteins.
Anaerobic respiration
Metabolic process in which ATP is produced by the oxidation of carbohydrates (respiration) not involving oxygen.
Apoptosis
Controlled cell death, after irreparable damage to DNA or the infection of a cell by viruses or bacteria.
Archaea
Together with Bacteria and Eukaryotes, one of the three domains of living organisms.
ATP (Adenosine triphosphate)
An energy-rich molecule that enables most molecular-scale cellular processes. As it supplies energy, it breaks down to form adenosine diphosphate (ADP) and a free phosphate group.
Budding
A form of asexual reproduction or cell division that results in two identical daughter cells. A new cell grows as a “bud” on the existing cell, unlike simple cell division, in which one cell divides in two.
Cell cycle
A repeating series of events by which a cell replicates its contents—in particular the contents of its nucleus by mitosis—then divides.
Chromatin
Stringy material found in the nucleus of eukaryotic cells and composed of DNA packed around histone proteins.
Chromosome
Structures in eukaryotic cells, made of chromatin in its most compacted state. Chromosomes form during mitosis. Chromosome is also the name given to any isolated length of DNA, so the DNA inside a prokaryotic cell is sometimes referred to as a chromosome.
Codon
A set of three bases (nucleotides) along a length of DNA. In general, each codon codes for a specific amino acid and is important in the process of translation, by which the protein recipes in genes make protein molecules.
Cytoskeleton
A dynamic network of protein filaments and tubes found inside eukaryotic cells. It is responsible for a number of vital processes, including transporting vesicles around the cell and dragging duplicated chromosomes apart during mitosis.
Describes a (eukaryotic) cell that has two sets of corresponding chromosomes. Most cells of an organism are diploid. See Haploid.
DNA (Deoxyribonucleic acid)
The double helical molecule that carries genetic information in all living organisms.
Endoplasmic reticulum
An organelle found in eukaryotic cells.
Eukaryotes
Together with Bacteria and Archaea, one of the three domains of living organisms. Eukaryotic cells are larger and more complex than the prokaryotic cells of the other two domains.
Gamete
A haploid (eukarytotic) cell, produced by meiosis, which can join with another gamete to form a new, unique organism.
Gametophyte
A part of a multicellular (eukaryotic) organism in which all the cells are haploid gametes. All plants and fungi produce gametophytes for at least some of their life cycles.
Golgi complex
An organelle found in eukaryotic cells, made of folded phospholipid membranes, upon which protein molecules that have been made by transcription may be altered by adding other proteins or removing sections or by folding.
Gram stain
A chemical stain that is routinely used in the identification of bacteria. Those bacteria that have an outer membrane as well as an ordinary cell membrane have thinner cell walls, so do not take up the stain and are “gram negative.”
Describes a (eukaryotic) cell that has only one set of each chromosome. Sex cells (gametes) are haploid. See Diploid.
Meiosis
A process in eukaryotic cells consisting of two rounds of cell division, the result of which is four haploid gamete cells, or “sex cells.”
Micron
One millionth of a meter, equal to one thousandth of a millimeter (0.001 mm), about 0.00004 inches.
An organelle in eukaryotic cells that are described as cellular power stations. They are composed of phospholipid membranes, on which molecules of ATP synthase produce ATP.
Mitosis
A crucial part of the cell cycle in eukaryotic cells, in which already-duplicated chromsomes are pulled apart into two new nuclei, ready for cell division to take place.
mRNA see RNA
Multipotent see Potency
Nucleic acid
Large (long) molecules found in living organisms, made up of smaller molecules (nucleotides). The two most important nucleic acids are DNA and RNA.
Nucleobase
A nitrogen-containing compound found in nucleotides and, therefore, crucial parts of nucleic acids. Four nucleobases are found in DNA: adenine (A), cytosine (C), guanine (G), and thymine (T). The same is true for RNA, except that thymine is replaced by uracil (U).
Nucleotide
A compound whose molecules bond together to form nucleic acids. A nucleotide molecule is composed of a nucleobase plus a sugar and a phosphate group. Four nucleotides make up DNA, and are distinguished by the nucleobase they contain (A, C, G, and T).
Organelle
A structure with a specific function found inside cells. Only eukaryotic cells have organelles.
Oxidation
The opposite of Reduction. The part of a chemical reaction in which atoms or molecules lose electrons. Oxygen has a high affinity for electrons, and reactions with oxygen are archetypal example of oxidation.
Pathogen
Any organism that does harm to another. Many bacteria are pathogenic to humans but most are not.
Peptidoglycan
A compound composed of sugars and amino acids that forms the cell wall of bacteria.
Phospholipid
A compound whose molecules have a hydrophilic end, which will mix with water, and a hydrophobic end, which will not. Phospolipids form double layered membranes around cells, around organelles, and around vesicles.
Pluripotent see Potency
The extent to which the daughters of a cell in a multicellular organism can become any of a range of different types of cell. The daughters of multipotent cells can become any of several types within a certain tissue, while the daughters of pluripotent cells can become almost any type of cell. Embryonic stem cells are totiptent; through repeated cell divisions, they can give rise to an entire organism.
Prokaryote
A single-celled organism that is not a eukaryote—in other words, an archaeon or a bacterium. Prokaryotic cells are simpler than eukaryotic ones; they have no nucleus or organelles.
Reduction
The opposite of Oxidation. The part of a chemical reaction in which atoms or molecules gain electrons.
Ribosome
A molecular-scale “machine” that provides a site at which amino acids carried by tRNA are built up to form proteins, according to the instructions carried on lengths of mRNA. See also RNA.
A nucleic acid that is single stranded. Inside cells, lengths of messenger RNA (mRNA) are made as copies of genes (during transcription) and short lengths of transfer RNA (tRNA) carry amino acids, ready to be joined together to make proteins (during translation).
Stem cell
A pluripotent, multipotent, or totipotent cell in a multicellular organism. See Potency.
Totipotent see Potency
Transcription
The process by which genes are copied into lengths of mRNA. See RNA.
Translation
The process by which proteins are built up inside ribosomes. See RNA.
tRNA see RNA
Vesicle
A membrane-enclosed globule in which proteins and other molecules are transported or stored inside (eukaryotic) cells.
Zygote
A diploid cell produced by the union of two (haploid) gametes.