macromolecule
A macromolecule is a large molecule, and may be a protein, a lipid, a nucleic acid, or a polysaccharide (i.e., a starch). Polysaccharides, proteins, and nucleic acids are all polymers; lipids are not strictly polymers.

meiosis
Meiosis is a biological cell division process in eukaryotes by which a diploid parent cell produces four haploid daughter cells. It consists of two cycles of nuclear division, usually accompanied by cell division (especially in multicellular forms, where it is generally used to produce gametes (gametogenesis), preceded by DNA replication.

mitochondria
A mitochondrion (plural mitochondria; Fig. 1) is a membrane-enclosed cellular organelle. Mitochondria are distributed through the cytosol of most eukaryotic cells. Their main function is to convert the potential energy (via electron transport) of food molecules into ATP (the universal energy currency of the cell). They are composed of folds called cristae which give a much increased surface area on which chemical reactions can occur.

• The outer membrane encloses the entire organelle and contains channels made of protein complexes through which molecules and ions can move in and out of the mitochondrion. Large molecules are excluded from traversing this membrane.
• The inner membrane, folded into cristae, encloses the matrix (the internal fluid of the mitochondrion). It contains several protein complexes. Stalked particles are found on the cristae: these are the ATP synthetase enzyme molecules, which produce ATP.
• The intermembrane space between the two membranes contains enzymes that use ATP to phosphorylate other nucleotides and that catalyze other reactions.

mitosis
In biology, Mitosis is the process of chromosome segregation and nuclear division that follows replication of the genetic material in eukaryotic cells. This process assures that each daughter nucleus receives a complete copy of the organism's genome. In most eukaryotes mitosis is accompanied with cell division or cytokinesis, but there are many exceptions, for instance among the fungi. There is another process called meiosis, in which the daughter nuclei receive half the chromosomes of the parent, which is involved in gamete formation and other similar processes.

Mitosis is divided into several stages, with the remainder of the cell's growth cycle considered interphase. Properly speaking, a typical cell cycle involves a series of stages: G1, the first growth phase; S, where the genetic material is duplicated; G2, the second growth phase; and M, where the nucleus divides through mitosis. Mitosis is divided into prophase, prometaphase, metaphase, anaphase, and telophase.

The whole procedure is very similar among most eukaryotes, with only minor variations. As prokaryotes lack a nucleus and only have a single chromosome with no centromere, they cannot be properly said to undergo mitosis.

monomer
In chemistry, a monomer (from Greek mono "one" and meros "part") is any of several small molecular structures that may be chemically bonded together to form long multi-part polymer molecules.

Amino acids are natural monomers, and polymerize to form proteins. Glucose monomers can also polymerize to form starches and glycogen polymers. The polymerization reaction is known as a condensation reaction because of the loss of a hydrogen atom and a hydroxyl (-OH) group from the two monomer units. The bond between the monomers is an oxygen molecule with a bond with each monomer unit. The result of this reaction is H20.

monosaccharide
Monosaccharides are carbohydrates in the form of simple sugars.

Monosaccharides are sweet, water soluble and crystalline. Examples include the hexoses (glucose, fructose, and galactose) and pentoses (ribose, deoxyribose).

morphogenesis
Morphogenesis (from the Greek morphê shape and genesis creation) describes the process of cellular differentiation that takes place during the embryonic development of an organism. The change from a cluster of unitary cells to structured tissues, specialized cells and organs is controlled by the genetic "program" and can be modified by environmental factors. The morphogenes (proteins that control morphogenesis) that determine the fate of cells are proteins that interact with DNA. They can either activate or deactivate genes that, in turn, can activate other genes (Fig. 1). The localized expression (production) of a protein results in a protein gradient. Above a threshold of concentration, the protein is active and works as a transcription factor. (A transcription factor regulates the amount of protein that is produced from a gene.)

1. addition of a 5' cap - A modified guanine nucleotide is added to the "front" of the message. This is critical for recognition and proper attachment of the ribosome.
2. splicing - The pre-mRNA is modified to remove certain stretches of non-coding sequences called introns; the stretches that remain include protein-coding sequences and are called exons. Sometimes one pre-mRNA message may be spliced in several different ways, allowing 1 gene to encode multiple functions. Most RNA splicing is performed by enzymes, but some RNA molecules are also capable of catalyzing their own splicing (see ribozymes).
3. polyadenylation - A sequence (often several hundred) of adenine nucleotides is added to the 3' end of the pre-mRNA. This helps increase the half-life of the message, so that the transcript lasts longer in the cell and consequently is translated more and produces more protein.

After the mRNA has been processed, it is exported from the nucleus into the cytoplasm, where it is bound to ribosomes and translated into protein. After a certain amount of time the message degrades into its component nucleotides, usually with the assistance of RNAses.

mutation
Mutations are permanent, transmissible changes to the genetic material (usually DNA or RNA) of an organism. Mutations can be caused by copying errors in the genetic material during cell division and by exposure to radiation, chemicals, or viruses. Mutations often lead to the malfunction or death of a cell and can cause cancer in higher organisms. Mutations are considered the driving force of evolution, where less favorable mutations are removed by natural selection, but favorable ones tend to accumulate. Neutral mutations do not affect the organism and can accumulate over time, which might result in what is known as Punctuated Equilibrium; a modern variation on classic evolutionary theory.