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Home >> Dictionary of Bioinformatics, Biochemistry, Biotechnology >> Membrane Bioreactors - Meristem Culture
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Membrane An asymmetric lipid bilayer that exhibits lateral fluidity and contains proteins.
Membrane attack complex (MAC) Complement proteins which form a pore leading to cell lysis.
Membrane bioreactors Bioreactors in which cells grow on or behind a permeable membrane, which allows the nutrients for the cell through but retains the cells themselves. A variation of this is the hollow-fibre reactor.
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Membrane channel A transmembrane protein complex that permits inorganic ions and other small molecules to diffuse passively across the lipid bilayer.
Membrane filtration A method of calssifying microbial cell extracts. Since gelatinous microbial preparations can block the filter, membranes with an asymmetric pore structure are used in large-scale operations to isolate enzymes from lysed microorganisms.
Membrane potential The difference in electrical potential across a biological membrane that is measured by the insertion of a microelectrode. The membrane potentials generally range from-25 mV to greater than – 100mV negative inside relative to the outside.
Membrane proteins Proteins containing hydrophobic regions that allow a portion or all of the protein structure to reside within the membrane.
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Membrane ruffling A wave-like movement at the leading edge of a cell membrane during movement. The ruffled portion is an indicator of the direction of cell movement.
Membrane transport The facilitated transport of a molecule across a membrane. The movement of a polar solute via a specific membrane protein (transporter) across a membrane.
Membrane transport protein A membrane protein that mediates the movement of ions and molecules across a membrane. Examples include ion channels and carrier proteins.
Memory cells Long-lived B and T cells that mediate secondary immune responses to an antigen to which hey have been previously exposed.
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Memory, immunologic The ability of the immune system to respond to antigens that it has been previously exposed to; immunity to an antigen for a prolonged period.
Memory response A repeat response to an antigen that is faster and greater than a primary response.
Menadione A synthetic compound which exhibits vitamin K activity.
Mendel, Gregor (1822-1884) The father of genetics whose experiments on crossbreeding of peas led to the formulation of the principles of heredity.
Mendel’s Laws Two laws that summarise Mendel’s theory of inheritance. The Law of Segregation states that each hereditary characteristics is controlled by two ‘factors’ (alleles), which segregate and pass into separate germ cells. The Law of Independent Assortment states that pairs of ‘factors’ segregate independently of each other when germ cells are formed. See independent assortment; linkage.
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Mendelian genetics Genetics based on the laws proposed by Mendel; that is genetic traits are dependent on independent, randomly reassorting genetic elements.
Mendelian population A natural, interbreeding unit of sexually reproducing plants or animals that share a common gene pool.
Mendelism The theory of heredity, which forms the basis of classical genetics, proposed by Gregor Mendel in 1866 and formulated into laws. See Mendel’s Laws.
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Meninges The layers that cover the central nervous system (CNS)- the innermost plamater, middle arachnoid mater and outermost dura mater.
Meningitis Inflammation of the meninges.
Menkes’ disease (kinky hair disease) An X-linked recessive condition characterised by low plasma copper, defective synthesis of copper containing enzymes, depigmentation of skin and hair, cerebral degeneration and vascular defects.
Menopause A stage in the reproductive cycle of women when all the ovarian follicles atrophy, and menstruation ceases. Oestrogens are derived solely from the peripheral aromatization of adrenal androstenedione. Plasma concentrations of oestrogens are low. Consequently, LH and FSH levels rise due to insufficient feedback inhibition. Due to these hormonal changes, women are prone to osteoporosis and atrophy of urogenital epithelium and skin after menopause. The progressive loss of ovarian function is accompanied by vasomotor instability manifested as hot flushes, nervousness, anxiety, irritability and depression. Oestrogen therapy is useful in relieving symptoms in postmenopausal women.
Menstruation Characteristic cyclic changes in the secretion of ovarian hormones the occur in women every 4 weeks that are regulated by gonadotrophins from the anterior pituitary. The menstrual cycle can be divided into preovulatory, ovulatory and post-ovulatory phases. In the pre-ovulatory phase FSH stimulates the development of the follicle with resulting increase in oestrogen secretion. One of the follicles, which becomes sensitive to FSH develops associated with proliferative changes in the uterine and vaginal epithelium. The ovulatory phase involves ripening of the follicle with increase in plasma oestrogen levels. AT midcycle, there is a surge of LH and FSH secretion by the anterior pituitary with ovulation and rupture of the follicle. In the post-ovulatory phase, the ruptured follicle is transformed into a yellow structure termed the corpus luteum with hypertrophy and development of the glandular cells of the endometrium. The corpus luteum produces progesterone and some amount of oestradiol. If the ovum is not fertilised, the corpus luteum regresses with fall in hormone secretion and menstruation ensues. If the ovum is fertilised, pregnancy occurs.
β-mercaptoethanol A reducing agent that breaks disulphide bonds in proteins
6-mercaptopurine An analogue of hypoxanthine that is metabolised to 6-thioinosine monophosphate (6-thio-IMP) which blocks key steps in purine biosynthesis. It is used as a cancer chemotherapeutic agent.
Mericlinal Refers to a chimera with tissue of one genotype partly surrounded by that of another genotype.
Meristem A group of dividing cells whose derivatives develop into the organs and tissues of a flowering plant.
Meristem culture A technique used to produce pathogen-free plants. The meristem contains actively dividing cells resistant to microbial contamination. When meristem growth is combined with micropropagation, disease free plants can be cultured.
Merodiploid An organism that is diploid for only some of its genes.
Merozygote A partial zygote generated by a process of partial genetic exchange, such as transformation in bacteria.
Meselson, Matthew (b-1930) A biochemist who together with Franklin Stahl demonstrated the semiconservative nature of DNA replication in 1957.
Mesenchymal stem cells (MSCs) Cells that can develop into distinct mesenchymal tissue such as bone, endons, muscles, adipose tissue, cartilage, nerve tissue and blood and blood vessels.
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