Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter by by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morg

Glossary G:19
lysosomal storage diseases Genetic diseases resulting
from defects in or a lack of one or more functional hydrolases in
lysosomes of some cells, leading to accumulation of undigested
substrates in lysosomes and consequent cell pathology.
lysosome Membrane-enclosed organelle in eukaryotic cells
containing digestive enzymes, which are typically most active at
the acid pH found in the lumen of lysosomes. (Figure 13–37)
lysozyme Enzyme that catalyzes the cutting of
polysaccharide chains in the cell walls of bacteria.
M-Cdk (M-phase Cdk) Cyclin-Cdk complex formed in
vertebrate cells by an M-cyclin and the corresponding cyclindependent
kinase (Cdk). (Figure 17–11 and Table 17–1, p. 969)
M-cyclin A cyclin found in all eukaryotic cells that promotes
the events of mitosis. (Figure 17–11)
M6P receptor proteins Transmembrane receptor proteins
present in the trans Golgi network that recognize the mannose
6-phosphate (M6P) groups added exclusively to lysosomal
enzymes, marking the enzymes for packaging and delivery to
early endosomes.
macromolecule Polymers constructed of long chains of
covalently linked, small organic (carbon-containing) molecules.
The principal building blocks from which a cell is constructed
and the components that confer the most distinctive properties
of living things.
macrophage Phagocytic cell derived from blood monocytes,
resident in most tissues but able to roam. It has both scavenger
and antigen-presenting functions in immune responses.
macropinocytosis Clathrin-independent, dedicated
degradative endocytic pathway induced in most cell types by
cell-surface receptor activation by specific cargoes.
malaria Protozoal disease caused by four species of
Plasmodium, which are transmitted to humans by the bite of
the female Anopheles mosquito.
malignant Of tumors and tumor cells: invasive and/or
able to undergo metastasis. A malignant tumor is a cancer.
(Figure 20–3)
MAP kinase module (mitogen-activated protein kinase
module) An intracellular signaling module composed of
three protein kinases, acting in sequence, with MAP kinase as
the third. Typically activated by a Ras protein in response to
extracellular signals. (Figure 15–49)
master transcription regulator A transcription regulator
specifically required for formation of a particular cell type.
Artificial expression of master transcription regulators (alone or
in combination with others) will often convert one cell type into
another.
maternal inheritance A form of inheritance observed
when following mitochondria in animals and plants, where
mitochondrial DNA is inherited only through the female
germ line.
maternal-effect gene Gene that acts in the mother to
specify maternal mRNAs and proteins in the egg. Maternaleffect
mutations affect the development of the embryo even if
the embryo itself has not inherited the mutated gene.
maternal-zygotic transition (MZT) Event in animal
development where the embryo’s own genome largely takes
over control of development from maternally deposited
macromolecules.
matrix metalloprotease Ca 2+ - or Zn 2+ -dependent
proteolytic enzyme present in the extracellular matrix that
degrades matrix proteins. Includes the collagenases.
matrix space Large internal compartment of the
mitochondrion.
mechanosensitive channels Transmembrane ion channels
that open in response to a mechanical stress on the lipid bilayer
in which they are embedded.
megakaryocyte Large myeloid cell with a multilobed nucleus
that remains in the bone marrow when mature. Buds off
platelets from long cytoplasmic processes. (Figures 22–29)
meiosis I The first of two rounds of chromosome segregation
following meiotic chromosome duplication; segregates the
homologs, each composed of a tightly linked pair of sister
chromatids.
meiosis II The second of two rounds of chromosome
segregation following meiotic chromosome duplication;
segregates the sister chromatids of each homolog.
membrane potential Voltage difference across a membrane
due to a slight excess of positive ions on one side and of
negative ions on the other. A typical membrane potential for
an animal cell plasma membrane is –60 mV (inside negative
relative to the surrounding fluid). (Figure 11–23)
membrane protein Amphiphilic protein of diverse structure
and function that associates with the lipid bilayer of cell
membranes. (Figure 10–17)
membrane transport protein Membrane protein that
mediates the passage of ions or molecules across a
membrane. The two main classes are transporters (also called
carriers or permeases) and channels. (Figure 11–4)
membrane-associated protein Membrane protein not
extending into the hydrophobic interior of the lipid bilayer
but bound to either face of the membrane by noncovalent
interactions with other membrane proteins. (Figure 10–17)
membrane-bending proteins Attach to specific membrane
regions as needed and act to control local membrane curvature
and thus confer on membranes their characteristic threedimensional
shapes.
membrane-bound ribosome Ribosome attached to
the cytosolic face of the endoplasmic reticulum. The site of
synthesis of proteins that enter the endoplasmic reticulum.
(Figure 12–38)
memory cell In immunology: a T or B lymphocyte generated
following antigen stimulation that is more easily and more
quickly induced to become an effector cell or another memory
cell by a later encounter with the same antigen. (Figure 24–17)
mesoderm Embryonic tissue that is the precursor to muscle,
connective tissue, skeleton, and many of the internal organs.
(Figure 21–3)
messenger RNA (mRNA) RNA molecule that specifies the
amino acid sequence of a protein. Produced in eukaryotes by
processing of an RNA molecule made by RNA polymerase as
a complementary copy of DNA. It is translated into protein in a
process catalyzed by ribosomes. (Figure 6–20)
metabolism The sum total of the chemical processes that
take place in living cells. All of catabolism plus anabolism.
(Figure 2–14)
metabotropic receptors Neurotransmitter receptors that
regulate ion channels indirectly through the activation of
second-messenger molecules.