Key terms Flashcards

1
Q

bacteriorhodopsin

A

Pigmented protein found in abundance in the plasma
membrane of the salt-loving archaeon Halobacterium
halobium; pumps protons out of the cell, fueled by light
energy.

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2
Q

cell cortex

A

Specialized layer of cytoplasm on the inner face of the

plasma membrane.

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3
Q

cholesterol

A

Short, rigid lipid molecule present in large amounts in the
plasma membranes of animal cells, where it makes the lipid
bilayer less flexible.

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4
Q

detergent

A

Soapy substance used to solubilize lipids and membrane

proteins.

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5
Q

fat droplet

A

Large cluster of hydrophobic fats or oils that forms inside

the cells.

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6
Q

glycocalyx

A

Protective layer of carbohydrates on the outside surface
of the plasma membrane formed by the sugar residues of
membrane glycoproteins, proteoglycans, and glycolipids.

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7
Q

lipid bilayer

A

Thin pair of closely juxtaposed sheets, composed mainly of phospholipid molecules, that forms the structural basis for
all cell membranes.

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8
Q

membrane domain

A

Functionally and structurally specialized region in the membrane of a cell or organelle; typically characterized by
the presence of specific proteins.

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9
Q

membrane protein

A

Voltage difference across a membrane due to a slight
excess of positive ions on one side and of negative ions on
the other.

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10
Q

phosphatidylcholine

A

phosphatidylcholine
Common phospholipid present in abundance in most cell
membranes; uses choline attached to a phosphate as its
head group.

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11
Q

phospholipid

A

A major type of lipid molecule in many cell
membranes. Generally composed of two fatty
acid tails linked to one of a variety of phosphatecontaining
polar groups.

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12
Q

plasma membrane

A

The protein-containing lipid bilayer that surrounds a living

cell.

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13
Q

saturated

A

Describes an organic molecule that contains a full
complement of hydrogen; in other words, no double or
triple carbon–carbon bonds.

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14
Q

unsaturated

A

Describes an organic molecule that contains one or more

double or triple bonds between its carbon atoms.

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15
Q

action potential

A

Traveling wave of electrical excitation caused by rapid,
transient, self-propagating depolarization of the plasma
membrane in a neuron or other excitable cell; also called
a nerve impulse.

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16
Q

active transport

A

The movement of a solute across a membrane against its
electrochemical gradient; requires an input of energy, such
as that provided by ATP hydrolysis.

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17
Q

antiport

A

Type of coupled transporter that transfers two different
ions or small molecules across a membrane in opposite
directions, either simultaneously or in sequence.

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18
Q

axon

A

Long, thin extension that conducts electrical signals away

from a nerve cell body toward remote target cells.

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19
Q

Ca2+ pump

A

Enzyme that phosphorylates target proteins in response to
an increase in Ca2+ ion concentration through its interaction
with the Ca2+-binding protein calmodulin.

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20
Q

channel

A

A protein that forms a hydrophilic pore
across a membrane, through which
selected small molecules or ions can
passively diffuse.

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21
Q

dendrite

A

Short, branching structure that extends from the surface of

a nerve cell and receives signals from other neurons.

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22
Q

depolarization

A

A shift in the membrane potential, making it less negative

on the inside of the cell.

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23
Q

electrochemical gradient

A

Driving force that determines which way an ion will move
across a membrane; consists of the combined influence
of the ion’s concentration gradient and the membrane
potential.

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24
Q

gradient-driven pump

A

A protein that uses energy stored in the electrochemical
gradient of ions to actively transport a solute across a
membrane.

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25
H+ pump
A protein or protein complex that uses energy supplied by ATP hydrolysis, an ion gradient, or light to actively move protons across a membrane.
26
ion channel
Transmembrane protein that forms a pore across the lipid bilayer through which specific inorganic ions can diffuse down their electrochemical gradients.
27
k+ leak channel
Ion channel permeable to K+ that randomly flickers between an open and closed state; largely responsible for the resting membrane potential in animal cells.
28
ligand gated channel
An ion channel that is stimulated to open by the binding of | a small molecule such as a neurotransmitter
29
mechanically-gated channel
An ion channel that allows the passage of select ions across | a membrane in response to a physical perturbation.
30
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.
31
membrane transport protein
A protein associated with the lipid bilayer of a cell | membrane.
32
Na+ pump
Transporter found in the plasma membrane of most animal cells that actively pumps Na+ out of the cell and K+ in using the energy derived from ATP hydrolysis.
33
Nernst equation
An equation that relates the concentrations of an inorganic ion on the two sides of a permeable membrane to the membrane potential at which there would be no net movement of the ion across the membrane.
34
nerve terminal
Structure at the end of an axon that signals to another | neuron or target cell.
35
Neuron
ormation as part of the nervous system; a nerve cell.
36
Neurotransmitter
Small signaling molecule secreted by a nerve cell at a synapse to transmit information to a postsynaptic cell. Examples include acetylcholine, glutamate, GABA, and glycine.
37
Optogenetics
Technique that uses light to control the activity of neurons into which light-gated ion channels have been artificially introduced.
38
Osmosis
Passive movement of water across a cell membrane from a region where the concentration of water is high (because the concentration of solutes is low) to a region where the concentration of water is low (and the concentration of solutes is high).
39
Passive transport
oncentration gradient across a cell membrane via a membrane transport protein, such as a channel or a transporter.
40
Patch-clamp recording
Technique used to monitor the activity of ion channels in a membrane; involves the formation of a tight seal between the tip of a glass electrode and a small region of cell membrane, and manipulation of the membrane potential by varying the concentrations of ions in the electrode.
41
pump
Transporter that uses a source of energy, such as ATP hydrolysis or sunlight, to actively move a solute across a membrane against its electrochemical gradient.
42
resting membrane potential
Voltage difference across the plasma membrane when a | cell is not stimulated.
43
symport
A transporter that transfers two different solutes across a | cell membrane in the same direction.
44
synapse
Specialized junction where a nerve cell communicates with another cell (such as a nerve cell, muscle cell, or gland cell), usually via a neurotransmitter secreted by the nerve cell.
45
synaptic vesicle
Small membrane-enclosed sac filled with neurotransmitter | that releases its contents by exocytosis at a synapse.
46
transmitter-gated ion channel
Transmembrane receptor protein or protein complex that opens in response to the binding of a neurotransmitter, allowing the passage of a specific inorganic ion; its activation can trigger an action potential in a postsynaptic cell.
47
transporter
Membrane transport protein that moves a solute across a cell membrane by undergoing a series of conformational changes.
48
voltage-gated channel
Channel protein that permits the passage of selected ions, such as Na+, across a membrane in response to changes in the membrane potential. Found primarily in electrically excitable cells such as nerve and muscle cells.
49
voltage-gated Na+ channel
rotein in the plasma membrane of electrically excitable cells that opens in response to membrane depolarization, allowing Na+ to enter the cell. It is responsible for action potentials in these cells.
50
autophagy
Mechanism by which a cell “eats itself,” digesting molecules | and organelles that are damaged or obsolete.
51
clathrin
Protein that makes up the coat of a type of transport vesicle that buds from either the Golgi apparatus (on the outward secretory pathway) or from the plasma membrane (on the inward endocytic pathway).
52
coated vesicle
Small membrane-enclosed sac that wears a distinctive layer of proteins on its cytosolic surface. It is formed by pinching-off of a protein-coated region of cell membrane.
53
endocytosis
Process by which cells take in materials through an invagination of the plasma membrane, which surrounds the ingested material in a membrane-enclosed vesicle. (See also pinocytosis and phagocytosis.)
54
endomembrane system
Interconnected network of membrane-enclosed organelles in a eukaryotic cell; includes the endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, and endosomes.
55
endoplasmic reticulum
Labyrinthine membrane-enclosed compartment in the cytoplasm of eukaryotic cells where lipids and proteins are made.
56
endosome
Membrane-enclosed compartment of a eukaryotic cell through which material ingested by endocytosis passes on its way to lysosomes.
57
exocytosis
Process by which most molecules are secreted from a eukaryotic cell. These molecules are packaged in membrane-enclosed vesicles that fuse with the plasma membrane, releasing their contents to the outside.
58
golgi apparatus
``` Membrane-enclosed organelle in eukaryotic cells that modifies the proteins and lipids made in the endoplasmic reticulum and sorts them for transport to other sites. ```
59
lysosome
Membrane-enclosed organelle that breaks down worn-out proteins and organelles and other waste materials, as well as molecules taken up by endocytosis; contains digestive enzymes that are typically most active at the acid pH found inside these organelles.
60
membrane-enclosed organelle
Any organelle in a eukaryotic cell that is surrounded by a lipid bilayer—for example, the endoplasmic reticulum, Golgi apparatus, and lysosome.
61
nuclear envelope
Double membrane surrounding the nucleus. Consists of | outer and inner membranes, perforated by nuclear pores.
62
nuclear pore
Channel through which selected large molecules move between the nucleus and the cytoplasm.
63
peroxisome
Small membrane-enclosed organelle that contains enzymes | that degrade lipids and destroy toxins.
64
phagocytic cell
A cell such as a macrophage or neutrophil that is specialized to take up particles and microorganisms by phagocytosis.
65
phagocytosis
The process by which particulate material is engulfed (“eaten”) by a cell. Prominent in predatory cells, such as Amoeba proteus, and in cells of the vertebrate immune system, such as macrophages.
66
pinocytosis
Type of endocytosis in which soluble materials are taken up from the environment and incorporated into vesicles for digestion. (Literally, “cell drinking.”)
67
rab protein
One of a family of small GTP-binding proteins present on the surfaces of transport vesicles and organelles that serves as a molecular marker to help ensure that transport vesicles fuse only with the correct membrane.
68
receptor-mediated endocytosis
Mechanism of selective uptake of material by animal cells in which a macromolecule binds to a receptor in the plasma membrane and enters the cell in a clathrin-coated vesicle.
69
rough endoplasmic reticulum
Region of the endoplasmic reticulum associated with ribosomes and involved in the synthesis of secreted and membranebound proteins.
70
secretion
Production and release of a substance from a cell.
71
signal sequence
Amino acid sequence that directs a protein to a specific | location in the cell, such as the nucleus or mitochondria.
72
SNARE
One of a family of membrane proteins responsible for the selective fusion of vesicles with a target membrane inside the cell.
73
tethering protein
Filamentous transmembrane protein involved in the | docking of transport vesicles to target membranes
74
transport vesicle
Membrane vesicle that carries proteins from one intracellular compartment to another—for example, from the endoplasmic reticulum to the Golgi apparatus.
75
unfolded proteins response
Molecular program triggered by the accumulation of misfolded proteins in the endoplasmic reticulum. Allows cells to expand the endoplasmic reticulum and produce more of the molecular machinery needed to restore proper protein folding and processing.
76
vesivular transport
Movement of material between organelles in the eukaryotic | cell via membrane-enclosed vesicles.
77
active site
Region on the surface of an enzyme that binds to a substrate | molecule and catalyzes its chemical transformation.
78
allosteric
Describes a protein that can exist in multiple conformations depending on the binding of a molecule (ligand) at a site other than the catalytic site; such changes from one conformation to another often alter the protein’s activity or ligand affinity.
79
alpha helix
Folding pattern, common in many proteins, in which a single polypeptide chain twists around itself to form a rigid cylinder stabilized by hydrogen bonds between every fourth amino acid.
80
amino acid sequence
The order of the amino acid subunits in a protein chain. | Sometimes called the primary structure of a protein.
81
antibody
Protein produced by B lymphocytes in response to a foreign molecule or invading organism. Binds to the foreign molecule or cell extremely tightly, thereby inactivating it or marking it for destruction.
82
antigen
Molecule or fragment of a molecule that is recognized by | an antibody.
83
Beta sheet
``` olding pattern found in many proteins in which neighboring regions of the polypeptide chain associate side-by-side with each other through hydrogen bonds to give a rigid, flattened structure. ```
84
binding site
Region on the surface of a protein, typically a cavity or groove, that interacts with another molecule (a ligand) through the formation of multiple noncovalent bonds.
85
C-terminus
The end of a polypeptide chain that carries a free carboxyl | group (–COOH).
86
chromatography
Technique used to separate the individual molecules in a complex mixture on the basis of their size, charge, or their ability to bind to a particular chemical group. In a common form of the technique, the mixture is run through a column filled with a material that binds the desired molecule, and it is then eluted from the column with a solvent gradient.
87
coiled-coil
Stable, rodlike protein structure formed when two or more | α helices twist repeatedly around each other.
88
conformation
Precise, three-dimensional shape of a protein or other macromolecule, based on the spatial location of its atoms in relation to one another.
89
coenzyme
Small molecule that binds tightly to an enzyme and helps it | to catalyze a reaction.
90
cryoelectron microscopy
Technique for observing the detailed structure of a macromolecule at very low temperatures after freezing native structures in ice.
91
disulfide bond
Covalent cross-link formed between the sulfhydryl groups on two cysteine side chains; often used to reinforce a secreted protein’s structure or to join two different proteins together.
92
electrophoresis
Technique for separating a mixture of proteins or DNA fragments by placing them on a polymer gel and subjecting them to an electric field. The molecules migrate through the gel at different speeds depending on their size and net charge.
93
enzyme
A protein that catalyzes a specific chemical reaction.
94
feedback inhibition
A form of metabolic control in which the end product of a chain of enzymatic reactions reduces the activity of an enzyme early in the pathway.
95
fibrous protein
A protein with an elongated, rodlike shape, such as collagen | or a keratin filament.
96
globular protein
Any protein in which the polypeptide chain folds into a | compact, rounded shape. Includes most enzymes.
97
GTP-binding protein
Intracellular signaling protein whose activity is determined by its association with either GTP or GDP. Includes both trimeric G proteins and monomeric GTPases, such as Ras.
98
helix
An elongated structure whose subunits twist in a regular | fashion around a central axis, like a spiral staircase.
99
intracellular condensate
A large aggregate of phase-separated macromolecules that creates a region with a special biochemistry without the use of an encapsulating membrane.
100
intrinsically disordered sequence
Region in a polypeptide chain that lacks a definite structure.
101
ligand
General term for a small molecule that binds to a specific | site on a macromolecule.
102
lysozyme
Enzyme that severs the polysaccharide chains that form the cell walls of bacteria; found in many secretions including saliva and tears, where it serves as an antibiotic.
103
mass spectrometry
Sensitive technique that enables the determination of the | exact mass of all of the molecules in a complex mixture.
104
michaelis constant
The concentration of substrate at which an enzyme works at half its maximum velocity; serves as a measure of how tightly the substrate is bound.
105
motor protein
Protein such as myosin or kinesin that uses energy derived from the hydrolysis of a tightly bound ATP molecule to propel itself along a protein filament or polymeric molecule.
106
N-terminus
The end of a polypeptide chain that carries a free α-amino | group.
107
nuclear magnetic resonance
Technique used for determining the three-dimensional | structure of a protein in solution.
108
peptide bond
Covalent chemical bond between the carbonyl group of one amino acid and the amino group of a second amino acid.
109
polypeptide, polypeptide chain
Linear polymer composed of multiple amino acids. Proteins | are composed of one or more long polypeptide chains.
110
polypeptide backbone
Repeating sequence of the atoms (–N–C–C–) that form the core of a protein molecule and to which the amino acid side chains are attached.
111
primary structure
The amino acid sequence of a protein.
112
protein
Macromolecule built from amino acids that provides cells with their shape and structure and performs most of their activities.
113
protein domain
Segment of a polypeptide chain that can fold into a compact, | stable structure and that often carries out a specific function.
114
protein family
A group of polypeptides that share a similar amino acid sequence or three-dimensional structure, reflecting a common evolutionary origin. Individual members often have related but distinct functions, such as kinases that phosphorylate different target proteins.
115
protein kinase
Enzyme that catalyzes the transfer of a phosphate group from ATP to a specific amino acid side chain on a target protein.
116
protein machine
Assembly of protein molecules that operates as a cooperative unit to perform a complex series of biological activities, such as replicating DNA.
117
protein phosphatase
Enzyme that catalyzes the removal of a phosphate group from a protein, often with high specificity for the phosphorylated site.
118
protein phosphorylation
The covalent addition of a phosphate group to a side chain of a protein, catalyzed by a protein kinase; serves as a form of regulation that usually alters the activity or properties of the target protein.
119
quaternary structure
Complete structure formed by multiple, interacting | polypeptide chains that form a larger protein molecule.
120
scaffold protein
Protein with multiple binding sites for other macromolecules, holding them in a way that speeds up their functional interactions.
121
secondary structure
Regular local folding pattern of a polymeric molecule. In | proteins, it refers to α helices and β sheets.
122
side chain
Portion of an amino acid not involved in forming peptide bonds; its chemical identity gives each amino acid unique properties.
123
substrate
A molecule on which an enzyme acts to catalyze a chemical | reaction.
124
subunit
A monomer that forms part of a larger molecule, such as an amino acid residue in a protein or a nucleotide residue in a nucleic acid. Can also refer to a complete molecule that forms part of a larger molecule. Many proteins, for example, are composed of multiple polypeptide chains, each of which is called a protein subunit.
125
tertiary structure
Complete three-dimensional structure of a fully folded | protein.
126
transition state
Transient structure that forms during the course of a chemical reaction; in this configuration, a molecule has the highest free energy; it is no longer the substrate, but is not yet the product.
127
turnover number
The maximum number of substrate molecules that an | enzyme can convert into product per second.
128
Vmax
The maximum rate of an enzymatic reaction, reached when the active sites of all of the enzyme molecules in a sample are fully occupied by substrate.
129
x-ray crystallography
Technique used to determine the three-dimensional structure of a protein molecule by analyzing the diffraction pattern produced when a beam of x-rays is passed through an ordered array of the protein.
130
acetyl CoA
Activated carrier that donates the carbon atoms in its readily transferable acetyl group to many metabolic reactions, including the citric acid cycle and fatty acid biosynthesis; the acetyl group is linked to coenzyme A (CoA) by a thioester bond that releases a large amount of energy when hydrolyzed.
131
Acid
A molecule that releases a proton when dissolved in water; this dissociation generates hydronium (H3O+) ions, thereby lowering the pH.
132
Actin filament
Thin, flexible protein filament made from a chain of globular actin molecules; a major constituent of all eukaryotic cells, this cytoskeletal element is essential for cell movement and for the contraction of muscle cells.
133
Actin-binding protein
Protein that interacts with actin monomers or filaments to control the assembly, structure, and behavior of actin filaments and networks.
134
Activated carrier
A small molecule that stores energy or chemical groups in a form that can be donated to many different metabolic reactions. Examples include ATP, acetyl CoA, and NADH.
135
activation energy
The energy that must be acquired by a molecule to undergo | a chemical reaction.
136
adaptation
Adjustment of sensitivity following repeated stimulation; allows a cell or organism to register small changes in a signal despite a high background level of stimulation.
137
Adenyl cyclase
Enzyme that catalyzes the formation of cyclic AMP from ATP; an important component in some intracellular signaling pathways.
138
adherens junction
Cell junction that helps hold together epithelial cells in a sheet of epithelium; actin filaments inside the cell attach to its cytoplasmic face
139
ADP
Nucleoside diphosphate produced by hydrolysis of the | terminal phosphate of ATP.
140
allele
An alternative form of a gene; for a given gene, many alleles may exist in the gene pool of the species.
141
alternative splicing
The production of different mRNAs (and proteins) from the | same gene by splicing its RNA transcripts in different ways.
142
alu sequence
Family of mobile genetic elements that comprises about 10% of the human genome; this short, repetitive sequence is no longer mobile on its own, but requires enzymes encoded by other elements to transpose.
143
amino acid
Small organic molecule containing both an amino group and a carboxyl group; it serves as the building block of proteins.
144
aminoacyl-tRNA synthase
During protein synthesis, an enzyme that attaches the correct amino acid to a tRNA molecule to form a “charged” aminoacyl-tRNA.
145
amphipatic
Having both hydrophobic and hydrophilic regions, as in a | phospholipid or a detergent molecule
146
anabolic pathway
Series of enzyme-catalyzed reactions by which large biological molecules are synthesized from smaller subunits; usually requires an input of energy.
147
anabolism
Set of metabolic pathways by which large molecules are | made from smaller ones.
148
anaphase
Stage of mitosis during which the two sets of chromosomes separate and are pulled toward opposite ends of the dividing cell.
149
anaphase-promoting complex (APC/C)
A protein complex that triggers the separation of sister chromatids and orchestrates the carefully timed destruction of proteins that control progress through the cell cycle; the complex catalyzes the ubiquitylation of its targets.
150
antenna complex
In chloroplasts and photosynthetic bacteria, the part of the membrane-bound photosystem that captures energy from sunlight; contains an array of proteins that bind hundreds of chlorophyll molecules and other photosensitive pigments.
151
anticodon
Set of three consecutive nucleotides in a transfer RNA molecule that recognizes, through base-pairing, the threenucleotide codon on a messenger RNA molecule; this interaction helps to deliver the correct amino acid to a growing polypeptide chain.
152
apical
Describes the top or the tip of a cell, structure, or organ; in an epithelial cell, for example, this surface is opposite the base, or basal surface.
153
apoptosis
A tightly controlled form of programmed cell death that allows excess cells to be eliminated from an adult or developing organism.
154
archaeon
Microscopic organism that is a member of one of the | two divisions of prokaryotes; often found in hostile environments such as hot springs or concentrated brine.
155
Asexual reproduction
Mode of reproduction in which offspring arise from a single parent, producing an individual genetically identical to that parent; includes budding, binary fission, and parthenogenesis.
156
Aster
Star-shaped array of microtubules emanating from a | centrosome or from a pole of a mitotic spindle.
157
Atom
The smallest particle of an element that still retains its distinctive chemical properties; consists of a positively charged nucleus surrounded by a cloud of negatively charged electrons.
158
atomic weight
The mass of an atom relative to the mass of a hydrogen atom; equal to the number of protons plus the number of neutrons that the atom contains
159
ATP
Activated carrier that serves as the principal carrier of energy in cells; a nucleoside triphosphate composed of adenine, ribose, and three phosphate groups
160
ATP synthase
Abundant membrane-associated enzyme complex that catalyzes the formation of ATP from ADP and inorganic phosphate during oxidative phosphorylation and photosynthesis.
161
Avogadro's number
The number of molecules in a mole, the quantity of a substance equal to its molecular weight in grams; approximately 6 × 1023.
162
bacterium
Microscopic organism that is a member of one of the two divisions of prokaryotes; some species cause disease. The term is sometimes used to refer to any prokaryotic microorganism, although the world of prokaryotes also includes archaea, which are only distantly related to each other.
163
Basal
Situated near the base; opposite of apical.
164
Basal lamina
Thin mat of extracellular matrix, secreted by epithelial cells, upon which these cells sit.
165
Base
Molecule that accepts a proton when dissolved in water; also used to refer to the nitrogen-containing purines or pyrimidines in DNA and RNA.
166
base pair
Two complementary nucleotides in an RNA or a DNA molecule that are held together by hydrogen bonds— normally G with C, and A with T or U.
167
Bcl2family
Related group of intracellular proteins that regulates apoptosis; some family members promote cell death, others inhibit it