Akt   Serine/threonine protein kinase that acts in the PI-3kinase/Akt intracellular signaling pathway involved especially in signaling cells to grow and survive. Also called protein kinase B (PKB).
allele   One of several alternative forms of a gene. In a diploid cell, each gene will typically have two alleles, occupying the corresponding position (locus) on homologous chromosomes.
allosteric protein   A protein that can adopt at least two distinct conformations, and for which the binding of a ligand at one site causes a conformational change that alters the activity of the protein at a second site; this allows one type of molecule in a cell to alter the fate of a molecule of another type, a feature widely exploited in enzyme regulation.
allostery (adjective allosteric) Change in a protein’s conformation brought about by the binding of a regulatory ligand (at a site other than the protein’s catalytic site), or by covalent modification. The change in conformation alters the activity of the protein and can form the basis of directed movement. (Figures 3–57 and 16–29) alpha helix (α helix) Common folding pattern in proteins, in which a linear sequence of amino acids folds into a right-handed helix stabilized by internal hydrogen-bonding between backbone atoms. (Figure 3–7) alternative RNA splicing   Production of different RNAs from the same gene by splicing the transcript in different ways. (Figure 7–57) amino acid Organic molecule containing both an amino group and a carboxyl group. Those that serve as building blocks of proteins are alpha amino acids, having both the amino and carboxyl groups linked to the same carbon atom. (NH2CHRCOOH, Panel 3–1, pp. 112–113) aminoacyl-tRNA synthetase Enzyme that attaches the correct amino acid to a tRNA molecule to form an aminoacyltRNA. (Figure 6–54)
AMPA receptor Glutamate-gated ion channel in the mammalian central nervous system that carries most of the depolarizing current responsible for excitatory postsynaptic potentials.
amphiphilic   Having both hydrophobic and hydrophilic regions, as in a phospholipid or a detergent molecule.
amyloid fibrils   Self-propagating, stable β-sheet aggregates built from hundreds of identical polypeptide chains that become layered one over the other to create a continuous stack of  β sheets. The unbranched fibrous structure can contribute to human diseases when not controlled.
anaphase   (1) Stage of mitosis during which sister chromatids separate and move away from each other. (2) Anaphase I and
II: stages of meiosis during which chromosome homolog pairs separate (I), and then sister chromatids separate (II). (Panel 17–1, pp. 980–981) anaphase A   Stage of mitosis during which chromosome segregation occurs as chromosomes move toward the two spindle poles.
anaphase B   Stage of mitosis during which chromosome segregation occurs as spindle poles separate and move apart.
anaphase-promoting complex (APC/C; cyclosome) Ubiquitin ligase that catalyzes the ubiquitylation and destruction of securin and Mand S-cyclins, initiating the separation of sister chromatids in the metaphase-to-anaphase transition during mitosis.
anchorage dependence   Dependence of cell growth, proliferation, and survival on attachment to a substratum.
anchoring junction Cell junction that attaches cells to neighboring cells or to the extracellular matrix. (Table 19–1, p. 1037) angiogenesis   Growth of new blood vessels by sprouting from existing ones.
antenna complex   Part of a photosystem that captures light energy and channels it into the photochemical reaction center. It consists of protein complexes that bind large numbers of chlorophyll molecules and other pigments.