General Biology: Cell Signaling, Genetics, Meiosis, and Cell Division

Comprehensive vocabulary flashcards covering cell signaling pathways, Mendelian genetics, the chromosomal theory of inheritance, meiotic reproduction, and the eukaryotic cell cycle.

Ligand

A signaling molecule that binds specifically to a complementary receptor protein on or inside a target cell to initiate a cellular response.

Quorum Sensing

A cell-signaling phenomenon in prokaryotes where bacteria monitor their own local population density by sensing the concentration of secreted signaling molecules.

Signal Transduction Pathway

A multistep sequence of molecular relays inside a cell that converts an extracellular chemical signal into a specific cellular response.

Synapse

The narrow junction or cleft between a transmitting nerve cell and its target cell across which neurotransmitters diffuse rapidly.

Hormones

Chemical messengers used for long-distance signaling that are secreted into circulatory fluids or vascular networks to reach and regulate distant target cells.

G Protein-Coupled Receptor (GPCR)

The largest family of human cell-surface receptors that responds to external signaling molecules by activating an intracellular membrane-bound G protein.

Protein Kinase

An enzyme that transfers a phosphate group from ATP to a specific target protein, typically activating it within a phosphorylation cascade.

Receptor Tyrosine Kinase

A plasma membrane receptor that dimerizes upon ligand binding and autophosphorylates tyrosine amino acid residues on its cytoplasmic tails to activate relay proteins.

Protein Phosphatase

An enzyme that removes phosphate groups from proteins (dephosphorylation), serving as a molecular switch to shut off a signal transduction pathway and recycle kinases.

Second Messenger

A small, non-protein, water-soluble molecule or ion (such as cyclic AMP, $Ca^{2+}$, or $IP_3$) that rapidly relays and diffuses a signal throughout the cell's interior.

Cyclic AMP (cAMP)

A prominent second messenger synthesized from ATP by the enzyme adenylyl cyclase that functions primarily by activating protein kinase A (PKA).

Apoptosis

A regulated process of programmed cell death in which aging, infected, or damaged cells shrink, condense, and form cellular lobes ("blebs") to be cleared without causing tissue damage.

Chromosomal Theory of Inheritance

A fundamental theory proposed by Walter Sutton and Theodor Boveri stating that genes are located at specific sites on chromosomes and that chromosome segregation during meiosis accounts for Mendel's laws.

Centimorgan (Genetic Map Unit)

A unit of measure for genetic linkage and chromosome mapping that corresponds to a $1\%$ recombination frequency between linked genes.

Polygenic Inheritance

An inheritance pattern where a single trait (such as skin color or height) is determined by the cumulative, additive effects of two or more independent genes.

Codominance

A pattern of inheritance in which both alleles for a given characteristic are distinctly and simultaneously expressed in the heterozygous phenotype (such as human AB blood type).

Nondisjunction

The failure of homologous chromosomes to separate in anaphase I, or of sister chromatids to separate in anaphase II of meiosis, resulting in gametes with abnormal numbers of chromosomes.

Turner Syndrome

A human female genetic condition characterized by a monosomy X ($45,XO$) karyotype, causing short stature, a webbed neck, cardiac defects, and ovarian dysgenesis leading to infertility.

Klinefelter Syndrome

A human male chromosomal condition characterized by an $XXY$ genotype, resulting in reduced facial hair, breast tissue development, and small testicular size.

Barr Body

A dense, condensed structure formed by the random transcriptional inactivation of one X chromosome in female mammalian somatic cells to ensure dosage compensation.

Pericentric Inversion

A structural chromosomal mutation in which a segment that includes the centromere breaks, flips $180^\circ$, and reinserts, potentially shifting the relative lengths of the chromosome arms.

Translocation

A chromosomal alteration where a detached segment of one chromosome reattaches to a completely different, nonhomologous chromosome.

Mendel's Law of Segregation

Mendel's First Law stating that the two alleles of a gene separate during gamete formation so that every gamete carries only one allele for each gene locus.

Mendel's Law of Independent Assortment

Mendel's Second Law stating that the alleles of two or more different genes segregate into gametes completely independently of each other during meiosis.

Test Cross

A genetic mating between an individual showing a dominant phenotype (unknown genotype) and a homozygous recessive individual to reveal the unknown genotype based on progeny phenotypes.

Incomplete Dominance

A pattern of inheritance in which neither allele is completely dominant, resulting in a heterozygous phenotype that is an intermediate blend between both homozygous phenotypes.

Epistasis

A gene interaction in which an allele of one gene alters or completely masks the phenotypic expression of an allele at a second, independent gene locus.

Gametogenesis

The cellular process of producing mature haploid gametes ($n=23$ in humans) from diploid progenitor cells ($2n=46$) through the divisions of meiosis.

Synaptonemal Complex

A protein lattice structure that forms between homologous chromosomes during prophase I, holding them tightly together in precise gene-by-gene alignment during synapsis.

Crossing Over

The reciprocal exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I of meiosis at sites called chiasmata.

Alternation of Generations

A plant and algal life cycle that alternates between a multicellular haploid gametophyte phase and a multicellular diploid sporophyte phase.

Chromatin

The complex of genomic DNA and histone proteins that forms eukaryotic chromosomes inside the nucleus of non-dividing or dividing cells.

Sister Chromatids

Two identical copies of a duplicated chromosome produced during the S phase, joined along their length by cohesin complexes and attached most closely at the centromere.

Kinetochore

A specialized disc-like protein complex assembled on the centromeric region of each sister chromatid that anchors mitotic spindle microtubules.

Cleavage Furrow

A contractile ring of actin microfilaments that forms at the metaphase plate and pinches the plasma membrane inward to divide an animal cell during cytokinesis.

Phragmoplast

An assembly of microtubules and Golgi-derived vesicles that gathers at the former metaphase plate in dividing plant cells to construct the cell plate.

Cell Cycle Checkpoint

A critical control point in the eukaryotic cell cycle ($G_1$, $G_2$, or $M$) where internal stop and go-ahead molecular signals assess cellular conditions before proceeding.

Cyclin

A cellular protein whose concentration fluctuates cyclically, binding to and activating specific cyclin-dependent kinases to regulate passage through cell cycle stages.

p53 Protein

A crucial tumor-suppressor protein that senses DNA damage and hypoxia, halting cell division to permit enzymatic repair or triggering apoptosis if the genome is damaged beyond repair.

Metastasis

The spread of malignant cancer cells away from their primary site of origin to distant body organs and tissues through blood or lymphatic circulation.

Binary Fission

An asexual mode of cell division utilized by prokaryotes where a single circular DNA molecule is replicated and the cell cleaves into two genetically identical organisms.

Anaphase I

Homologous chromosomes are pulled apart to opposite poles (sister chromatids remain attached at their centromeres). [1, 2, 3]

prophase I

Chromosomes condense, homologous chromosomes pair up (synapsis) to form tetrads, and crossing over occurs where non-sister chromatids exchange DNA segments

metaphase I

Homologous pairs align randomly at the center (metaphase plate) of the cell.

telophase I

The cell divides into two haploid daughter cells, though each chromosome still consists of two sister chromatids

prophase II

Chromosomes condense again in the two new cells

metaphase II

Chromosomes line up in a single file along the metaphase plate. [1, 2]

anaphase II

Sister chromatids separate and move toward opposite poles as individual chromosomes

telophase II

Both cells divide, resulting in four genetically distinct haploid gametes. [1, 2]

prophase

Chromosomes condense into tight, visible structures, the nuclear envelope begins to break down, and spindle fibers start to form from the centrosomes.

metaphase

The chromosomes line up along the middle of the cell, known as the metaphase plate, and attach to the spindle fibers.

anaphase

Sister chromatids are pulled apart by the spindle fibers and move toward opposite poles (ends) of the cell.

telophase

New nuclear membranes and nucleoli re-form around each set of separated chromosomes, and the chromosomes begin to decondense