Cell Communication, Cell Cycle, Mitosis, and Meiosis

Comprehensive vocabulary flashcards covering cell signaling pathways, cell cycle checkpoints and cancer regulation, and meiotic cell division from Chapters 11, 12, and 13.

Ligand

A signaling molecule that specifically binds to a receptor protein, causing the receptor to change shape and initiate cellular transduction.

G Protein-Coupled Receptor (GPCR)

A universal cell-surface transmembrane receptor that functions with the aid of a G protein; approximately $50\%$ of all commercial drugs target this family of receptors.

Cyclic AMP (cAMP)

A small, water-soluble second messenger synthesized from ATP by adenylyl cyclase that activates protein kinase A (PKA) to trigger cellular responses.

Phosphodiesterase

An intracellular enzyme that terminates signaling by hydrolyzing cyclic AMP (cAMP) into inactive AMP using $\text{H}_2\text{O}$.

Receptor Tyrosine Kinase (RTK)

An enzymatic cell-surface receptor that dimerizes upon ligand binding and undergoes auto-phosphorylation on tyrosine residues using ATP to activate relay proteins.

Herceptin

A monoclonal antibody (mAb) therapy engineered to bind to HER2 receptor tyrosine kinases on breast cancer cells, blocking downstream signaling to inhibit proliferation and flagging cells for immune destruction.

Inositol Trisphosphate ($\text{IP}_3$)

A second messenger produced by phospholipase C cleavage of $\text{PIP}_2$ that binds to and opens ligand-gated calcium channels on the endoplasmic reticulum membrane, releasing $\text{Ca}^{2+}$ into the cytosol.

Intracellular Receptor

A receptor situated in the cytoplasm or nucleus that binds hydrophobic or lipid-soluble signal molecules (such as steroid hormones like testosterone) to form complexes that act directly as transcription factors.

1986 Nobel Prize in Physiology or Medicine

Awarded jointly to Stanley Cohen and Rita Levi-Montalcini for their foundational discovery of growth factors (such as Nerve Growth Factor, NGF).

Sister Chromatids

Two identical copies of a duplicated chromosome produced during S phase of interphase, joined along their length and attached at a specialized constriction called the centromere.

Centromere

The constricted DNA region of a duplicated chromosome where sister chromatids are most closely attached and where kinetochores assemble.

Mitotic Spindle

A subcellular structure consisting of microtubules and associated proteins (including asters, kinetochore microtubules, and nonkinetochore microtubules) that segregates chromosomes during mitosis.

Maturation-Promoting Factor (MPF)

A cyclin-CDK complex formed when cyclin binds to a cyclin-dependent kinase, triggering cell passage through the $\text{G}_2$ checkpoint into M phase (mitosis).

Density-Dependent Inhibition

A growth-regulatory phenomenon where normal cultured mammalian cells stop dividing once they form a complete, single layer due to physical cell-cell contact.

Anchorage Dependence

The requirement that animal cells must adhere to a solid substratum or extracellular matrix surface in order to divide.

Angiogenesis

A biological hallmark of cancer involving the growth of new blood vessels (frequently mediated by VEGF) to supply developing tumors with oxygen and nutrients.

Oncogenes

Cancer-promoting genes resulting from gain-of-function mutations in proto-oncogenes that cause excessive cellular proliferation (e.g., Ras mutations found in $>30\%$ of all cancers).

Tumor Suppressor Genes

Genes that encode proteins providing critical 'stop signals' to inhibit cell division or initiate apoptosis; loss-of-function mutations in both copies promote cancer (e.g., p53 mutations present in $>50\%$ of cancers).

Henrietta Lacks (HeLa Cells)

The source of the first continuously cultured 'immortal' human cell line, obtained without consent in 1951, which transformed modern cellular and medical research.

Homologous Chromosomes

Pairs of matching chromosomes—one inherited from each parent—that have the same length, centromere location, and carry genes controlling the same inherited characters.

Karyotype

An ordered display of an individual's paired homologous chromosomes arranged according to length, centromere position, and banding pattern.

Meiosis I

The first division of meiosis, termed reductional division, in which homologous chromosomes pair, synapse, cross over, and segregate, reducing chromosome ploidy from diploid ($2n$) to haploid ($n$).

Meiosis II

The second division of meiosis, termed equational division, in which sister chromatids separate, resulting in four genetically distinct haploid ($n$) daughter cells.

Chiasmata

X-shaped microscopic intersection points between nonsister chromatids of homologous chromosome pairs where physical crossing over occurs during prophase I of meiosis.

Spermatogenesis vs. Oogenesis

Spermatogenesis produces four viable haploid sperm cells continuously from each primary spermatocyte, whereas oogenesis yields only one functional ovum and non-viable polar bodies due to unequal cytokinesis.

Nondisjunction

An error during cell division in which homologous chromosomes fail to separate in meiosis I or sister chromatids fail to separate in meiosis II, resulting in aneuploid gametes ($n+1$ and $n-1$).

Trisomy 21 (Down Syndrome)

An aneuploid condition characterized by the presence of three copies of chromosome 21 ($47, 21+$), occurring in approximately $1:700$ live births.