General chemistry cell cycle

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Cell division

The process by which life continues, involving the distribution of identical genetic material to two daughter cells.

Three key roles of cell division

Asexual reproduction, development (growth), and tissue renewal/repair.

Genome

A cell's total endowment of DNA; single molecule in prokaryotes, multiple molecules in eukaryotes.

Chromosomes

Threadlike structures made of DNA molecules packaged with proteins, visible during cell division.

Chromatin

The entire complex of DNA and proteins that condenses to form eukaryotic chromosomes during cell division.

Somatic cells

All non-reproductive body cells containing a full characteristic number of chromosomes (e.g., 46 in humans).

Gametes

Reproductive cells (sperm and eggs) containing half the number of chromosomes as somatic cells (e.g., 23 in humans).

Sister chromatids

Joined copies of the original duplicated chromosome, attached along their lengths by cohesins.

Centromere

The specific region of chromosomal DNA where two sister chromatids are attached most closely.

Mitosis

The specific process of dividing the replicated genetic material within a cell's nucleus.

Cytokinesis

The division of the cell's cytoplasm to create two separate daughter cells.

Walther Flemming

German anatomist who in 1882 developed dyes to first observe chromosome behavior during mitosis.

Interphase

The long growth period accounting for 90% of the cell cycle, divided into G1, S, and G2 phases.

G1 phase

First gap phase of interphase characterized by intense metabolic activity and cell growth.

S phase

Synthesis phase of interphase where metabolic growth continues and DNA replication occurs entirely.

G2 phase

Second gap phase of interphase where final preparations and organelle duplication for cell division happen.

Mitotic (M) phase

The shortest part of the cell cycle consisting of both mitosis and cytokinesis.

Five stages of mitosis

Prophase, prometaphase, metaphase, anaphase, and telophase.

Mitotic spindle

A cytoplasmic structure made of microtubules and proteins that controls chromosome movement during mitosis.

Centrosome

The primary microtubule-organizing center in animal cells that duplicates during interphase.

Centrioles

A pair of barrel-shaped structures located at the center of animal centrosomes, though not essential for spindle assembly.

Aster

A radial array of short, star-like microtubules extending from each centrosome.

Kinetochore

A specialized protein structure assembled on sections of DNA at each centromere where spindle fibers attach.

Kinetochore microtubules

Spindle microtubules that attach directly to chromosome kinetochores to jerk them into place.

Nonkinetochore microtubules

Spindle microtubules from opposite poles that overlap and interact to elongate the cell.

Metaphase plate

An imaginary plane equidistant between the two spindle poles where chromosome centromeres align.

Borisy experiment conclusion

Chromosomes move poleward because kinetochore microtubules shorten primarily at their kinetochore ends.

Pac-man mechanism

Chromosome movement where motor proteins on kinetochores walk along microtubules while depolymerizing their ends.

Reeled-in mechanism

Chromosome movement where motor proteins at the spindle poles pull chromosomes inward while depolymerizing microtubules.

Cleavage furrow

A shallow groove in the animal cell surface near the old metaphase plate, marking the start of cytokinesis.

Contractile ring

A ring of actin microfilaments and myosin proteins that contracts like a drawstring to pinch an animal cell in two.

Binary fission

The type of asexual reproduction in prokaryotes where a cell doubles in size and splits in half without mitosis.

Origin of replication

The specific site on a bacterial chromosome where DNA replication begins and moves outward.

Evolutionary origin of mitosis

Mitosis presumably evolved from simpler prokaryotic binary fission mechanisms over billions of years.

Cell cycle control system

A cyclically operating set of molecules in the cell that triggers and coordinates key cycle events.

Cell cycle checkpoints

Control points (G1, G2, M) where stop and go-ahead signals regulate the progression of the cell cycle.

Cell fusion experiment conclusion

Signaling molecules present in the cytoplasm of S or M phase cells actively control progression into those phases.

Regulatory proteins of cell cycle

Cyclins and cyclin-dependent kinases (Cdks).

Cyclin-dependent kinase (Cdk)

A cell cycle enzyme that must be attached to a fluctuating cyclin protein to become active.

MPF

Maturation-promoting factor; a specific cyclin-Cdk complex that triggers a cell's passage past the G2 checkpoint into M phase.

G0 phase

A nondividing, state that cells enter if they fail to receive a go-ahead signal at the G1 checkpoint.

Growth factor

A protein released by specific cells that stimulates other cells to proliferate or divide.

Density-dependent inhibition

A phenomenon where crowded cells stop dividing once they form a complete single monolayer.

Anchorage dependence

The requirement that most animal cells must be attached to a solid substratum or extracellular matrix to divide.

Benign tumor

A localized mass of abnormal cells that remains at its original site because it lacks genetic changes to migrate.

Malignant tumor

A cancerous mass of cells that invades surrounding tissues and can travel to distant parts of the body.

Metastasis

The spread of malignant cancer cells to locations far from their original primary tumor site.

PDGF

Platelet-derived growth factor; a protein made by blood platelets that triggers connective tissue fibroblasts to divide.