Cell Cycle, Mitosis and Meiosis: every key term you need (+ practice quiz)
25 flashcard terms for General Biology I Topic 7, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 15-question quiz — free, no account needed.
The ordered sequence from one division to the next, comprising a long growth and synthesis interphase and a short division phase. In a typical cultured human cell the whole cycle takes about a day.
Interphase gap one
The growth period after division in which the cell enlarges, makes proteins and organelles, and monitors nutrients and size before committing to duplicate its genome.
Synthesis phase
The interval in which every chromosome is replicated, converting each into two identical sister chromatids joined at a shared centromere. Chromosome number is unchanged while DNA content doubles.
Interphase gap two
The final preparation before division, when the cell finishes growing, duplicates centrosomes if needed, and verifies that replication is complete and undamaged.
Quiescent state
A reversible exit from cycling in which a cell remains alive and active but does not divide. Most neurons and mature muscle cells are permanently parked here.
Chromatin and chromosome condensation
The packaging of DNA with histones into fibers that coil far tighter as division begins. Condensing turns a fragile, tangled molecule into a compact body that can be moved without breaking.
Sister chromatids
The two identical copies produced by replication of a single chromosome, held together by cohesin rings until their separation is triggered. Once separated each counts as a chromosome in its own right.
Centromere and kinetochore
The constricted chromosomal region and the protein platform assembled on it, which is the site where spindle microtubules attach and where pulling force is applied.
Mitotic spindle
The bipolar microtubule apparatus that captures chromosomes, aligns them and pulls the copies apart. Kinetochore fibers shorten while overlapping polar fibers slide to push the poles apart.
Prophase
The first mitotic stage, in which chromatin condenses into visible chromosomes, the nucleolus disperses and the spindle begins to form between the separating centrosomes.
Prometaphase
The stage in which the nuclear envelope breaks down and microtubules invade the nuclear space, capturing kinetochores in a trial and error process until each chromosome is attached on both sides.
Metaphase plate
The imaginary midplane at which chromosomes come to rest when the pulling forces from opposite poles are balanced. Alignment there is the visual sign that attachment is complete.
Anaphase
The stage triggered by cleavage of cohesin, in which sister chromatids abruptly separate and move to opposite poles. Because it is all or nothing, the preceding checkpoint is critical.
Telophase
The stage in which chromosomes reach the poles and decondense, nuclear envelopes reassemble around each set, and the spindle disassembles, restoring two interphase-like nuclei.
Cytokinesis
Division of the cytoplasm, accomplished in animals by an actin and myosin ring that pinches a cleavage furrow and in plants by vesicles fusing into a cell plate that becomes a new wall.
Cyclin dependent kinase
An enzyme that is catalytically inert until it binds a cyclin whose concentration rises and falls through the cycle. The oscillating partner turns the kinase into a timer that phosphorylates stage-specific targets.
Spindle assembly checkpoint
The surveillance system that delays chromatid separation while any kinetochore remains unattached, since a single unattached site emits a wait signal that prevents anaphase and thus prevents missegregation.
Cancer as cycle failure
Uncontrolled proliferation arising when checkpoint and growth-signal controls fail, so cells divide without external signals, ignore crowding and evade the normal limits on division number.
Homologous chromosomes
The maternal and paternal members of a chromosome pair, matching in length and gene order but potentially carrying different alleles. Their behavior distinguishes meiosis from mitosis.
Ploidy
The number of chromosome sets in a nucleus. Human somatic cells are diploid with forty six chromosomes in twenty three pairs, while gametes are haploid with twenty three.
Synapsis and the synaptonemal complex
The lengthwise pairing of homologs in early meiosis, zipped together by a protein lattice that holds them in register while crossovers are made and resolved.
Crossing over
Reciprocal exchange of segments between non-sister chromatids of paired homologs, visible later as a chiasma. It creates recombinant chromatids and physically links homologs for correct orientation.
Independent assortment of homologs
The random orientation of each homolog pair at the first meiotic midplane, giving two raised to the number of pairs possible combinations, over eight million in humans before crossing over.
Meiosis first division
The reductional division that separates homologs while sister chromatids stay joined, halving chromosome number. This is the step where ploidy changes and where nondisjunction most often occurs.
Meiosis second division
The equational division that separates sister chromatids without prior replication, mechanically like mitosis but starting from haploid cells and yielding four genetically distinct products.