Cell Division — Chapter 6 Flashcards

Front

Cell cycle

Back

The cell cycle is the sequence of events that makes up the life of a typical eukaryotic cell from its origin to the time it divides to produce two daughter cells. It includes a long interphase (when the cell grows and duplicates its DNA) followed by cell division. Checkpoints in the cycle regulate progression to ensure conditions are appropriate for division.

Front

Interphase

Back

Interphase is the portion of the cell cycle when the cell performs its normal functions and prepares for division. It occupies about $90\%$ or more of a cell’s life and is subdivided into the $G_1$, $S$, and $G_2$ phases. DNA is replicated during the $S$ phase while $G_1$ and $G_2$ are growth and checkpoint periods.

Front

$G_1$ phase

Back

The $G_1$ phase is a growth period after cell division during which the cell increases in size and makes proteins needed for DNA replication. Cells check internal and external conditions in $G_1$ before committing to DNA replication. It can act as a checkpoint to prevent progression if conditions are unfavorable.

Front

$S$ phase

Back

The $S$ phase is when the cell synthesizes and duplicates all of its DNA, producing two identical sister chromatids for each chromosome. Replication creates chromatin fibers that will later condense for mitosis or meiosis. Accurate DNA replication is essential for proper chromosome segregation.

Front

$G_2$ phase

Back

The $G_2$ phase is the final growth and preparation period before cell division, during which the cell produces proteins and organelles needed for mitosis. $G_2$ also includes checkpoints to ensure DNA replication completed correctly and to repair damage. Cells that pass $G_2$ proceed into the mitotic stages.

Front

$G_0$ phase

Back

The $G_0$ phase is a nondividing state entered by some cells that exit the cell cycle. Cells in $G_0$ can remain quiescent for a few days or for the organism's lifetime, performing specialized functions rather than dividing. Entry into $G_0$ can be reversible or permanent depending on cell type.

Front

Checkpoints

Back

Checkpoints are control mechanisms in the cell cycle that verify whether key processes (like DNA replication and chromosome attachment) have been completed correctly before progression. They prevent damaged or incomplete cells from entering the next phase, reducing mutation risk. Bypassing checkpoints can lead to uncontrolled division and cancerous growth.

Front

Cell cycle regulatory proteins

Back

Cell cycle regulatory proteins (such as cyclins and cyclin-dependent kinases) enable the cell to pass through critical checkpoints by integrating internal and external signals. Some signals act like a gas pedal to promote division, while others act like brakes to pause the cycle. Disruption of these regulators can lead to inappropriate cell division or cell cycle arrest.

Front

Mitosis

Back

Mitosis is the process of nuclear division in eukaryotes that separates copied chromosomes into two identical nuclei. It consists of four main phases in order: prophase, metaphase, anaphase, and telophase, and is followed by cytokinesis which divides the cytoplasm. Mitosis produces two genetically identical diploid daughter cells for growth and tissue repair.

Front

Cytokinesis

Back

Cytokinesis is the division of the cytoplasm that follows nuclear division (mitosis or meiosis), producing separate daughter cells. In animal cells it typically occurs by cleavage furrow formation, and in plant cells by cell plate formation. Cytokinesis ensures each daughter cell receives organelles and cytosolic components.

Front

Prophase

Back

Prophase is the first stage of mitosis during which chromatin condenses into visible chromosomes and the mitotic spindle begins to form. The nuclear envelope starts to break down, allowing spindle microtubules to interact with chromosomes. Sister chromatids become more distinct and centrosomes move toward opposite poles.

Front

Metaphase

Back

Metaphase is the mitotic stage when condensed chromosomes align along the metaphase plate (the cell's equatorial plane). Spindle fibers attach to kinetochores at the centromeres of sister chromatids, ensuring proper tension and attachment. Proper metaphase alignment is checked before anaphase proceeds.

Front

Anaphase

Back

Anaphase is the mitotic stage when sister chromatids separate and are pulled toward opposite poles by the shortening of spindle microtubules. This separation ensures each future daughter cell receives one copy of each chromosome. Anaphase defects can cause unequal chromosome distribution and aneuploidy.

Front

Telophase

Back

Telophase is the final stage of nuclear division when separated chromosomes arrive at opposite poles and begin to decondense into chromatin. Nuclear envelopes re-form around each set of chromosomes, creating two distinct nuclei. Telophase transitions into cytokinesis to complete cell division.

Front

Sister chromatids

Back

Sister chromatids are two identical copies of a single replicated chromosome, produced during the $S$ phase and held together at the centromere. They separate from each other during anaphase of mitosis (or during meiosis II) so that each daughter cell receives one copy. They are genetically identical barring replication errors or recombination events.

Front

Homologous chromosomes

Back

Homologous chromosomes are a pair of chromosomes in a diploid organism that carry the same genes in the same order, one inherited from each parent. They are similar but not identical because each may carry different alleles. Homologous pairs pair up and can exchange genetic material during meiosis I.

Front

Binary fission

Back

Binary fission is the asexual reproduction method used by most prokaryotes, where the cell copies its single circular chromosome and splits into two daughter cells. Each daughter receives one copy of the DNA loop, creating genetically identical offspring. Binary fission is simpler than eukaryotic mitosis because there is no nuclear envelope or multiple chromosomes to segregate.

Front

Asexual reproduction

Back

Asexual reproduction produces offspring from a single parent without meiosis or fertilization, generating genetically identical clones. In eukaryotes it often occurs via mitosis; in prokaryotes it occurs via binary fission. Asexual reproduction is efficient but does not generate genetic diversity through recombination.

Front

Sexual reproduction

Back

Sexual reproduction involves meiosis to produce haploid gametes and fertilization to fuse two gametes into a diploid zygote. It generates genetic diversity because offspring inherit a mix of parental chromosomes and alleles. Sexual reproduction maintains a species' chromosome number while enabling variation in the population.

Front

Meiosis

Back

Meiosis is a two-stage cell division process that produces haploid gametes for sexual reproduction. It includes meiosis I (separating homologous chromosome pairs) and meiosis II (separating sister chromatids), resulting in four haploid ($n$) daughter cells from a single diploid ($2n$) parent. Meiosis introduces genetic variation through crossing-over and independent assortment.

Front

Meiosis I

Back

Meiosis I is the first meiotic division in which homologous chromosome pairs are separated into two daughter cells while sister chromatids remain joined. This reductional division produces two haploid cells with duplicated chromosomes. Key events include pairing of homologues and crossing-over during prophase I.

Front

Meiosis II

Back

Meiosis II resembles mitosis and is the second meiotic division, during which sister chromatids separate into individual chromosomes. It produces a total of four haploid ($n$) cells with unduplicated chromosomes from the two cells generated in meiosis I. Meiosis II completes gamete formation.

Front

Crossing-over

Back

Crossing-over is the physical exchange of corresponding chromosomal segments between nonsister chromatids of homologous chromosomes during prophase I of meiosis. This genetic recombination creates chromatids with mixed parental alleles, increasing genetic diversity in offspring. Crossing-over occurs at chiasmata and reshuffles linked genes.

Front

Independent assortment

Back

Independent assortment is the random orientation and distribution of different homologous chromosome pairs into daughter cells during meiosis I. Each pair lines up independently at the metaphase plate, producing many possible maternal-paternal chromosome combinations. This random segregation is a major source of genetic variation among gametes.

Front

Fertilization

Back

Fertilization is the fusion of two haploid gametes ($n$) to form a diploid ($2n$) zygote. The zygote inherits one set of chromosomes from each parent, restoring the species' chromosome number. The zygote then divides by mitosis as it develops into an organism.

Front

Zygote

Back

A zygote is the single diploid ($2n$) cell formed by the fusion of two haploid ($n$) gametes during fertilization. It contains one chromosome of each homologous pair from each parent and will undergo repeated mitotic divisions during development. The zygote is the first cell of a new individual.

Front

Chromatin fiber

Back

A chromatin fiber consists of DNA and its associated proteins (histones) when chromosomes are in the less condensed interphase state. During replication each chromatin fiber is duplicated to form sister chromatids that later condense for mitosis or meiosis. Chromatin organization regulates gene expression and replication accessibility.

Front

Centromere

Back

The centromere is the constricted region of a chromosome where sister chromatids are most tightly connected and where kinetochores form to attach spindle microtubules. It ensures coordinated movement of chromatids during anaphase. Centromere dysfunction can cause mis-segregation and aneuploidy.

Front

Tumor

Back

A tumor is a mass of cells resulting from uncontrolled, rapid cell division. Benign tumors are confined to one site and are usually removable and not life-threatening, while malignant tumors invade surrounding tissues and can metastasize. Tumors often arise from failures in cell cycle regulation or checkpoints.

Front

Anchorage dependence

Back

Anchorage dependence is the requirement of most normal adult cells to be attached to a substrate or extracellular matrix in order to divide. Loss of anchorage dependence is a hallmark of cancer cells and enables them to grow unattached and invade other tissues. Anchorage independence contributes to metastasis.

Front

Angiogenesis

Back

Angiogenesis is the formation of new blood vessels from existing vasculature, often stimulated by growing tumors to increase nutrient and oxygen supply. Enhanced blood flow allows tumors to expand and facilitates metastasis by providing access to the circulatory system. Anti-angiogenic therapies aim to limit tumor growth by blocking vessel formation.

Front

Metastasis

Back

Metastasis is the spread of cancer cells from the original tumor site to distant organs, forming secondary tumors. It requires cells to invade surrounding tissue, enter the bloodstream or lymphatics, survive transit, exit into new tissue, and proliferate. Metastatic disease is the major cause of cancer-related mortality.

Front

Bisphenol A (BPA)

Back

Bisphenol A (BPA) is a synthetic chemical used in many plastics that can mimic estrogen and act as an endocrine disruptor. Exposure to BPA has been linked to abnormal cell division, chromosomal defects during meiosis, miscarriage, birth defects, and various health problems. BPA can leach from plastic when heated or damaged and has been detected in human fluids.

Front

Endocrine disruptor

Back

An endocrine disruptor is a chemical that interferes with hormone signaling by mimicking, blocking, or altering hormone actions. Such compounds can push cells toward inappropriate division or disrupt developmental processes. BPA is an example that mimics estrogen and perturbs cell cycle control and meiosis.

Front

Genetic recombination

Back

Genetic recombination refers to the reshuffling of genetic material, such as through crossing-over during meiosis, producing new combinations of alleles on chromosomes. Recombination increases genetic diversity among gametes and offspring and can unlink genes on the same chromosome. It is a key mechanism driving evolution and variation.