Cell Division and Mitosis Quiz

Cell Cycle

• A cell spends most of its life in interphase, which has three phases: G1, S, and G2.
• In G1, the cell grows and takes in nutrients.
• In the S phase, the cell's DNA is replicated. Each replicated chromosome consists of two sister chromatids connected at the centromere.
• The G2 phase is another growth phase; after which the cell is ready for mitosis.

Stages of the Cell Cycle

• To divide, a cell must complete several important tasks: It must grow, copy its genetic material (DNA), and physically split into two daughter cells.
• Cells perform these tasks in an organized, predictable series of steps that make up the cell cycle.
• The cell cycle is a cycle, not a linear pathway because at the end of each go-round, the two daughter cells can start the exact same process over again from the beginning.

Eukaryotic Cell Cycle

• In eukaryotic cells, the cell cycle is divided into two major phases: interphase and the mitotic (M) phase.
• During interphase, the cell grows and makes a copy of its DNA.
• During the mitotic (M) phase, the cell separates its DNA into two sets and divides its cytoplasm, forming two new cells.

Interphase

• Let's enter the cell cycle just as a cell forms, by division of its mother cell.
• What must this cell do next if it wants to continue dividing itself?

G1 Phase

• Preparation for division happens in three steps: G1 Phase
• During this phase, the cell grows physically larger, copies organelles, and produces the molecular building blocks for later steps.

S Phase

• In S phase, the cell synthesizes a complete copy of the DNA in its nucleus.
• The cell also duplicates a microtubule-organizing structure called the centrosome; the centrosomes help separate DNA during the M phase.

G2 Phase

• During G2 phase, also called the second gap phase, the cell grows more, builds proteins and organelles, and begins reorganizing its contents in preparation for mitosis.
• G2 phase ends when mitosis begins.

M Phase

• During the mitotic (M) phase, the cell divides its copied DNA and cytoplasm to make two new cells.
• M phase involves two distinct division-related processes: mitosis and cytokinesis.

Mitosis

• In mitosis, the nuclear DNA of the cell condenses into visible chromosomes and is pulled apart by the mitotic spindle, which is a specialized structure made of microtubules.
• Mitosis takes place in four stages: prophase (sometimes divided into early prophase and prometaphase), metaphase, anaphase, and telophase.
• In cytokinesis, the cytoplasm of the cell is split into two, making two new cells.

Animal Cells

• In animal cells, cytokinesis occurs when a band of cytoskeletal fibers called the contractile ring contracts inward and pinches the cell in two, which is called cleavage furrow.

Plant Cells

• Plant cells are stiffened and have high internal pressure, so plant cells divide in two by building a new structure down the middle of the cell.
• This structure, called a cell plate, is made up of plasma membrane and cell wall components; they're delivered in vesicles, partitioning the cell in two.

Cell Cycle Exit and G0

• What happens to the two daughter cells produced in one round of the cell cycle?
• This depends on what type of cells they are.
• Some types of cells divide rapidly, and in these cases, the daughter cells may immediately undergo another round of cell division.
• Many cell types in an early embryo divide rapidly, and so do cells in a tumor.
• Other types of cells divide slowly or not at all. These cells may exit the G1 phase and enter a resting state called a G0 phase.
• In the G0 phase, a cell is not actively preparing to divide. Instead, these cells conduct tasks like signaling as a neuron or storing carbohydrates (a liver cell), for instance.
• The G0 phase may be permanent for some cells, but others might restart their division if they encounter certain signals.

Length of the Cell Cycle

• Different cells take different lengths of time to complete the cell cycle.
• A typical human cell might take about 24 hours to divide, but fast-cycling mammalian cells, like those lining the intestine, can complete a cycle every 9-10 hours when grown in culture.

Meiosis

• Process in which a single cell divides twice to form four haploid daughter cells.
• These are the gametes—sperm in males and egg in females.
• The process of meiosis is divided into two stages, each subdivided into several phases
• Meiosis has the following stages:
  • Meiosis I
    • Prophase I
    • Metaphase I
    • Anaphase I
    • Telophase I
    • Cytokinesis I
  • Meiosis II
    • Prophase II
    • Metaphase II
    • Anaphase II
    • Telophase II
    • Cytokinesis II

Prophase I

• In Prophase I, the nuclear envelope disintegrates.
• The chromosomes begin to condense.
• Spindle fibres appear.

Prometaphase II

• In prometaphase II, the spindle fibres attach to the chromosomes at centromeres.

Metaphase I

• In this stage, the homologous chromosomes align at the equatorial plate ensuring genetic diversity among offspring.

Anaphase I

• In Anaphase I, the homologous chromosomes are pulled to the opposite poles.

Telophase I

• In Telophase 1, the spindle fibres disappear.
• The nuclear envelope is reformed.
• Cytokinesis I results in two non-identical haploid daughter cells.

Prophase II

• In Prophase II, the chromatin condenses into chromosomes.
• The nuclear envelope disintegrates.
• Centrosomes migrate to either poles.
• Spindle fibres are reformed.

Metaphase II

• The chromosomes align along the equatorial plate.

Anaphase II

• Sister chromatids are pulled to the opposite poles.

Telophase II

• In Telophase II, the nuclear envelope redevelops, and spindle fibres disappear.

Cytokinesis II

• Cytokinesis II results in four non-identical haploid daughter cells.

Mitosis versus Meiosis

• The end product of mitosis is two daughter cells whereas meiosis produces four daughter cells.
• Mitosis forms diploid cells that have the same number of chromosomes as the parent cell; meiosis forms haploid cells with half the original number of chromosomes.
• Mitosis produces somatic cells (all cells except sex cells); meiosis produces sex cells (e.g., egg or sperm).
• Mitosis includes one round of cell division while meiosis includes two rounds of cell division.

The Mitosis Phase

• Spindle microtubules that do not engage with the chromosomes are called polar microtubules.
• They overlap and contribute to cell elongation.
• Astral microtubules aid in spindle orientation and are required for mitosis regulation.

Osmosis

• Movement of water through a semipermeable membrane according to the concentration gradient of water across the membrane.

Tonicity

• Describes how an extracellular solution can change the volume of a cell by affecting osmosis.
• Osmolarity is the total solute concentration in a solution.
• A lower osmolarity solution has a greater number of water molecules and vice versa.

Hypotonic

• The cells inflate and eventually burst.
• Water is transported into the cell.

Hypertonic

• The cells shrink.
• Water is transported out of the cell.

Isotonic

• Amount of water transported into the cell is equal to the amount of water transported out of the cell.
• Solute concentration inside the cell is equal to that outside the cell.

Active Transport

• Requires energy—in the form of ATP—to move substances against the concentration gradient.

Primary Active Transport

• In this process of transportation, energy is utilized by the breakdown of ATP, which transports molecules across the membrane against a concentration gradient.

Secondary Active Transport

• This secondary process is used to store high-energy hydrogen ions in the mitochondria of plant and animal cells for ATP production.
• The stored hydrogen ions translate into kinetic energy for ions to surge through channel protein ATP synthase.

Bulk Transport

• Endocytosis. The process by which a cell engulfs external fluid, macromolecules, or other large particles.
• Exocytosis. The process by which a substance is released from a cell through a vesicle to the cell surface; it fuses with the cell membrane and the waste material is released to the exterior.

Test your knowledge on cell division and the mitosis process. This quiz covers key phases such as G2, cytokinesis, and the stages of mitosis. Understand the differences in cell division between animals and plants and learn about the various phases a typical cell undergoes.