Mitotic Spindle and Chromosome Movement Quiz

Cell Division and Genetics

• The ability of organisms to reproduce distinguishes living things from nonliving matter.
• Cell division is an integral part of the cell cycle, which is the life of a cell from formation to its own division.

Cell Division Results in Genetically Identical Daughter Cells

• Most cell division results in daughter cells with identical genetic information, DNA.
• A special type of division produces nonidentical daughter cells (gametes, or sperm and egg cells).

Cellular Organization of the Genetic Material

• The DNA in a cell constitutes the cell's genome.
• A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells).
• DNA molecules in a cell are packaged into chromosomes.
• Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus.
• Somatic cells (nonreproductive cells) have two sets of chromosomes.
• Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells.

Distribution of Chromosomes During Eukaryotic Cell Division

• In preparation for cell division, DNA is replicated and the chromosomes condense.
• Each duplicated chromosome has two sister chromatids, which separate during cell division.
• The centromere is the narrow “waist” of the duplicated chromosome, where the two chromatids are most closely attached.

Mitosis and Meiosis

• Mitosis is the division of the nucleus, followed by cytokinesis, the division of the cytoplasm.
• Meiosis is a variation of cell division that yields nonidentical daughter cells that have only one set of chromosomes, half as many as the parent cell.

Cell Cycle

• The cell cycle consists of:
  • Mitotic (M) phase (mitosis and cytokinesis)
  • Interphase (cell growth and copying of chromosomes in preparation for cell division)
• Interphase can be divided into subphases:
  • G1 phase (“first gap”)
  • S phase (“synthesis”)
  • G2 phase (“second gap”)
• The cell grows during all three phases, but chromosomes are duplicated only during the S phase.

Structure of DNA and Chromosomes

• Chromosomes are long threadlike associations of genes, consisting of DNA (40%) and protein (60%).
• Chromatin is the complex of DNA, RNA, histones, and nonhistone proteins that make up uncoiled chromosomes, characteristic of the eukaryotic interphase nucleus.
• Nucleosomes are nuclear complexes consisting of four pairs of histone molecules wrapped by two turns of a DNA molecule.
• The centromere is the location of the narrow “waist” of the duplicated chromosome.

Mitosis Importance

• Mitosis provides the basis for asexual reproduction (single-celled organisms: protozoans and some fungi and algae).
• Mitotic activity of the zygote (fertilized egg) leads to the development and growth of the organism.
• In adult organisms, mitosis is involved in wound healing and other forms of cell replacement.
• In abnormal conditions, mitotic activity can lead to tumors.

Phases of Mitosis

• Prophase: Chromosomes coil up and condense; centrioles divide and move apart.
• Prometaphase: Chromosomes are clearly double structures; centrioles reach the opposite poles; spindle fibers form.
• Metaphase: Centromeres align on the metaphase plate.
• Anaphase: Centromeres split, and daughter chromosomes migrate to opposite poles.
• Telophase: Daughter chromosomes arrive at the poles; cytokinesis commences.

Mitotic Spindle

• The mitotic spindle is an apparatus of microtubules that controls chromosome movement during mitosis.
• The spindle includes the centrosomes, the spindle microtubules, and the asters.

Cell Cycle Regulation

• The frequency of cell division varies with the type of cell.
• Cell cycle differences result from regulation at the molecular level.
• Regulatory mechanisms of cell division include G1, G2, and M checkpoints.
• Cyclins and cyclin-dependent kinases (CDKs) are regulatory proteins involved in cell cycle control.

Meiosis

• Meiosis is a process that halves the chromosome number, resulting in gametes (sperm and egg cells).
• Meiosis involves two rounds of nuclear division, resulting in four haploid daughter cells.
• Meiosis increases genetic diversity through the shuffling of genes during gamete formation.
• Meiosis involves the separation of homologous chromosomes and the separation of sister chromatids.

Phases of Meiosis

• Meiosis I:
  • Prophase I: pairing and disjunction of sister chromatids
  • Metaphase I: separation of homologous chromosomes
  • Anaphase I: separation of sister chromatids
  • Telophase I: formation of two haploid cells
• Meiosis II:
  • Prophase II: separation of sister chromatids
  • Metaphase II: separation of sister chromatids
  • Anaphase II: separation of sister chromatids
  • Telophase II: formation of four haploid gametes