Cell Biology Chapter: Mitosis and Meiosis Quiz

Cell Cycle

• Continuity of life depends on cell reproduction, or cell division
• Unicellular organisms reproduce by cell division
• Multicellular organisms rely on cell division for growth and repair
• Cell division can develop from a fertilized cell (zygote)

Most Cell Division Results in Genetically Identical Daughter Cells

• Most cell division (mitosis) produces daughter cells with identical genetic information (DNA)
• Meiosis is a special type of cell division for producing sperm and egg cells
• The genome is all the DNA in a cell
  • Single DNA molecule in prokaryotic cells
  • Multiple DNA molecules in eukaryotic cells
  • DNA in eukaryotic cells is organized into chromosomes
• Every eukaryotic species has a specific number of chromosomes per cell nucleus
• Somatic cells (non-reproductive cells) have two sets of chromosomes
• Gametes (reproductive cells) have half the number of chromosomes as somatic cells (one set)

Distribution of Chromosomes During Eukaryotic Cell Division

• Before cell division, DNA is replicated, and chromosomes condense
• Each duplicated chromosome has two sister chromatids (joined copies of the original chromosome) that separate during division
• The centromere is the narrow "waist" of the duplicated chromosome, where sister chromatids are most tightly attached

Stages of Mitosis

• During mitosis (cell division), two sister chromatids of each duplicated chromosome separate and move into two nuclei
• Once separated, the chromatids are called chromosomes

The Cell Cycle

• The cell cycle is the life cycle of a cell, from formation to division
• Interphase (about 90% of the cell cycle)
  • G1 phase ("first gap"): cell growth
  • S phase ("synthesis"): DNA replication
  • G2 phase ("second gap"): preparation for mitosis
• Mitotic (M) phase: mitosis and cytokinesis

Eukaryotic Cell Division

• Mitosis is the division of the genetic material (DNA) within the nucleus, divided into 5 phases:
  • Prophase
  • Prometaphase
  • Metaphase
  • Anaphase
  • Telophase
• Cytokinesis: the division of the cytoplasm

Mitosis Stages Summarized (P.M.A.T)

• Prophase: Chromosomes condense, nuclear envelope breaks down, and spindle fibers form
• Metaphase: Chromosomes align in the middle of the cell
• Anaphase: Sister chromatids separate and move toward opposite poles
• Telophase: Two new nuclei form, chromosomes decondense, nuclear envelope reforms

The Mitotic Spindle

• The spindle is a microtubule-based structure that controls chromosome movement
• Mitotic spindle = centrosomes + spindle microtubules + asters
• Centrosome: microtubule-organizing center
• Centrosome replicates during interphase, forming two centrosomes that migrate to opposite ends of the cell
• Spindle microtubules attach to kinetochores of chromosomes to move the chromosomes
• Kinetochores are protein complexes associated with centromeres

Mitosis Continued

• In anaphase, sister chromatids separate, move along kinetochore microtubules to opposite poles.
• Nonkinetochore microtubules overlap and push against each other, elongating the cell
• In telophase, genetically identical daughter nuclei form at opposite ends of the cell
• Cytokinesis begins in anaphase or telophase

Cytokinesis

• In animal cells, cytokinesis occurs via cleavage, forming a cleavage furrow
• In plant cells, a cell plate forms
• Vesicles form the cell plate, which will form the new cell wall

Cell Cycle Control System

• Frequency of cell division varies depending on cell type
• Cell cycle is driven by specific chemical signals (in cytoplasm)
• Growth factors: proteins released by cells that stimulate cell division
• Checkpoints (G1, G2, M) regulate the cell cycle (where the cell cycle stops until a go-ahead signal is received)
• The G1 checkpoint is most important for most cells

Loss of Cell Cycle Controls in Cancer Cells

• Cancer cells escape usual cell cycle controls
• Cancer cells can make their own growth factors to grow/divide
• Transformation: when a normal cell becomes a cancerous cell
• Tumors: masses of abnormal cells within otherwise normal tissue
  • Benign tumors stay localized
  • Malignant tumors can metastasize (spread to other parts of the body)
• Recent advances in cell cycle understanding have improved cancer treatment

Cancerous Cells

• Characteristics of cancerous cells include variations in size and shape, a larger and darker nucleus than normal cells, and an abnormal number of chromosomes
• Sarcomas: tumors in connective tissue
• Carcinomas: tumors in epithelial tissue (frequently associated with lung, colon, breast, and leukemia/lymphomas)
• The frequent cell division in epithelial cells makes them prone to genetic mutations
• 90% or more of adult cancers arise in epithelial tissues

p53 Gene

• p53 is a tumor-suppressor gene
• Cancer cells repeatedly undergo cell division without being halted at the G1 checkpoint when p53 is nonfunctional