Biology Chapter 12: The Cell Cycle

Chapter 12: The Cell Cycle

• Cell division is essential for life
• Organisms reproduce by cell division
• Cell division distinguishes living from nonliving matter.
• In unicellular organisms, cell division creates new organisms.
• Multicellular organisms use cell division for development, growth, and repair
• Cell division is the core functionality of the cell cycle.

Overview: The Key Roles of Cell Division

• The ability to reproduce distinguishes living things from nonliving matter.
• Life's continuity depends on cell reproduction (cell division)

Cellular Organization of the Genetic Material

• A cell's genome is all the DNA within a cell.
• Some prokaryotic genomes consist of a single DNA molecule.
• Eukaryotic genomes contain multiple DNA molecules.
• DNA in a cell is organized into chromosomes.

Distribution of Chromosomes During Eukaryotic Cell Division

• DNA replicates and condenses before cell division.
• Each duplicated chromosome has two sister chromatids.
• Sister chromatids separate during cell division.
• The centromere is the narrow "waist" of a duplicated chromosome
• The centromere holds the sister chromatids together.

Eukaryotic Cell Division

• Eukaryotic cell division includes mitosis (nuclear division) and cytokinesis (cytoplasmic division).
• The cell cycle includes the mitotic (M phase) and interphase.

Phases of the Cell Cycle

• Interphase, which is approximately 90% of the cell cycle, includes G1, S, and G2 phases.
• Cell growth happens in the G1, S, and G2 phases.
• DNA replication occurs during the S phase.

Mitosis

• Mitosis consists of five stages: prophase, prometaphase, metaphase, anaphase, and telophase.
• Cytokinesis begins during late telophase.

The Mitotic Spindle: A Closer Look

• The mitotic spindle is a cytoskeletal structure made of microtubules.
• The centrosome is the microtubule organizing center.
• During prophase, spindle microtubules assemble in the centrosome.
• Centrosomes move to opposite poles of the cell.
• An aster is a radial array of short microtubules extending from each centrosome.

Cytokinesis: A Closer Look

• Cytokinesis divides the cytoplasm.
• In animal cells, a cleavage furrow forms.
• In plant cells, a cell plate forms.
• Binary fission is the type of cell division in prokaryotes.

The Cell Cycle Control System

• Cell cycle events are regulated by a molecular control system.

• The frequency of cell division varies with the cell type.

• Internal and external controls regulate the cycle.

• The system involves checkpoints where the cell cycle stops until the proper signal is received.

• The G₁ checkpoint is often the most critical.

• If the cell gets a go-ahead signal at the G₁ checkpoint, it will complete the rest of the cycle. Otherwise, cells enter a nondividing state called G₀.

• The cell cycle clock has Cyclins and cyclin-dependent kinases (Cdks).

• MPF is a type of cyclin-Cdk complex.

• Some internal signals include the attachment of kinetochores to microtubules or growth factors.

• Some external signals include density-dependent inhibition and anchorage dependence.

  • Cancer cells lack density-dependent inhibition and anchorage dependence.
  • Cancer cells do not respond normally to the body's control mechanisms.
  • Cancer cells may not need growth factors to grow and divide.
  • Cancer cells may have an abnormal cell cycle control system.

• Normal cells are transformed into cancer cells.

• Benign tumors stay in one place; malignant tumors can metastasize.