CHAPTER 8 The Cellular Basis of Reproduction and Inheritance Modules 8.4 – 8.11

THE EUKARYOTIC CELL CYCLE AND MITOSIS 8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division A eukaryotic cell has many more genes than a prokaryotic cell The genes are grouped into multiple chromosomes, found in the nucleus The chromosomes of this plant cell are stained dark purple Figure 8.4A

Chromosomes contain a very long DNA molecule with thousands of genes Individual chromosomes are only visible during cell division They are packaged as chromatin

Before a cell starts dividing, the chromosomes are duplicated Sister chromatids This process produces sister chromatids Centromere Figure 8.4B

Chromosome distribution to daughter cells When the cell divides, the sister chromatids separate Chromosome duplication Two daughter cells are produced Each has a complete and identical set of chromosomes Sister chromatids Centromere Chromosome distribution to daughter cells Figure 8.4C

8.5 The cell cycle multiplies cells The cell cycle consists of two major phases: Interphase, where chromosomes duplicate and cell parts are made The mitotic phase, when cell division occurs Figure 8.5

8.6 Cell division is a continuum of dynamic changes Eukaryotic cell division consists of two stages: Mitosis Cytokinesis

In mitosis, the duplicated chromosomes are distributed into two daughter nuclei After the chromosomes coil up, a mitotic spindle moves them to the middle of the cell

Centrosomes (with centriole pairs) Early mitotic spindle Centrosome INTERPHASE PROPHASE Centrosomes (with centriole pairs) Early mitotic spindle Centrosome Fragments of nuclear envelope Kinetochore Chromatin Centrosome Spindle microtubules Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Figure 8.6

The sister chromatids then separate and move to opposite poles of the cell The process of cytokinesis divides the cell into two genetically identical cells

TELOPHASE AND CYTOKINESIS METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Cleavage furrow Nucleolus forming Metaphase plate Nuclear envelope forming Spindle Daughter chromosomes Figure 8.6 (continued)

8.7 Cytokinesis differs for plant and animal cells In animals, cytokinesis occurs by cleavage This process pinches the cell apart Cleavage furrow Cleavage furrow Contracting ring of microfilaments Figure 8.7A Daughter cells

In plants, a membranous cell plate splits the cell in two Cell plate forming Wall of parent cell Daughter nucleus In plants, a membranous cell plate splits the cell in two Cell wall New cell wall Vesicles containing cell wall material Cell plate Daughter cells Figure 8.7B

Most animal cells divide only when stimulated, and others not at all 8.8 Anchorage, cell density, and chemical growth factors affect cell division Most animal cells divide only when stimulated, and others not at all In laboratory cultures, most normal cells divide only when attached to a surface They are anchorage dependent

Cells continue dividing until they touch one another This is called density-dependent inhibition Cells anchor to dish surface and divide. When cells have formed a complete single layer, they stop dividing (density-dependent inhibition). If some cells are scraped away, the remaining cells divide to fill the dish with a single layer and then stop (density-dependent inhibition). Figure 8.8A

Growth factors are proteins secreted by cells that stimulate other cells to divide After forming a single layer, cells have stopped dividing. Providing an additional supply of growth factors stimulates further cell division. Figure 8.8B

8.9 Growth factors signal the cell cycle control system Proteins within the cell control the cell cycle Signals affecting critical checkpoints determine whether the cell will go through a complete cycle and divide G1 checkpoint Control system M checkpoint G2 checkpoint Figure 8.9A

Cell cycle control system The binding of growth factors to specific receptors on the plasma membrane is usually necessary for cell division Growth factor Plasma membrane Relay proteins Receptor protein G1 checkpoint Signal transduction pathway Cell cycle control system Figure 8.8B

Cancer cells have abnormal cell cycles 8.10 Connection: Growing out of control, cancer cells produce malignant tumors Cancer cells have abnormal cell cycles They divide excessively and can form abnormal masses called tumors Radiation and chemotherapy are effective as cancer treatments because they interfere with cell division

Malignant tumors can invade other tissues and may kill the organism Lymph vessels Tumor Glandular tissue Metastasis 1 A tumor grows from a single cancer cell. 2 Cancer cells invade neighboring tissue. 3 Cancer cells spread through lymph and blood vessels to other parts of the body. Figure 8.10

8.11 Review of the functions of mitosis: Growth, cell replacement, and asexual reproduction When the cell cycle operates normally, mitotic cell division functions in: Growth (seen here in an onion root) Figure 8.11A

Cell replacement (seen here in skin) Dead cells Epidermis, the outer layer of the skin Dividing cells Dermis Figure 8.11B

Asexual reproduction (seen here in a hydra) Figure 8.11C