Chapter 9 Cell Reproduction

Cell Division Cell division is the process by which cells reproduce themselves

Cell division in eukaryotes includes the division of the nucleus (mitosis) and division of the cytoplasm (cytokinesis)

Concept All cells come from cells The division of cells into more cells enables living things to repair damage, to grow and to produce offspring

Cell Repair & Growth Enables your body to produce new cells to replace dead cells

Reproduction Asexual  Single cell duplicates its genetic material and splits into 2 genetically IDENTICAL cells Sexual  Genetic material from each of 2 parents combine, producing offspring that differ genetically from either parent

Asexual Reproduction Asexual reproduction is the formation of offspring from one parent Offspring produced by asexual reproduction are genetically identical to the parent

Binary fission is the process of cell division in prokaryotes

Sexual Reproduction Sexual reproduction is the formation of offspring through the union of a sperm and an egg Offspring produced by sexual reproduction are genetically different from the parents

Concept 9.2 – The cell cycle multiples cells At this moment, millions of cells in your body are dividing, each forming 2 new cells.

Chromosomes Almost all of the genes of a eukaryotic cell are located in the nucleus. Most of the time, this genetic material exists in long fibers too thin to be seen under a light microscope. As a cell prepares to divide – these fibers condense and become visible as chromosomes.

Chromosomes

Chromosomes are tightly coiled DNA molecules and associated proteins

In eukaryotes, histone proteins help maintain the compact structure of chromosomes DNA Histone

In dividing cells, chromosomes are composed of 2 identical chromatids constricted together at a centromere

Chromosomes are categorized as either sex chromosomes or autosomes Sex Chromosomes

Homologous chromosomes consist of one autosomal chromosome from each parent

Cell Cycle The cell cycle goes from the “birth” of a cell until it reproduces itself.

Cell Cycle Interphase  90% of the cell cycle is spent here  Stage where the cell performs its functions Increasing proteins, releasing enzymes, etc  G 1, S, and G 2 stages G 1 – Gap 1 = Cell grows S – DNA Synthesis = Genetic material copied G 2 – Gap 2 = Cell prepares to divide

Cell Cycle Mitotic Phase  Contains 2 processes Mitosis Nucleus and duplicated chromosomes divide and are evenly distributed, forming 2 “daughter” nuclei Cytokinesis Cytoplasm is divided into 2

Cell Cycle The cell cycle is the repeating of events that make up the life of a cell The cell cycle consists of cell division and interphase

Cell Division Concept 9.3 Cells divide during the mitotic phase

Interphase Interphase consists of a phase of growth (G 1 ), a phase of DNA replication (S), and a phase of preparation for cell division (G 2 )

Interphase G 1 = Cell is in a resting phase, performing cell functions S = DNA replicates (copies) G 2 = Organelles double in number, to prepare for division Interphase (technically not part of mitosis, but it is included in the cell cycle) Cell is in a resting phase, performing cell functions DNA replicates (copies) Organelles double in number, to prepare for division Interphase (technically not part of mitosis, but it is included in the cell cycle) Cell is in a resting phase, performing cell functions DNA replicates (copies) Organelles double in number, to prepare for division

Mitotic Phase Mitosis is divided into prophase, metaphase, anaphase, and telophase PMAT Mitosis results in two offspring cells that are genetically identical to the original cell

Prophase Spindle forms Centrioles move to opposite poles Chromosomes become visible

Metaphase Chromosomes line up along the equator

Anaphase Centromeres divide Chromatids separate and move to opposite poles

Telophase Nuclear membrane forms around each group of chromosomes Chromosomes unwind Cytokinesis begins

Cytokinesis The process by which the cytoplasm divides and one cell becomes two individual cells Animals - cell pinches inward Plants - a new cell wall forms between the two new cells

Mitosis Summary

Concept 9.4 – Cancer cells grow and divide out of control. Timing during normal cell division is critical to normal growth and development. When the “control system” malfunctions, cells may reproduce at the wrong time or in the wrong place.

Tumors & Cancer Benign tumors  Abnormal mass of essentially normal cells  Depending on their location they sometimes cause health problems  Often removed via surgery Malignant tumors  Masses of cells that result from reproducing cancer cells  Cancer disrupts the timing of cell division – this disruption leads to uncontrolled cell division Metastasis  Spread of cancer beyond its original site

Metastasis

Cancer Treatment When possible, malignant tumors are removed with surgery To treat cancer on the cellular level – radiation and chemotherapy is often used  Radiation exposes the cells to high energy radiation, which disrupts cells division  Chemotherapy involves treating patients with cytotoxic chemicals which prevent cell division Different types of chemotherapy drugs affect cell division in different ways (preventing the spindle fibers from forming, “freezing” the spindle, etc)

Cancer Treatment Radiation & Chemotherapy often causes undesirable side effects in normal body cells that rapidly divide  Radiation can affect ovaries & testes – and can cause sterility  Chemotherapy often damages intestinal cells or hair follicles (fast growing cells), causing nausea or hair loss

Concept 9.5 – Meiosis functions in sexual reproduction. Only dogs produce more dogs, only trees produce more trees, and only people produce more people.  BUT: “Like begets similar to, but not exactly like.”

Diploid v. Haploid Cells Almost all human cells are diploid  2n = 2 sets of homologous chromosomes  Human cells = 46 chromosomes Only exception – sex cells are haploid  n = 1 set of homologous chromosomes  Human sex cells = 23 chromosomes

Diploid (2n) is the number of chromosomes in cells that have homologous pairs of autosomes and 2 sex chromosomes

Haploid cells (n) have half the number of chromosomes that are present in diploid cells

Meiosis

Meiosis produces haploid daughter cells from specialized cells in diploid organisms. Despite the similarity in their names, meiosis is different from mitosis in two major ways.  The first major difference is that meiosis produces four new offspring cells, each with one set of chromosomes—thus half the number of chromosomes as the parent cell.  The second major difference is that meiosis involves the exchange of genetic material between homologous chromosomes.

Meiosis Goes through two divisions  Meiosis 1  Meiosis 2

Each pair of homologous chromosomes is called a tetrad Homologous chromosomes (each with sister chromatids) A tetrad

Crossing-over during meiosis results in genetic recombination

During meiosis, a cell divides twice

Spermatogenesis is the process by which sperm cells are produced

Oogenesis is the process that produces egg cells (ova)