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 9.1 - 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

Interphase90% of the cell cycle is spent hereStage where the cell performs its functions

Increasing proteins, releasing enzymes, etc

G1, S, and G2 stagesG1 – Gap 1 = Cell growsS – DNA Synthesis = Genetic material copiedG2 – Gap 2 = Cell prepares to divide

Cell Cycle

Mitotic PhaseContains 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 (G1), a phase of DNA replication (S), and a phase of preparation for cell division (G2)

Interphase

G1 = Cell is in a resting phase, performing cell functions

S = DNA replicates (copies)

G2 = 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

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)