The Cell Life Cycle. S DNA replication, INTERPHASE. G 2 Protein. G 1 Normal THE CELL CYCLE. Indefinite period. synthesis. of histones.

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1 Mitosis & Meiosis

2 The Cell Life Cycle INTERPHASE G 1 Normal cell functions plus cell growth, duplication of organelles, protein synthesis S DNA replication, synthesis of histones THE CELL CYCLE M G 2 Protein synthesis MITOSIS AND CYTOKINESIS (See Figure 2.21) Indefinite period G 0 Specialized cell functions

3 Mitosis A cell divides to produce two identical cells To heal an injury To grow (increase cell number) Cells are not always dividing- most of their life is spent between divisions (interphase G1)- carrying out the organelle jobs Division costs lots in terms of energy! Uncontrolled cell division produces tumors (cancers).

4 Stages of cell s life cycle: (PMAT) Interphase- (between divisions, can t see chromosomes) G1- cell is not ready to divide, carries out normal functions S- cell commits to divide, and copies all the DNA G2- cell prepares for division, and generates more lipids and Proteins Mitosis- Division of genetic information (division of the nucleus): think P.M.A.T. ( Passed My Anatomy Test ) Prophase- preparations (preliminary steps)- package chromosomes Metaphase- chromosomes line up in the middle of the cell Anaphase- chromosomes separate and the two halves move apart to opposite sides of the cell Telophase chromosomes are surrounded by membranes to form two nuclei

5 Interphase and Mitosis INTERPHASE EARLY PROPHASE LATE PROPHASE Nucleus Astral rays Spindle fibers Centriole Chromosome with two sister chromatids MITOSIS BEGINS Centrioles (two pairs) No chromosomes visible Regular functions Chromosomes condense; Centrioles attach to them; Microtubules form the spindle

6 Interphase and Mitosis METAPHASE ANAPHASE TELOPHASE INTERPHASE Chromosomal microtubule Daughter chromosomes Daughter cells Metaphase plate Cleavage furrow CYTOKINESIS Chromosomes line up in the middle (metaphase plate) Chromosomes separate at the centromere; each identical chromatid (piece of DNA) goes to the opposite side 2 nuclei form 2 cells form

7 Development of Gametes: Meiosis Mitosis is the production of two identical daughter cells through DNA replication and division of a cell. Meiosis: production of four unique haploid cells from one diploid cell. Meiosis is the mechanism for producing haploid sex cells (spermatozoa and oocytes).

8 Spermatogenesis Stem cells (spermatagonia) constantly undergo mitosis, to produce more spermatagonia (2n) Spermatagonia can differentiate (mature) to form primary spermatocytes (still 2n) Primary spermatocytes enter meiosis. At the end of the first meiotic division, each primary spermatocyte forms two secondary spermatocytes (two identical copies of 23 chromosomes) Each secondary spermatocyte undergoes second meiotic division to form two spermatids (1 n).

9 Spermiogenesis Spermatids are round cells. To be functional, spermatids must mature into spermatazoa, by the process of spermiogenesis. During spermiogenesis, sperm develop distinct head and tail regions. Head contains acrosomes (enzymes required to fertilize egg) Tail required form motility

10 Spermatogenesis

11 Oogenesis Oogenesis: development of oocytes Oocytes are found in ovary, enclosed within follicles. During development, all stem cells for oocytes enter first part of meiosis, and then stops (at prophase I, primary oocyte ). Follicles remain suspended for years (or decades) During each ovulatory cycle, some follicles begin growth. Each month, one follicle reaches full maturation (preovulatory or Graafian follicle). The ova is released from the follicle (ovulated) due to the midcycle surge of LH.

12 Follicle Development & Ovulation

13 Oogenesis Just before ovulation, in response to the LH surge, the oocyte completes meiosis I (now secondary oocyte ). End product of meiosis I: secondary oocyte and 1st polar body. If the ovulated secondary oocyte is fertilized, it finishes meiosis II, becoming a mature ova (egg) End product of meiosis II: mature ova and second polar body.

14 Summary of Oogenesis

15 End Products of Spermatogenesis and Oogenesis Spermatogenesis: One primary spermatocytes results in four spermatids, which result in four spermatazoa. Oogenesis: One primary oocyte gives rise to one mature ova and three polar bodies.