CELL REPRODUCTION THE CELL CYCLE AND MITOSIS

Lesson Objectives—Cell Cycle Describe the properties of cell division in prokaryotes. Describe cell division in eukaryotes. Explain the main differences between cell division in prokaryotic and eukaryotic cells. Describe the basic properties of chromosomes. Describe the key steps in the cell cycle. Identify and describe the main processes in mitosis. Describe how the cell cycle is controlled and define cancer.

CELL REPRODUCTION Cell Division: process by which a cell divides to form two new cells (daughter cells) Three types of cell division, or cell reproduction Prokaryotes (bacteria) Binary fission divides forming two new identical cells Eukaryotes Mitosis Cell or organism growth Replacement or repair of damaged cells Meiosis formation of sex cells, or gametes

Why do cells divide? 1: DNA Overload 2: Exchange of materials If cells grow without limit, an “information crisis” would develop DNA cannot serve the needs of the increasing size of cell 2: Exchange of materials Food and oxygen have to cross membrane very quickly Waste must get out If cell is too large, this occurs too slowly and cell will die

PROKARYOTIC CELL DIVISION Binary fission 3 main steps: 1: DNA Replication—DNA is copied, resulting in 2 identical chromosomes 2: Chromosome Segregation—2 chromosomes separate, move towards ends (poles) of cell 3: Cytokinesis—cytoplasm divides, forming 2 cells Each new daughter cell is genetically identical to parent cell

THE CELL CYCLE G1 phase M phase S phase G2 phase

CELL CYCLE-INTERPHASE Interphase: period of growth and DNA replication between cell divisions Three phases: G1 Phase cell increases in size S Phase Replication of chromosomes Now two strands called sister chromatids joined by a centromere G2 Phase organelles double new cytoplasm forms All other structures needed for mitosis form

DNA containing cell’s genetic code Each chromosome has a matching pair -- Homologous Pair During interphase, each chromosome copies itself

EUKARYOTIC CELL DIVISION DNA found on chromosomes located in nucleus of cell Cell cycle continuous process Cells grow DNA replicated Organelles duplicated Divide to form daughter cells 2 Main steps: 1: Mitosis (4 steps—Prophase, Metaphase, Anaphase, Telophase) Nucleus divides 2: Cytokinesis—Cytoplasm divide, forming 2 cells Each new daughter cell is genetically identical to parent cell

Mitosis = nuclear division Mitosis is followed by cytokinesis (cell division) The steps of mitosis ensure that each new cell has the exact same number of chromosomes as the original

MITOSIS Process that divides cell nucleus to produce two new nuclei each with a complete set of chromosomes Continuous process Four phases (PMAT) Prophase Metaphase Anaphase Telophase

PMAT (1)Prophase (2)Metaphase (3)Anaphase (4)Telophase Interphase 1 2 Cytokinesis

1. chromosomes visible (sister chromatids) 2. centrioles migrate to the poles (only in animals) 3. nuclear membrane disappears 4. spindle forms

chromosomes line up on the equator of the cell spindles attach to centromeres Equator

sister chromatids separate centromeres divide sister chromatids move to opposite poles

1. chromosomes uncoil • now chromatin 2. nuclear membranes reform 3. spindle disappears

Occurs at end of Mitosis --division of the cytoplasm to form 2 new daughter cells --organelles are divided -Daughter cells are genetically identical Cells return to interphase

Name the phases starting at the top. Mitosis Name the phases starting at the top.

2.Name the phase 3.Identify X 4.Identify Y

5. Name the phase

6. Name the phase

Control of the Cell Cycle Regulatory proteins called cyclins control the cell cycle at checkpoints: G1 Checkpoint—decides whether or not cell will divide S Checkpoint—determines if DNA has been properly replicated Mitotic Spindle Checkpoint—ensures chromosomes are aligned at mitotic plate

Cell Cycle Checkpoints

CANCER CELLS Result of uncontrolled cell division of cells that have lost ability to regulate cell cycle Reproduce more rapidly than normal cells Masses formed called ‘tumors’ Can be caused by: Cell’s DNA is damaged Radiation Toxic chemicals May form a tumor (mass of abnormal cells)

Lesson Summary—Cell Cycle The cell cycle is a repeating series of events, characterizing the life of a eukaryotic cell. Binary fission is a form of cell division in prokaryotic organisms that produces identical offspring. As a eukaryotic cell prepares to divide, the DNA and associated proteins coil into a structure, known as a chromosome. The DNA copies during the S phase of the cell cycle, resulting in a chromosome that consists of two identical chromatids, known as sister chromatids, attached at a region called the centromere. Any cell containing two sets of chromosomes is said to be diploid; the zygote forms from the fusion of two haploid gametes. The cell cycle has five phases: the first growth (G1) phase, the synthesis (S) phase, the second growth (G2) phase, mitosis, and cytokinesis. Mitosis is the division of the nucleus; four distinct phases of mitosis have been recognized: prophase, metaphase, anaphase, and telophase. Cytokinesis is the division of the cytoplasm. The cell cycle is controlled through feedback mechanisms. Cancer results from uncontrolled cell division, due to the loss of regulation of the cell cycle.