Cell Division. Genetic info must be copied. Each cell gets a complete copy of that info. It occurs in two main stages:

Transcription

1 10-2 Cell Division Key Questions: 1)What is the role of chromosomes in cell division? 2) What are the main events of the cell cycle? 3) What events occur during each of the four phases of mitosis? 4) How do daughter cells split apart after mitosis?

2 Cell Division What happens before cell division? How does cell division occur in eukaryotes? Genetic info must be copied. Each cell gets a complete copy of that info. It occurs in two main stages: Mitosis-division of nucleus Cytokinesis-division of cytoplasm

3 Cell Division Repro by mitosis is asexual since the cells produced are genetically identical to the parent cell. In humans, mitosis begins shortly after the egg is fertilized so the embryo can take form.

4 Chromosomes The genetic information that is passed on from one generation of cells to the next is carried by chromosomes. Every cell must copy its genetic information before cell division begins. Each daughter cell gets its own copy of that genetic information. Cells of every organism have a specific number of chromosomes.

5 Chromosomes In eukaryotic orgs, what carries the genetic info? What role do chromosome play in cell division How many chromosomes does a cell have? When can I see chromosomes? Chromosomes--which are made up of DNA. Chromosomes make it possible to separate DNA precisely during cell division The cells of every orgs have a specific # of chromosomes. Fruit flies=8 humans-=46 Carrots=18 Chromosomes are not visible except during cell division. This is because the DNA and protein that make up the chromosomes are spread out in the nucleus. They condense into visible structures during division. They can then be seen with a microscope.

6 Chromosomes What happens before cell division? What does each chromosome consist of? Each chromosome is replicated, or copied. 2 identical sister chromatids. When a cell divides the sister chromatids separate from each other. One chromatid goes to each of the 2 new cells.

7 Chromosomes What holds the two chromatids together? They are attached at the centromere. Centromeres are located in the middle of the chromatids some toward the end. A human body cell entering division contains 46 chromosomes, each consisting of 2 chromatids.

8 Prokaryotic Chromosomes Prokaryotic cells lack nuclei. Instead, their DNA molecules are found in the cytoplasm. Most prokaryotes contain a single, circular DNA molecule, or chromosome, that contains most of the cell s genetic information.

9 Eukaryotic Chromosomes In eukaryotic cells, chromosomes are located in the nucleus, and are made up of chromatin. Chromatin is composed of DNA and histone proteins DNA coils around histone proteins to form nucleosomes. The nucleosomes interact with one another to form coils and supercoils that make up chromosomes

10 The Prokaryotic Cell Cycle The prokaryotic cell cycle is a regular pattern of growth, DNA replication, and cell division. Most prokaryotic cells begin to replicate, or copy, their DNA once they have grown to a certain size. When DNA replication is complete, the cells divide through a process known as binary fission.

11 The Prokaryotic Cell Cycle Binary fission is a form of asexualreproduction during which two genetically identical cells are produced. For example, bacteria reproduce by binary fission.

12 Important Cell Structures Involved in Mitosis Chromatid each strand of a duplicated chromosome Centromere the area where each pair of chromatids is joined Centrioles tiny structures located in the cytoplasm of animal cells that help organize the spindle Spindle a fanlike microtubule structure that helps separate the chromatids

13 The Eukaryotic Cell Cycle The eukaryotic cell cycle consists of four phases: G1, S, G2, and M. Interphase is the time between cell divisions. It is a period of growth that consists of the G1, S, and G2 phases. The M phase is the period of cell division.

14 G 1 Phase: Cell Growth In the G 1 phase, cells increase in size and synthesize new proteins and organelles.

15 S Phase: DNA Replication In the S (or synthesis) phase, new DNA is synthesized when the chromosomes are replicated.

16 G 2 Phase: Preparing for Cell In the G 2 phase, many of the organelles and molecules required for cell division are produced. Division

17 M Phase: Cell Division In eukaryotes, cell division occurs in two stages: mitosis and cytokinesis. Mitosis is the division of the cell nucleus. Cytokinesis is the division of the cytoplasm.

18 The Cell Cycle What is interphase? It is the period of time between cell divisions. A great deal happens during this time. What is the cell cycle? Series of events the cell goes through as it grows & divides.

19 Events in the Cell Cycle How long is interphase? What parts make up interphase? Quite long G1 Phase Short, cell do most of growing, increase in size, synthesize new proteins & organelles. S Phase Chromosomes are replicated and synthesis of DNA molecules takes place. G2 Phase Shortest of 3 phases Organelles and molecules required for cell division are produced. Cells then enter M Phase

20 Phases of Mitosis: Prophase First & longest phase Chromosomes visible Centrioles (only in animal cells) separate and move to opposite sides of the nucleus. Chromosomes become attached to the spindle near the centromere. Nucleolus disappears & nuclear envelope breaks down.

21 Phases of Mitosis: Metaphase Second phase Lasts only a minutes Chromosomes lie across the center of cell. The spindle fibers connect the centromere of each chromosome to the two poles of the spindle

22 Phases of Mitosis: Anaphase Third phase Centromeres that join sister chromatids split Sister chromatids separate and become individual chromosomes Chromsomes separate into 2 groups near the poles of the spindle.

23 Phases of Mitosis: Telophase Fourth & final phase Chromosomes disperse into tangled chromatin. Nuclear envelope reforms around each cluster of chromosomes. Spindle breaks apart Nucleolus becomes visible in each daughter cell Mitosis is complete

24 Cytokinesis: Division of Cytoplasm Is cell division complete? No! Mitosis forms two individual nuclei, each with a duplicate set of chromosomes. Now the cytoplasm must divide CYTOKINESIS! The process of cytokinesis is different in animal and plant cells.

25 Cytokinesis: Division of Cytoplasm In Animal Cells, CM is drawn inward until the cytoplasm is pinched into 2 equal parts. Each part contains its own nucleus and organelles in the cytoplasm. In plants, the cell membrane is not flexible enough to draw inward because of the rigid cell wall. Instead, a cell plate forms between the divided nuclei that develops into cell membranes. A cell wall then forms in between the two new membranes

26 The Stages of the Cell Cycle