1. Cell Division-Proliferation Cell Division: An overview

2.  Two fundamental characteristics of life are:  Ability to grow  Ability to reproduce  Both of these characteristics depend on the process of cell division.  Cell division is the process by which a single cell generates new daughter cells.

3. Types of reproduction  Asexual Reproduction-A form of duplication that requires only one parent and results in two organisms that are genetically identical to the parent.  Sexual Reproduction-The process of reproduction involving the union of gametes from two different parents.

4. Asexual Reproduction:  For single-celled organisms, binary fission and mitosis are methods of asexual reproduction.  Prokaryotes typically undergo binary fission whereas single-celled and multicellular eukaryotes undergo mitosis.

5. Binary Fission:

7. Mitosis:  Mitosis produces new cells in multicellular organisms that-  Cause growth by increasing the number of cells  Replace lost cells  Repair injuries

9. Sexual Reproduction: As sexual reproduction requires two parents, this process results in genetically unique individuals. Meiosis is the process that produces the cells needed for sexual reproduction. Meiosis is different from mitosis. In meiosis reproductive cells receive half of the parent cell’s genetic information.

10. The Cell Cycle and Mitosis  The cell cycle consists of all the stages of growth and division for a eukaryotic cell.  All eukaryotic cells go through the same basic life cycle, but different cells vary in the amount of time they spend in various stages.  The cell’s life cycle is a continuous process without a beginning or an end. As cells complete one cycle, they begin the next.

11. Mitosis:Stages  Interphase  Prophase  Metaphase  Anaphase  Telophase  Cytokinesis

12. Interphase

13. 1 st Phase-Interphase  During this stage the cell engages in normal metabolic activities and prepares for the next cell division.  Most cell spend greater part of their life in the interphase stage.  Interphase contains three phases-G1, S and G2.

14. The G1 stage of Interphase  During this phase the cell gathers nutrients and other resources from its environment.  This allows the cell to grow in volume and to carry out its usual metabolic roles, such as producing tRNA, mRNA, ribosomes, enzymes and other cell components.  G1 stage is often known as G0 stage in a cell when a cell remains in G1 stage for a long time and the cell is not moving forward through cell cycle.  Cell divides in G1 and moves towards S phase.

15.  G1 and G0 phase

16. The S stage of Interphase  During this stage DNA synthesis (replication) takes place.  Two copies of the genetic material are formed in the chromosomes.  DNA is found as a component of chromosomes.  The structure of a chromosome consists of DNA wrapped around histone proteins to form chromatin.  As a cell gets ready to divide, the chromatin coils and become visible as Chromosome.

17.  Chromosome appears as two thread like parts lying side by side known as chromatid.  A chromatid is one of the two parallel parts of a chromosome.  Each chromatid contains one DNA.  Sister chromatids are the 2 chromatids of a chromosome attached by centromere

18. m

19. The G2 stage of Interphase  Final stage of interphase is G2.  During this stage final preparations are made for mitosis.  The cell makes the cellular components it will need to divide successfully.  At this stage the nuclear membrane is intact.  The chromatin is replicated but individual chromosomes are not yet visible.  Nucleolus, the site of ribosome manufacture is seen during this stage.

20. Summary of Interphase  I. Gap 1 (G1)  This stage is characterized by the rapid growth and development of cell after nuclear division. The cell will grow into its original size.  II. Synthesis (S stage)  The stage when cell actively duplicate its genetic information in preparation for the next cell division.  III. Gap 2 (G2)  The stage in which cells are actively synthesize energy, organelles and grow to prepare for cell division.  Characteristics of cells during interphase  Nucleus and nucleolus are visible.  Genetic information is in the form of loosely coil chromatin instead of chromosomes

21. Let’s revise…………..

22. Concept Review  What is a cell cycle?  What happens to chromosomes during interphase?  What are the types of cellular reproduction?  What is the purpose of binary fission and mitosis in comparison to meiosis?  What is the role of interphase in cell cycle?