Cell Division-Mitosis (Prophase,Meaphase,Anaphase,Telophase).pptx

Biology 11th grade

1. Cell Division

2. Introduction Living organisms are made of cells, so this means that cells must be able to grow and reproduce . All multicellular organisms use cell division for growth, maintenance, and repair of tissues . a crucial function of most cell divisions is the distribution of identical genetic material (DNA – Chromosome) to two daughter cells (except meiosis)

3. Chromosome Just before a eukaryotic cell divides, a number of threadlike structures called chromosomes gradually become visible in the nucleus . Chromosomes are made of chromatin . Chromatin consists mainly of DNA wrapped around basic protein molecules called histones

4. Cell cycle To divide , a cell must complete several important tasks : it must grow, copy its genetic material (DNA), and physically split into two daughter cells . In eukaryotic cells, the stages of the cell cycle are divided into two major phases:  interphase   and the   mitotic (M) phase .

5. Interphase Interphase is the longest stage of cell cycle, Interphase can be divided into three phases: G1 phase , S phase , and G2 phase. G1 phase, During G phase , the cell grows physically larger, copies organelles. S phase, In S phase, the cell synthesizes a complete copy of the DNA in its nucleus . It also duplicates a microtubule-organizing structure called the centrosome . G2 phase, During the second gap phase, or G phase, the cell grows more, makes proteins and organelles.

6. Mitosis Mitosis  is a type of cell division in which one cell (the mother) divides to produce two new cells (the daughters) that are genetically identical to itself . Mitosis consists of four basic phases: prophase, metaphase, anaphase , and telophase . 

7. Prophase Prophase is the first stage of cell division ,   beginning after interphase , DNA has already been replicated when the cell enters prophase .

8. Metaphase Key Features of metaphase : Chromosomes are completely condensed and can be seen under the microscope. The nuclear envelope disintegrates completely and chromosomes are present in the cytoplasm. Sister chromatids are attached to each other at centromere by a protein complex called cohesin .

9. Centrosomes, Centromere, Kinetochore Centrosomes centrosomes are responsible for making the spindle , which is made of microtubules , The spindle is needed for separation of the chromatids C entromere During mitosis the centromere is the site of attachment of spindle microtubules Kinetochore protein structure found at the centromere of a chromatid to which microtubules attach during nuclear division

10. Anaphase Key Features Anaphase : The main characteristic of the   anaphase of mitosis is the separation of two sister chromatids and their migration to the poles of the cell . During the process, the centromeres readily divide to give birth to two chromosomes.

11. Telophase The mitotic spindle is broken down into its building blocks Two new nuclei form , one for each set of chromosomes. Nuclear membranes and nucleoli reappear . The chromosomes begin to decondense and return to their “stringy” form In  telophase , the cell is nearly done dividing,

12. Cytokinesis Cytokinesis in animal cells is accomplished through the " outside-in " constriction of a contractile ring (actin ring) , which forms a cleavage furrow that eventually "pinches" the two cells apart. Cytokinesis is the division of cytoplasm to form two new cells, overlaps with the final stages of mitosis . Plant cells can’t be divided like this because they have a cell wall and are too stiff . Instead, a structure called the  cell plate  forms down the middle of the cell,

13. Telomeres DNA is replicated (copied) during the S phase of the cell cycle . If part of the DNA is not copied , that piece of information is lost . the loss of vital genes would result in cell death . The main function of telomeres is therefore to prevent the loss of genes during cell division and to allow continued replication of a cell . Telomeres are found at the ends of chromosomes

14. Telomeres Telomere is repetitive sequence of DNA at the end of a chromosome that protects genes from the chromosome shortening that happens at each cell division . They have no useful information , but allow the copying enzyme to complete copying all the meaningful DNA With each division, their telomeres get a little shorter until the vital DNA is no longer protected and the cell dies . This could be one of the mechanisms of ageing , by which humans grow old and die .

15. Cancer Cancers is a group of diseases that result from a breakdown in the usual control mechanisms that regulate cell division ; certain cells divide uncontrollably and form tumours , from which cells may break away and form secondary tumours in other areas of the body. Cancers start when changes occur in the genes that control cell division . A change in any gene is called a mutation .