LECTURE 9: MITOSIS AND CYTOKINESIS INTRODUCTION 1. Cell division is accomplished by MITOSIS = division of chromosomes and CYTOKINESIS = division of the cytoplasm 2. Mitosis is the division of somatic cells in which the appropriate number of chromosomes is maintained 3. A somatic cell is a body cell of an organism or a cell that is not involved in reproduction of a new organism. Somatic cells divide to recreate themselves 4. Cytokinesis is division of the cytoplasm to produce two daughter cells, usually begun during telophase 5. Difference between animals and plants: plants are divided by the formation of a cell plate (=pelat), where animal cells are divided through the formation of a cell cleavage (=belahan). Cell plate materials originate in the golgi complex. KRT INTRODUCTION 4. When the somatic cell has its complete complement of chromosomes it is said to be in the diploid condition 5. At the end of mitosis daughter cells are diploid Terminology Genome : cells genetic information Somatic : body cells Gametes : reproductive cells (sperm and egg cells) Chromosomes : DNA molecules Diploid (2n) : 2 sets of chromosomes Haploid (1n) : 1 set of chromosomes KRT BASIC PRINCIPLE Cell Division: Key Roles KRT Coordination of Mitosis and Cytokinesis Cell Division demands coordination of DNA replication (Mitosis) and division of the cytoplasm (Cytokinesis). Cell Division at cellular level KRT Whats so important about cell division? The process KRT The Knit of Identity - Mitosis Precisely and Evenly Divides Duplicated Chromosomes Precisely dividing the duplicated chromosomes has the consequence of providing each new cell with an identical and complete set of genetic instructions. INTERPHASE PROPHASE METAPHASE KRT Mitosis Precisely and Evenly Divides Duplicated Chromosomes Cytokinesis is the process of cell division and it is distinct and separable from mitosis. KRT In Animal Cells, a Cleavage Furrow Forms and Separates Daughter Cells Cleave furrow in a dividing frog cell. KRT The Plant Cell Wall Forces Cytokinesis to Play by Different Rules KRT Cancer Transformation Tumor: benign (=jinak) or malignant (=ganas) Metastasis KRT Cancer Is One Outcome of A Runaway Cell Cycle Licentious division - prostate cancer cells during division. KRT Chromosome and DNA What is the difference between DNA and Chromosome? What is Karyotype ? KRT Cell Devision at chromosome level CHROMOSOME DUPLICATION AND SEPERATION KRT DNA Replication Simple in Principle, Complicated in Practice Cell Devision at DNA level KRT DNA is Packaged into Chromosomes The packaging is impressive 2 meters of human DNA fit into a sphere about meters in diameter. chromatin duplicated chromosome DNA in the cell is virtually always associated with proteins. KRT The Link Between DNA Replication and Chromosome Duplication KRT DNA is Condensed into Visible Chromosomes Only For Brief Periods in the Life of a Cell 95% of the time, chromosomes are like this. Easily visible chromosomes are apparent perhaps 5% of the time in an actively growing cell and less in a non-growing cell. KRT A normal human karyotype Boy or girl? Note that almost all chromosomes come in homologous pairs. A Karyotype is an arranged picture of chromosomes at their most condensed State KRT The Cell Cycle KRT From Birth to Rebirth, a Cell Progresses Through Characteristic Stages That Constitute the Cell Cycle In multicellular organisms like us, progress through the cell cycle is carefully regulated. KRT The Cell Cycle 1. Interphase (90% of cycle) G1 phase~ growth S phase~ synthesis of DNA G2 phase~ preparation for cell division 2. Mitotic phase 3. Mitosis~ nuclear division 4. Cytokinesis~ cytoplasm division INTERPHASE - It is the time between divisions KRT The Cell Cycle G1 S G2 Mitosis & cytokinesis KRT Cell Cycle regulation Growth factors Density- dependent inhibition Anchorage (=tempat) dependence KRT Stages of Mitosis KRT Mitosis 1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase 5. Telophase KRT Mitosis in Action Blue shows DNA, green shows spindle fibers. KRT Stages of mitosis KRT Stages of mitosis PROPHASE, METAPHASE, ANAPHASE,TELOPHASE 1. Prophase: Chromosomes condense and become visible, each Chromosome contains several cm of DNA condensed into 5 10 micrometers. During the S Phase each chromosome has been duplicated into a sister chromatid. (A chromotid is one of the two halves of duplicated chromosomes) S Phase = synthesis of DNA KRT Prometaphase Nuclear membrane fragments Spindle interaction with chromosomes Kinetochore develops KRT Centrosomes at opposite poles Centromeres are aligned (=disejajarkan) Kinetochores of sister chromatids attached to microtubules (spindle) 2. Metaphase: 1. Chromosomes line up along the cell equator. 2. The cell itself condenses and the chromosomes are more clearly visible than during any other phase of mitosis KRT Paired centromeres separate; sister chromatids liberated Chromosomes move to opposite poles Each pole now has a complete set of chromosomes 3. Anaphase 1. is defined as the sister chromatids begin to separate 2. By now each chromatid is an independent and functional chromosome 3. The chromosomes are pulled toward opposite poles. Anaphase is complete when a complete set of chromosomes reaches each pole. 4. Telophase: 1. The final stage of mitosis, chromosomes uncoil (= mengurai) into chomatin threads 2. A nuclear envelope forms around each set of chromosomes, nucleoli appear Daughter nuclei form Nuclear envelopes arise Chromatin becomes less coiled (= menggulung) Two new nuclei complete mitosis KRT Structure of a replicated chromosome KRT Counting chromosomes and chromatids n = haploid number of chromosomes Example: the humans have 23 different chromosomes (n=23). Diploid cells have 2n chromosome #. Human diploid cells, have 46 chromosomes (2n=46). c = number of chromatids in unreplicated (G1) haploid state. KRT Replication of a chromosome during mitosis 1. Frequency of mitosis varies between species or even with location within an organismskin cell versus nerve cells for example, but under similar conditions the length of the cell cycle is constant for a particular type of cell. 2. The rate and frequency of mitosis in a multicelluar organism must be controlled 3. The cell requires a protein called maturation promoting factor (MPF). Scientists are still learning how MPF works and controls the cell mitosis. CONTROLS ON DIVISION Read about the effects of Colchicine and the condition of polypoidy When mitosis occurs each daughter cell receives exactly the same number and kind of chromosomes as the parent When a haploid cell undergoes mitosis, two haploid cells are produced. KRT These are Organisms (living things)