Mitosis and Cell Cycle Asexual Reproduction
Organization of the DNA: Chromatin DNA is coiled around proteins called HISTONES to form chromatin A strand of DNA is wound two and a half times around two copies of histones. There are 4 different types of Histones (H2a, H2b, H3, H4) Histones are proteins with a positive charge. DNA has a negative charge. A unit of DNA around histones is called nucleosome The chromatin is organized in chromosomes The dense rod like structure of the chromosomes becomes visible during cell division. Each organism has a specific number of chromosomes. Humans have 23 pairs of chromosomes (46 in total)
Asexual reproduction In asexual reproduction cells divide to form identical daughter cells Each round of growth and cell division is called cell cycle. In some organisms (one cell-unicellular), cell division is the only method of reproduction.
Cell cycle
Mitosis
Interphase: resting cell
Prophase
Metaphase
Anaphase
Telophase
Mitosis Mitosis is a continuous process Scientist have divided mitosis into phases.
Phases of mitosis Interphase: resting stage, cells grow in size and produce organelles. At some point they replicate DNA Prophase: the doubled chromosomes become visible. Each strand of doubled chromosome is called chromatid. Chromatids are connected by a centromere. Metaphase: chromosomes line up in the cell center (equator). Chromatides become separated. Anaphase: duplicate chromatides move at the opposite poles of the cell. Telophase: chromosomes uncoil and get longer. Spindle and aster dissapear. Nuclear membrane form. Nucleolus comes back. Cytokinesis: Division of the cytoplasm.
Role of the cytoskeleton in mitosis The cytoskeleton provides structure and organizes mitosis Microtubules pull the chromatids to the poles of the cell during anaphase. Chromatids are attached to the microtubules with the kinetochore. Without proper function of microtubules, mitosis cannot occur. Centrioles are organizing the mitotic spindle.
Organization of the chromatids at metaphase.
The microtubules and fibers attach to the kinetochore
Organization of microtubules
Some chemotherapy for cancer treatment disable the mitotic spindle