Why do cells divide? Cells divide in order to make more cells they multiply in order to create a larger surface to volume ratio!!!
Chromosomes Are made of chromatin: a mass of genetic material composed of DNA and proteins (called histones) ) that condense to form chromosomes in the cell's nucleus.
What exactly are chromosomes? Structures s within a cell that carry genetic material in the form of threadlike strands of DNA bonded to histones in the nucleus of eukaryotic cells Rod-shaped Each chromosome consists of two indentical halves called sister chromatids which are attached together at a centromere
Chromosome Numbers Each species has a set number of chromosomes in every cell Higher number of chromosomes does NOT mean it is a more complicated species! Humans have 46 chromosomes, but crayfish have 200!
Cell Division in Eukaryotes!!! Division of the nucleus and the cytoplasm Involves only one cycle of cell division The division of regular cells 1 cell and 1 set of chromosomes become 2 identical cells (and two identical sets of chromosomes) called daughter cells
Introduction to Mitosis Apoptosis cell death
The series of events involving the growth, replication, and division of a eukaryotic cell
Mitosis Division of cells and cell nuclei It s s divided into 4 phases: Prophase, Metaphase, Anaphase, Telophase
Before Cell Division Interphase time for growth and regular cell activity before cell division; consists of three phases Most of a cell s s life is spent in Interphase. Interphase is NOT part of mitosis!
Interphase Phases G1 (Gap 1) is when the cell grows and functions normally and during this time, protein synthesis occurs and the cell grows producing more organelles, increasing the volume of the cytoplasm. Synthesis (S) is when the cell duplicates its DNA G2 (Gap 2) is where the cell resumes its growth in preparation for mitosis
Prophase First stage of Mitosis Chromatin condenses into rod- shaped chromosomes Nuclear membrane and nucleolus break down and disappear Two pairs of dark spots called centrosomes appear next to the disappearing nucleus
In animal cells, each centrosome contains a pair of long, cylindrical bodies called centrioles Centrioles separate to opposite ends (poles) and spindle fibers begin to form; they are made of microtubules of protein
Fibers, Fibers Everywhere Polar fibers are spindle fibers that extend from the two poles of a dividing cell Kinetchore fibers are microtubules that connect kinetochores to a centrosome. Both of these types of spindle fibers make up the mitotic spindle Aster formation protein fibers which radiate from each centriole (not found in plant cells)
Early Prophase
Late Prophase
Metaphase Second Phase of Mitosis Chromosomes move and line up in the center of the cell the equator. Each chromosome is connected to a spindle fiber.
ASTERS Metaphase
Anaphase Third Phase of Mitosis Centromere of each pair of chromatids divide and move towards opposite poles Kinetichore and polar fibers work together to move chromosomes Spindle fibers start to break down When chromosomes separate, they are considered to be individual chromosomes!
Anaphase
Telophase 4th and Final Stage of Mitosis Spindle fibers completely disappear Chromosomes gather at opposite ends of the cell, unwind and lose their distinct shapes becoming chromatin again Nuclear envelope and nucleolus reappear. Cell membrane begins to pinch in forming a cleavage furrow (only in animal cells)
Telophase
Cytokinesis division of the cytoplasm Two new cells are formed Cells are equal in size Each new daughter cell has an identical set of duplicate chromosomes
Plant Cell Mitosis Has no asters Has a cell plate rather than a cleavage furrow
Animal Cells Plant Cells
Regulating the Cycle A protein called cyclin helps regulate the cell cycle in eukaryotic cells. These proteins are regulators and respond to internal and external events.
When Things Go Wrong Cancer cells do not respond to the signals that regulate the growth of most cells. As a result, they form masses of cells called tumors that can damage surrounding tissues.
Cancer