Cell Division and Mitosis Ch. 5

God’s Command to Nature Genesis 1 God created all living things and gave them a command: “Be fruitful and multiply, fill the earth and subdue it…”

There are FOUR main functions of Cell Division: 1. In unicellular organisms, cell division is the way these organisms reproduce. The cell DIVIDES producing a duplicate or copy of itself

Cell Division In multicellular organisms, cell division has several functions: 2. Regeneration- occurs when parts of organisms that have been damaged grow back or are replaced. Ex. A starfish can grow a new arm if one is cut off. Do you know of any other animals that can replace lost parts?

Cell Division 3. Healing- another function of cell division is the healing of wounds. Whenever you have a cut or scrape on your skin, you can see the healing take place over a period of time. While the wound heals, new cells are made through cell division to replace the destroyed and damaged cells.

Cell Division 4. A fourth important result of cell division is the growing process. After a cell divides, both new cells grow and divide to form more new cells Some cells can divide every few hours

Prokaryotic Cell Division Bacterial cells reproduce by Binary Fission Begins with DNA replication; each copy moves to opposite sides of cell Followed by elongation of cell and replication of all internal cell parts, then split down the center between the two halves Results in two cells that are identical versions (clones) of original cells

Binary Fission

Eukaryotic Cell Division Two forms: Mitosis grow, replace dead or worn out cells, or to repair wounds Asexual reproduction in fungi, protists, some plants/animals Meiosis Formation of gametes for sexual reproduction

The Cell Cycle The length of time the cell cycle takes depends on the type of cell. Usually the more specialized the cell the less likely it is to divide.

How often your cells regenerate? Intestinal lining 2 to 30 days Skin 21 to 30 days Red blood cells 90 to 120 days The pancreas 5 to 12 months Muscles 6 months to 3 years Tissues 1 to 7 years Bones 8 months to 4 years Nerve cells (in brain or from spinal cord) – after fetal development – never

Cell Cycle interphase G1 S telophase anaphase Mitosis G2 metaphase prophase

The Cell Cycle: Interphase When a cell is not dividing it is said to be in Interphase:  G1: Gap 1, cells are recovering from an earlier cell division, synthesizing organelles and growing  S: Synthesis, DNA replication occurs G2: Gap 2, cells are making sure all the DNA was replicated correctly; a little more growth; the chromosomes start to undergo condensation, becoming tightly coiled; Centrioles replicate and one centriole moves to each pole. G0: Cell has a specific job and does not divide

Interphase interphase

DNA and Cell Division (Interphase) During cell division, the genetic material DNA, needs to be copied and divided between the two new cells DNA in cells is divided into long chains called chromosomes (“volumes” of DNA) Chromosome DNA is wrapped around proteins called histones to organize it

Eukaryotic Chromosome Structure Normally, chromosomes are spread out in a form called chromatin During mitosis, chromatin folds up and condense to become chromosomes

Eukaryotic Chromosomes sister chromatids: are 2 copies of the chromosome The sister chromatids are bound together in the middle at a centromere

The Cell Cycle: Cell Division Mitosis (M Phase) Nuclear Division Cytokinesis (C phase) Cytoplasmic Division

Mitosis Video

Mitosis Nuclear Division Dividing up the genetic material (DNA)

Mitosis Mitosis is divided into 4 phases: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

Mitosis 1. Prophase: chromosomes condense and appear as sister chromatids joined at centromere cytoskeleton disassembles centrioles move to each pole of the cell; spindle apparatus is assembled nuclear envelope dissolves

The Spindle Apparatus Moves chromosomes during mitosis In both plant and animal cells, spindle fibers originate from centrosomes; in animal cells, centrosomes are called centrioles

Spindle Apparatus one spindle pole one of the condensed chromosomes spindle equator microtubules organized as a spindle apparatus one spindle pole

Prophase

Mitosis 2. Metaphase: spindle fibers pull the chromosomes to align them at the middle of the cell called the metaphase plate

Metaphase

Mitosis 3. Anaphase: - Spindle pulls sister chromatids away toward the poles

Anaphase

Mitosis 4. Telophase: spindle apparatus disassembles nuclear envelope forms around each set of sister chromatids chromosomes begin to uncoil nucleolus reappears in each new nucleus

Telophase

Cytokinesis Division of the cytoplasm Usually occurs between late anaphase and end of telophase Two mechanisms Cell plate formation (plants) Cleavage furrow (non-plants or organisms without a cell wall)

Cytokinesis: Animal Cell Cleavage furrow – is the pinching in of the cell membrane to divide the cell into 2 new cells

Cleavage Furrow

Cytokinesis: Plant Cells Cell Plate Formation In plant cells, a cell plate will form between the two dividing nuclei to form the new cell wall

Mitosis/Cytokinesis outcome 1 parent cell  2 identical daughter cells Chromosome number remains the same from one generation to the next

Mitosis: plant vs. animal cells Plant cell Animal Cell Centrioles Absent Present Cytokinesis Cell plate formation Cleavage furrow

Control of the Cell Cycle The cell cycle is controlled at three checkpoints: 1. G1/S checkpoint -the cell “decides” to divide 2. G2/M checkpoint -the cell makes a commitment to mitosis 3. late metaphase (spindle) checkpoint -the cell ensures that all chromosomes are attached to the spindle

Control of the Cell Cycle Proto-oncogenes: -become oncogenes when mutated -oncogenes can cause cancer when they are introduced into a cell