Mitosis Topic 2-5

Viruses are not cells: have no membranes or organelles, do not carry out metabolism/life functions, can only reproduce inside living cells. Contain RNA or DNA, surrounded by a protein coat of various 3D shapes. Not considered to be living organisms

Cell Division: Mitosis Method of reproduction for unicellular organisms (asexual reproduction) Growth and repair for all cells Allows organism to develop from a zygote (fertilized egg cell) into an adult Repairs torn or damaged tissue (cuts, broken bones)

Cell Cycle 1. Interphase: all normal life functions occur, cell performs its normal duties 2. Mitosis: period of cell division, in four phases 3. Cytokinesis: cell physically divides in half into two separate cells

Phases of the cell cycle Interphase: growth and normal cell functions Cell must duplicate DNA and cell organelles prior to division for new daughter cells

Terms related to cell division 1. Chromatin: threads of DNA in nucleus during interphase, not easily visible without special staining 2. Chromosomes: form prior to cell division (end of interphase), chromatin bunches and coils up to form dark, X- shaped structures arranged in pairs

Chromosome number Gametes (sex cells) have only one of each chromosome Somatic cells (body cells) have 2 of each chromosome (matching pair)

3. Sister chromatid: one side of each chromosome joined at the center, called the centromere (think of just the right or left shoe in a matching pair). Matching areas/sections on each sister chromatid correspond to the same area on the other chromatid (genes) centromere Sister chromatid

4. Centrioles: cylinder-shaped structures found only in animal cells. Helps divide the cell contents between them: as cell division begins, they move away from each other to opposite ends of the cell. 5. Spindle fibers: protein strands that form between the centrioles. Chromosomes attach to the spindle fibers, helps pull contents apart to each end of the cell during cytokinesis.

Phases of Mitosis End of Interphase DNA has replicated (formed another copy of itself, one for each new cell) Chromatin coils up to form chromosomes

Cells Undergoing Mitosis

1. Prophase Transition from normal cell activities to cell division Nuclear envelope disappears, nucleus not visible Chromosomes become visible Centrioles begin to move apart and spindle fibers form between them

Eukaryotic Chromosome

Human Chromosomes

2. Metaphase centrioles reach opposite sides of the cell Chromosomes line up on the cell equator (very easy to see under the microscope) Attach to spindle fibers by the centromere (center)

Metaphase

3. Anaphase spindle fibers shorten and pull sister chromatids apart Each sister chromatid is considered now a separate chromosome

Mitotic Spindle

Anaphase

4. Telophase chromosomes now on opposite sides of the cell Reverses the process of prophase: nuclear envelope reforms Chromosomes unwind into chromatin, no longer visible All cell organelles and cytoplasm are divided equally

Telophase Plant Animal

5. Cytokinesis the physical division into two separate cells Plant cells: a new cell wall forms by laying down cellulose fibers (called a cell plate) across the equator of the cell. Animal cells: the plasma membrane pinches in until it meets in the center, forms two new cells

Cytokinesis Cell Plate Forming in Plant Cells

Both new cells (daughter cells) are identical to the original cell, with identical DNA in each nucleus

Comparison of plant and animal cells during mitosis: PLANT CELLS No centrioles or spindle fibers Cell plate forms to divide cell in half ANIMAL CELLS Centrioles and spindle fibers present Plasma membrane pinches in to divide cell in half

Cancer: the uncontrolled division of cells May form tumors (unusual growths) in any part of the body Usually do not carry out normal life functions, inhibit the normal function of that organ or body part May starve nearby normal cells or nutrients, blood supply or oxygen

Causes of cancer Appear to be many factors that trigger uncontrolled growth: genes or enzymes that signal cell division to stop are turned off; changes/damage to DNA due to radiation or toxins (carcinogens), viruses (HPV virus = increased risk of cervical cancer), hormonal changes, genetic triggers passed from parent to offspring

Cancer terms  Metastasis (verb: metastasize): spreading of localized cancer cells to new areas in the body Malignant: cancerous. Benign: harmless, noncancerous growth Biopsy: removal of cells or tissue for examination (may be surgical or outpatient, depending on location in the body)

Cancer treatments 1. Surgery: removal of abnormal tissue 2. Chemotherapy: drugs that target rapidly dividing cells. 3. Radiation: targeted high dose X-rays to destroy cancer cells Most patients treated with a combination of the three treatments