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MitosisTopic 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: MitosisMethod of reproduction for unicellular
organisms (asexual reproduction)Growth and repair for all cellsAllows organism to develop from a
zygote (fertilized egg cell) into an adultRepairs torn or damaged tissue (cuts,
broken bones)
Cell Cycle1. 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 cycleInterphase: growth
and normal cell functions
Cell must duplicate DNA and cell organelles prior to division for new daughter cells
Terms related to cell division1. 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 InterphaseDNA has replicated
(formed another copy of itself, one for each new cell)
Chromatin coils up to form chromosomes
Cells Undergoing MitosisCells Undergoing Mitosis
1. Prophase Transition from normal cell activities
to cell divisionNuclear envelope disappears, nucleus
not visibleChromosomes become visibleCentrioles begin to move apart and
spindle fibers form between them
Eukaryotic ChromosomeEukaryotic Chromosome
Human ChromosomesHuman Chromosomes
2. Metaphase centrioles reach opposite sides of the
cellChromosomes line up on the cell
equator (very easy to see under the microscope)
Attach to spindle fibers by the centromere (center)
MetaphaseMetaphase
3. Anaphase spindle fibers shorten and pull sister
chromatids apartEach sister chromatid is considered
now a separate chromosome
Mitotic SpindleMitotic Spindle
AnaphaseAnaphase
4. Telophase chromosomes now on opposite sides of
the cellReverses the process of prophase:
nuclear envelope reformsChromosomes unwind into chromatin,
no longer visibleAll cell organelles and cytoplasm are
divided equally
TelophaseTelophase
Plant Animal
5. Cytokinesis
the physical division into two separate cellsPlant 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
CytokinesisCytokinesis
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 CELLSNo centrioles or
spindle fibersCell plate forms to
divide cell in half
ANIMAL CELLSCentrioles 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 cancerAppear 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 tissue2. Chemotherapy: drugs that target
rapidly dividing cells.3. Radiation: targeted high dose X-rays
to destroy cancer cellsMost patients treated with a
combination of the three treatments