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