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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)
 1.
Cell Cycle
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, Xshaped 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