2. Mitosis - lewishardaway
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Transcript 2. Mitosis - lewishardaway
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