ib biology sl 1 2 - hrsbstaff home pagehrsbstaff.ednet.ns.ca/cchriste/01 cell division ib bio core...
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Topic 2.5 Cell Division
IB Biology SL
� 2.5.1 Outline the stages in the cell cycle, including interphase (G1, S, G2), mitosis and cytokinesis.
� 2.5.2 State that tumours (cancers) are the result of uncontrolled cell division and that these can occur in any organ or tissue.
� 2.5.3 State that interphase is an active period in the life of a cell when many metabolic reactions occur, including protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplasts.
� 2.5.4 Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase).
� 2.5.5 Explain how mitosis produces two genetically identical nuclei.
� 2.5.6 State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis.
� As you will recall from Topic 1.1.3, all cells
come from pre-existing cells.
� All cells go through a cycle over and over
again known as the cell division cycle.
� It involves:
� Interphase
� Mitosis
� Cytokinesis
� Some cells divide constantly: cells in the embryo, skin cells, gut lining cells, etc. Other cells divide rarely or never: only to replace themselves.
� Actively dividing cells go through a cycle of events that results in mitosis. Most of the cycle was called “interphase” by the microscopists who first studied cell division. During interphase the cell increases in size, but the chromosomes are invisible.
� The cell lifecycle is well defined and can be divided into four stages:� Gap 1 (G1) - The growth phase in which
most cells are found most of the time
� Synthesis (S) - During which new DNA is synthesized
� Gap 2 (G2) - The period during which no transcription or translation occurs and final preparations for division are made
� Mitosis - Cell division
G1G1
MM
G2G2
SS
The Cell Life Cycle
Gap 1 - Doubling
of cell size.
Regular cellular
activities. Making
proteins and
energy etc.
Synthesis of DNA -
Regular cell
activities cease and
a copy of all
nuclear DNA is
made so the
chromosomes are
now doubled and
look like Xs
Gap 2 - Final
preparation for
division
Mitosis - Cell
division
� During mitosis an exact copy of the genetic material in the “mother” cell must be distributed to each “daughter” cell
� Each stage of mitosis is designed to achieve equal and exact distribution of the genetic material which has been copied during the S phase of the cell cycle
� http://www.youtube.com/watch?v=0oJZDK
dperU&feature=related
� Cancer is often referred to as mitosis gone wrong and this is because cancer is abnormal cell division.
� Normal cells will grow and divide until a certain point.
� Cells will experience contact inhibition which is basically contact with an adjacent cell that stops cell division.
� Cancer cells do not respond to contact inhibition so they will continue to grow and divide, piling one on top of another until a tumor is formed. A tumor is a mass of cancer cells.
� Tumors can grow very large in size and then spread to other areas of the body.
� The spreading of cancer is referred to as metastasis and the cancer will be described as having metastasized in the body.
� Terry Fox is an example of
an individual who
experienced metastasis.
His cancer began in his
leg and eventually
metastasized in his
lungs.
� http://www.youtube.com/watch?v=DD3IQ
knCEdc&feature=related
� Remember this from Junior High!???!?!?
� Here’s one with creepy music:
� http://www.youtube.com/watch?v=NR0md
DJMHIQ&feature=related
� Interphase is a very active stage and also
the longest phase of the cell cycle.
� There are many metabolic reactions
occurring including
protein synthesis
which includes
transcription and
translation.
� DNA is also being replicated during the
interphase stage of the cell cycle in
preparation for the cell to divide once it
reaches a certain size.
� Organelles also increase in number to be
divided among the two daughter cells.
� The process of mitosis in the cell cycle is when
the nucleus of the cell divides and forms two
new genetically identical nuclei.
� This takes place over the four phases of mitosis
and towards the end there is a division of the
cytoplasm and all its contents.
� Then the cell begins to form two separate new
daughter cells, each containing one nucleus
and they are an exact copy of each other.
� stage is often divided into:
� early and late prophase
� or there is prophase and then prometaphase.
� the chromatin (DNA) begins to condense by
super-coiling.
� Spindle fibres begin to form from the pair of
centrioles in animal cells that begin to move
to opposite poles of the cell.
� The shorter spindle fibres resemble stars so
at this point they are referred to as “asters”.
� The nuclear envelope surrounding the
nucleus begins to dissolve.
� the DNA has condensed to form dark chromosomes consisting of two identical sister chromatids which are very visible.
� The sister chromatids are joined in the center by a centromere.
� The centrioles have each arrived at either pole and the spindle fibres which are composed of microtubules extend out to the equator (middle) of the cell.
� The nuclear envelope has now completely disappeared.
� During this stage of mitosis, the spindle fibres attach to the chromosomes (sister chromatids) at the centromere.
� The chromosomes are guided by the spindle fibres to line up along the equatorial plate in the cell.
� One spindle fibre microtubule from each pole is attached to each of the sister chromatids.
� This is the longest phase in mitosis lasting about 20 minutes.
� During this phase of mitosis the spindle
fibres begin pulling the sister chromatids to
opposite poles.
� The chromatids separate at the centromere
and are pulled toward opposite ends of the
cell as the spindle fibres shorten.
� This phase is very short lasting only a few
minutes.
� During this phase in mitosis, the
chromosomes have arrived at each end and
a nuclear membrane begins to form around
them.
� The chromosomes uncoil and become less
dense which makes them no longer visible.
� The spindle fibres begin to break down and
the process of cytokinesis begins.
� This involves the division of the cytoplasm
and all its contents.
� In animal cells a cleavage furrow starts to
develop while a cell plate begins to form in a
plant cell which divides the cell into two
new daughter cells.
� The process of cytokinesis is often referred
to as late telophase.
� http://www.sumanasinc.com/webcontent/
animations/content/mitosis.html
� Mitosis and Cytokinesis:
http://highered.mcgraw-
hill.com/sites/0072495855/student_view0
/chapter2/animation__mitosis_and_cytokin
esis.html
� Mitosis in plants is very similar to
animals with 2 exceptions:
� plant cells lack centrioles
� plant cells form a cell plate between the
two daughter cells in telophase.
� During the mitosis the nucleus of the parent
cell is divided equally to produce two
daughter cells with identical genetic
information.
� The DNA, referred to as chromosomes
during mitosis, was replicated during
interphase of the cell cycle.
� A cell will replicate its DNA when it is
preparing to divide.
� This ensures that each new cell produced
during mitosis gets an equal and identical
copy of the cell’s DNA.
� Eukaryotic cells use the process of mitosis when identical cells are required.
� This can be during growth of an organism, when there has been tissue damage that needs to be repaired, or when an organism reproduces asexually.
� This also occurs during embryonic development when the zygote begins mitotic cell division and the organism begins to grow and develop.
� http://www.youtube.com/watch?v=HYKesI
9jL8c
� Draw Labelled Diagrams of the four stages
of mitosis in an animal cell with 4
chromosomes. (5 marks)
� A chemical called colchicine disrupts the
formation of microtubules. What effect
would this drug have on a cell going through
mitosis?
� If a parent cell has 24 chromosomes, how
many chromatids would be present during
metaphase of mitosis?
� Explain where cytokenisis occurs in the cell
cycle.