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Exam Review
Reproduction
The Cell Cycle
• The Cell Cycle takes place in the
nucleus of the cell.
• The Cell Cycle is the continuous
process of mitosis, cell division and
interphase.
Interphase
• Longest phase of the cell cycle.
• Cell growth and DNA replication
occur during this phase.
Mitosis
• Mitosis results in the separation of
replicated DNA into 2 identical sets
of DNA, one for each new cell.
• Consists of 4 phases:
– Prophase, Metaphase, Anaphase and
Telophase
Phases of Mitosis
• Prophase: Nuclear membrane
disappears, genetic material
becomes visible and spindle fibres
form.
• Metaphase: Spindle fibres line the
double stranded chromosomes along
the middle of the cell.
• Anaphase: Spindle fibres pull
double stranded chromosomes
apart.
• Telophase: Single stranded
chromosomes reach opposite ends
of the cell. Spindle fibres disappear
and the nuclear membrane reforms.
At this point there are 2 nuclei in
one cell.
Cell Division
• Cytokinesis: The process of the
pinching in of cytoplasm separating
the cell into 2 new identical cells.
Cancer and the Cell Cycle
• When a cell begins to divide
uncontrollably the result is cancer.
• A cancerous cell becomes stuck in
the cell division phase of mitosis.
Since the cell does not enter
interphase, DNA is not replicated,
resulting in new cells being
produced without all of the
instructions.
Meiosis
• Meiosis occurs only in reproductive
cells called gametes; eggs and sperm
cells.
• Gametes are haploid, which means
they have half the number of
chromosomes than regular body or
somatic cells.
• Somatic cells have a diploid number
of chromosomes.
Meiosis
• The process of meiosis ensures that
each gamete has only one half set of
chromosomes.
• Meiosis also ensures that each
gamete has a different combination
of chromosomes present before
meiosis.
Phases of Meiosis
• Meiosis consists of 2 stages:
Meiosis I and Meiosis II.
• In Meiosis I there are 2 sets of
double stranded chromosomes.
• These sets match up in homologous
pairs.
Meiosis I
• Prophase I: Single strands from
each double stranded chromosome
cross over and exchange parts of
DNA.
• Metaphase I: Homologous pairs line
up along the middle of the cell.
• Anaphase I: Homologous
chromosomes are pulled to opposite
ends of the cell.
• Telophase I: Cytoplasm divides and 2
daughter cells are formed (each cell
contains one from each pair of homologous
chromosomes).
Meiosis II
• Prophase II: Nuclear membrane
disappears.
• Metaphase II: Chromosomes lineup
along middle of cell.
• Anaphase II: double stranded
chromosomes are separated and
chromatids are pulled to opposite
ends of the cell.
• Telophase II: Cytoplasm pinches in
and cell divides producing 4 haploid
daughter cells.
DNA
• DNA: Deoxyribonucleic acid
• Genetic information is contained in
DNA.
• Chromosomes are made up of tiny
DNA molecules.
What does DNA do?
• DNA contains the “blueprints” for the
cell.
• DNA gives directions to your cells to
either repair damaged cell parts or to
make new cells.
• DNA tells the cell how to respond to
changes in their environment and how to
respond to messages sent by other cells.
Structure of DNA
• DNA is made up of many
nucleotides.
• A nucleotide consists of a
phosphate, a sugar and a nitrogen
base.
• The sugar in DNA is called
deoxyribose.
• There are 4 nitrogen bases:
–
–
–
–
Adenine
Thymine
Cytosine
Guanine
• Adenine and Thymine always pair together.
• Cytosine and Guanine always pair together.
Sugar
Phosphate
Sugars and
phosphates
molecules make up
the sides of the
ladder to give
DNA its shape.
The rungs
of the
ladder are
made up of
nitrogen
bases.
Nitrogen
bases
Importance of DNA
• DNA removal or duplication can
help scientists and individuals in
many ways:
–
–
–
–
–
–
Elimination of harmful genes
Determining Paternity
Forensics (Who done it?)
Genetic Screening
Cloning
Trait Selection