Cell Cycle and Reproduction

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Cell Cycle and Reproduction

• Lecture 6 NatSci II
• Josephine B. Guerrero, MD
• Asst. Professor, Department of Biology

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Chromosomes, Bacterial
Note Closed, Circular, Singular, and Haploid
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Chromosomes, Eukaryotic
chromosome
chromatin
DNA
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Cells have different life spans and life cycles.

• The Young and Restless
• Skin cells live for about a month. Thus, they
  must be replaced.
• If you get a cut, new cells are needed for the
  wound to heal.
• If you fracture your leg, new cells in the bone
  will be needed to repair the injury.
• The Wise and Mature
• You are born with most of the brain cells that
  you will ever have.
• Woman are born with all of the eggs cells that
  they will ever carry.

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Cells have different life spans and life cycles.

• The Young and Restless
• Skin cells live for about a month. Thus, they
  must be replaced.
• If you get a cut, new cells are needed for the
  wound to heal.
• If you fracture your leg, new cells in the bone
  will be needed to repair the injury.
• The Wise and Mature
• Your brain cells are not replicating at the same
  rate throughout your life, so hold on to what
  youve got.
• Woman are born with all of the eggs cells that
  they will ever carry.

Cell is doing its job
The Cellular Life Cycle
Cell is dividing to generate new cells.
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Cells have different life spans and life cycles.
Cell is doing its job
The Cellular Life Cycle

• Cell division is critical because
• Dying cells must be replaced in certain tissues.
• Injuries must be healed.
• Growth from the time of conception requires rapid
  increase in the number of cells.

Cell is dividing to generate new cells.
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There are two types of cell division.

• Mitosis
• Makes an exact copy of a cell through cell
  division.
• The new cells (daughter cells), have the same
  amount of DNA as the old (mother) cell.
• This occurs all over your body.
• Meiosis
• Creates cell with only half the amount of DNA
• Why would you want to do this?

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The Human life cycle requires both mitosis and
meiosis.
Fusion of egg and sperm restores the number of
chromosomes.
haploid (n)
Sexual Reproduction
Egg cell
Sperm cell
MEIOSIS
FERTILIZATION
diploid (2n)
Development And Growth
Lots of MITOSIS
Figure 8.13
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There are two types of cell replication in the
normal human life cycle.

• Mitosis to form a human skin cell (for example).
• A skin cell with 46 chromosomes divides,
  producing two cells that each still have 46
  chromosomes.
• These cells are said to be diploid (they have the
  normal number of chromosomes).
• Meiosis to form a human egg or sperm.
• A cell with 46 chromosome divides in such a way
  as to produce an egg or sperm with 23
  chromosomes.
• These eggs and sperm are said to be haploid (they
  have half the normal of number of chromosomes.

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The Cellular Life Cycle

• Interphase
• The cell is doing its normal activities and, for
  a time (S), uses energy to replicate its DNA.
• The Mitotic Phase
• Over several stages, the cell divides.

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The Cellular Life Cycle

• The Mitotic Phase
• Over several stages, the cell divides.

Figure 8.1A
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The Cellular Life Cycle
Figure 8.1A
The goal of Mitosis is two make two cells that
are diploid (each has two copies of every
chromosome) and that have all the organelles to
function.
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The Cellular Life Cycle

• The S phase
• In order for each cell to have the same DNA, the
  DNA must replicate.

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DNA Replication
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DNA Replication
The hydrogen bonds between complementary bases
break. The enzyme helicase facilitates the
untwisting, and special proteins keep it from
twisting back up.
Figure 10.4B
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DNA Replication
Parental strand
Origin of replication
Daughter strand
Bubble
Two daughter DNA molecules
Figure 10.5A
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DNA Replication
DNA polymerasemolecule
3?
5?

• The enzyme DNA polymerase moves along a strand
  and reads the bases. The appropriate complement
  is brought in and the new nucleotides are bound
  together through dehydration synthesis.

5? end
Daughter DNA
Parental DNA
5?
3?
3?
P
5?
5?
P
3?
Figure 10.5C
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DNA Replication Review
DNA polymerasemolecule
3?
5?

• The leading strand is made continuously, while
  the lagging strand is made in chunks. The chunks
  are linked together by DNA ligase.

5? end
Daughter strandsynthesizedcontinuously
Parental DNA
5?
3?
Daughter strandsynthesizedin pieces
3?
P
5?
5?
P
3?
DNA ligase
Figure 10.5C
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All 46 chromosomes replicate.
For most of the life of the human cell, there are
46 chromosomes (seen here in homologous pairs).
During replication, each of these chromosomes is
copied. The cell has 92 chromosomes until it
divides.
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All 46 chromosomes replicate.
Each of the 46 original chromosomes is attached
to its copy at the centromere. The two identical
chromsomes are called sister chromatids.
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The Cellular Life Cycle

• Mitotic Phase (M)
• Once the cell has two copies of all the
  chromosomes, then it can divide. This occurs in
  specific stages.

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The Stages of the Mitotic Phase

• Prophase and Prometaphase
• Metaphase
• Anaphase
• Telophase and Cytokinesis
• One blends into another.

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The Stages of the Mitotic Phase

• Prophase and Prometaphase
• The DNA compacts (supercoils).
• Duplicated centrosomes head to each pole and
  spindles begin to form.
• The nuclear membrane and nucleolus breakdown.

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The Stages of the Mitotic Phase

• Metaphase
• The spindle fibers attached to the duplicated
  chromsomes and drag them to the center of the
  cell (the equator).

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The Stages of the Mitotic Phase

• Anaphase
• The sister chromatids separate and are pulled to
  opposite sides of the cell as the spindles
  shorten. Each side now has the exact same set of
  chromosomes.

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The Stages of the Mitotic Phase

• Telophase and Cytokinesis
• New nuclear membranes and nucleoli form around
  the two sets of chromosomes.
• The cytoplasm begins to divide and the cells
  pinch off into two.

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After the mitotic phase, the cell reenters
interphase.

• During all of interphase, the cell looks like
  what we are used to seeing. The DNA is in the
  nucleus. There is a clear boundary between the
  nucleus and the cytoplasm.

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The Stages of the Mitotic Phase
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The Stages of the Mitotic Phase
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Mitosis in plant cells
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