Transcript CELLS

The Cell Cycle
The life cycle of a cell is called the cell
cycle.
The cell cycle begins when the cell is
formed and ends when the cell
divides and forms new cells.
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Review 1
• The regular cycle of growth and
division that cells undergo is called
___.
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How does a cell make more cells?
Making more prokaryotic cells…
Cell division in bacteria is called binary
fission, which means “splitting into
two parts.”
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How does a cell make more cells?
Making more eukaryotic cells…
The eukaryotic cell cycle includes three
stages
• Interphase
• Mitosis
• cytokinesis
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The Cell Cycle
In the first stage, called interphase, the
cell grows and copies its organelles
and chromosomes.
After each chromosome is duplicated
or undergoes replication, the two
copies are called chromatids.
Chromatids are held together at a
region called the centromere.
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DNA Replication during Interphase
Before a cell divides it must make a
copy of its DNA.
The DNA of a cell is organized into
structures called chromosomes.
Copying chromosomes ensures that
each new cell will be an exact copy
of its parent cell.
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Review 2
• What is the process by which a cell
makes an exact copy of its DNA?
• Replication occurs during what stage
of the cell cycle?
• So a cell makes a copy of its DNA or
chromosomes during what stage of
the cell cycle?
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The Cell Cycle
In the second stage, the chromatids
separate and a cell’s nucleus
divides to form two identical nuclei.
The process of chromosome
separation is called mitosis which
takes place in four phases.
Mitosis ensures that each new cell
receives a copy of each
chromosome.
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Mitosis 1… Prophase
The nuclear membrane dissolves.
Chromosomes condense into rodlike
structures.
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Mitosis 2… Metaphase
The chromosomes line up along the
equator of the cell.
Homologous chromosomes pair up.
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Mitosis 3… Anaphase
The chromatids separate and move to
opposite sides of the cell.
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Mitosis 4… Telophase
A nuclear membrane forms around
each set of chromosomes and the
chromosomes unwind.
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Review 3
• A cell’s nucleus divides to form two
identical nuclei during the stage of the
cell cycle known as ___.
• What are chromatids?
• What forms around the chromatids
during mitosis?
• What is the correct order for the
phases of mitosis?
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The Cell Cycle
In the third stage called cytokinesis, the
cytoplasm divides and the cell splits
into two cells.
Two new daughter cells are formed and
these cells are identical to each
other and to the original cell.
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Cytokinesis in Plant Cells
In eukaryotic cells that have a cell wall,
a cell plate forms in the middle of
the cell.
The cell plate becomes the new cell
membranes that separate the new
cells.
After the cell splits into two, a new cell
wall forms where the cell plate was.
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Review 4
• The final stage of the cell cycle,
during which the cytoplasm divides, is
called ___.
• What happens during cytokinesis in
animal cells?
• During cytokinesis in plant cells, a(n)
___ forms across the middle of the
cell. What forms this?
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More about DNA Replication
DNA replication ensures that each
daughter cell will have the genetic
information it needs to carry out its
activities.
A DNA molecule looks like a twisted
ladder, or spiral staircase.
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More about DNA Replication
The two sides of the DNA ladder are
made up of molecules of a sugar
called deoxyribose, alternating with
molecules known as phosphates.
Each rung is made up of a pair of
molecules called nitrogen bases.
DNA has four kinds of nitrogen bases:
adenine, thymine, guanine, and
cytosine.
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More about DNA Replication
The bases on one side of the ladder
pair with the bases on the other
side.
Adenine (A) only pairs with thymine (T).
Guanine (G) only pairs with cytosine
(C).
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More about DNA Replication
DNA replication begins when the two
sides of the DNA molecule unwind
and separate.
Next, nitrogen bases that are floating in
the nucleus pair up with the bases
on each half of the DNA molecule.
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Review 5
• A DNA molecule is shaped like a ___.
• During DNA replication, adenine (A) always pairs with
___.
• Each rung of the DNA ladder is made of ___.
• In a DNA molecule, quanine always pairs with ___.
• The sides of the DNA ladder are made of molecules of
deoxyribose and ___.
• Define DNA replication and explain its function.
• Suppose one side of a piece of DNA contains the
following series of nitrogen bases: A-C-G-C-T-T. What is
the series of nitrogen bases on the other side of that
piece of DNA? Explain how you arrived at your answer.
• What might happen if prior to cell division, a cell did not
completely replicate, or copy, its DNA?
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The Cell Cycle
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