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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
