copyright © by holt, rinehart and winston. all rights reserved. resources chapter menu chapter 5...

Copyright © by Holt, Rinehart and Winston. All rights reserved.

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Chapter 5

What You Will Learn, continued

• Cytokinesis differs in animals and plants.

• Cancer occurs when cells replicate abnormally.

Section 2 The Cell Cycle



Chapter 5

The Life of a Cell

• Your cells pass through different stages in their life cycle, which is called the cell cycle.

• The cell cycle results in two new cells that are exact copies of the original cell.

• The cell cycle begins when the cell is formed and ends when the cell divides to form two new cells.




Chapter 5

• Before a cell divides, it must make a copy of its DNA.

• The DNA of a cell is organized into structures called chromosomes.

• Copying the chromosomes ensures that each new cell receives all the DNA of the parent cell.


The Life of a Cell, continued



Chapter 5

• Prokaryotic cells are less complex than eukaryotic cells.

• Prokaryotes divide by binary fission.

• Binary fission means “splitting into two parts.”

• Each of the two new prokaryotic cells has a single, identical, circular chromosome.





Chapter 5

• Eukaryotic cells have many chromosomes, and have more DNA than prokaryotic cells do.

• The number of chromosomes varies.Fruit flies have 8, potatoes have 48, an humans have 46.

• Each chromosome has a similar pair, or homologous chromosome. – Humans have 23 pairs of homologous

chromosomes, for a total of 46.





Chapter 5

Control of the Cell Cycle

• Cells spend most of their lives in interphase, carrying out their functions.

• Feedback switches monitor the size and health of the cell. When a healthy cell reaches a certain size, the “GO” signal is given to divide.

• The feedback switches that control the stop and go signals are proteins.




Chapter 5

Control of the Cell Cycle, continued

• Since the directions for making proteins come from DNA, changes in the DNA can change the proteins.

• If the DNA is damaged, the stop and go signals may not function properly. Cells may begin dividing out of control.

• Cells dividing uncontrollably may form a tumor and become invasive. This is called cancer.




Chapter 5

• During mitosis, the chromatids separate so that each new cell receives a copy of each chromosome.

• Mitosis is divided into four phases: prophase, metaphase, anaphase, an telophase.


The Life of a Cell, MItosis



Chapter 5

Interphase

• Most metabolic activity takes place in Interphase• Cells increase in mass• Cell organelles such as ribosomes, mitochondria and

ER are duplicated• Chromosomes are duplicated or copied. Together

they are considered to be one chromosome comprising of two parts called sister chromatids.


Interphase



Chapter 5

Prophase

• During prophase, the long chromosomes condense into rod like structures.

• Sister chromatids are now visible

• Nuclear membrane and Nucleolus disappear

• Spindle begins to form• In animal cells centriole

pairs begin move to opposite side of the cell.




Metaphase

• During metaphase, the nuclear membrane dissolves

• Chromosomes with sister chromatids align at the cell’s equator (middle)



Anaphase

• During anaphase, the sister chromatids separate and move to opposite ends of the cell.

• The chromatid is now considered to be a full chromosome.



Telophase

• The spindle starts to disappear

• a new nuclear membrane forms around each set of chromosomes,

• the rodlike structures de-condense



Cytokenesis (animal cells)

• Cytokinesis is the division of cytoplasm and all of the organelles in the cytoplasm.

• During cytokinesis, the cell splits into two daughter cells.

• In eukaryotes without a cell wall, the cell is split by a pinching of the cell membrane

• Sister cells are both identical to the original cell.



Chapter 5

Cytokenesis (Plant Cell)

• In plant cells and other eukaryotes with cell walls, the cell is split by a cell plate that forms in the middle of the cell.

• The cell plate contains materials needed to make the cell membrane and cell wall between the daughter cells.




Section 2 The Cell CycleChapter 5

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cell cycle cells

cell cycle slide

cell divides

original cell

healthy cell

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