Transcript Cell Cycle
Chapter 5 Section 2 The Cell Cycle What You Will Learn, continued • Cytokinesis differs in animals and plants. • Cancer occurs when cells replicate abnormally. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 2 The Cell Cycle 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 menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 2 The Cell Cycle The Life of a Cell, continued • 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. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 2 The Cell Cycle The Life of a Cell, continued • 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 menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 2 The Cell Cycle The Life of a Cell, continued • 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 menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 2 The Cell Cycle 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 menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 2 The Cell Cycle 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 menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 2 The Cell Cycle The Life of a Cell, MItosis • 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. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 2 The Cell Cycle Interphase 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. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 2 The Cell Cycle 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. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Metaphase • During metaphase, the nuclear membrane dissolves • Chromosomes with sister chromatids align at the cell’s equator (middle) Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. 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. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Telophase • The spindle starts to disappear • a new nuclear membrane forms around each set of chromosomes, • the rodlike structures de-condense Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. 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 menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 2 The Cell Cycle 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. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 2 The Cell Cycle Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.