Lecture 18 - Cell Cycle-Regulation | Cell Biology- Botany PDF Download

 Page 1


Cell Cycle - Regulation 
Institute of Lifelong Learning, University of Delhi 0 
 
 
 
 
 
 
 
 
 
Lesson:  Cell Cycle: Regulation 
Lesson Developer: Rama Sisodia 
College/ Department: Department of Botany, Maitreyi College, University 
of Delhi 
  
Page 2


Cell Cycle - Regulation 
Institute of Lifelong Learning, University of Delhi 0 
 
 
 
 
 
 
 
 
 
Lesson:  Cell Cycle: Regulation 
Lesson Developer: Rama Sisodia 
College/ Department: Department of Botany, Maitreyi College, University 
of Delhi 
  
Cell Cycle - Regulation 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents       
Chapter:  Cell Cycle - Regulation 
? Introduction  
? Cell cycle regulation by internal check points 
? G1 check point 
? G2 check point 
? M check point 
? Regulator molecules of the cell cycle 
? Cyclin dependent kinases 
? Identification 
? Regulation 
? Classes of Cdks and Cyclins  
? Cdk regulation of M phase 
? Extracellular signals 
? Checkpoint control 
? DNA damage induced check points 
? Spindle assembly check point 
 
? Regulation of meiosis 
? Fertilization 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Readings 
 
 
 
 
Page 3


Cell Cycle - Regulation 
Institute of Lifelong Learning, University of Delhi 0 
 
 
 
 
 
 
 
 
 
Lesson:  Cell Cycle: Regulation 
Lesson Developer: Rama Sisodia 
College/ Department: Department of Botany, Maitreyi College, University 
of Delhi 
  
Cell Cycle - Regulation 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents       
Chapter:  Cell Cycle - Regulation 
? Introduction  
? Cell cycle regulation by internal check points 
? G1 check point 
? G2 check point 
? M check point 
? Regulator molecules of the cell cycle 
? Cyclin dependent kinases 
? Identification 
? Regulation 
? Classes of Cdks and Cyclins  
? Cdk regulation of M phase 
? Extracellular signals 
? Checkpoint control 
? DNA damage induced check points 
? Spindle assembly check point 
 
? Regulation of meiosis 
? Fertilization 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Readings 
 
 
 
 
Cell Cycle - Regulation 
Institute of Lifelong Learning, University of Delhi 2 
Introduction 
An understanding of the mechanisms that control cell cycle is important not only for basic 
biology but also since it underlies the basis of studying cancer- the uncontrolled proliferation 
of cells. The transition from one phase to other of the cell cycle is very well coordinated and 
is under the control of extracellular signals as well as certain internal signals.  
Cell cycle regulation by internal checkpoints 
The progression of the cell cycle is regulated by check points in response to specific 
signals.  
 
Figure: Cell cycle check points 
Source: http://setarosite.org/images/biobook_images/Checkpoints1.jpg 
? G1 check point  
o Start a regulatory check point characterized in budding yeast Saccharomyces 
cerevisiae that occurs in G1 and controls the transition from G1 to S in 
response to signals like presence of nutrients, cell size and mating factors.  
 
Page 4


Cell Cycle - Regulation 
Institute of Lifelong Learning, University of Delhi 0 
 
 
 
 
 
 
 
 
 
Lesson:  Cell Cycle: Regulation 
Lesson Developer: Rama Sisodia 
College/ Department: Department of Botany, Maitreyi College, University 
of Delhi 
  
Cell Cycle - Regulation 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents       
Chapter:  Cell Cycle - Regulation 
? Introduction  
? Cell cycle regulation by internal check points 
? G1 check point 
? G2 check point 
? M check point 
? Regulator molecules of the cell cycle 
? Cyclin dependent kinases 
? Identification 
? Regulation 
? Classes of Cdks and Cyclins  
? Cdk regulation of M phase 
? Extracellular signals 
? Checkpoint control 
? DNA damage induced check points 
? Spindle assembly check point 
 
? Regulation of meiosis 
? Fertilization 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Readings 
 
 
 
 
Cell Cycle - Regulation 
Institute of Lifelong Learning, University of Delhi 2 
Introduction 
An understanding of the mechanisms that control cell cycle is important not only for basic 
biology but also since it underlies the basis of studying cancer- the uncontrolled proliferation 
of cells. The transition from one phase to other of the cell cycle is very well coordinated and 
is under the control of extracellular signals as well as certain internal signals.  
Cell cycle regulation by internal checkpoints 
The progression of the cell cycle is regulated by check points in response to specific 
signals.  
 
Figure: Cell cycle check points 
Source: http://setarosite.org/images/biobook_images/Checkpoints1.jpg 
? G1 check point  
o Start a regulatory check point characterized in budding yeast Saccharomyces 
cerevisiae that occurs in G1 and controls the transition from G1 to S in 
response to signals like presence of nutrients, cell size and mating factors.  
 
Cell Cycle - Regulation 
Institute of Lifelong Learning, University of Delhi 3 
 
 
Figure: Cell cycle regulation in Saccharomyces cerevisiae  
Source: http://commons.wikimedia.org/wiki/File:Ch14f5a.jpg 
 
? Similarly in animal cells a restriction point regulates the progression of cell 
cycle from G1 to S phase is controlled by extracellular signals like growth 
regulators. When the required growth factors are present the cell cycle 
progresses beyond the restriction point into the S phase. However in the 
absence of appropriate growth factors the cells enter a quiescent stage- Go and 
remain metabolically active but stop dividing and have reduced size. On 
availability of suitable growth factor these regain their ability to divide and 
reenter the cell cycle. 
 
 
Figure: Regulation of cell cycle in animal cells in response to growth factors 
Source: http://upload.wikimedia.org/wikipedia/commons/c/c2/Ch14f6.jpg 
Page 5


Cell Cycle - Regulation 
Institute of Lifelong Learning, University of Delhi 0 
 
 
 
 
 
 
 
 
 
Lesson:  Cell Cycle: Regulation 
Lesson Developer: Rama Sisodia 
College/ Department: Department of Botany, Maitreyi College, University 
of Delhi 
  
Cell Cycle - Regulation 
Institute of Lifelong Learning, University of Delhi 1 
 
Table of Contents       
Chapter:  Cell Cycle - Regulation 
? Introduction  
? Cell cycle regulation by internal check points 
? G1 check point 
? G2 check point 
? M check point 
? Regulator molecules of the cell cycle 
? Cyclin dependent kinases 
? Identification 
? Regulation 
? Classes of Cdks and Cyclins  
? Cdk regulation of M phase 
? Extracellular signals 
? Checkpoint control 
? DNA damage induced check points 
? Spindle assembly check point 
 
? Regulation of meiosis 
? Fertilization 
? Summary  
? Exercise/ Practice 
? Glossary 
? References/ Bibliography/ Further Readings 
 
 
 
 
Cell Cycle - Regulation 
Institute of Lifelong Learning, University of Delhi 2 
Introduction 
An understanding of the mechanisms that control cell cycle is important not only for basic 
biology but also since it underlies the basis of studying cancer- the uncontrolled proliferation 
of cells. The transition from one phase to other of the cell cycle is very well coordinated and 
is under the control of extracellular signals as well as certain internal signals.  
Cell cycle regulation by internal checkpoints 
The progression of the cell cycle is regulated by check points in response to specific 
signals.  
 
Figure: Cell cycle check points 
Source: http://setarosite.org/images/biobook_images/Checkpoints1.jpg 
? G1 check point  
o Start a regulatory check point characterized in budding yeast Saccharomyces 
cerevisiae that occurs in G1 and controls the transition from G1 to S in 
response to signals like presence of nutrients, cell size and mating factors.  
 
Cell Cycle - Regulation 
Institute of Lifelong Learning, University of Delhi 3 
 
 
Figure: Cell cycle regulation in Saccharomyces cerevisiae  
Source: http://commons.wikimedia.org/wiki/File:Ch14f5a.jpg 
 
? Similarly in animal cells a restriction point regulates the progression of cell 
cycle from G1 to S phase is controlled by extracellular signals like growth 
regulators. When the required growth factors are present the cell cycle 
progresses beyond the restriction point into the S phase. However in the 
absence of appropriate growth factors the cells enter a quiescent stage- Go and 
remain metabolically active but stop dividing and have reduced size. On 
availability of suitable growth factor these regain their ability to divide and 
reenter the cell cycle. 
 
 
Figure: Regulation of cell cycle in animal cells in response to growth factors 
Source: http://upload.wikimedia.org/wikipedia/commons/c/c2/Ch14f6.jpg 
Cell Cycle - Regulation 
Institute of Lifelong Learning, University of Delhi 4 
? G2 check point 
In contrast to these examples cell cycle is regulated by a check point that exists 
in the G2 phase and controls the progression into the M phase as seen in fission 
yeast Schizosaccharomyces pombe monitored by appropriate cell size and 
availability of nutrients. Similarly in vertebrate oocytes the control of cell cycle in 
G2 phase is seen in response to hormones and the cells remain arrested in G2 
phase until triggered to divide.  
? M check point 
A checkpoint exists at the end of the mitosis – the spindle assembly checkpoint 
that monitors the assembly and alignment of the spindle and therefore ensures 
that a complete set of chromosomes are distributed between the two newly 
formed daughter cells. 
 
In addition to these, several checkpoints in the G1, S, and G2 exist to ensure integrity of 
genome i.e. detect the presence of damaged and unreplicated DNA and coordinate the 
recruitment of repair machinery to these sites.  
 
 
 
Figure: The three main cell cycle checkpoints 
Source: ILLL Inhouse    
 
Animation: http://outreach.mcb.harvard.edu/animations/checkpoints.swf 
http://sites.sinauer.com/cooper5e/animation1603.html 
 
Regulator molecules of the cell cycle