CHAPTER 1
Cell Cycle, Cell Division and Structure of Chromosomes
1.1 Introduction
Every organism, whether simple or complex, starts its life as a single cell. This cell
undergoes repeated divisions to form a multicellular body. The process of formation
of new cells from pre-existing cells is known as Cell Division. In this chapter, we
explore the intricate details of how cells prepare for this event and the structural
changes that occur within the nucleus.
Did You Know?
The human body has about 37.2 trillion cells. Almost all of these were produced
by the division of a single fertilized egg (zygote).
1.2 Structure of Chromosome
Chromosomes are the carriers of heredity. When a cell is not dividing, the DNA
exists as a tangled mass of threads called Chromatin. During cell division, these
threads condense into thick, rod-like structures called chromosomes.
Chemical Composition
• DNA (Deoxyribonucleic Acid): About 40%
• Histones (Proteins): About 60%
Page 1
, 3D VISUAL: NUCLEOSOME STRUCTURE (DNA wrapping Histones)
Figure 1.1: Organization of DNA into Nucleosomes and Chromatin fiber.
Page 2
Cell Cycle, Cell Division and Structure of Chromosomes
1.1 Introduction
Every organism, whether simple or complex, starts its life as a single cell. This cell
undergoes repeated divisions to form a multicellular body. The process of formation
of new cells from pre-existing cells is known as Cell Division. In this chapter, we
explore the intricate details of how cells prepare for this event and the structural
changes that occur within the nucleus.
Did You Know?
The human body has about 37.2 trillion cells. Almost all of these were produced
by the division of a single fertilized egg (zygote).
1.2 Structure of Chromosome
Chromosomes are the carriers of heredity. When a cell is not dividing, the DNA
exists as a tangled mass of threads called Chromatin. During cell division, these
threads condense into thick, rod-like structures called chromosomes.
Chemical Composition
• DNA (Deoxyribonucleic Acid): About 40%
• Histones (Proteins): About 60%
Page 1
, 3D VISUAL: NUCLEOSOME STRUCTURE (DNA wrapping Histones)
Figure 1.1: Organization of DNA into Nucleosomes and Chromatin fiber.
Page 2
