1. Eukaryotic Chromosomes Change in form through the Cell Cycle
Chromosome Structure
Eukaryotic Chromosomes
Change in form through the
Cell Cycle

2. Objective #1 Describe the structure of Chromosomes in Eukaryotes.
Explain how the structure changes at different times during the cell cycle

3. Historical Perspective
Before there was any knowledge or understanding of molecular genetics, there were people with microscopes who looked at cells
Frequently they stained cells to see the contents of the cell more clearly
There were consistencies in the structures they observed, which they gave names

4. Colored Things in the Cell
Chromatin = Colored Material
Chromosome = Colored Body

5. Chromatin Colored material “Chromo” means “color”
Consists of DNA, RNA, and proteins
The DNA is “extended”
Extended = Unwound
The DNA is too thin to see individual molecules through a microscope

6. Chromosomes Colored Bodies “soma” means “body”
Also consist of DNA, RNA and Protein
The DNA is “condensed” coiled, supercoiled and packed into a denser structure
Chromosomes are visible as individual structures through a microscope

7. The Process of Condensation

8. Condensation
The electron micrograph shows a part of a condensed strand of DNA
The process of Condensation involves wrapping the DNA around spools of protein called Histone

9. Condensation Illustrated

10. Significance of Condensation
When extended, the DNA double helix is exposed
Remember, DNA is the genetic material
Extended DNA is in a form that allows the Genetic code to be used to provide information to the cell

11. Significance of Condensation
When extended, the DNA double helix is NOT exposed
Condensed DNA is in a form that prevents the Genetic code from being used to provide information to the cell
But the DNA is protected from structural damage

12. Summary Chromatin Chromosomes DNA is extended
DNA is not visible as individual structures
The nucleus appears as a ball of amorphous colored material through the microscope
The DNA Genetic Code is available for the cell to use
DNA is condensed
DNA is visible as individual structures
The nucleus is no longer a separate structure in the cell, but the individual chromosomes are
The DNA Genetic Code is not available any longer