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

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

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

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

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

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

The Process of Condensation

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

Condensation Illustrated

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

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

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