Experimental evidence demonstrates that the nucleosomes present in a cell after the completion of S phase are composed of some 'old' histone dimers and some newly synthesized histone dimers. Describe the general design for an experiment that uses a protein label such as ³⁵S to show that nucleosomes are often a mixture of old and new histone dimers following DNA replication.

Key Concepts

Nucleosome Structure

Nucleosomes are the fundamental units of chromatin, consisting of DNA wrapped around a core of histone proteins. Each nucleosome is made up of two copies of four different histone proteins (H2A, H2B, H3, and H4), forming an octamer. Understanding nucleosome structure is essential for grasping how histones can be old or newly synthesized after DNA replication.

DNA Replication and Histone Dynamics

During DNA replication, the original histones are distributed between the two daughter strands, while new histones are synthesized to fill in the gaps. This process results in nucleosomes that contain a mix of old and new histone dimers. Recognizing this dynamic is crucial for designing experiments that track histone incorporation into nucleosomes post-replication.

Protein Labeling Techniques

Protein labeling techniques, such as using radioactive isotopes like ³⁵S, allow researchers to trace the incorporation of specific proteins into cellular structures. By labeling newly synthesized histones, one can distinguish between old and new histone dimers in nucleosomes. This method is vital for demonstrating the mixture of histone types in nucleosomes after DNA replication.