Question

Below is a form of chromatin often referred to as beads on a string. Use this image to answer the questions.Referring to the image, there appears to be a span of 13 beads present. Ignoring the DNA before the first bead and after the 13th bead, how much DNA is present in the photo? (Assume ~54 bp in the linker region)

Answer 1

There are 2559 base pairs of DNA present in the photo, which includes 13 nucleosomes, each with approximately 147 base pairs of DNA wrapped around histone proteins, and 12 linker DNA segments, each about 54 base pairs long.

Step-by-step explanation:

The student is asking about the structure of chromatin in the context of DNA packaging within a cell nucleus. Specifically, they are focusing on a structure known as "beads on a string," where the beads represent nucleosomes and the string represents the linker DNA between them.

Calculation of DNA Length in Nucleosomes

Based on the provided information, to calculate the amount of DNA present in the photo with 13 nucleosomes and excluding the DNA before the first bead and after the 13th bead:

• Each nucleosome consists of DNA wrapped around histone proteins, and this wrapped DNA is approximately 147 base pairs long.
• Linker DNA, which connects nucleosomes, is approximately 54 base pairs.
• To find the total length of DNA present in the 13 nucleosomes, we add the DNA length in the nucleosomes and the linker DNA between them:
• (13 nucleosomes * 147 base pairs/nucleosome) + (12 linker DNA segments * 54 base pairs/linker DNA) = 1911 + 648 = 2559 base pairs

Therefore, excluding the DNA before the first bead and after the 13th bead, there are 2559 base pairs of DNA present in the photo.