Question

What are those structures that appear as 'beads-on-string' in the chromosomes when viewed under electron microscope?

• A. base pairs
• B. genes
• C. nucleotides
• D. nucleosomes

Answer 1

The correct option is D

nucleosomes

The correct option is D.

Explanation of the correct option:

1. Chromosomes are the threadlike structures found inside the nucleus, which will be placed in a network form responsible for carrying proteins and nucleic acids and genetic information in the form of genes from one generation to the next generation.
2. An electron microscope is a type of microscope in which the very smallest structures and molecules can be visualized on a computer.
3. The structures that appear as beads-on-string in the chromosomes are nucleosomes.
4. Nucleosomes are a group of base pairs and proteins (histone) that are wrapped around DNA.
5. A nucleosome is the fundamental structural unit of DNA packing in eukaryotes.
6. A nucleosome is the most fundamental, repeating structural element of chromatin.
7. The chromatin structure resembles beads on a thread when expanded and seen under a microscope.

Explanation of the incorrect options:

Option A:

There are four bases Adenine (A), Guanine (G), Cytosine (C), and Thymine (T). These bases are found in pairs on the DNA where A pairs with T and C pairs with G.

Option B:

Genes are the smallest unit of chromosomes.

Option C:

Nucleotides are building blocks of DNA where A, T, G, and C are found with phosphate and sugar molecules.

Final Answer: Hence, nucleosomes are those structures that appear as 'beads-on-string' in the chromosomes when viewed under an electron microscope.