Question

True chromosomes absent in prokaryotes due to the absence of

• A. Nucleus
• B. Nucleolus
• C. Histone
• D. All of the above

Answer 1

Answer: (C)

Histone

Histones are highly alkaline proteins found in eukaryotic cell nuclei that package and order the DNA into structural units called nucleosomes. They are the chief protein components of chromatin, acting as spools around which DNA winds, and play a role in gene regulation. Without histones, the unwound DNA in chromosomes would be very long (a length to width ratio of more than 10 million to 1 in human DNA). For example, each human cell has about 1.8 meters of DNA, but wound on the histones it has about 90 micrometers (0.09 mm) of chromatin, which, when duplicated and condensed during mitosis, result in about 120 micrometers of chromosomes. In prokaryotic cells, no organized nucleus is found. Due to the absence of histone proteins, chromosomes are also not found. Instead, a fibrillar area called nucleoid is found attached to the inner side of the membrane. Nucleoid is occupied by an extremely involuted double stranded circular DNA. Nuclear membrane and nucleolus are absent in nucleoid.