Q19 / 180 · AIIMS 2018 (26 May) · Botany

Thermococcus, Methanococcus and Methanobacterium exemplify

  • A
    bacteria whose DNA is relaxed or supercoiled but which have a cytoskeleton as well as mitochondria
  • B
    bacteria that contain a cytoskeleton and ribosomes and endoplasmic reticulum
  • C
    archaebacteria that contain protein homologous to eukaryotic core histones
  • Correct answer
    D
    archaebacteria that lack any histones resembling those found in eukaryotes but whose DNA is supercoiled.

Solution

Thermococcus, Methanococcus and Methanobacterium exemplify archaebacteria that lack any histones resembling those found in eukaryotes but whose DNA is negatively supercoiled. Archaebacteria do not have a nucleus, the genetic material floats freely in the cytoplasm. They consist of ribosomal RNA. DNA contains a single, circular molecule, which is compact and tightly wound. No protein is associated with DNA. The archaebacterial cell may contain plasmids, which are small, circular pieces of DNA and have a highly negatively supercoiled DNA.

Hence, the correct answer is option: 'D'.

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