Question

Which one of the following lacks an active site of RNA polymerase?
A. αα'β2σ
B. αββ′σ
C. αα'β, β′σ
D. α2 ββ′

Answer 1

Hint: The above options mentioned are the core enzymes. It has five core units (390,000D) and a 6th subunit.

Step by step answer:
The DNA dependent RNA polymerase is a large and complex holoenzyme. It has five core units (390,000D) and a 6th subunit. The five core units are the two copies of the alpha subunit, one copy of each beta (β), beta prime (β’), and omega (σ) subunit. The sigma subunit carries the active site of the RNA polymerase enzyme and binds transiently to the core to direct the enzyme towards the specific binding sites on the DNA.

Additional Information:
An apoenzyme is an inactive enzyme. The activation of the enzyme occurs upon binding with an organic or inorganic cofactor/ coenzyme. Holoenzyme is the apoenzyme together with its cofactor (holoenzyme = apoenzyme + Cofactor). The holoenzyme is catalytically active and shows all the properties of enzyme dynamics. RNA polymerase (RNAP) is an enzyme that is required for the synthesis of mRNA (messenger RNA) from a DNA template. Using the enzyme helicase, the RNA polymerase/ RNAP opens the double-stranded DNA locally. This is done so that only one strand of the exposed nucleotides can be used as a template for the synthesis of RNA (to avoid complementary proteins). This process is called transcription.
All eukaryotes have three different types of RNA polymerases (RNAPs). Each of them is responsible for the transcription of different types of genes. RNA polymerase I transcribe the rRNA (ribosomal RNA) genes, RNA polymerase II transcribes mRNA, miRNA (micro RNA), snRNA (small nuclear RNA), and snoRNA genes. RNA polymerase III transcribes the tRNA (transport RNA) and 5S rRNA genes
The active site of an enzyme is the peptide sequence where the substrate attaches to get metabolized

Hence option D is correct.

Note: All eukaryotes have three different types of RNA polymerases (RNAPs). RNA polymerase I, RNA polymerase II, and RNA polymerase III.