)which of the following statements about transcriptional regulators is false? (a) transcriptional regulators usually interact with the sugar–phosphate backbone on the outside of the double helix to determine which dna sequence to bind. (b) transcriptional regulators will form hydrogen bonds, ionic bonds, and hydrophobic interactions with dna. (c) the dna-binding motifs of transcriptional regulators usually bind in the major groove of the dna helix. (d) the binding of transcriptional regulators generally does not disrupt the hydrogen bonds that hold the double helix together.

The false statement is: (a) Transcriptional regulators usually interact with the sugar–phosphate backbone on the outside of the double helix to determine which DNA sequence to bind.

Transcriptional regulator or factor is protein with the ability to control and regulate gene expression at the transcription level by binding to DNA. Transcriptional factors have domain-DNA-binding domain which contains structural motif that recognizes DNA and it is responsible for the attachment to specific DNA sequence. It usually binds to the DNA major groove (hydrogen bonding) because it is less degenerate than that of the DNA minor groove.  

Transcriptional factors also contain trans-activating domain for the binding of other proteins and signal-sensing domain for the detection of external signals.

organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.