Question

can someone help solves these???

37. After looking at the genetic code table, you can tell that the degeneracy (or redundancy) in the genetic code is best illustrated by: A) stop codons. B) threonine (thr) codons. C) tryptophan (trp) codons. D) methionine (met) codons. E) operator sequences. 38. The phenomenon in D. melanogaster known as Position-Effect Variegation (PEV) provides powerful evidence that: A) DNA is the genetic material. B) posttranscriptional mechanisms regulate gene expression. C) transcriptional mechanisms regulate gene control. D) chromatin structure is unable to regulate gene expression. E) chromatin structure is able to regulate gene expression. 39. DNA elements that prevent the spreading of heterochromatin into adjacent euchromatic regions are called: A) enhancer blocking elements. B) euchromatin buffers. C) barrier insulators. D) barrier buffers. E) barrier-blocking elements.

Answer 1

37)

Few amino acids are encoded by more than one codon, thus, the genetic code is degenerate.

Stop codons do not code for any amino acid, thus, stop codons cannot best illustrate the degeneracy in the genetic code. Hence, the option (a) is incorrect.

Tryptophan and methionine codons just code for one amino acid each, therefore, the options (c) and (d) are incorrect.

Operator sequences are involved in the process of transcription, therefore, the option (e) is incorrect.

Threonine is encoded by four different codons (ACU, ACC, ACA, and ACG), therefore, the option (b) best illustrates the degeneracy in the genetic code.

Hence, option (b) is correct.

(38)

The PEV (Position-effect variegation) is a result of gene silencing in few cells due to transposition that results in abnormal juxtaposition with heterochromatin. The prevention of the gene expression by regulating the gene expression is known as gene silencing. The access of transcriptional machinery and transcription factors to the DNA sequences along with the promoter regions is regulated by the chromatin structure. Thus, chromatin structure and dynamics are important for gene expression.

Hence, the option (e) is correct.

(39)

The enhancer blocking elements interfere with the interaction between the promoter and enhancer when it is placed between them, whereas, barrier elements prevent or blocks the spreading/propagation of heterochromatin into the adjacent euchromatin region. Therefore, barrier insulators are the DNA elements that prevent the spreading of heterochromatic structures into the euchromatin regions.

Hence, the option (c) is the correct option.