1)Consider the lac operon when filling out the following table. Indicate whether
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Question
1)Consider the lac operon when filling out the following table. Indicate whether the lacZ gene will be expressed under the following conditions:
2)Label each figure depicting the different levels of DNA packaging. Which would you expect to have the most gene expression and the least?
3)Describe nucleosome remodeling and how it affects gene expression, include histone tails in your answer.
Genotype Glucose Present Transcription of lacZ? (Yes or No & High/moderate Lactose Present Functional beta- galactosidase (Yes or No Yes 0 Yes Yes 0 Yes 0 Yes Yes 0 Yes Yes Yes 0 Yes 0Explanation / Answer
Please find the answers below:
Answer 1: The lac operon is an inducible operon which is expressed in presence of the substrate. Generally, lactose represents to be the substrate for this system and the operon is expressed when the system contains lactose and no glucose. Presence of glucose acts as a negative regulator for this system leading to depression in the system. On the other hand, presence of lactose provides positive feedback and induces the RNA polymerase to scan the cistron and induce gene expression. Thus, the presence or absence of gene expression in different cases of the table can be found as below:
Transcription Functional enzyme
Answer 2: The different types of DNA packaging levels range from primary DNA duplex, secondary coilded structures in the form of solenoids, tertiary nucleosomal structure and quarternary chromosomal structure. Thus, the correct labels can be found as below:
Since the primary structure is most easily accessible by the transcriptional machinery, the linear structure would show maximum gene expression. On the other hand, due to compact binding of the DNA in chromosomal quarternary structure, the gene expression would be least as the transcriptional machinery would have no access to DNA.
Answer 3: A nucleosome represents a tertiary structure of DNA compaction in which nearly 250 base pair length of DNA is wounded over an octamer of proteins called histones. Each octameric nucleosome is attached to next nucleosome by a linear extension of DNA. These histones carry N and C termini which are composed of specific and highly conserved amino acids. Specifically, the histone molecule's tails show extreme conservation of the sequences. Any chemical/biological modification in these tails or amino acids thereof promote direct alteration in the extent of gene expression. For example, methylation of these tails cause compaction of the nucleosome and hence downregulate gene expression. On the other hand, acetylation or phosphorylation of these tails and amino acids thereof promotes loosening of the chromatin to enahance gene expression.
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