#Question id: 2853
#Unit 2. Cellular Organization
Not all bacteria need to maintain their DNA in a negatively supercoiled state. Bacteria that prefer to grow at very high temperatures must expend energy. Which of the following observation found to be true?
A. Bacteria don’t need to expend energy to prevent their DNA from unwinding due to thermal denaturation
B. These bacterial organisms have a different topoisomerase called reverse gyrase
C. Reverse gyrase decrease the linking number of relaxed DNA in the presence of ATP
#Question id: 2854
#Unit 2. Cellular Organization
Negatively charged phosphate groups in the DNA backbone must be neutralized in order for folding of DNA to occur. In bacterial DNA, this charge neutralization is carried out by small positively charged molecules called polyamines. What proteins carry out this same function in eukaryotic cells?
#Question id: 2855
#Unit 2. Cellular Organization
Which statements are correct about lac operator;
I. The site bound by the Lac repressor.
II. The lac operator overlaps the promoter, and so the repressor bound to the operator physically prevents RNA polymerase from binding to the promoter and thus inhibit the RNA synthesis.
III. Have 21-bp sequence with twofold symmetric and is recognized by four subunits of Lac repressor, two binding to each half-site.
IV. CAP binds as a dimer to a site similar in length to that of the lac operator, but different in sequence. This site is located some 60 bp upstream of the start site of transcription.
#Question id: 2856
#Unit 2. Cellular Organization
Match the lac genes with their enzymes & functions;
|
lac genes |
Enzyme |
Functions |
|
lacZ |
b-galactosidase |
which rids the cell of toxic thiogalactosides that also get transported in by lacY. |
|
lacY |
thiogalactoside transacetylase |
which cleaves the sugar lactose into galactose and glucose, both of which are used by the cell as energy sources |
|
lacA |
lactose permease |
a protein that inserts into the cell membrane and transports lactose into the cell |
#Question id: 2857
#Unit 2. Cellular Organization
In one experiment, another protein –protein interaction is used in place of that between CAP and polymerase. This is done by taking two proteins known to interact with each other, attaching one to a DNA-binding domain, and, with the other, replacing the carboxy-terminal domain of the polymerase a subunit (aCTD), which one is appropriate result of this experiment-
I. The modified polymerase can be inhibited if the appropriate DNA-binding site is introduced near the promoter.
II. The modified polymerase can be activated by the makeshift “activator” as long as the appropriate DNA-binding site is introduced near the promoter.
III. The activator having only to help polymerase bind to the promoter
#Question id: 2858
#Unit 2. Cellular Organization
When lactose enters the cell, it is converted to allolactose. It is allolactose (rather than lactose itself) that controls the Lac repressor. Paradoxically, the conversion of lactose to allolactose is catalyzed by b-galactosidase, itself encoded by one of the lac genes. How is this possible? Which statement is incorrect according lac genes expressions?