assignment Lactose operon (lac operon) codes for three proteins, all of which ar
ID: 266058 • Letter: A
Question
assignment
Lactose operon (lac operon) codes for three proteins, all of which are involved in bacterial lactose metabolism. One of the three proteins is the enzyme ?-galactosidase encoded by the gene lacZ.
1. Explain the role of ?-galactosidase in bacterial lactose metabolism. Specify what reaction b-galactosidase catalyzes (no chemical formulas should be drawn).
The synthesis of ?-galactosidase has been investigated in a variety of bacterial cultures containing X-gal and IPTG in the growth medium. X-gal is a lactose analogue which turns blue by digestion with ?-galactosidase, but X-gal can not induce the expression (expression) of lactose operon.
IPTG is another lactose analog that acts as an inducer without being cleaved by bgalactosidase.
2. We will now look at the function of the drugs lactose (or allolactose), X-gal and IPTG. (a) What (s) of the three substances do you expect to bind to ?-galactosidase? Justify your answer.
(b) Which (s) of the three substances do you expect to bind to the lac repressor? Justify your answer.
A bacterial culture is irradiated with UV light to introduce mutations into the bacteria's DNA. One identifies two mutants, Mut 1 and Mut 2, both of which show a modified regulation of lactose operon expression. Each mutant has been altered such that a single area of ??lactose operon has been destroyed. The mutants are cultured in a variety of growth media with different combinations of lactose and glucose (+ means that the sugar is present - meaning that the sugar is not present). All growth media contain X-gal. One observes the color of the bacterial colonies formed on the growth medium (see table below).
3. Which DNA areas in lactose operon may be mutated in mut 1? Name everyone possible and reasoned answer.
Choose from the following components: lacI gene, promoter of lacI gene, area where
The CAP protein binds, lacO, lacZ or the promoter in lactose operon,
4. Which DNA areas in lactose operon may be mutated in mut 2? Name everyone possible and reasoned answer.
Choose from the following components: lacI gene, promoter of lacI gene, area where The CAP protein binds, lacO, lacZ or the promoter in lactose operon,
Explanation / Answer
answer : lac operon is lactose operon present in bacterial cell specialy in E. Coli.
Beta galactosidase also known as beta -gal is an glycoside hydrolase enzyme which catalyses the hydrolysis of beta galactosides to monosachharides.
B-galactosidase breaks down lactose sugar to simple sugar glucose and galactose.
The gene product of lacz is beta galactosidase which cleaves lactose. This enzyme is used in molecular biology as reporter marker. The presence or absence of an active beta galactosidase may be detected by X gal which produces a characteristic blue by which easy detection of clones are possible in a plasmid.
Beta galactosidase is also known for its Alpha complementation activity.
Note: there are some? Marks in the question and few sentences are not clear..
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.