assignment Lactose operon (lac operon) codes for three proteins, all of which ar

Question

assignment

Lactose operon (lac operon) codes for three proteins, all of which are involved in the bacterial
lactose metabolism. One of the three proteins is the enzyme ?-galactosidase which is encoded
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 all possible and reasoned answers.
Choose from the following components: lacI gene, promoter of lacI gene, region where CAP protein binds, lacO, lacZ or promoter in lactose operon,

4. Which DNA areas in lactose operon may be mutated in mut 2? Name all possible and reasoned answers.
Choose from the following components: lacI gene, promoter of lacI gene, region where CAP protein binds, lacO, lacZ or promoter in lactose operon,

Groth medium +glucose lactose +X-gal White white Bacterial strain +glucose +lactose +X-gal white white lucose lactose +X-gal white white lucose -+actose +X-gal blue white Wild type Mut 1

Explanation / Answer

Q1:- Explanation:- The beta galactosidase enzyme coded by lacz gene changes lactose a diasaccharide into allolactose and glucose and galactose.

Q2:-

Part A :- Explanation:- All X gal and lactose bind to the beta galactosidase.

Part B :- lactose and IPTG bind to the lac repressor make it inactive and is not able to bind at operator.

Q3:- Explanation:- In mut 1 lac operon beta galactosidase gene lacz is mutated

Q4-: Explanation:- In mut2 Lac I is mutated since it is not able bind operator hence lac operon is constitutively expressed even in absence of glucose and lactose.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.