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Biochemistry 2280A Lecture : Lac Operon

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orchidotter238
26 Dec 2011
School
Western University
Department
Biochemistry
Course
Biochemistry 2280A
Professor
Eric Ball

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Document Summary

They are turned on when lactose is around. They are not required for biosynthesis of lactose but for metabolism of lactose. We got operon, lac z lac y and lac a. Also got operator this case, its down stream for -10. Operator is downstream from minus 10. operator binds to protein lac repressor. Rna polymerase cant get in and start transcription. In absence of lactose lac repressor binds the lac operator inhibiting access of rnap. It s the lac repressor that doesn t have the lac bound to it which is a bit different than what we saw with tryptophan. In presence of lactose lac repressor binds lactose and dissociates from operator. Falls of dna and polymerease come and transcribe gene. Minus 10 and -35 for lac promoter are not good not strong. Positive regulation of lac operon is sensitive to the presence//absence of glucose in the cellular environment. Plsitve regulation for lac operon is more complicated.

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Related Questions

QUESTION 1

In the bacterial lac repressor, which of these occurs: (select all that apply)

(a)In the presence of glucose and the absence of lactose, the repressor is actively produced.

(b)The lac operon can be hyper-induced in the presence of low glucose by the 'cAMP binding protein' (CAMP).

(c)In the presence of lactose and the absence of glucose the lac operon is repressed.

(d)Allolactose is a byproduct of β-galactosidase, indicating high lactose when it builds up.

1.5 points

QUESTION 2

In eukaryotes the enhancer elements can be quite a distance upstream or downstream from the promoter, and transcriptional regulation is helped by protein:protein interactions.

True

False

1.5 points

QUESTION 3

The prokaryotic promoter contains a TATA box that is at -10bp upstream from the transcriptional start site.

True

False

1.5 points

QUESTION 4

During the addition of the poly A tail which of these occurs:(select all that apply)

(a)The transcript is synthesized beyond the poly A site (AAUAAA).

(b)The mRNA contains a 5Ҁ™ cap.

(c)The transcript is cleaved 35nt downstream from the poly A site.

(d)An enzyme complex containing an exonuclease and polyadenylate polymerase cleaves nearby the AAUAA site.

(e)100-300 AҀ™s are added to the 5Ҁ™ end.

1. The following shows the genotype of a partial diploid bacterial cell - where one chromosomal region containing the lac operon in E,coli is given, and the other fragment is from a plasmid carrying another lac operon from another source. The two are separated by a slash (/).

The possible answers indicate with a ʺ+ʺ or a ʺ-ʺ whether β-galactosidase would be expected to be produced at induced levels under two circumstances: 1) first in the absence of lactose and 2) second in the presence of lactose. (Assume that glucose is not present in the medium.)

Genotype C: Is Oc Z+/ Fʹ I + O+ Z+
KEY:

I+ = wild-type repressor
I- = mutant repressor (unable to bind to the operator)
Is = mutant repressor (insensitive to lactose)
O+ = wild-type operator
Oc = constitutive operator (insensitive to repressor)

a. +,+ d. -,+

b. -,- e. cannot tell

c. +,-

2. The following shows the genotype of a partial diploid bacterial cell - where one chromosomal region containing the lac operon in E,coli is given, and the other fragment is from a plasmid carrying another lac operon from another source. The two are separated by a slash (/).

The possible answers indicate with a ʺ+ʺ or a ʺ-ʺ whether β-galactosidase would be expected to be produced at induced levels under two circumstances: 1) first in the absence of lactose and 2) second in the presence of lactose. (Assume that glucose is not present in the medium.)

Genotype D: I- O+ Z+/ Fʹ I- O+ Z+
KEY:

I+ = wild-type repressor
I- = mutant repressor (unable to bind to the operator)
Is = mutant repressor (insensitive to lactose)
O+ = wild-type operator
Oc = constitutive operator (insensitive to repressor)

a. +,+ d. -,+

b. -,- e. cannot tell

c. +,-

3. The following shows the genotype of a partial diploid bacterial cell - where one chromosomal region containing the lac operon in E,coli is given, and the other fragment is from a plasmid carrying another lac operon from another source. The two are separated by a slash (/).

The possible answers indicate with a ʺ+ʺ or a ʺ-ʺ whether β-galactosidase would be expected to be produced at induced levels under two circumstances: 1) first in the absence of lactose and 2) second in the presence of lactose. (Assume that glucose is not present in the medium.)

Genotype E: I + O+ Z+/ Fʹ I + O+ Z+
KEY:

I+ = wild-type repressor
I- = mutant repressor (unable to bind to the operator)
Is = mutant repressor (insensitive to lactose)
O+ = wild-type operator
Oc = constitutive operator (insensitive to repressor)

a. +,+ d. -,+

b. -,- e. cannot tell

c. +,-

The Lac repressor protein binds to the:

A)

lacZ gene in the presence of allolactose.
B)

operator in the presence of allolactose.
C)

operator in the absence of allolactose.
D)

operator regardless of the presence or absence ofallolactose.