L6 lac Operon

Question 1

Why does opeon exist

Answer 1

To prevent overproduction of proteins, leading to energy and raw materials waste.
Ability to switch genes off and on.

Question 2

Polycistronic mRNA and monocistronic mRNA

Answer 2

Polycistronic mRNA: mRNA that encodoes for two of more protein.
Monocistronic mRNA: mRNA that codes for only one protein.

Question 3

Components of lac operon

Answer 3

Pi - i—Plac, OP, lac Z, lac Y, lac A

Question 4

Is Lac Operon continuously synthesized?

Answer 4

No, only switched on in the presence of lactose.
Off 24/7

Question 5

Components of lac Operon (Enzymes in structural genes)

Answer 5

Lac Z: B-galactosidase
Lac Y: Lactose permease
Lac A: Galactosidase transacetylase

Question 6

What happens when the lac operon is off?

Answer 6

The repressor is bound to the Operator, blocking the binding of RNA polymerase to the promoter, and preventing the transcription of structural genes. No synthesis of proteins

Question 7

what happens when lac operon is on??

Answer 7

Lactose (allolactose) binds to the repressor on its allosteric binding site, changing its 3D conformational shape, causing it to dissociate from the operator, RNA polymerase is able to detect promoter and bind, enabling transcription and translation to produce proteins required for lactose metabolism.

Question 8

Lactose analogs and their effects

Answer 8

IPTG: non-metabolizable analog, binds to the receptor, unable to dissociate, allows continuous transcription of structural genes for synthesis of the enzymes even in absence of lactose.
X-Gal: is a lactose analag that can be hydrolyzed by B-galactosidase to produce a blue product, allows identification of enzyme Z presence.

Question 9

Function of Lac Z, Lac Y

Answer 9

Z: B-galatocidase aids in break down of lactose to glucose and galactose
Y: Lactose permeate, allows transport of lactose across plasma membrane into the cell

Question 10

Components of Trp Operon

Answer 10

PR,trp R–Ptrp, operator, trp E, trp D, trp C, trp B, trp A

Question 11

Is trp operon continuously synthesized?

Answer 11

Yes, until trptophan concentration reaches a threshold, it is continuously synthesized.
On 24/7

Question 12

High trptophan

Answer 12

In High trptophan, co-repressor, trptophan binds to trp repressor, changing its 3D conformation shape and activating it to allow it to bind to the promoter region. Binding prevents RNA polymerase from binding and facilitating transcription

Question 13

Low trptophan

Answer 13

In low trptopan, concentration is not enough to reach threshold to bind to repressor, repressor is inactive, promoter is clear for transcription and binding of RNA polymerase

Question 14

c

Answer 14

Prevent gene-expression by binding to repressor protein, changing its 3D conformational shape to an active conformation, allowing binding to operator

Question 15

Inducer function (Lactose, IPTG)

Answer 15

Allow gene expression

Question 16

Repressor

Answer 16

Prevent gene expression