6.8.2 Jacob and Monod's Model: The lac Operon Flashcards Preview

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Flashcards in 6.8.2 Jacob and Monod's Model: The lac Operon Deck (10)
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1
Q

note

A
  • Review: In prokaryotes, mRNA transcription requires a promoter. The promoter serves as a recognition site for RNA polymerase. RNA polymerase binds to the promoter and then proceeds to direct transcription of the mRNA molecule.
    • Experiments conducted by Francois Jacob and Jacques Monod determined the mechanisms underlying the lac operon. The lac operon regulates mRNA transcription of enzymes responsible for digesting lactose.
  • Here we see the basic components of the lac operon. A single stretch of DNA regulates and synthesizes lactose-digesting enzymes.
  • Three enzymes are responsible for digesting lactose: beta galactosidase, permease, and trans-acetylase. The genes coding for them are found adjacent to one another on the DNA strand and are called lacZ, lacY, and lacA, repectively.
  • The promoter site is located to the left of the genes. Jacob and Monod identified an operator site—a sequence of bases that is located between the genes and the promoter. They hypothesized that when a specific protein occupies the operator site, RNA polymerase is unable to bind to the promoter; therefore, transcription would not occur.
  • Since the protein prevents transcription, it is called a
    repressor protein. In the absence of lactose, the repressor protein binds to the operator and thus transcription of the lactose-digesting enzymes is prevented.
  • As lactose enters the cell, it is converted into allolactose. Allolactose prevents therepressor protein from binding to the operator. RNA polymerase binds to the promoter and transcription of the three enzymes occurs.
  • The lac operon is an inducible operon. An inducible operon is stimulated when a specific molecule interacts with a regulatory protein.
2
Q

The ___________ gene codes for the repressor in the lac operon.

A
  • lac I
3
Q

An operon is the same as

A
  • a regulated set of genes and their regulatory sequences
4
Q

When lactose is taken into the cell, it is isomerized into ___________, which binds to ____________, preventing it from binding to ___________.

A
  • allolactose; the repressor; the operator
5
Q

Transcriptional controls

A
  • control whether or not mRNA is produced

- include repressor proteins.

6
Q

True or false?

A repressor is a protein that is present in both repressible and inducible operons.

A
  • true
7
Q

When the lactose (lac) operon is actively transcribing,

A
  • the lactose repressor is bound to the inducer
8
Q

Which of the following is the correct order of genes on the lac operon?

A
  • regulatory gene; promoter; operator; lac Z; lac Y; lac A
9
Q

In the lac operon, when lactose is present, an mRNA molecule is transcribed containing nucleotide sequences complementary to

A
  • genes coding for enzymes.
10
Q

In a(n) ___________ operon transcription is activated when a molecule interacts with the repressor and in a(n) __________ operon, transcription is inhibited when a molecule interacts with the repressor.

A
  • inducible; repressible

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