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Chapter 16 Outline. 16.4 Some Operons Regulate Transcription Through Attenuation, the Premature Termination of Transcription, 442 16.5 Antisense RNA Molecules Can Affect the Translation of mRNA, 445 16.6 Riboswitches Function as Regulatory Elements in mRNAs, 446.

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Chapter 16 outline
Chapter 16 Outline

  • 16.4 Some Operons Regulate Transcription Through Attenuation, the Premature Termination of Transcription, 442

  • 16.5 Antisense RNA Molecules Can Affect the Translation of mRNA, 445

  • 16.6 Riboswitches Function as Regulatory Elements in mRNAs, 446



Genes and regulatory elements
Genes and Regulatory Elements Bacterial and Eukaryotes

  • Structural genes: encoding proteins

  • Regulatory genes: encoding products that interact with other sequences and affect the transcription and translation of these sequences

  • Regulatory elements: DNA sequences that are not transcribed but play a role in regulating other nucleotide sequences


Genes and regulatory elements1
Genes and Regulatory Elements Bacterial and Eukaryotes

  • Constitutive expression: continuously expressed under normal cellular conditions

  • Positive control: stimulate gene expression

  • Negative control: inhibit gene expression


Level of gene regulation
Level of Gene Regulation Bacterial and Eukaryotes

  • Many levels at which gene expression may be regulated

    • DNA access

    • Transcription

    • RNA modification and stability

    • Translation

    • Post-translational modification


Dna binding proteins
DNA-Binding Proteins Bacterial and Eukaryotes

  • Domains: 60 ~ 90 amino acids, responsible for binding to DNA, forming hydrogen bonds with DNA

  • Distinctive types of DNA-binding proteins based on the motif

    • Motif: within the binding domain, a simple structure that fits into the major groove of the DNA


Concept check 1
Concept Check 1 Bacterial and Eukaryotes

How do amino acids in DNA-binding proteins interact with DNA?

  • By forming covalent bonds with DNA base

  • By forming hydrogen bonds with DNA base

  • By forming covalent bonds with sugars


Concept check 11
Concept Check 1 Bacterial and Eukaryotes

How do amino acids in DNA-binding proteins interact with DNA?

  • By forming covalent bonds with DNA base

  • By forming hydrogen bonds with DNA base

  • By forming covalent bonds with sugars


16 3 operons control transcription in bacterial cells
16.3 Operons Control Transcription in Bacterial Cells Bacterial and Eukaryotes

  • Operon: promoter + additional sequences that control transcription (operator) + structure genes

  • Regulator gene: DNA sequence encoding products that affect the operon function, but are not part of the operon


Negative and positive control inducible and repressible operons
Negative and Positive Control; Inducible and Repressible Operons

  • Inducible operons: Transcription is usually off and needs to be turned on.

  • Repressible operons: Transcription is normally on and needs to be turned off.


Negative and positive control inducible and repressible operons1
Negative and Positive Control; Inducible and Repressible Operons

  • Negative inducible operons: The control at the operator site is negative. Molecule binding is to the operator, inhibiting transcription. Such operons are usually off and need to be turned on, so the transcription is inducible.

  • Inducer: small molecule that turns on the transcription


Negative and positive control inducible and repressible operons2
Negative and Positive Control; Inducible and Repressible Operons

  • Negative repressible operons: The control at the operator site is negative. But such transcription is usually on and needs to be turned off, so the transcription is repressible.

  • Corepressor: a small molecule that binds to the repressor and makes it capable of binding to the operator to turn off transcription


Negative and positive control inducible and repressible operons3
Negative and Positive Control; Inducible and Repressible Operons

  • Positive inducible operon

  • Positive repressible operon


The lac operon of e coli
The Operonslac Operon of E. coli

  • A negative inducible operon

  • Inducer: allolactose

  • lacI: repressor encoding gene

  • lacP: operon promoter

  • lacO: operon operator


The lac operon of e coli1
The Operonslac Operon of E. coli

  • Structural genes

    • lacZ: encoding β-galactosidases

    • lacY: encoding permease

    • lacA: encoding transacetylase

  • The repression of the lac operon never completely shuts down transcription.


Concept check 4
Concept Check 4 Operons

In the presence of allolactose, the lac repressor .

  • binds to the operator

  • binds to the promoter

  • cannot bind to the operator

  • binds to the regulator gene


Concept check 41
Concept Check 4 Operons

In the presence of allolactose, the lac repressor .

  • binds to the operator

  • binds to the promoter

  • cannot bind to the operator

  • binds to the regulator gene


Positive control and catabolite repression
Positive control and catabolite repression Operons

  • Catabolite repression: using glucose when available, and repressing the metabolite of other sugars

  • This is a positive control mechanism: The positive effect is activated by catabolite activator protein (CAP). cAMP is binded to CAP, together CAP–cAMP complex binds to a site slightly upstream from the lac gene promoter.


Positive control and catabolite repression1
Positive control and catabolite repression Operons

  • cAMP – adenosine-3′,5′-cyclic monophosphate

  • The concentration of cAMP is inversely proportional to the level of available glucose.


Concept check 42
Concept Check 4 Operons

What is the effect of high levels of glucose on the lac operon?

  • Transcription is stimulated.

  • Little transcription takes place.

  • Transcription is not affected.

  • Transcription may be stimulated or inhibited, depending on the levels of lactose.


Concept check 43
Concept Check 4 Operons

What is the effect of high levels of glucose on the lac operon?

  • Transcription is stimulated.

  • Little transcription takes place.

  • Transcription is not affected.

  • Transcription may be stimulated or inhibited, depending on the levels of lactose.


The trp operon of e coli
The Operonstrp Operon of E. coli

  • A negative repressible operon

  • Five structural genes

    • trpE, trpD, trpC, trpB, and trpA – five enzymes together convert chorismate to typtophane.


16.4 Some Operons Regulate Transcription Through Attenuation, the Premature Termination of Transcription

  • Attenuation: affects the continuation of transcription, not its initiation. This action terminates the transcription before it reaches the structural genes.


Attenuation in the trp operon of e coli
Attenuation in the Attenuation, the Premature Termination of Transcriptiontrp Operon of E. coli

  • Four regions of the long 5′ UTR (leader) region of trpE mRNA

    • When tryptophan is high, region 1 binds to region 2, which leads to the binding of region 3 and region 4, terminating transcription prematurely.


Attenuation in the trp operon of e coli1
Attenuation in the Attenuation, the Premature Termination of Transcriptiontrp Operon of E. coli

  • Four regions of the long 5′ UTR (leader) region of trpE mRNA

    • When tryptophan is low, region 2 binds to region 3, which prevents the binding of region 3 and region 4, and transcription continues.


Concept check 6
Concept Check 6 Attenuation, the Premature Termination of Transcription

Attenuation results when which regions of the 5′ UTR region pair?

  • 1 and 3

  • 2 and 3

  • 2 and 4

  • 3 and 4


Concept check 61
Concept Check 6 Attenuation, the Premature Termination of Transcription

Attenuation results when which regions of the 5′ UTR region pair?

  • 1 and 3

  • 2 and 3

  • 2 and 4

  • 3 and 4


16 5 antisense rna molecules can affect the translation of mrna
16.5 Antisense RNA Molecules Can Affect the Translation of mRNA

  • Antisense RNA:

    • Complementary to targeted partial sequence of mRNA


16 6 riboswitches function as regulatory elements in mrnas
16.6 Riboswitches Function as Regulatory Elements in mRNAs mRNA

  • Riboswitch: the regulatory sequence of mRNA molecules where molecules can bind and affect gene expression by influencing the formation of secondary structure in the mRNA


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