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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
  • 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
  • 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
  • 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
  • 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

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

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
  • 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 lac 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 lac 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

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

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
  • 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
  • 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

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

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 trp Operon of E. coli
  • A negative repressible operon
  • Five structural genes
    • trpE, trpD, trpC, trpB, and trpA – five enzymes together convert chorismate to typtophane.
slide39
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 trp 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 trp 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 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 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
  • 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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