Updated: 5/6/2017

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Overview
  •  Process
    • initiation
      • RNAp binds the template DNA strand at the promoter site with the help of transcription factors
    • elongation
      • RNAp synthesizes the mRNA strand in 5' → 3' direction 
        • reads template strand in 3' → 5' direction
        • eukaryotic RNAps transcribe introns as well as exons
      • RNAp inhibited by alpha-amanitin (ingestion of the amanita phalloides mushroom) 
    • termination
      • prokaryotes
        • two mechanisms
          • rho-dependent
            • rho protein binds the mRNA
            • causes RNAp to fall off
          • rho-independent
            • mRNA has a GC-rich segment that naturally forms a hairpin
            • causes RNAp to fall off
      • eukaryotes
        • transcription continues past the gene and eventually falls off
  • Mono/polycistronic
    • monocistronic = mRNA codes for 1 protein
      • eukaryotes only have monocistronic mRNA
    • polycistronic = mRNA codes for >1 protein
      • e.g. bacterial lac operon 

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Questions (3)
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(M1.BC.15.74) E. coli has the ability to regulate its enzymes to break down various sources of energy when available. It prevents waste by the use of the lac operon, which encodes a polycistronic transcript. At a low concentration of glucose and absence of lactose, which of the following occurs? Tested Concept

QID: 106639
1

Increased allolactose levels bind to the repressor

5%

(11/216)

2

Increased cAMP levels result in binding to the catabolite activator protein

43%

(93/216)

3

Decreased cAMP levels result in poor binding to the catabolite activator protein

29%

(62/216)

4

Trascription of the lac Z, Y, and A genes increase

5%

(10/216)

5

Repressor releases from lac operator

16%

(34/216)

M 1 D

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