A catabolite-activating protein (CAP) exerts positive control over the lac opero

Question

A catabolite-activating protein (CAP) exerts positive control over the lac operon. Indicaté the level 8 activity of the lac operon under the medium (growth) conditions below: (OFF, HIGH or LOW expression) -No glucose present, lactose present ON -Glucose present, lactose present For each of the following questions identify the appropriate t 1) Term for contiguous bacterial genes that share a promoter tose present 6FF erm or example that fits the statement or answers the question. 1) Tern for contiguous bacterial genes that share a promoter. Operon 2) The inhibitor protein of Lac system is transcribed when induced (True or Falsg 2)TheinhibitorproteinofLae systern istranscribedwhen induced (True-G 3) A gene in the lac operon that codes for acetyltransferase. La rue orf als9). CLC

Explanation / Answer

ON

OFF

1. Operon

2. True

3. Gene A

The A gene codes for transacetylase, whose function is controlled coordinately with the Z and Y genes.

The lac operon consists of three structural genes, Z, Y and A, which code for the enzymes necessary to catabolize lactose and a regulator gene, I, which codes for a regulator protein. The regulator protein regulates the operon. It turns the operon “on” or “off” depending upon the presence of lactose by binding to an operator region. The structural gene, Z, codes for ß-galactosidase which is primarily responsible for the hydrolysis of lactose into its monomeric units, galactose and glucose. The Y gene codes for the enzyme lac permease which functions specifically in the transport of lactose into the bacterial cell. The cell is otherwise impermeable to lactose. The A gene codes for transacetylase, whose function is controlled coordinately with the Z and Y genes. The structural genes are under the control of a promoter, P, onto which RNA polymerase binds. It is necessary for the transcription of the structural genes. The RNA polymerase binds to the promoter and transcribes a single continuous mRNA molecule for all three structural genes. Because the mRNA molecule contains the transcripts of more than one gene, it is called a polycistronic or polygenic mRNA.

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