Give two examples of transcriptional control in prokaryotes.?

Cells have 2 ways of controlling metabolism: Regulating enzyme activity and regulating enzyme synthesis.

1. Regulating enzyme activity: The end product of an anabolic pathway may turn off its own production by inhibiting activity of an enzyme at the beginning of the pathway. (feedback inhibition).

2. Regulating enzyme synthesis: Accumulation of products triggers a mechanism that inhibits mRNA production by genes that code for an enzyme at the beginning of the pathway. (gene repression).

most genes are always exressed but there are some that needs to be controlled at transcriptional level larggely to conserve energy.

there are two major transcriptional controls in bacteria positive (induction of gene transcription) and negative (repression of transcription) controls.

an example of positive control would be lactose utilization operon. adding a new substrate like lactose to the culture medium induces the formation of new enzymes capable of metabolizing this substrate.

and an example of negative control would be a repression of tryptophan biosynthesis operon, when tryptophan is present in the medium and the bacteria shuts down the synthesis of its own tryptophan so as not to spend extra energy on making something that is already present in the medium.

1. rate of transcription initiation. the presence of enhancer/silencer DNA sequences will cause protein-mediated bending, facilitating the binding of RNA polymerases, which increases the rate of transcription initiation

2. state of compactness of DNA. transcription cannot start if DNA is still associated with proteins.