Fundamentals of Biochemical Engineering, Part 1 - Bailey, J., Ollis, D. 1989

Molecular Genetics and Regulatory Systems
Molecular Genetics
General scheme of information flow within the cell

As the well-known proverb says, seeing is believing. Fig. 6.13, which provides a compact schematic Overview of the pathways for cellular regulation and information transfer, further reinforces this truth. The diagram clearly illustrates the interplay between regulation and Information Flow. Note that the control system operates in a cascade fashion: enzyme-level Activation and inhibition allow The Cell to adapt rapidly to transient fluctuations in its chemical balance, whereas Gene-level Induction and Repression enable a complete shift in the metabolic profile whenever environmental conditions and medium composition undergo long-term stabilization.

Class="center">Table 6.3. Methods for the Selection and detection of various bacterial mutantsa

Mutant type

Selection methods

Detection

Capable of utilizing a compound as a carbon source that is not utilized by the wild-type strain

Plating on an Agar medium containing the specified compound as the sole carbon source

The plating method is entirely selective; only the desired mutant forms colonies

Resistant to chemical inhibitors, such as penicillin, streptomycin, sulfonamides, or Dyes

Plating on an agar medium containing the inhibitor

The plating method is entirely selective; only the desired mutant forms colonies

Bacteriophage-resistant

Plating on an agar medium pretreated with a phage suspension

The plating method is entirely selective; only the desired mutant forms colonies

Auxotrophic (requiring one or more growth factors not needed by the wild-type strain)

Incubation in the absence of the growth factor but in the presence of penicillin; wild-type Cells grow and largely perish, whereas auxotrophic mutants do not grow in the absence of the growth factor and survive (penicillin only kills actively growing cells)

Plating on an agar medium lacking the growth factor; after wild-type colonies develop, they are marked, and an overlay of agar containing the growth factor is added; auxotrophs form colonies only after The addition of the growth factor

Unable to utilize a given carbohydrate

Application of the penicillin technique described above, using the specified carbohydrate as the sole carbon source

Plating on an agar medium containing the specified carbohydrate and a chemical indicator that changes color in the presence of fermenting cells (e.g., a pH indicator); mutant colonies are distinguished by their specific coloration

Unable to synthesize DNA at elevated temperatures

Incubating the cell suspension at 42 °C for 15 min, adding 5-bromouracil (5-BU) and continuing incubation for an additional 60 min, then irradiating with light at λ = 310 nm; under these conditions, cells whose DNA incorporates 5-BU are killed, whereas cells whose DNA failed to replicate at 42 °C survive

Testing colonies for growth capability at 42 °C, for example, by replica plating

Ultraviolet-sensitive (unable to repair UV-induced damage)

Infecting the culture with a mildly UV-inactivated bacteriophage; normal cells repair the UV-induced phage damage and subsequently succumb to the same phage, whereas cells incapable of repairing the damage survive

Preparation of Suspensions from isolated colonies; determination of survival rates across various UV doses.

a Stanier R. Y., Doudoroff M., Adelberg E. A., The Microbial World, 3rd ed., p. 450, Prentice-Hall, Inc., Englewood Cliffs, N. J., 1970.



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