Adapting to a changing world, biologically

Organisms have a dynamic relationship with their environment; they modify it and adapt to it.

Adaptation can take place quickly. Genes can be turned on and off, proteins activated or inactivated.

For example, bacteria can respond rapidly to presence of specific molecules in their environment by altering their movements.

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Very rapid adaptive behavior is based on changes in RNA and protein stability and the post-translational modification of proteins. together these can produce rapid changes in cellular behavior.

A less rapid form of adaptation involves changes in the expression of genes. Again this leads to changes in cellular behavior.

The slowest form of adaptation is evolution, which occurs over much longer periods of time and only at the population level. It is based on the selection of mutations.

Individuals do not evolve, only populations.

The heroic age of molecular biology

During World War II, and while fighting with the French resistance against the Nazis, Jacques Monod studied E. coli's ability to metabolize various sugars.

After the war he was joined by Françoise Jacob, who had been severely wounded during the D-Day invasion of Normandy.

Their studies built on the work of Eugene & Elisabeth Wollman (sent to their deaths in the Auschwitz concentration camp) and André Lwoff, an active member of the French resistance.

The work of this group on the activation of lysogenic phage, provided the first insights into how genes are regulated.

Monod, Jacob & Lwoff
won the Nobel Prize in 1965.

Monod found that the sugar glucose suppressed E. coli's ability to use other sugars, specifically the milk sugar lactose.

When glucose was present, it was used it first. Only after the glucose had been consumed was lactose used.

Intriguingly, there was "lag" between when glucose was used up and the bacteria started to grow on lactose.

This behavior is known as diauxie.

What can we deduce from the diauxic behavior of E. coli?

First, the ability to utilize lactose appears to be inhibited by glucose.

Second, the ability to utilize lactose takes time to appear. The cells have to adapt.

Monod & Jacob asked, what is the mechanism of this adaptation?

What is happening inside the bacterial cell?

Our understanding of how bacteria adapt to using lactose was built using a combination of biochemical and genetic approaches. One of the key advances was the identification of the enzyme ß-galactosidase, originally known as lactase

ß-galactosidase converts lactose (and other ß-linked disaccharides) into monosaccharides. arrow
Hydrolysis means
Breaking apart through the addition of water
Linking together through the addition of water

If there was no diauxie, when both sugars were present the cells would ...
grow faster
grow slower
grow at the same rate
I would have to know the relative concentrations of the sugars

revised 9 July 2003