What most folks don’t understand is that the next most prominent ingredient is lactose. Most folks realize that the milk they drink is mostly water. But before we get too far, let’s take a look at how much lactose is actually in the milk starting off. Understanding why/how much/when lactose is converted into lactic acid can have dramatic effects on cheese. So why does any of this matter? For many cheesemakers the chief concern is not breaking lactose into its two parts, but instead having bacteria convert it to lactic acid. The scientific name for lactose is β-D-galactopyranosyl-(1→4)-D-glucose None of which our digestive system likes very much. Just like other fermentation reactions, common by-products include acid, gas, etc. If the enzyme doesn’t get a chance to break that bond, the microbes in your gut will take a whack at it and will ferment the lactose. If you don’t produce that enzyme in high enough amounts, you’ll suffer from lactose intolerance. That’s important because our intestines need to produce lactase enzyme to break that bond. Those two monosaccharides are linked together by a particular type of bond, a β-1→4 glycosidic bond to be exact. Lactose is made of a molecule of glucose and a molecule of galactose. We’re pretty familiar with disaccharides lactose is probably the second most popular disaccharide after sucrose (table sugar). This means lactose is a sugar made up of two simple sugars (or monosaccharides as scientists would say). More precisely, lactose is a disaccharide. Watch an animated tutorial about the workings of lac operon here.Lactose is a type of sugar. Signals that Induce or Repress Transcription of the lac Operon Only when glucose is absent and lactose is present is the lac operon transcribed ( Table). If either of these conditions is met, then transcription remains off. If lactose is absent, then the repressor binds to the operator to prevent transcription. If glucose is present, then CAP fails to bind to the promoter sequence to activate transcription.
coli, the trp operon is on by default, while the lac operon is off. Transcription of the lac operon is carefully regulated so that its expression only occurs when glucose is limited and lactose is present to serve as an alternative fuel source. This combination of conditions makes sense for the cell, because it would be energetically wasteful to synthesize the enzymes to process lactose if glucose was plentiful or lactose was not available. When lactose is present, it binds to the lac repressor and changes its shape so that it cannot bind to the lac operator to prevent transcription. In the absence of glucose, the binding of the CAP protein makes transcription of the lac operon more effective. Only when glucose is absent and lactose is present will the lac operon be transcribed ( Figure). First, the level of glucose must be very low or non-existent. However, for the lac operon to be activated, two conditions must be met. The Z gene of the lac operon encodes beta-galactosidase, which breaks lactose down to glucose and galactose. The lac operon encodes the genes necessary to acquire and process the lactose from the local environment. coli is able to use other sugars as energy sources when glucose concentrations are low. The lac operon is a typical inducible operon. The third type of gene regulation in prokaryotic cells occurs through inducible operons, which have proteins that bind to activate or repress transcription depending on the local environment and the needs of the cell.