Biology - sugar supplement and bacteria growth

[Henza]

Hey,

Im doing a bio pract to determine the effect of a sugar supplement when growing E. coli with nutrient broth

I'm using glucose, sucrose and lactose and comparing them to a control (no sugar)

What results should i expect??

I think there will be greater growth with glucose (cell respiration etc.)

but im not sure with sucrose and lactose??

any takers? thanks

[Taigan]

I'm sorry but I don't take IB Biology yet. I'll be starting it in September.

But I'll still try and answer your question as best as I can.

Firstly, I think you're right about the fact that the glucose would yield the most growth. As it doesn't need to be broken down into anything simpler before being used in respiration.

Next it would be Lactose because it is a disaccharide and so would only have to be broken down once. This takes some energy to break down so the surplus energy would be less than using glucose.

Sucrose would be the last. It would have to be broken down into maltose and then glucose because it is a polysaccharide. This takes energy and so the total growth would be less than using glucose or lactose.

So the one that would yield the most energy is the monosaccharide (glucose), then the disaccharide (lactose) and finally the polysaccharide (sucrose). Also, to make sure the test is accurate, ensure that equal amounts of glucose, lactose and sucrose are used...

I hope this helps you.

Good luck

EDIT: sorry, there are better responses down below!

Edited August 25, 2009 by taigan

[Max]

Next it would be Lactose because it is a disaccharide and so would only have to be broken down once. This takes some energy to break down so the surplus energy would be less than using glucose.

Sucrose would be the last. It would have to be broken down into maltose and then glucose because it is a polysaccharide. This takes energy and so the total growth would be less than using glucose or lactose.

Unfortunately your theory is flawed. You clearly didn't consider how the poly- and disaccharides are being broken down - usually this is done by enzymes. Sucrase breaks down sucrose into fructose and glucose (not maltose, as you mentioned) and lactase breaks down lactose into galactose and glucose. I don't know if E. Coli produces sucrase or lactase, but I read that it was once believed that E. Coli produced the latter in the human gut - that turned out to be false though.

Nothing should therefore happen with sucrose and lactose due to the lack of specific enzyme. If, however, sucrase is present, the fructose that results from the breakdown of sucrose will probably have the same effect upon the growth of the bacteria as glucose:

As you can see, fructose(-6-phosphate) is an intermediate in glycolysis. If fructose is provided directly, the conversion of glucose to fructose would not have to occur, as it can be phosphorylized directly and hence the rate would be similar to that with glucose. This would, however, depend on the conditions sucrase is exposed to.

Edited August 25, 2009 by Max