Enzymes… Particularly lactase.

[Johnnyvw]

Hello Everyone,

I’m new to biology online. Have a few questions enzymes (particlualry lactase) and about endergonic/exergonic characteristics.

I was assigned a virtual lab in which I was to measure the effects of pH on a Lactase + Lactose solution. The lab contained a video ( http://www.youtube.com/watch?v=V4OPO6JQLOE ) which gives a brief summary of how enzymes work.

Here’s what I’m having trouble understanding.

1. The video is an anabolic reaction – it’s building a molecule from substrates.
Is there any way to tell from the video whether it is endergonic or exergonic? I’m guessing it’s endergonic because anabolic reactions require energy.

2. All of the research that I’ve done has shown lactase+Lactose is a catabolic reaction. Lactase is involved in the accelerated hydrolysis of Lactose, resulting in gluclose and galactose.
Why does my lab want me to record the number of product molecules/min? There shouldn’t be any product molecules… It’s a catabolic reaction.

3. I was asked if the actions of Lactase are endergonic or exergonic. I do understand the differences between the two, but I’m having a hard time with this one.
Does anyone know any good facts, analogies or tricks to help determine whether a reaction is endergonic or exergonic?

If I get those 3 questions answered I should be in good shape. I hate doing the work without understanding the content…

[mith]

2. Product means result of reaction, has nothing to do with catabolic or anabolic. So you’re probably reporting glucose and galactose.

3. See definition of catabolic and anabolic.

[plasmodesmata11]

Regarding the endergonic and exergonic reactions…delta G is negative for exergonic and positive for endergonic. Also, if you have a graph of an endergonic reaction, there is a bit of energy that needs to go in first; this is evident by a bump on the graph. It’s like giving a little push to a ball at the top of a hill; the energy yielded is greater than the energy put in. But since energy cannot appear out of nowhere, often exergonic reactions are coupled with endergonic reactions. At one point the ball was not at the top of the hill. And for tricks….. understanding prefixes helps and knowing lots of latin, but the only one I can think of that applies to this is:
Ana builds AND anabolism is building up
Cats destroy catabolism is breaking down
hope that helps?
and you can measure the rate of a reaction by the appearance of products or disappearance of reactants

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