evaluation of anaerobic fermentation by yeast using sugars

[kowslip]

hey i've just registered, hello all
I know this experiment has been spoken about a lot in other posts, but my question is unanswered.
I was reading one post on here about the limiting factor, as to whether the yeast even has the appropriate enzymes or carrier proteins for certain sugars (e.g lactose) to facilitate into the yeast cell membrane.
i'm not sure if that fits with my conclusion. MY I.V was the differing sugars, and my D.V was the effect on the production of CO2. This therefore meant that the results and trends must be due to the sugars biological properties alone...as all other factors were kept constant. Can I still maintain this? As now I am unsure as to whether the presence of any suitable enzyme or carrier protein also is a main influence. However my method was maintaining the enzyme activity if there were suitable ones to do so. Not having a suitable enzyme for certain sugars cannot be controlled in my plan surely?
Please help, I think i may be somewhat confused here...
Thanks, kowslip.

[Happydadtoo]

hi!
Yes, I think you are a bit confused!
What you controlled (or tried to) was the concentration of yeast in each mixture. The yeast cells are alive and so respond to their environment, in this case, by synthesising the carrier proteins and enzymes needed to respire whatever the primary external sugar is..... but that takes some time.
So, if you mix yeast and new sugar and test it within 5 mins, the yeast will still be responding to the change in external carbohydrate. Did you mix each different sugar + yeast and allow to react for, say, 30 mins BEFORE you started the experiment?
Or did you just mix them and IMMEDIATELY start the experiment?
Your conclusions will be different depending on your experimental procedure.
Disaccharide sugars have greater osmotic properties than monosaccharides (since the yeast hydrolyses them into monosaccharides) and therefore will affect the yeast is way OTHER than simply through respiration. I don't think that point needs labouring, just make sure that you write a little about the yeast responding to the change in external sugar, rather than just blindly carrying on with the enzymes and carrier proteins it had at the start. I don't know how quickly yeast responds to a change in sugar substrate, but I would guess it will certainly do so within an hour or so, particularly if the original sugar was ALL removed (ie you mixed yeast + water and allowed it to sit and sulk overnight before you added each sugar in turn and started the experiment).