our lab today:
evaluating enzyme activity in yeast undergoing anaerobic respiration/fermentation

when oxygen is present, all three steps occur allowing the glucose to be  completely broken down producing  H2O, CO2 and a lot of energy

we can measure the relative volume of CO2 produced in cm3 (ml)

​Zymase ​is an enzyme complex that catalyzes the fermentation of sugar into ethanol and carbon dioxide. It occurs naturally in yeasts.

step 3

carbonic acid is produced

adding an acid lowers pH

and every step along the way requires a different enzyme...

= much less than 3000kJ

the more CO2 produced, the greater the activity of the enzyme.

6 carbon glucose --->

 3000kJ !

​          how will enzyme activity be affected by...
 


1. substrate concentration





2. presence of enzyme inhibitor




​                 3. temperature



​                               enzyme​
            substrate-----------> product
           the substrate = sugar
                         the enzyme produced by yeast = Zymase
                                         the products = CO2, ethanol, energy
                               we will measure CO2
  the more CO2 produced = the greater the enzyme activity

steps 2 and 3 occur in the mitochondria and require O2

2 pyruvate (3C each)

          3 steps of                        AEROBIC 
 cellular respiration 
1. glycolysis
2. Kreb (TCA) cycle
3. electron transport chain
        steps 2 and 3
      require oxygen                      = aerobic

this cycle relies in aerobic respiration

we will use Phenolphthalein
as our pH indicator

   Anaerobic Respiration and Enzyme Activity

step 2

without O2, steps 2 and 3 can not occur and the cell may anaerobically respire 

when oxygen is absent, only step one, glycolysis,
 occurs so the glucose is only partially broken down producing CO2, ethanol and a lot less energy (<1/15th)

AND 
we can test for the presence of CO2 using a pH indicator...
why pH?

Other enzymes may be required
depending on what the yeast is having for dinner...
Maltase converts maltose into 2 glucose monomers
Ivertase converts sucrose into ​one glucose and one fructose monomer

STEP 1: GLYCOLYSIS:
​one 6 glucose with 6 carbon atoms is broken down into 2 pyruvates with 3 carbons each

Anaerobic respiration by yeast/bacteria is called fermentation.

During this process glycolysis 
​occurs but not the other steps in cellular respiration. the other steps require the presence of oxygen.  

step 1