Yeast
yeast (Saccharomyces cerevisiae).
yeast is a living organism that requires a warm, moist
environment and a food source to grow and thrive.
 unicellular, faculative anaerobic fungi
Under Microscope
Cellular respiration
 In this lab, you will be using yeast to measure the rate
of cellular respiration.
 Yeast is a single-celled eukaryotic organism that
utilizes carbohydrates for ATP production in the same
way that plant and animal cells utilize carbohydrates.
 Yeast will convert a carbohydrate into water and
carbon dioxide during cellular respiration.
 The greater the carbon dioxide production, the
greater the rates of cellular respiration.
 The reactions within cells which result in the synthesis of ATP using
energy stored in glucose are referred to as cellular respiration
 Aerobic respiration requires oxygen as the final electron acceptor.
 Fermentation does not require oxygen.
The equation for aerobic respiration is below.
C6H12O6 + 6O2 → 6CO2 + 6 H2O + 36 or 38 ATP
 In aerobic respiration (equation above) glucose is completely broken
down to CO2 + H2O but during fermentation, it is only partially broken
down.
 Much of the energy originally available in glucose remains in the
products produced.
 Plant and fungal cells produce alcohol as a result of fermentation and
animal cells produce lactic acid.
 The equation for alcohol fermentation is below.
C6H12O6 → 2CO2 + 2C2H5OH + 2 ATP
Glycolysis
Glycolysis
Glycolysis occurs in the cytoplasm
(cytosol) and does not require
oxygen.
There are ten steps in glycolysis
and each one is catalyzed by a
specific enzyme.
2 ATP molecules are used to
phosphorylate and activate
compounds that will eventually
become converted to pyruvate (or
pyruvic acid).
Two hydrogen atoms are removed
by NAD+ forming 2 NADH.
Additional phosphorylation results
in intermediate 3-carbon
molecules with 2 phosphate
groups.
Four ATP are produced by
substrate-level phosphorylation.
For one glucose molecule , the citric acid
cycle repeated two
 NADH and FADH2 carry electrons to the electron
transport system.
 Acetyl CoA formation and the citric acid cycle occur in
the inner space called the matrix of mitochondria.
Calculation of energy
Substrate-Level
Phosphorylation
Pathway
Glycolysis
2 ATP
CoA
Oxidative
Phosphorylation
2 NADH = 4 - 6
ATP
Total
ATP
6-8
2 NADH = 6 ATP
6
24
Citric Acid Cycle
2 ATP
6 NADH = 18 ATP
2 FADH2 = 4 ATP
TOTAL
4 ATP
32 ATP
38 - 36
The electron transport system is found in the mitochondrion and chloroplast
of eucaryotes and in the plasma membrane of procaryotes.
The system contains membrane-bound electron carriers that pass electrons
from one to another.
The vast majority of the ATP (90%) comes from the energy in the
electrons carried by NADH and FADH2.
Fermentation
 Anaerobic respiration
 Alcoholic fermentation
 The rate of fermentation can be affected by several
factors:
Concentration of yeast
Concentration of glucose
Temperature
 For the yeast cell, this chemical reaction is necessary to
produce the energy for life. The alcohol and the carbon
dioxide are waste products produced by the yeast. It is
these waste products that we take advantage of. The
chemical reaction, known as fermentation can be
watched and measured by the amount of carbon
dioxide gas that is produced from the break down of
glucose.
 S cerevisiae can live in both aerobic as well as anaerobic conditions.
 In the presence of oxygen, yeast can undergo aerobic respiration, where
glucose is broken to CO2 and ATP is produced by protons falling down
their gradient to an ATPase.
 When oxygen is lacking, yeast only get their energy from glycolysis and
the sugar is instead converted into ethanol, a less efficient process than
aerobic respiration.
 The main source of carbon and energy is glucose, and when glucose
concentrations are high enough, gene expression of enzymes used in
respiration are repressed and fermentation takes over respiration.
 However, yeast can also use other sugars as a carbon source. Sucrose
can be converted into glucose and fructose by using an enzyme called
invertase, and maltose can be converted into two molecules of glucose
by using the enzyme mannase.
Reagents and instrument
 Respirometer is a device used to measure the rate of
respiration of a living organism by measuring its rate
of exchange of oxygen and/or carbon dioxide.
Consist of test tube, graduated pipette, aquarium tubing
flask and blinder clips
Procedure
Obtain 5 flasks and fill with approximately 200 ml of
tap water label the flasks
2. Place the water filled flasks into separate beakers
3. Obtain 5 test tubes and label them add solutions as
follows to the appropriate tubes:
1.
Tube
Water ml
Yeast
suspensio
n ml
Glucose
solution
ml
1
4
0
3
2
6
1
0
3
3
1
3
4
1
3
3
5
2
2
3
4. Attach a piece of aquarium tubing to the end of each
1 ml graduated pipette
5. Then place the pipette with attached tubing into each
test tube containing fermentation solutions.
6. Attach the pipette pump to the free end of the tubing
on the first pipette.
7. Use the pipette pump to draw the fermentaion
solution up into the pipette.
8. Fill it past the calibrated portion of the tube but do
not draw the solution into the tubing.
9. Fold the tubing over and clamp it shut with the binder
clip so the solution does not run out.
10. Open the clip slightly and allow the solution to drain
down to the 0 ml calivration line or slightly bellow
11. Quickly do the same for the other four pipette
12. Record your intial reading for each pipette(initial
time)
13. 2 mints after the initial readings for each pipette
record the actual readings A in ml for each pipette in
the acual A column.
14. Subtract I form a to determine the total amount of
co2 evolved A – I
15. Record this value in the co2 evolved a-I column
16. From now on you will subtract the initial reading
from each actual reading to determine the total
amount of co2 evolved
17. Continue taking readings every 2 minutes for each of
the solutions for 20 minutes
18. Remember take the actual reading from the pipette
and subtract the initial reading to get the total amount
of co2 evolved in each test tube.