Energy metabolism in yeast

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 levelphosphorylation.

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 Pathway Substrate-Level

PhosphorylationOxidative

PhosphorylationTotalATP

Glycolysis 2 ATP 2 NADH = 4 - 6 ATP

6-8

CoA   2 NADH = 6 ATP

6

Citric Acid Cycle

2 ATP

6 NADH = 18 ATP

2 FADH2 = 4 ATP

24

TOTAL 4 ATP 32 ATP 36 - 38

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 respirationAlcoholic fermentationThe rate of fermentation can be affected by

several factors:Concentration of yeastConcentration of glucoseTemperature

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 instrumentRespirometer 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 1. 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:

Glucose solution

ml

Yeast suspensi

on ml

Water ml Tube

3 0 4 1

0 1 6 2

3 1 3 3

3 3 1 4

3 2 2 5

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.