Fermentation

H. BiologyMs. Kim

Fermentation• Fermentation enables some cells to

produce ATP without the use of oxygen (O2)

• Cellular respiration–Relies on oxygen to produce ATP

• In the absence of oxygen–Cells can still produce ATP through

fermentation

Cellular respiration vs. fermentationOxygen Present → Aerobic Respiration (efficient!)

Oxygen NOT Present → Fermentation (not efficient)

Respiration = 66% efficientFermentation = 3.5% efficient

Fermentation

• If there is no oxygen present (anaerobic) the pyruvate (from glycolysis) goes to fermentation

• The main goal of fermentation is:– To make NAD+ to put back into glycolysis– This makes NO ATP on its own (it just keeps

glycolysis going so that it can make 2 ATP at a time)• Occurs in the cytosol• 2 types of fermentation– 1) Alcohol– 2) Lactic acid

•Glycolysis–Can produce ATP with or

without oxygen, in aerobic or anaerobic conditions–Couples with fermentation to

produce ATP

Types of Fermentation

• Fermentation consists of–Glycolysis plus reactions that regenerate

NAD+, which can be reused by glyocolysis

Alcohol Fermentation

• Pyruvate is converted to ethanol (ethyl alcohol) in two steps, one of which releases CO2

• Ex: bacteria and yeast

• In alcohol fermentation–Pyruvate is converted to

ethanol (ethyl alcohol) in two steps, one of which releases CO2

GLUCOSE Pyruvate Ethanol and CO2

•Ex: bacteria and yeast do this

- Pyruvate is turned into ethanol- CO2 is released (bubbles!)- Done by yeast for brewing

3C Pyruvate → 2C Ethanol

Remember: Goal is to produce NAD+ to send back to glycolysis so it can keep going and produce more ATP

Alcoholic Fermentation

Lactic Acid Fermentation

• During lactic acid fermentation–Pyruvate is reduced directly to NADH

to form lactate as a waste product–NO CO2 is released• Ex #1: fungus and bacteria in dairy industry

to make cheese/ yogurt• Ex #2: Human muscle cells

Lactic acid fermentation

- Pyruvate is turned into Lactate (or lactic acid)- Lactate is eventually

carried away by the blood to the liver where it gets converted back into pyruvate

- Example: Muscle Cells- The lactic acid is what makes your muscles sore after lifting or intensive exercise- No CO2 is released

3C Pyruvate → 3C Lactate

Remember: Goal is to produce NAD+ to send back to glycolysis so it can keep going and produce more ATP

Lactic acid vs. alcohol fermentation

Similarities: 1. Both start with pyruvate from glycolysis 2. Both create NAD+ to be sent back to glycolysis 3. Neither make any ATP on their own

Differences: 1. Lactic acid is made and does NOT give off CO2

2. Alcohol makes ethanol and gives off CO2

Fermentation - Overview Obligate Aerobes → needs oxygen; can do respiration only

Obligate Anaerobes → can’t have oxygen; fermentation only

Facultative Anaerobes → can live with or without oxygen; prefer oxygen b/c more efficient

Respiration is 19 times more efficient than fermentation (38 ATP vs. 2 ATP)

2 ADP + 2 P1 2 ATP

GlycolysisGlucose

2 NAD+ 2 NADH2 Pyruvate

2 Acetaldehyde (gets reduced by NADH. It is

the oxidizing agent.)

2 Ethanol

(a) Alcohol fermentation2 ADP + 2 P1 2 ATP

GlycolysisGlucose

2 NAD+ 2 NADH

2 Lactate

(b) Lactic acid fermentation

H

H OH

CH3

C

O –

OC

C O

CH3

H

C O

CH3

O–

C O

C O

CH3O

C O

C OHH

CH3

CO22

NO CO2

made 2 Pyruvate (gets reduced by NADH. It is

the oxidizing agent.)

Fermentation and Cellular Respiration Compared

• Both fermentation and cellular respiration–Use glycolysis to oxidize glucose and other

organic fuels to pyruvate• Fermentation and cellular respiration– Differ in their final electron acceptor• Cell respriraition uses O2

• Fermentation uses NAD+• Cellular respiration– Produces more ATP (~36-38 ATP)

• Fermentation– Produces 2 ATP per cycle

Exit Slip1) Alcoholic fermentation converts

glucose to2) Alcoholic fermentation is

utilized by what organisms? 3) Lactic acid fermentation converts

glucose to4) Lactic acid fermentation is

utilized by what organisms? 5) What is the final acceptor for

alcoholic fermentation?6) What is the final acceptor for

lactic acid fermentation?7) What is the final acceptor for

cellular respiration?

8) Draw and label the diagram