Fermentation

2/10/25

Why does anaerobic respiration occur?

• After glycolysis produces pyruvate

• With no oxygen, pyruvate cannot go into mitochondria 

• Oxygen cannot be used as the final electron acceptor

• No etc needed

• Organic compound is used as final electron acceptor

• Produces less atp than aerobic respiration: no figure, less and less overtime 

• Waste products besides CO2 and water accumulate in extracellular space

What is the electron receptor here?

Sulfate

Glycolysis with and without oxygen

• With oxygen: cellular respiration

• Without oxygen: fermentation allows glycolysis to continue

Fermentation types

• Lactic acid fermentation: in mammals and bacteria

• Alcohol fermentation: producing ethanol, in yeast, beer, wine

• Mixed acid fermentation: many different acids, in e. Coli

Depends on 

• availability of nutrient

• Tolerance of waste product

• Energy yield 

• Type of organism

Lactic acid fermentation

• Occurs during intense physical movement when oxygen is not available for our cells

• Muscle cells switch from respiration to fermentation 

• Glycolysis occurs, 2 pyruvate formed

• 2 pyruvate -> 2 lactic acid 

• With no oxygen, NADH cannot be oxidized and travel to etc

• Potential energy from pyruvate conversion to lactic acid used to change NADH -> NAD+ (oxidation)

• Waste (lactic acid) accumulates in muscles preventing muscle function and causing burning, painful sensation

• Clears up about one hour later with proper oxygen intake

• formula: glucose → pyruvic acid → lactic acid + energy 

What build up causes burning and pain?

Lactic acid build up in tissues

Lactic acid fermentation can also be called

a Fate of pyruvate under anaerobic condition

Alcohol fermentation

• Occurs in yeasts and some bacteria

• 2 Pyruvate converted to 2 acetaldehyde converted to 2 ethanol 

• Acetaldehyde is intermediary step 

• Potential energy from acetaldehyde -> ethanol used to oxidize NADH to NAD+ (can also be called NAD+ regeneration)

Applications of fermentation SPALD

• Alcoholic beverages: wine, beer, ethanol makes it intoxicating

• Acidic dairy products: yogurt, accounts for sour taste

• Spoilage of food

• Lactic acid build up in muscle cells

• Pharmaceutical medical purposes 

• Baking: yeast, yeast rises and releases CO2

• Starch, fruit and veggies processing

Difference between yeast/alcohol fermentation and muscle/lactic acid fermentation

• Yeast fermentation has the extra step of converting pyruvate -> acetaldehyde 

• Lactic acid fermentation: glucose -> pyruvate -> NADH

• Yeast/alcohol fermentation: glucose -> pyruvate -> acetaldehyde -> ethanol

What is NADH?

Coenzyme and electron carrier

label

1 = lactic acid fermentation

2 = glucose

3 = 2 pyruvate

4 = 2 lactic acid

5 = 2 adp

6 = 2 atp

7 = 2 nad+

8 = 2 nadh

9 = 2 nadh 

10 = 2 nad+

label

1 = glucose

2 = 2 pyruvate

3 = 2 acetaldehyde

4 = 2 ethanol

5 = glycolysis

6 = NAD+ regeneration

7 = 2 NAD+

8 = 2 NADH+

9 = 2 ADP

10 = 2 ATP

11 = CO2

12 = 2 NADH

13 = 2 NAD+