Fermentation

A.P. Biology Ch. 9

Goals and Objectives• Identify verbally and in written form the steps

involved in fermentation.• Identify verbally and in written form the

factors that influence fermentation.• Compare and contrast fermentation and

cellular respiration

Status Check• Define a redox reaction.• Define “oxidation” & “reduction”

(remember The Lion King)• What is the chemical equation for cellular

respiration?• In cellular respiration, what is oxidized and

what is reduced?• What are the three major steps in cellular

respiration?• What is NAD+ used for in cellular respiration?

Cellular Respiration ReviewC6H12O6 + 6 O2 6 CO2 + 6 H2O + energy

• Exergonic reaction, spontaneous, -ΔG, energy released• Electrons moves from carbon in glucose to oxygen• Glucose turns into CO2; O2 turns into H2O

• Electrons are carried throughout the reaction by NAD+ • Glycolysis will always happen• Krebs Cycle and Oxidative Phosphorylation will only

occur if O2 is present

So the $1,000,000 QUESTION(S)…

What happens when we DON’T have oxygen?How do we still get energy?

What is Fermentation?• Occurs when O2 is not present (anaerobic

reaction)• Involves glycolysis (only step that does not

need O2)• Allows the organism to keep producing small

amounts of ATP without O2 as a final e- acceptor

• Some bacteria use some form of fermentation as main source of ATP

Glycolysis In-Depth C6H12O6 2 C3H4O3 (pyruvate)+ energy (2 ATP)

• Glucose is split into 2 pyruvate molecules• Net gain of 2 ATP created (energy)• e- transferred from glucose to NAD+• Problem: if no O2, all NAD+ gets used up!!!!

2 e-, 4 H+

2 NAD+ 2 NADH + H+

Fermentation In-Depth• Goal of fermentation is to keep glycolysis going, producing 2 ATP

• In order for glycolysis to happen, need constant supply of NAD+ (e- acceptor)

• e- given back to pyruvate from NADH to form lactate, NAD+ renewed

Lactic Acid Fermentation (Humans)

Gain e-

Lose e-

NAD+ able to go back to glycolysis

*As long as NAD+ is available, glycolysis can still happen!!

Transported to liver, converted back to pyruvate

*Too much lactic acid build-up causes muscle fatigue

Alcohol Fermentation (Beer)•Found in some bacteria and fungi

•Same principle as Lactic Acid Fermentation (make NAD+ to keep glycolysis going)

•End product is ethanol (ethyl alcohol)

•CO2 gas is produced (ex. yeast in bread)

• Both ethanol and CO2 are waste products

In General…

NAD+ + 2 H+ NADH + H+ NAD+ + 2 H+ Glycolysis Fermentation

Gain e- from glucose, NAD+ reduced to NADH

Lose e- to pyruvate,NADH oxidized to NAD+

• Glycolysis reduces NAD+ to make NADH

• Fermentation oxidizes NADH to make NAD+

Decisions, decisions…

• Presence of O2 determines steps after glycolysis

• Fermentation can switch to cellular respiration once [O2] is sufficient

Cell. Res. Vs. Fermentation• Cell Respiration

– Produces massive amounts of ATP (~38 ATP)

– Needs O2

– Thought to have evolved after fermentation.

– Final e- acceptor is O2

• Fermentation– Produces little ATP (only

2 ATP through glycolysis)– Does not need O2

– Thought to have evolved first.

– Final e- acceptor is pyurvate

Status Check!!!!!Clicker Time!!!!

Question 1

• One end product of fermentation is:A) Acetyl CoAB) PyruvateC) LactateD) Glucose

Fermentation

Question 2• In fermentation, the electrons from NADH are

given to:A) LactateB) GlucoseC) AlcoholD) Pyruvate

Fermentation

Question 3

• After fermentation, lactate is:A) Turned into glucoseB) Turned into pyruvateC) Turned into alcoholD) Turned into fatty acid

Fermentation

Question 4• In fermentation,

A) NADH is oxidized to NAD+B) NAD+ is oxidized to NADHC) NADH is reduced to NAD+D) NAD+ is reduced to NADH

Fermentation

Question 5

• In fermentation,A) Pyruvate is oxidized, NADH reducedB) Pyruvate is reduced, NADH oxidizedC) Lactate is oxidized, NADH reducedD) Lactate is reduced, NADH oxidized

Fermentation

So the BIG PICTURE…• Fermentation happens when there is little or

no oxygen• Fermentation keeps producing energy by

keeping glycolysis going• Fermentation recycles the NADH into NAD+

that is needed for glycolysis.