L22: Glycolysis and Fermentation

Question 1

How many ATP molecules are used in phase 1 of glycolysis?

Answer 1

• None

Question 2

Is CO2 output of glycolysis?

Answer 2

• No

Question 3

What is fermentation?

Answer 3

• it is a metabolic process that converts sugars to acids, gases or alcohol

Question 4

Which cells can ferment?

Answer 4

• Bacteria
• Yeast
• Muscle cells

Question 5

When does fermentation occur?

Answer 5

• alternate pathway after stage 1 - glycolysis

- not all cells can ferment! (need specific enzymes)

Question 6

Why does fermentation occur?

Answer 6

• pyruvate cannot continue in cellular respiration
• i.e. cannot enter the mitochondria, undergo acetyl Co-A synthesis and citric acid cycle
• most likely reason is the lack of terminal electron acceptor O2

Question 7

What occurs if glucose is available?

Answer 7

• the cell will undergo glycolysis and produce ATP and NADH, but ends there

Question 8

In the absence of a terminal electron acceptor (CR cannot continue after glycolysis), a cell…

Answer 8

• can make enough ATP for survival by SLP in glycolysis if pyruvate is converted to lactate or ethanol

Question 9

In the absence of TEA/CR a cell can still make ATP by SLP in glycolysis if it…

Answer 9

• Oxidized NADH to NAD+

Question 10

What happens in fermentation?

Answer 10

• there is no TEA
• pyruvate will undergo “fermentation”
• NADH will deliver electrons to fermentation intermediates

Question 11

What are 2 types of fermentation?

Answer 11

• ethanol fermentation

- lactic acid fermentation

Question 12

What compounds are produced in fermentation?

Answer 12

• waste products
• not all the carbons have been oxidized - therefore energy in the reduced carbon bonds is not utilized
• ethanol and lactic acid

Question 13

What does NADH do in fermentation?

Answer 13

• NADH donates electrons to re-generate NAD+
• now, NAD+ can return to glycolysis to pick up more electrons
• delivering electrons and picking up electrons

Question 14

How is ethanol fermentation different from lactic acid fermentation?

Answer 14

CO2 is also produced as a waste product

Question 15

Respiration vs. fermentation

Answer 15

RESPIRATION:

• ATP made in stage 1, 3, 4
• i.e. cell makes most of its ATP by oxidative phosphorylation
• when cells “respire” they use O2 as a terminal acceptor electron

FERMENTATION:
- cell makes ALL of its ATP by substrate-level phosphorylation

Question 16

Key points: CR vs. Fermentation

Answer 16

CR:

• all 6 carbon atoms in glucose are completely oxidized to CO2
• oxidized C atoms discarded as CO2 waste
• more ATP can be synthesized IF the cell can complete all 4 stages

FERMENTATION:

• no net oxidation of C
• electrons removed from some C atoms and returned to others
• the products of fermentation are waste products
• lactic acid has some reduced carbons however there is no pathway to oxidize these further to CO2 = waste
• much less ATP if a cell can only complete stage 1 (glycolysis) and fermentation