Learn: BIO 120 Session 11 — Fermentation

What is fermentation?

A form of anaerobic catabolism where organic compounds both donate and accept electrons.

Does fermentation require an external electron acceptor?

No.

What type of oxidation occurs during fermentation?

Incomplete oxidation of organic compounds under anaerobic conditions.

Does fermentation use an electron transport chain (ETC)?

No.

Does ATP synthase produce ATP during fermentation?

No.

How is ATP produced during fermentation?

Substrate-level phosphorylation.

Why must NADH be converted back to NAD+ during fermentation?

To regenerate NAD+ so glycolysis can continue.

What happens if a cell cannot regenerate NAD+?

Glycolysis stops, so ATP production through glycolysis stops.

What happens to NAD+ during glycolysis?

It accepts electrons and is reduced to NADH.

What happens to NADH during fermentation?

It donates electrons and is oxidized back to NAD+.

Main purpose of fermentation regarding NAD+/NADH

Regenerate NAD+ so glycolysis can continue.

Fermentation = what type of phosphorylation?

Substrate-level phosphorylation.

Respiration = what type of phosphorylation?

Oxidative phosphorylation.

What is substrate-level phosphorylation?

Direct transfer of a phosphate from an energy-rich substrate to ADP to make ATP.

Does substrate-level phosphorylation require an ETC?

No.

What is oxidative phosphorylation?

ATP production associated with an ETC and ATP synthase.

Does oxidative phosphorylation require an ETC?

Yes.

What does respiration use as a terminal electron acceptor?

An external electron acceptor such as O2 or another exogenous molecule.

Fermentation vs respiration: external electron acceptor?

Fermentation does not require one; respiration does.

What do fermentation and respiration have in common?

Both conserve energy from oxidation-reduction reactions.

What is another name for the main glycolysis pathway?

Embden-Meyerhof-Parnas pathway.

What molecule begins glycolysis?

Glucose.

What are the major carbon products of glycolysis?

2 pyruvate.

How many ATP are produced during glycolysis before subtracting those used?

4 ATP.

How many ATP are consumed during glycolysis?

2 ATP.

What is the NET ATP yield of glycolysis?

2 ATP per glucose.

One glucose produces how many pyruvate during glycolysis?

2 pyruvate.

Why is glycolysis especially important during fermentation?

It provides ATP through substrate-level phosphorylation.

What is homofermentative lactic acid fermentation?

Fermentation in which glucose is converted mainly to lactate.

Main product of homofermentative lactic acid fermentation

Lactate only.

HOMOfermentative = memory trick

Homo = one main product: lactate.

What is heterofermentative lactic acid fermentation?

Fermentation producing lactate, ethanol, and CO2.

Products of heterofermentative lactic acid fermentation

Lactate + ethanol + CO2.

HETEROfermentative = memory trick

Hetero = several different products.

Which microbes are examples of homolactic fermenters?

Streptococcus and some Lactobacillus.

Which microbes are examples of heterolactic fermenters?

Leuconostoc and some Lactobacillus.

What are the two major glucose fermentation patterns in enteric bacteria?

Mixed-acid fermentation and 2,3-butanediol fermentation.

What is mixed-acid fermentation?

A fermentation pathway producing a mixture of acids and other products.

Products associated with mixed-acid fermentation

Lactate, acetate, formate, succinate, ethanol, H2, CO2, and other products.

What type of bacteria can perform mixed-acid fermentation?

Enteric bacteria.

What major product identifies 2,3-butanediol fermentation?

2,3-butanediol.

What intermediate is shown before 2,3-butanediol in the lecture pathway?

Acetoin.

Simplified 2,3-butanediol pathway

Pyruvate → α-acetolactate → acetoin → 2,3-butanediol.

Can microbes ferment compounds other than glucose?

Yes; some microbes ferment amino acids.

What is the Stickland reaction?

Coupled amino acid fermentation where one amino acid is oxidized and another is reduced.

What organisms does the lecture associate with the Stickland reaction?

Some species of Clostridium.

In the Stickland reaction, how many amino acids participate functionally?

Two: one is oxidized and another is reduced.

What phosphorylation produces ATP during the Stickland reaction?

Substrate-level phosphorylation.

Stickland reaction = memory trick

Two amino acids work as a pair: one oxidized, one reduced.

What are the products of alcoholic fermentation listed in the lecture?

Ethanol + CO2.

What organisms are associated with alcoholic fermentation in the lecture?

Yeast and Zymomonas.

How can fermentation be used in food?

Food preservation and food/beverage production.

What biomedical/industrial uses of fermenting microbes are listed?

Antibiotic, vitamin, and amino acid production.

What environmental uses of fermenting microbes are listed?

Composting, sewage treatment, and landfills.

Where can fermentation naturally occur?

Anaerobic environments such as sediments, swamps, soils, animals, and decaying material.

What types of microbes are potential fermentors?

Strict anaerobes, facultative aerobes, and aerotolerant anaerobes.

A microbe is fermenting glucose without using an ETC. How is it making ATP?

Substrate-level phosphorylation.

A cell has no usable respiration pathway and NADH is accumulating. What must happen?

NADH must be oxidized back to NAD+ through fermentation.

Why would glycolysis stop if NAD+ were unavailable?

NAD+ is needed as an electron acceptor during glycolysis.

A bacterium produces only lactate from glucose. What fermentation is occurring?

Homofermentative lactic acid fermentation.

A bacterium produces lactate, ethanol, and CO2. What fermentation is occurring?

Heterofermentative lactic acid fermentation.

A bacterial culture produces many different acids plus products such as ethanol and gases. What pathway fits best?

Mixed-acid fermentation.

A microbe produces acetoin and then 2,3-butanediol. What fermentation is occurring?

2,3-butanediol fermentation.

A Clostridium species oxidizes alanine while reducing another amino acid. What process is this?

Stickland reaction.

A pathway directly transfers phosphate from a metabolic intermediate to ADP. What is this?

Substrate-level phosphorylation.

A pathway uses an ETC, proton motive force, and ATP synthase. What is this?

Oxidative phosphorylation.

Fermentation is occurring. Would you expect oxidative phosphorylation to be the main ATP source?

No; fermentation uses substrate-level phosphorylation.

If oxygen is absent, can fermentation still regenerate NAD+?

Yes; organic fermentation products accept electrons from NADH.

One glucose enters glycolysis. What should you remember for the quiz?

2 pyruvate + 2 net ATP, with NADH produced.

Which gives more than one major fermentation product: homo- or heterofermentation?

Heterofermentation.

Which gives lactate only: homo- or heterofermentation?

Homofermentation.

What is the key energetic reason fermentation matters to microbes?

It regenerates NAD+ and allows glycolysis and ATP production to continue.