fermentation and the TCA cycle

fermentation is the completion of catabolism without

an electron transport system or an external source to accept electrons

major role of fermentation is the regernation of

NAD+ (NADH → NAD+ and pyruvate products)

fermentation is not considered effecient because

ATP is generally only generated from substrate-level phosphorylation; microbes compensate by consuming large quantities of substrate and excreting large quantities of products

partly oxidized fermentation products are formed because

there is no net change in redox state for fermentation products; the H from NADH is transferred back onto the pyruvate products

purposes of fermentation

• food preservation (waste products of fermentation accumulate and inhibit growth of spoilage organisms and food pathogens)

• improve digestibility (helps break down macromolecules and tenderize)

• add nutrients and flavors

major types of fermentation

• lactate fermentation

• ethanolic fermentation

• heterolactic fermentation

• mixed acid fermentation

products of fermentation are

excreted from the cell

cheese is classified based on water content:

• fermentation of lactose, just like milk and yogurts

• soft cheese like cottage cheese only relies on bacterial fermentation to acidify and coagulate proteins to curd

• ripened cheeses undergo further processing to expel water, further fermentation to develop flavor

pickling vegetables

• lactic acid fermentation

• does not use starter cultures but naturally occurring lactic acid bacteria on the vegetables

what must be produced from pyruvate before it can enter the TCA cycle?

acetyl-coA

what large multisubunit enzyme catalyzed the conversion of pyruvate to acetyl-coA?

pyruvate dehydrogenase complex (PDC)

pyruvate dehydrogenase complex (PDC) activity is highly regulated:

• induced when carbon sources are plentiful, lots of NAD+ and CO2

• reduced when low carbon and oxygen, high amount of products NADH and acetyl-coA

the decarboxylation of pyruvate into acetyl-coA also produces

1 NADH

net output of the TCA cycle

one acetyl-coA =

• 3 NADH

• 1 FADH2

• 1 ATP