Microbial Metabolism (Catabolism) Flashcards
What is substrate-level phosphorylation?
- used in fermentation and other pathways
- ATP is synthesized during steps in the catabolism of an organic compound (glycolysis)
- transferring a phosphate from an energy rich compound to ADP to make ATP
What is oxidative phosphorylation?
- used in respiration
- ATP is produced by proton motive force
What is fermentation?
- takes place in the absence of an exogenous electron acceptor (don’t need oxygen)
- uses pyruvate or a pyruvate derivative as the electron acceptor
- continues recycling of electron carriers (NADH from glycolysis oxidized to NAD+)
- forms ATP via substrate level phosphorylation
- produces various fermentation products (waste products)
- does not use an ETC or proton motive force
What are the different kinds of fermentation products?
- ethanol: used to make breads, wine, and beer
- lactic acid (homolactic): lactic acid is the only fermentation product; used to make certain cheeses, sour cream, and yogurt
- lactic acid (heterolactic): makes lactic acid and other products; used to make sauerkraut, pickles, buttermilk; involved in food spoilage
- mixed acid: tested for by MR test
- 2,3-butanediol: tested for by the VP test, detects the intermediate acetoin
- propionic acid: used to make swiss cheese
What is aerobic respiration?
- respiration in which the final electron acceptor is oxygen
- ATP is made primarily by oxidative phosphorylation where electron transport is used to generate proton motive force
- ATPase involved
What is anaerobic respiration?
- respiration in which the final electron acceptor is a different exogeneous acceptor such as NO3-, SO4-, CO2, Fe3+, or SeO42-
- organic acceptors such as fumarate may also be used
- still uses oxidative phosphorylation and an electron transport chain
- yields less energy than aerobic respiration
- E0’ of final electron acceptor is less positive than the E0’ of oxygen
What is the purpose of the MRVP test?
- the MR test detects the production of mixed acids as a product of fermentation
- the MR test uses methyl red as an indicator which turns red if the pH is below 5 (positive test)
- the VP test detects the production of butanediol as a product of fermentation by testing for the precursor acetoin
- the VP test uses Barritt’s A and Barrit’s B which will turn the solution red if acetoin is present, pH does not go below 5
- should only test positive for one or the other
Where is the electron transport chain located in eukaryotes?
the inner mitochondrial membrane
Where is the electron transport chain located in bacteria and archaeons?
the cytoplasmic membrane
What is the electron transport chain?
- a series of electron carriers that operate together
- transfers electrons from NADH and FADH2 to a terminal electron acceptor
- electrons flow from carriers with a more negative E’0 to carriers with a more positive E’0
- as electrons are transferred, energy is released to make ATP via oxidative phosphorylation
What is the P/0 ratio for NADH?
3 ATP per NADH
What is the P/0 ratio for FADH2?
2 ATP per FADH2
How does ATP synthase work?
- protons are moved from the mitochondrial matrix to the intermembrane space by the complexes of the electron transport chain
- the movement of protons establishes proton motive force
- ATP synthase uses the proton flow down the concentration gradient to make ATP
What is the structure of ATPase?
- C12: spinning C cylinders
- a: channel for H+ ions to enter
- b2: holds headpiece stationary
- beta: brings ADP and Pi together and releases ATP
- F1: headpiece
- Fo: motor
What are the functions of proton motive force?
- can be used to generate ATP
- can be used to rotate the flagella (explains why fermentative bacteria have ATPase because it can work backwards to generate PMF)
- PMF can sometimes be used instead of ATP to fuel active transport