39. Catabolism, respiration and fermentation Flashcards
1
Q
what are the phases of aerobic respiration?
A
- glycolysis
– oxidative decarboxylation of pyruvate - krebs cycle
- electron transport chain
2
Q
what does aerobic glycolysis do?
A
- converts glucose to pyruvate
– generating 2 ATP by substrate level phosphorylation - pyruvate decarboxylated to acetyl-coenzyme A (acetyl-CoA) and CO2
3
Q
what happens in the krebs cycle?
A
- acetyl CoA enters krebs cycle
– 2 CO2, 3 NADH, 1 FADH, 1 ATP
4
Q
what happens in the electron transport chain?
A
- generates ATP
- regenerates NAD+
– oxygen is terminal electron acceptor
5
Q
what is oxidative decarboxylation of pyruvate?
A
- not part of krebs cycle
– but main source of acetyl-CoA, also from catabolism of many lipids, carbohydrates and amino acids - pyruvate converted to acetyl-CoA and CO2
– enzyme containing coenzyme A removes CO2
– coenzyme A binds to C2 intermediate forming acetyl-CoA
– NAD+ reduced to NADH
6
Q
how is pyruvate oxidation regulated?
A
- irreversible conversion step
– controls amount of acetyl-CoA enters krebs - catalysed by enzyme pyruvate dehydrogenase
– inhibited by acetyl-CoA
– activated by pyruvate
– ensures acetyl-CoA only made when needed and plenty of pyruvate available - ATP and NADH inhibit enzyme, ADP activates
– acetyl-CoA formed when energy stores low
7
Q
what is the krebs cycle?
A
- tricarboxylic acid (TCA) cycle
– or citric acid cycle - mitochondrial matrix (eukaryotes)
- cytoplasmic matrix (prokaryotes)
- complete oxidation of glucose
- generates carbon skeletons for biosynthesis
– precursor metabolites
8
Q
what is the process of the krebs cycle?
A
- first reaction
– condensation of acetyl-CoA, C4 intermediate, oxaloacetate
– forms citrate (C6) - citrate oxidised and decarboxylated twice producing:
– 2 molecules CO2 (waste)
– 2 NADH - citrate converted back to oxaloacetate
– series of enzymatically catalysed steps
– produces 1 ATP, 1 FADH, 1 additonal NADH
9
Q
how is the krebs cycle regulates?
A
- pyruvate dehydrogenase
– enzyme that produces acetyl-CoA - two additonal steps
– CO2 molecules released
– NADH produces - isocitrate dehydrogenase turns C6 to C5
– inhibited by ATP and NADH
– activated by ADP - alpha-ketoglutarate dehydrogenase turns C5 to C4 bound by coenzyme (A) (succinyl-CoA)
– inhibited by ATP, NADH, and other molecules including succinyl-CoA
10
Q
what is produced by the krebs cycle?
A
- 2 molecules CO2
- three NAD+ reduced to NADH
- one FAD reduced to FADH2
- one ATP generated
- since two molecules pyruvate produced by one glucose
– krebs cycle occurs twice
11
Q
what happens post glycolysis, decarboxylation, krebs cycle?
A
- all carbon and oxygen from glucose released as:
– CO2
– H+ atoms and electrons reduce NAD+ and FAD and delivered to electron transport chain
12
Q
how are electrons transported and oxidative phosphorylation occur?
A
- glycolysis and krebs generate 4 ATP
– by substrate-level phosphorylation
– also generate 10 NADH, 2 FADH2 - most ATP generated during aerobic respiration from oxidation
– electron carriers in ETC - ETC consistes of series of tranmembrane proteins
– prokaryotes: cell membrane
– eukaryotes: mitochondrial membrane
– transfer of e- from donors to acceptors - H+ separated into protons and e-
– e- transported through chain, through series of donor/acceptor molecules (falling to successively lower energy states)
– released energy pump protons across membrane (Eukaryotes=intermembrane space of mitochondria; prokaryotes=outside cell) - forms proton gradient (pH) and charge gradient
– chemical/electrical potential differences (PMF=proton motive force)
– used to perform work (ATP generation) when protons flow back across membrane, down gradients - oxygen is terminal electron acceptor
– forms H2O with H+
13
Q
how is ATP generated?
A
- flow of protons down gradients released energy
– used to phosphorylate ADP to ATP
– oxidative phosphorylation - use PMF to generate ATP, catalysed by ATP synthase (ATPase)
– transmembrane protein
– smallest biological motor
– protons pumped back across membrane through ATPase down gradients causing physical rotation in socket - drives coupling of ADP with Pi to form ATP
– NADH - 3 ATP
– FADH2 - 2 ATP
14
Q
what does aerobic respiration result in?
A
- complete oxidation of glucose
– to CO2 in presence of oxygen - 38 ATP generated
– 4 ATP = substrate-level phosphorylation
– 34 ATP = oxidative phosphorylation
15
Q
what is anaerobic metabolism?
A
- metabolism of glucose without oxygen
– anaerobic respiration
– fermentation - for aerobic organisms
– temporary, facultative reactions to ‘weather storm’ whilst oxygen concentrations low
– if O2 remains low, organisms not able to survive
16
Q
what does anaerobic respiration involve?
A
- terminal electron acceptor
– nitrate, nitrite and sulphate - produces less ATP than aerobic
– slower growth
17
Q
what is fermentation?
A
- doesn’t require O2
- releases energy from oxidation of organic molecules
– sugars, organic acids, amino acids, purines, pyramidines - glycolysis common pathway
– no krebs cycle or ETC
– pyruvate used as terminal electron acceptor from NADH (regenerating NAD+ for glycolysis)
18
Q
what are the types of fermentation?
A
- lactic acid fermentation
– bacteria, protists, animal skeletal muscle - alcohol fermentation
– fungi, protists, bacteria
– saccharomyces cerevisiae (yeast)
19
Q
what is lactic acid fermentation?
A
- NADH reduces pyruvate
– generating lactate - NAD+ cycle back to glycolysis
- net yield of 2 ATP per molecule glucose
20
Q
what is alcohol fermentation?
A
- pyruvate broken down into C2 and CO2
- NADH reduces C2
– generates ethanol - NAD+ cycled back to glycolysis
- net yield of 2 ATP per molecule glucose
21
Q
what are the differneces between respiration and fermentation?
A
- oxidation
– complete
– partial - electrons
– from NADH go to O2 / other terminal e- acceptors
– NAD+ regenerated by pyruvate reduction - ATP
– large amount generated through ETC and oxidative phosphorylation
– few ATP generated
22
Q
A
