Electron Transport Chain and TCA Cycle Flashcards
Why is ATP so energetic?
Adenosine triphosphate (ATP) contains three phosphate groups, which are very hydrophilic and cause conformational changes of proteins
Hydrolysis of phosphoanhydride bonds is spontaneous and exothermic (delta H, delta G are negative) and can provide energy required for less energetically favorable rxns
Oxidative Phosphorylation
Oxidation reactions provide energy for phosphorylation
Requires presence of Oxygen as final electron acceptor which occur in the mitochondria
Energy comes from NADH and FADH2
NAD+
Nicotinamide adenine dinucleotide
Two nucleotides joined together by phosphate groups
One of base groups of one of the nucleotides in NAD+ can exist in either oxidized or reduced state
NADH acts as a soluble electron carrier- hydride ion is source of e-
Where is the most NADH produced in the cell?
Most NADH is produced in the citric acid cycle in the mitochondria
Citric acid cycle takes place in the mitochondrial matrix
Citric Acid Cycle
AKA Krebs Cycle or Tricarboxylic Acid Cycle (TCA)
A cycle involving the input of 1 Acetyl-CoA, output of 2CO2, 1 ATP, 3 NADH, and 1 FADH2 and regeneration of oxaloacetate
Note that glycolysis makes 1 NADH / 3 in TCA cycle
Reaction intermediates of Citric Acid Cycle
Oxaloacetate + Acetyl-CoA -> Citrate -> Isocitrate -> alpha-ketoglutarate + CO2 + NADH -> Succinyl CoA + CO2 + NADH -> Succinate + (GTP/ATP) -> Fumarate + FADH2 -> Malate + Oxaloacetate + NADH
How is the citric acid cycle regulated?
Regulated by the amount of NAD+ available
NAD+ generated by oxidation of ANDH by ETC
If ETC inhibited due to lack of Oxygen, NADH cannot be oxidized
Cell will use anaerobic pathways
TCA is considered aerobic due to this regulation
What other molecules can serve as substrates to the Citric Acid Cycle besides Acetyl-CoA?
Amino acids can enter after being deaminated in liver (to produce pyruvic acid or acetyl-CoA) or at various stages (glutamic acid can be converted into alpha-ketoglutarate)
Fats can be converted into acetyl-CoA in addition to polysaccharides
Electron Transport Chain
A series of redox reactions that result in the transfer of electrons from NADH and FADH2 to O2 resulting in H2O. This transfer of e- pumps H+ across the inner mitochrondrial membrane, creating a gradient that is used to synthesize ATP
Electron Transport Chain Protein Steps
- Complex I receives 2 e- from NADH and transfers to ubiquinone, pumps 4H+
- Complex II receives e- from FADH2, transfers to quinone carrier, Q -> QH2
- Complex III receives e- from QH2, transfers to cytochrome c, pumps 4H+
- Complex IV removes e- from cytochrome c, transfers to O2, pumps 2H+
Where are protons pumped to during the Electron Transport Chain?
The intermembrane space in the mitocondria
This is between the outer and inner membrane and builds the proton-motive force
How is ATP synthesized in the electron transport chain?
The proton-motive force which has built up in the intermembrane space flows along its concentration gradient through the membrane protein ATP synthase, causing ATP synthase to turn. The turning combines a phosphate group with an ADP to generate ATP, called chemiosmotic coupling
Around how many ATP are produced for each NADH and FADH2?
~ 2-3 ATP are produced per NADH
- net because NADH may use ATP to be transported into the mitochondrial matrix
~ 2 ATP are produced per FADH2
How does Oxygen regulate the ETC?
When Oxygen is present, the ETC runs as expected
When Oxygen is lacking, there is no acceptor to which the final electron carrier can pass electrons. The entire chain backs up and NADH cannot pass on electrons, so Citric Acid cycle slows and metabolism shifts into anaerobic fermentation to convert NADH to NAD+
How many net ATP are produced through aerobic respiration (including glycolysis)?
36 net ATP Glycolysis: 2 ATP, 2 NADH Pre-Krebs: 2 NADH Krebs: 2 ATP, 6 NADH, 2 FADH2 ETC: 36 ATP (28 from NADH, 4 from FADH2)
