Chapter 7 Flashcards
autotrophs
able to produce their own organic molecules through photosynthesis
heterotrophs
live on organic compounds produced by other organisms
respiration
all organisms use cellular respiration to extract energy from organic molecules
oxidations
loss of electrons
dehydrogenations
lost electrons are accompanied by protons
* a hydrogen atom is lost (1 electron, 1 proton)
T or F: cellular respiration is a series of reactions
true
nicotinamide adenosine dinucleotide (NAD+)
- An electron carrier
- NAD+ accepts 2 electrons and 1 proton to become NADH
- Reaction is reversible
aerobic respiration
final electron receptor is oxygen (O2)
anaerobic respiration
final electron acceptor is an inorganic molecule (not O2)
fermentation
final electron acceptor is an organic molecule
aerobic respiration formula
C6H12O6 + 6O2 —–> 6CO2 + 6H2O
* ΔG: -686kcal/mol of glucose
* This large amount of energy must be released in small steps rather than all at once.
electron carriers
- Many types of carriers used: soluble, membrane-bound, move within membrane
- All carriers can be easily oxidized and reduced
- Some carry just electrons, some electrons and protons
- NAD+ acquires 2 electrons and a proton to become NADH
ATP
Cells use ATP to drive endergonic reactions
-ΔG = -7.3 kcal/mol
2 mechanisms for synthesis of ATP
1. Substrate-level phosphorylation
* Transfer phosphate group directly to ADP
During glycolys
2. Oxidative phosphorylation
* ATP synthase uses energy from a proton gradient
oxidation of glucose
The complete oxidation of glucose proceeds in stages:
1. Glycolysis
2. Pyruvate oxidation
3. Krebs cycle
4. Electron transport chain & chemiosmosis
glycolysis
- converts 1 glucose (6 carbons) to 2 pyruvate (3 carbons)
- 10 step biochemical pathway
- occurs in the cytoplasm
- Net production of 2 ATP molecules by substrate level phosphorylation
- 2 NADH produced by the reduction of NAD+
for glycolysis to continue, NADH must be recycled to NAD by either:
Aerobic respiration:
* oxygen is available as the final electron acceptor
* produces significant amount of ATP
Fermentation:
* occurs when oxygen is not available
* organic molecule is the final electron acceptor
fate of pyruvate
depends on oxygen availability
* when oxygen is present, pyruvate is oxidized to acetly-CoA, which enters the Krebs cycle
* without oxygen, pyruvate is reduced in order to oxidize NADH back to NAD+
oxidation of pyruvate
if oxygen is present, pyruvate is oxidized
** occurs in the mitochondria in eukaryotes
** multienzyme complex called pyruvate dehydrogenase catalyzes the reaction
* occurs at the plasma membrane in prokaryotes
products of pyruvate oxidation
For each 3-carbon pyruvate molecule:
* 1 CO2
* 1 NADH
* 1 Acetyl-CoA which consists of 2 carbons from pyruvate attached to coenzyme A
* Acetyl-CoA proceeds to the Krebs cycle
Krebs Cycle
- oxidizes the acetyl group from pyruvate
- occurs in the matrix of the mitochondria
- Biochemical pathway of 9 steps in 3 segments
1. Acetyl-CoA + oxaloacetate –> citrate
2. Citrate rearrangement and decarboxylation
3. Regeneration of oxaloacetate
Acetyl-CoA and the Krebs Cycle
- releases 2 molecules of CO2
- reduce 3 NAD+ to 3 NADH
- reduce 1 FAD (electron carrier) to FADH2
- produce 1 ATP
- regenerate oxaloacetate
Electron Transport Chain
= a series of membrane-bound electron carriers
* embedded in the inner mitochondrial membrane
* electrons from NADH and FADH2 are transferred to complexes of the ETC
* each complex:
- a proton pump creating proton gradient
- transfers electrons to next carrier
chemiosmosis
- accumulation of protons in the intermembrane space drives protons into the matrix via diffusion
- membrane relatively impermeable to ions
- most protons can only reenter matrix through ATP synthase
energy yield of respiration
Theoretical energy yield:
- 32 ATP per glucose for bacteria
- 30 ATP per glucose for eukaryotes
Actual energy yield:
- reduced yield is due to:
* “leaky” inner membrane
* use of the proton gradient for purposes other than ATP synthesis
