3.3 Flashcards
metabolic principles
consists of many metabolic pathways
1. complex chemical transformations occur in a series of separate reactions
2. each reaction is catalyzed by a specific enzyme
3. some key enzymes can be inhibited or activated to alter the rate of the pathway
4. many metabolic pathways are similar in all organisms
5. in eukaryotes, metabolic pathways are compartmentalized in specific organelles
cell energy
cells harvest energy from glucose in a series of metabolic pathways
aerobic - pyruvate oxidation, citric acid cycle, electron transport chain = CO2 + H2O
anaerobic - fermentation = lactate and alcoholic
glucose oxidation
in the presence of oxygen, glucose oxidation is highly exergonic and can drive the formation of a lot of ATP
glucose is oxidized in a series of controlled redox reaction (more efficient than direct burning)
oxidation-reduction (redox) reactions
chemical reactions that involve the transfer of electrons between two species
oxidation and reaction always occur together
reducing agent (e- donor): reduces other species by donating electrons
oxidizing agent (e- acceptor): oxidizes other species by accepting electrons
oxidation
loss of electrons
loss of hydrogen atoms
reduction
gain of electrons
gain of hydrogen atoms
partial electron transfer
electron transfer can be partial in redox reactions, where an atom’s share of electrons is changed
when electrons spend more time near an atom, it is reduced
a partial negative atom is more reduced than a neutral or partial positive atom
a partial positive atom is more oxidized than a neutral or partial negative atom
redox and free energy
the more reduced a molecule is, the more free energy it has stored in its bonds
most reduced state = highest free energy (high potential energy in its bonds)
most oxidized state = lowest free energy (low potential energy in its bonds)
NAD+/NADH
coenzyme nicotinamide adenine dinucleotide exists in two distinct forms: oxidized (NAD+) and reduced (NADH)
key electron carrier in redox reactions
some energy is transferred from the reducing agent to the reduced product
glucose metabolism
C6H12O6 + 6O2 –> 6CO2 + 6H2O + free energy
glucose is oxidized (reducing agent)
oxygen is reduced (oxidizing agent)
energy release from glucose oxidation is trapped via the reduction of NAD to NADH+
glycolysis
takes places in the cytoplasm
2 pyruvate
2 NADH
2 net ATP
10 step metabolic pathway (1-5 require energy, 6-10 yield NADH and ATP)
substrate-level phosphorlylation
phosphate is transferred directly from the phosphorylated substrate to ADP, forming ATP
in glycolysis, ATP is formed via substrate-level phosphorlylation
