Chapter 9 - Pathways that Harvest Chemical Energy Flashcards
Glucose
Most common fuel molecule in cells; used in cellular respiration to generate ATP
5 Principles of Metabolic Pathways
Complex transformations are a series of separate reactions; each reaction is catalyzed by a specific enzyme; many metabolic pathways are similar in all organisms; in eukaryotes, metabolic pathways are compartmentalized in specific organelles; key enzymes can be inhibited or activated (regulated) to alter the rate of the pathway
Glucose redox reaction
Glucose loses electrons (becomes oxidized) and oxygen gains them (becomes reduced)
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + free energy
Three catabolic processes that harvest energy from glucose
Glycolysis - glucose is converted into 2 pyruvate (oxygen independent)
Cellular respiration (Pyruvate Oxidation, Kreb’s Cycle, Oxidative Phosphorylation) - Converts pyruvate into 3 molecules of CO2
Fermentation - converts pyruvate into lactic acid or ethyl alcohol (ethanol)
Substrate level phosphorylation
The formation of ATP with a donated phosphate group from a compound
Oxidative phosphorylation
The formation of ATP by oxidation of electron carriers in the presence of O2; includes the electron transport chain and chemiosmosis
NAD+
Coenzyme that operates as a key electron carrier in glucose metabolism
Dehydrogenase
Enzyme that removes hydrogen from a molecule (ie. NADH)
Glycolysis
Takes place in the cytoplasmic area and oxygen independent; converts glucose (6C) into 2 pyruvate (3C) molecules; produces 2 ATP and 2 NADH; occurs in 10 steps catalyzed by a specific enzyme
Glycolysis investment phase
Requires an input of 2 ATP in the first 5 steps to complete glycolysis
Glycolysis energy payoff phase
4 ATP and 2 NADH are generated from the last 5 steps of glycolysis
3 possible outcomes for pyruvate
Oxidative phosphorylation, lactic acid fermentation or alcohol fermentation
Kreb’s Cycle
aka Citric Acid Cycle or Tricarboxlic Acid Cycle (TCA); 8 enzyme catalyzed steps producing 6 NADH, 2 FADH2, 2 ATP and releasing 4 CO2
Pyruvate Oxidation
If O2 is present, pyruvate is oxidized and converted to Acetyl-CoA in the mitochondrial matrix and then combines with oxaloacetate in the Kreb’s cycle; forms 2 NADH and 2 CO2
Electron transport chain
Requires a series of reactions so that energy can be captured by an endergonic reaction; energy is released as electrons (from NADH and FADH2) are passed between carriers; electrons from NADH and FADH2 are passed along the respiratory chain, a series of protein complexes in the inner mitochondrial membrane containing electron carriers and enzymes; the final electrons are donated to O2 where O2 is reduced to H2O; ATP is NOT created in this step
Proton motive force
Protons are actively transported across the mitochondrial inner membrane at the same time that electrons are being passed down the ETC; protons accumulate in the intermembrane space and create a concentration gradient and charge difference creating a potential energy
Chemiosmosis
Couples proton movement across a membrane with ATP synthesis using the enzyme ATP synthase (rotary motor mechanism)
ATP Synthase
A rotary motor mechanism that acts as a channel allowing H+ to diffuse back into the matrix (chemiosmosis); uses the energy of the diffusion to rotate the axle and combine ADP and Pi to make ATP
Fermentation
Process to continue to produce energy without undergoing oxidative phosphorylation (in the absence of O2); occurs in the cytosol; replenishes NAD+ to keep glycolysis going
Lactic acid fermentation
Fermentation that uses NADH as a reducing agent to reduce pyruvate to lactate, thus regenerating NAD+ to keep glycolysis operating; when lactate builds up, the increase in [H+] lowers pH and causes muscle pain
Alcohol fermentation
Pyruvate from glycolysis is converted into acetaldehyde, and CO2 is released. NADH from glycolysis is used to reduce acetaldehyde to ethanol, thus regenerating NAD+ to keep glycolysis operating.
