Quiz #6 Flashcards
What is cellular respiration?
the source of ATP in almost all eukaryotic organisms, and bacteria can perform a modified form of cellular respiration
the center of ATP formation in the eukaryotic cell is the mitochondrion
What is the general scheme for metabolizing glucose in eukaryotes?
cellular respiration is a catabolic process
glycolysis (in cytosol): 1 Glucose –> 2 Pyruvate + 2 NADH
further metabolism of pyruvate by one of two possible routes (which one used depends on abundance of oxygen): Krebs cycle and electron transport chain, or Fermentation
What are the stages of harvesting glucose?
- Glycolysis (breaks down glucose into two molecules of pyruvate)
- Citric acid cycle (Kreb’s Cycle, completes breakdown of glucose)
- Oxidative phosphorylation (accounts for most of ATP synthesis)
What is glycolysis?
“sugar splitting”
can be separated into two phases: Investment Phase (ATP is used), Energy payoff phase (ATP and other energy-containing products are formed)
represents the start of oxidation of glucose, 10 reactions occurs in the cytoplasm, anaerobic (no oxygen required), occurs in all domains of life
net: 2 ATP, 2 pyruvate, 2 NADH
divided in two phases: energy investment, energy payoff
What are the steps of glycolysis?
- Hexokinase enzyme transfers a phosphate group from ATP to glucose, this energy investment makes glucose more reactive
- Glucose-6-phosphate is converted to its isomer Fructos-6-phosphate
- Phosphofructokinase transfers a phosphate group from ATP to the opposite end of the sugar (requires a second ATP), this is a key step in regulation of glycolysis
- Aldolase cleaves the 6-carbon sugar into two 3-C sugars
- Isomerase causes a flip between these two isomers, the detection depends on the concentration of reactants, Glyceraldehyde 3-phosphate is quickly used up, so the equilibrium shifts to favor conversion in that direction
- This enzyme catalyzes two coupled reactions: each G3P is oxidized by transferring 2 electrons to NAD+ (exergonic), a phosphate bond is made producing a product with very high potential energy (endergonic)
- Phosphate added in step 6 is transferred to ADP (exergonic) = substrate level phosphorylation
- This enzyme changes the location of the phosphate
- Enolase creates a double bond and removes H2O
- Pyruvate kinase creates ATP via substrate level phosphorylation
What is the process of the oxidation of pyruvate into acetyl CoA?
pyruvate entry into mitochondria requires active transport
a multi-enzyme complex (pyruvate dehydrogenase complex) then catalyzes three reactions:
- Pyruvate’s carboxyl group is already oxidized and contains little energy - it is removed
- The remaining 2C molecule is oxidized, the electrons are transferred to NAD+
- Coenzyme A is attached via its sulfur atom to acetyl group, forming acetyl CoA
What is the citric acid cycle?
also called the Krebs Cycle
oxidizes the remaining 2 carbons from pyruvate to two CO2
generates 1 GTP (or ATP) per cycle by substrate level phosphorylation
reduces 3 NAD+ to 3 NADH and 1 FAD to 1 FADH2 per cycle
the reduced NADH and FADH2 shuttle electrons to an electron transport chain
occurs in the mitochondrial matrix
What are the steps of the Krebs Cycle?
- Acetyl group of acetyl CoA combines with oxaloacetate, forming citrate
- Citrate is converted to it’s isomer, isocitrate
- Isocitrate is oxidized, reducing NAD+ to NADH releasing CO2
- alpha-ketoglutarate is oxidized, reducing NAD+ to NADH, releasing CO2, CoA attaches to the 4-carbon product, creating an unstable intermediate
- CoA is displaced by inorganic phosphate, which is then quickly transferred to GDP (guanosine diphosphate) to make GTP by substrate level phosphorylation
- Two hydrogens are transferred from succinate to FAD, forming FADH2 (oxidizing succinate to fumarate) enzyme = succinate dehydrogenase complex
- H2O is added to fumarate, and bonds are rearranged to create malate
- Malate is oxidized, reducing NAD+ to NADH, this regenerates oxaloacetate and completes the cycle
What is the electron transport chain?
functionally similar to the electron transport chain between PSII and PSI in photosynthesis
couples the energy released from “falling” electrons with the pumping of protons
4 protons flowing through ATP synthase will generate 1 ATP
What is Complex I in the electron transport chain?
NADH dehydrogenase
FMN: flavin mononucleotide
Fe*S: iron-sulfur protein
What is Complex II in the electron transport chain?
Succinate dehydrogenase
this is the same enzyme that does step 6 in the Krebs Cycle
electrons are added directly to the ETC during the reaction of succinate —> fumartate
What is Complex III in the electron transport chain?
Cytostome bc1 complex
What is Complex IV in the electron transport chain?
Cytostome C oxidase
What is “Q” in the electron transport chain?
ubiquinone (also called coenzyme Q)
a small hydrophobic molecule (Q is not a protein)
it can move around within the membrane
What is cytochrome C?
this component is also mobile
is water soluble (hydrophilic), all cytochromes are proteins that have a special heme molecule that accepts and donates electrons
