lecture 4

Question 1

electron transport chain

Answer 1

• 4 protein complexes
• bound by prothetic groups (nonprotein components for catalysing redox rxns)
• electron carriers alternate reduced/oxidised states (accept/donate electrons)
• each components reduced when accept electrons (uphill neighbour), less electronegative
• oxidised when electron is passed downhill
• free energy released when electrons passed
• does not generate ATP
• electrons move along chain (includes cytochrome proteins)
• each cytochrome has prothetic group (heme group, iron accepts/donates electrons)
• last cytochrom (cyt a3) passes electron to oxygen (very electronegative)
• each oxygen atom pick up pair of hydrogen ions from aqueous soln (forms water)

Question 2

prothetic groups

Answer 2

• flavin mononucleotide
• Fe.S protein
• ubiquinone
• cytichrome species

Question 3

ETC complex 1

Answer 3

• NADH donates electrons to first molecule of chain
• flavoprotein in protein complex 1 (FMN - flavin mononucleotide)
• electrons drop free energy as move down chain

Question 4

ETC complex 2

Answer 4

• ETC provides 2/3 energy for ATP synthesis when electron donor is FADH2 (than NADH)
• FADH2 reduces complex 2 (lower energy level)
• has flavin adenine dinucleotide (FAD) prothetic group

Question 5

ETC complexes 3, 4

Answer 5

• ubiquionine reduces complex 3 and 4 via cytochromes
• last cyt (cyt a3) passes electrons to oxygen (very electronegative)

Question 6

why ETC?

Answer 6

• controlled release of free energy as pass down chain
• creation of H+ concentration gradient
  – is proton-motive force (emphasising capacity to do work)
  – has voltage and pH component

Question 7

oxidative phosphorylation

Answer 7

• combination of ETC and chemiosmosis
• chemiosmosis: energy-coupling using energy stored in form H+ conc/ gradient across membrane
• drives ATP synthesis

Question 8

ATP synthesis: molecular mill

Answer 8

• protein compleses spanning inner membrane of mitochondrion
• 4 main parts:
  – H+ ions flow down gradient enter half channel in a stator
  – H+ ions enter binding sites with a rotor (changing shape of subunit so rotor spins within membrane)
  – each H+ makes complete turn before leaving passing through second half channel (into mitochondrial matrix)
  – spinning of rotor causes internal rod to spin (extends like stalk into knob below, held stationary by part of stator)
  – rod turning activates catalytic sites in knob producing ATP from ADP and P
• chemiosis couples ET to ATP via ATP synthesase

Question 9

glucose oxidation producing ATP

Answer 9

• glycolysis (glucose –> pyruvate)
• pyruvate oxidation (Pyruvate –> acetyl CoA)
• citric acid cycle (forms ATP and electrons carried via NADH and FADH2)
• oxidative phosphorylation (AT and chemiosmosis, forms ATP and electrons carried via NADH)
• glycolysis (cytosol forms ATP)
• ATP formed by substrate level phosphorylation

Question 10

electron/energy flow for cellular respiration

Answer 10

• electrons
  – glucose > NADH > ETC > oxygen
• energy
  – glucose > NADH > proton motive force > ATP

Question 11

estimate of ATP output

Answer 11

• each NADH generate 2.5 ATP (10H+ across inner membrane, 4H+ to ATP synthesase to generate 1 ATP)
• each FADH2 generate 1.5 ATP

Question 12

ATP output from cellular respiration

Answer 12

• SLP
  – glycolysis = 2 ATP
  – oxidation of pyruvate (x2) = 0
  – citric acid cycle (x2) = 2 ATP
  — total = 4 ATP
• OP
  – glycolysis = 2 NADH
  – oxidation of pyruvate (x2) = 2 NADH
  – citric acid cycle (x2) = 6 NADH; 2 FADH2
  — total = 10 NADH; 2 FADH2
  – OP = 25 ATP from NADH; 3 ATP from FADH2
• grand total = 32 ATP

Question 13

effeciency of respiration generating ATP

Answer 13

• ATP produced per mol glucose
• complete oxidation = 686 kcal/mol
• phosphorylation of ADP>ATP = 7.3 kcal/mol
• efficiency = 7.3 x 32 ATP mol = 233.6 kcal/mol
• 233.6/686 = 34%
• about 66% energy lost from glucose heat