Oxidative Phosphorylation Flashcards
Two purposes of catabolic pathways
- breakdown of larger molecules into smaller building units
- release and (temporary) storage of energy in high-energy molecules (ATP/NTP’s, reduced cofactors: NADH/FADH₂)
State the subcellular location of oxidative phosphorylation
- processes are linked through a proton gradient across the inner mitochondrial membrane
- protons are exported from the inner mitochondrial membrane to the intermembrane space
- pH is high in the mitochondrial matrix and low in the intermembrane space
1) cofactor 2) coenzyme
- A molecule/compound (coenzyme or metal ion) that is required for the catalytic activity of an enzyme
- a type of organic molecule that is required for the catalytic activity of an enzyme. A coenzyme may be tightly associated with the enzyme as a prosthetic group (FAD) or a cosubstrate (NAD+)
cofactors in oxidative phosphorylation
- cofactors are reversibly oxidized/reduced during electron transport
- each cofactor has a characteristic reduction potential/affinity for electrons
- electrons move from cofactors with lower reduction potential to those with higher reduction potentials
List the six major components of the electron transport chain
- Complex I
- Coenzyme Q (cofactor/cosubstrate)
- Complex II
- Complex III
- Cytochrome c (peripheral membrane protein)
- Complex IV
all complexes are integral membrane proteins
what do cofactors do in oxidative phosphorylation?
- get reversibly oxidized/reduced and move electrons along the ETC
Identify 4 distinct electron carrying cofactors that play a role in re-oxidation of FADH₂ and NADH by the ETC
- Flavin mononucleotide (FMN) - PG
- Iron-sulfur clusters - PG
- cytochrome c heme group - LSCF
- Coenzyme Q (lipid soluble, transports electrons to complex III from complexes I and II in the inner mitochondrial membrane) - LSCF
Q + 2H⁺ + 2e- ⇋ QH₂
PG - prosthetic group, apart of protein complexes
LSCF - lipid soluble cofactors, found in the bilayer and are intermediarys between e- transport proteins
Explain why electrons move spontaneously through the components of the ETC and state how some of the FE they contain is “harnessed”
- higher reduction potential change → more negative ΔG
- electrons move from compounds with lower reduction potentials to those with higher reduction potentials
- transfer of electrons from electron donors (NADH, FADH2) to electron acceptors (O2) via a series of protein complexes creates an electrochemical membrane potential
- at CI, III, and IV, energy released by the transfer of electrons is used to pump protons across the membrane against their concentration gradient, from the matrix to the intermembrane space. This creates potential energy stored in the form of an electrochemical gradient.
- the flow of protons back into the mitochondrial matrix through ATP synthase drives the synthesis of ATP from ADP and inorganic phosphate
reduction potential: affinity for electrons
Identify which components of the ETC pump protons, and state how many are pumped at each site
- coenzyme I: 4H⁺
- coenzyme III: 4H⁺
- coenzyme IV: 2H⁺
Compare the paths taken through the ETC by electrons from NADH and FADH₂
NADH:
- 10 protons are moved out of the matrix when reoxidized
- electrons do not move through complex II
- CoQ moves from I → III
FADH₂
- 6 protons are moved out of the matrix when reoxidized
- electrons do not move through complex I
- CoQ moves from II → III
explain the proton electrochemical gradient and what it does
the pumping of protons from the matrix into the IMS creates an electrochemical gradient across the mitochondrial membrane:
- hydrogen ion concentration is high in the IMS and low in the matrix
- the IMS is more positively charged than the matrix (-)
this generates a negative free energy change → the potential energy of the H+ gradient is converted to chemical energy in the PAB in ATP
IMS - intermembrane space
PAB - phosphoanhydride bonds
How do complexes pump H⁺ ions across the membrane?
electron transport causes a conformational change in the complex (eg protein binds H on matrix side) and releases it to the intermembrane space) - redox reactions provide the energy needed to pump the protons (primary active transport)
Identify the source of energy which “drives” ATP synthesis by ATP synthase and state how this energy is used
the potential energy of the H+ gradient is converted to chemical energy in the PAB in ATP
- approximately 3H+ are needed per ATP synthesized by ATP synthase
- ATP synthase conducts the movement of 3 hydrogen ions down their concentration gradient to spin the catalytic component of the synthase that brings ADP, Pi together to create ATP
- every complete turn of the central shaft is associated with the generation of 3 ATP (3 active sites make ATP)
PAB - phosphoanhydride bonds
Identify the “terminal” electron acceptor in the ETC, and write and equation to illustrate it’s role in the electron transport
-
Oxygen is the terminal electron acceptor - it has a very high reduction potential
2e⁻ + 2H⁺ + ½O₂ → H₂O
Explain what is meant by the statement “oxidative phosphorylation is coupled”
- the production of ATP by ATPsyn (phosphorylation) is linked to the transfer of electrons in the ETC (oxidation)
- the rates of re-oxidation of NADH/FADH, through the ETC, and oxygen consumption are coupled to the rate of consumption/synthesis of ATP through the magnitude of the proton electrochemical gradient
