HL Bio: Unit 3.4 - Electron Transport Chain and Chemiosmosis

Electron Transport Chain

Releases energy stored within electron carries to synthesize ATP to produces and maintain a proton gradient across the inner mitochondrial membrane

Oxidative Phosphorylation

• Oxidation of electron carries in order to phosphorylate ADP to ATP

  • Takes place within the folds of the cristae of the mitochondrial membrane 

  • The folds provide extra Surface area to work on

NADH versus FADH₂

• NADH has a higher electron energy than FADH₂ making it yield more ATP’s in the end

  • 10 protons are pumped from the matrix to the intermembrane space from one pair of electrons of NADH

  • Whereas starting from FADH₂ transports 6 protons per electron pair 

• Whereas FADH₂ has a higher electron affinity

Process of the Electron Transport chain

1. Generating the Proton Motive Force

   • Oxidation of NADH intro a hydrogen ion and 2 electrons

   • The 2 electrons are then used to produce water by oxidizing oxygen and hydrogen 

2. The electron transport chain slowly goes down the chain of electron energy until it reaches the reduction process of oxygen forming water (the lowest energy state)

   • Each time it goes down an electron energy level, energy is released 

3. The energy released from going down the ETC is used in the pump proteins to pump hydrogen protons across the inner membrane of the mitochondria into the bit between the outer and inner membrane 

   • each level will pump a different amount of hydrogens

   • Attempts to increase the hydorgen concentration here to make it positive

Terminal Electron Acceptor - Oxygen

• Why oxygen molecules are used 

  • For each energy level it goes down it requires a stronger electron affinity in order to remove the electron from the last easily

  • Oxygen is used in the last electron carrier as it has a high electron affinity

    • This is what helps produce water

Chemiosmosis

Synthesis of ATP using the concentration gradient

Chemiosmosis Process

1. Due to the gradient the hydrogen ions now wants to enter the matrix

2. As it goes through the ATP synthase is a complex with a spinning axel within it that will rotate when hydrogen ions go through

3.  this causes the bottom compartment of the ATP synthase to close closer and make ADP in it with any free floating Pi to bind 

4. 3 ATP is formed from each NADH and only 2 ATP from every FADH₂

ATP Synthase

• A protein that allows the diffusion of hydrogen protons

• The top barrel half of the complex consists of identical sections that are proton binding site

• There are 2 half channels next to them

  1. One is where protons are brought down and then binded to the sections 

  2. The other takes of the protons from the subsection and then releases them to the matrix

• They aren’t aligned so the axel has to rotate the cylinder of subsections to get them all 

• The bottom bowl like part has both alpha and beta subunits that catalyze the phosphorylation of ADP to ATP

  • The axel rotation creates conformational changes to the beta subunit → allowing ADP and the phosphate group to bind and produce ATP

Endergonic Reaction

• Absorbs the energy from the reaction and stores it for when needed

• Adp to atp

Carbohydrates

•  need to go through glycolysis first 

  • Can be used for reaction with or without oxygen

  • Lower yield of energy

Lipids

• break down into the acetyl groups to begin with

  • Happens in the mitochondria so it has to be used only in aerobic respiration

  • Higher yield of energy