cellular respiration: electron transport chain

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Electron transport chain overview

• 4th step of cellular respiration

• Electron carriers loaded with electrons and protons (H+) from krebs cycle 

• Move to etc: chain like series of steps; staircase

• Electrons move through stairs and drop downwards to next protein 

• Electrons move through redox reactions 

• Protons transferred to intermembrane space 

• Oxygen, very EN element, pulls electrons and protons in at bottom of stair case

• Oxygen and proton becomes water

• Occurs in inner membrane 

• Forms a total of 34 atp

components of etc

• Complex I

• Complex II
  Complex III
  Complex IV

• CoQ and CytC are helper molecules 

Complex I

• NADH with potential energy is oxidated

• Electrons are given away

• Energy from electrons pumps protons into intermembrane space

• 4 H+ are transported per 2 electrons 

• One electron moves at a time; assembly line 

• Left over electrons moved by helper molecule to next complex

• Theoretical: 1 NADH = 3 ATP

Complex II

• Not transmembrane protein

• FADH₂ gives electrons

• 1 FADH₂ makes 2 atp, not as efficient as NADH 

• Energy and electrons continue to be moved across

• No protons pumped: oxidation of FADH2 isnt strong enough 

• FADH2 supplies more electrons to coQ so more oxygen is reduced to water

Complex III

• Electrons and energy taken and pushed onwards

• More H+ pumped into concentration gradient 

• 4 protons pumped out per transfer of 4 electrons

• two cycles required as CytC can only carry one electron at a time 

Complex IV

• Oxygen at the bottom pulling electrons to bottom of staircase/etc

• Oxygen is what allows etc to function

• Last pump of protons into intermembrane space

• Oxygen and proton forms water

Complex functions summary

• Complex I: NADH pumps protons

• Complex II: FADH₂ moved through to CoQ, no pumping protons 

• Complex III: pumps a lot more protons

• Complex IV: last proton pump, water formed

Atp produced from etc (etc tally)

• Per one molecule glucose

• 2 NADH from glycolysis -> 6 ATP

• 2 NADH from Pyruvate oxidation -> 6 ATP

• 6 NADH from Krebs -> 18 ATP

• 2 FADH2 from Krebs -> 4 ATP 

• Total: 34 atp

Total atp yield across cellular respiration

• Per one molecule glucose

• 2 ATP from Glycolysis

• 2 ATP from Krebs

• 34 ATP from ETC 

• Theoretical total yield: 38 atp 

• May be lower due to proton leaking out of intermembrane space, or free energy needed elsewhere before ATP is made

Atp synthase

• transport protein and enzyme

• after four complexes

• Movement of electrons and protons through complex I to IV causes high concentration in intermembrane space

• Protons flow through atp synthase through diffusion: high to low concentration

• Atp synthase spins like a turbine and produces atp 

• Oxidative phosphorylation occurs: moving phosphate group indirectly through a chain of reaction

• energy from spinning allows adp to bind to phosphate to make atp

Why do we breathe oxygen

• Oxygen is essential for the electron transport chain to function

• Since it is high electronegativaty, it pulls protons and electrons through staircase

• At complex IV, oxygen accepts electrons and protons to form water (waste product)

• This allows the cycle to continue and more atp to be produced

• Without atp our cells would die 

Steps of etc

• complex I

• complex II

• CoQ

• Compelx III

• CytoC

• Complex IV

• atp synthase

Why is mitochondria called the power house of the cell?

• Primary site of cellular respiration 

• Atp is our body’s energy currency

• Cellular respiration occurs outside of then inside of mitochondria

• It is essential for atp to form

• It powers our cells and us

Move electrons is the same as

Moving electricity which is why energy is created

chemiosmosis

• process of ions move across semipermeable membrane through atp synthase

• usually portons

• release energy to drive cellular work

• synthesis of atp