Cellular Respiration

How do we harvest energy from fuels? Digest large molecules into smaller ones – break bonds & move electrons from one molecule to another as electrons move they carry energy with them that energy is stored in another bond, released as heat, or harvested to make ATP + e-e- + e-e- +– loses e-gains e-oxidizedreduced oxidationreduction

How do we move electrons in biology? Moving electrons – in living systems, electrons do not move alone electrons move as part of H atom + H + H +– loses e-gains e-oxidizedreduced oxidationreduction C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ oxidation reduction H

Moving electrons in respiration Electron carriers move electrons by shuttling H atoms around – NAD +  NADH (reduced) – FAD +2  FADH 2 (reduced) + H reduction oxidation P O–O– O–O– O –O–O P O–O– O–O– O –O–O C C O NH 2 N+N+ H adenine ribose sugar phosphates NAD nicotinamide Vitamin B3 P O–O– O–O– O –O–O P O–O– O–O– O –O–O C C O NH 2 N+N+ H H NADH stores energy as a reduced molecule reducing power!

Coupling oxidation & reduction Redox reactions in respiration – release energy as breakdown molecules break C-C bonds strip off electrons from C-H bonds by removing H atoms – C 6 H 12 O 6  CO 2 = fuel has been oxidized electrons attracted to more electronegative atoms – in biology, the most electronegative atom? – O 2  H 2 O = oxygen has been reduced release energy to synthesize ATP C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ oxidation reduction  O2 O2

Oxidation & reduction Oxidation – adding O – removing H – loss of electrons – releases energy – exergonic Reduction – removing O – adding H – gain of electrons – stores energy – endergonic C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ oxidation reduction

Cellular Respiration Overview

Three Parts 1. Glycolysis 2. Krebs Cycle 3. Electron Transport Chain (Oxidative Phosphorylation)

Glycolysis In glycolysis, a glucose molecule is broken in half to produce 2 pyruvate molecules This process actually needs energy and 2 ATPs are used 4 ATPs are made by breaking the bonds in glucose so we have a net gain of 2 ATPs

Glycolysis Glycolysis happens in the cytoplasm It is the most ancient form of energy capture It is the starting point for cellular respiration

Glycolysis Input: Glucose Output: 2 Pyruvates, 2 ATPs

Pyruvate is a branching point Pyruvate O2O2 O2O2 Kreb’s cycle mitochondria fermentation

For today… we are going to focus on what happens when oxygen is present This is called aerobic respiration

Krebs Cycle Pyruvate is oxidized into Acetyl-CoA Acetyl-CoA is a 2 carbon molecule that then goes through the Krebs cycle and is converted into multiple other compounds – The first compound made is citrate As these new carbon compounds are made CO2 is released, NADH is made, and FADH2 is made At the end of the cycle oxaloacetate is made which can then combine with pyruvate to create another molecule of citrate starting the cycle again

Krebs Cycle

Input: Pyruvate Output: NADH, FADH2, CO2, ATP

So why the Krebs cycle? If the yield is only 2 ATP, then why? – value of NADH & FADH 2 electron carriers reduced molecules store energy! to be used in the Electron Transport Chain

ATP accounting so far… Glycolysis  2 ATP Kreb’s cycle  2 ATP Life takes a lot of energy to run, need to extract more energy than 4 ATP! Why stop here…

Electron Transport Chain

PGAL Glycolysis Kreb’s cycle 2 NADH 8 NADH 2 FADH 2 Remember the NADH?

Electron Transport Chain or Chemiosmosis NADH passes electrons to ETC – H cleaved off NADH & FADH 2 – electrons stripped from H atoms  H + (H ions) – electrons passed from one electron carrier to next in mitochondrial membrane (ETC) – transport proteins in membrane pump H + across inner membrane to intermembrane space

Electrons flow downhill Electrons move in steps from carrier to carrier downhill to O 2 – each carrier more electronegative – controlled oxidation – controlled release of energy

Why the build up H + ? ATP synthase – enzyme in inner membrane of mitochondria ADP + P i  ATP – only channel permeable to H + – H + flow down concentration gradient = provides energy for ATP synthesis molecular power generator! flow like water over water wheel flowing H+ cause change in shape of ATP synthase enzyme powers bonding of P i to ADP “proton-motive” force

Cellular respiration

Summary of cellular respiration Where did the glucose come from? Where did the O 2 come from? Where did the CO 2 come from? Where did the H 2 O come from? Where did the ATP come from? What else is produced that is not listed in this equation? Why do we breathe? C 6 H 12 O 6 6O 2 6CO 2 6H 2 O~36 ATP  +++

Taking it beyond… What is the final electron acceptor in electron transport chain? O2O2  So what happens if O 2 unavailable?  ETC backs up  ATP production ceases  cells run out of energy  and you die!