Download Intro. To Cellular Respiration and Redox

Intro. To Cellular
Respiration and Redox
Big Picture
• Sun gives energy to plants
• Plants store energy as organic molecules
• Animals eat plants
• Energy eventually leaves as heat
• Chemical elements are recycled
Working Together…
Photosynthesis
Cellular Respiration
• Occurs in chloroplasts
• Uses CO2 and H2O
• Generates Oxygen and
• Occurs in mitochondria
• Uses Oxygen and Organic
Organic Molecules
molecules
• Generates CO2 and H2O
Catabolism
• 2 Catabolic Pathways:
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Fermentation – degradation of sugars without O2
Cellular Respiration – degradation of sugars with O2
• Cellular Respiration has 3 Key Pathways: Glycolysis, Citric Acid Cycle, and
Oxidative Phosphorylation
• Uses enzymes to break down (catabolize) complex organic molecules (rich
in potential energy); some energy is released to do work, the rest is released
as heat
Overall Reaction
• Organic compound + Oxygen  Carbon Dioxide + Water +
Energy
• C6H12O6 + O2  CO2 + H2O + ATP and heat
• Why does this generate energy? Transfer of electrons releases
energy stored in organic molecules and helps make ATP
Redox Reactions
• “Oxidation-Reduction Reactions” = REDOX reactions
• Transfer of one or more electrons from one reactant to another
• Loss of Electrons = Oxidation
• Gain of Electrons = Reduction
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Reducing agent is oxidized (causes the other reactant to be reduced)
Oxidizing agent is reduced (causes the other reactant to be oxidized)
Respiration
• C6H12O6 is oxidized and O2 is reduced
• When C6H12O6 is oxidized, it releases energy and makes it
available for ATP synthesis
• Energy foods (fats and carbs) have lots of electrons
associated with Hydrogen, but require enzymes to lower
Activation Energy.
• Organic fuel is oxidized in a series of steps so energy can
be harnessed for work
Electron Transport Chain
• Composed of molecules (mostly proteins) embedded in the inner
membrane of the mitochondria
• Breaks the fall of electrons into several energy-releasing steps on their way
to Oxygen
• Electrons are stripped from glucose at key steps and travel with a proton (as
a H atom)
• A coenzyme NAD+ transports H
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•
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It is an electron acceptor and oxidizing agent
Enzymes take 2 H atoms from the sugar to give their electrons and 1 H to NAD+
(the other H+ is released)
NAD+ becomes NADH
Electron Transport Chain
• NADH shuttles electrons to the higher-energy end of the chain
and at the lower-energy end, Oxygen captures electrons to form
H2O
• Each carrier is more electronegative than the last
• Summary of e- pathway: Food  NADH  ETC  Oxygen
Stages of Cellular Respiration
• 1. Glycolysis – occurs in the cytosol, breaks down glucose into 2 pyruvate
• 2. Citric Acid Cycle – occurs in the mitochondrial matrix, oxidizes a derivative
of pyruvate into CO2
• 3. Oxidative Phosphorylation – occurs at the mitochondrion inner
membrane, includes ETC and chemiosmosis, produces most of ATP
• For every glucose molecule, ~38 molecules of ATP are produced
Glycolysis
• “splitting of sugar”
• Starts with a 6-C sugar breaking into two 3-C sugars
• Does not require Oxygen
• Has an “Energy investment phase” and an “Energy payoff phase”
• Spends 2 ATP… Produces 4 ATP and 2 NADH
• Net: 2 ATP and 2 NADH