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Lecture 4

LIFESCI 7A Lecture 4: Week 3-4- Cellular Respiration Notes

Life Sciences
Course Code
Debra Pires

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Week 3-4: Cellular Respiration Notes
Cellular respiration: glucose is broken down into CO2 and water to generate
useable energy in the form of ATP
Photosynthesis: light energy drives transformation of water and CO2 into glucose
Big picture: cell converts food molecules (glucose, fats, proteins) into CO2, free
energy is released, transformed, and used to make ATP from ADP + Pi
Feedback inhibition/activation
In citric acid cycle, more energy is transferred to energy management molecules
as acetyl-CoA is oxidized
Protons pumped slide--Protons are pumped as e- flow because as H+ go from
matrix to intermembrane space, they're going from low to high concentration. it
takes energy to move them against the gradient
Reducing pyruvate allows NADH to be recycled back toc NAD+ so that glycolysis
can proceed and generate 2 ATP per
An overview
Cellular respiration is catabolic. Glucose, fatty acids, proteins are catabolized into
smaller units, releasing energy stores in their bonds to power cell's work
Cellular respiration uses chemical energy stored in molecules such as
carbohydrates and lipids to produce ATP
C6H12O6 + 6O2 --> 6CO2 + 6H2O + energy
Can occur with or without oxygen
~32 molecules of ATP produced from aerobic respiration of 1 molecule of
G is at least 7.3 kcal, 34% of total energy is harnessed as ATP and the
rest is give off as heat
ATP is generated by substrate-level phosphorylation and oxidative
Substrate-level phosphorylation--phosphate group is transferred to ADP
from an enzyme substrate (in this case, an organic molecule)
A phosphorylated organic molecule directly transfers a phosphate
group to ADP
Hydrolysis of phosphorylated organic molecule and addition of
phosphate group to ADP
This hydrolysis releases enough free energy to drive synthesis of
This process produces small amount of total ATP generated in
cellular respiration
Oxidative phosphorylation (e- transport chain)
Chemical energy of organic molecules is transferred to electron

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E- carriers transport e- released during catabolism of organic
molecules to the electron transport chain (which transfers e- along
proteins to a final electron acceptor, and in the process harnesses
energy released to produce ATP)
In aerobic respiration, oxygen is the final e- acceptor, which forms
Redox reactions play a central role in cellular respiration
Oxidation-reduction reactions (redox reactions): chemical rxn in which e-
are transferred from one atom/molecule to another
Oxidation: loss of electrons
Reduction: gain of electrons
Electron carriers
Oxidized form--NAD+ and FAD
Reduced form--NADH and FADH2
Loss of e- is accompanied by gain of H+ --> reduced
molecules have an increase in C-H bonds
Oxidation of these two allows e- (and energy) to be
transferred to e- transport chain
NAD+ and FAD is produced, which accepts e- from the
breakdown of fuel molecules
E- carriers act as shuttles, transferring e-from oxidation of
glucose to the e- transport chain
Glucose is good e- donor because its oxidation to CO2 releases a lot of
Oxygen is good e- accepter because it has high electronegativity
Glucose is oxidized slowly in a series of rxns so energy is released in
controlled manner
Cellular respiration occurs in four stages
Stage 1: Glycolysis. Glucose is partially broken down to make
pyruvate & energy is transferred to ATP and reduced e- carriers
Stage 2: Pyruvate oxidation. Pyruvate is oxidized to acetyl-CoA,
producing reduced e- carriers and releasing CO2
Stage 3: Citric acid cycle aka Krebs cycle. Acetyl group in acetyl-
CoA is oxidized to CO2! and energy is transferred to ATP and
reduced e- carriers
Energy transferred to ATP and reduced e- carriers is 2x as
much as stages 1 + 2
Stage 4: Oxidative phosphorylation (e- transport chain). Reduced e-
carriers made in stages 1-3 donate e- to e- transport chain and! a
lot of ATP is produced
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