Lecture PowerPoint to accompany
Inquiry into Life
Twelfth Edition
Sylvia S. Mader
Chapter 7
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
7.1 Metabolism
7.1 Metabolism
• Catabolism: Breaking down of molecules
7.1 Metabolism
• Catabolism: Breaking down of molecules
• Anabolism: Building up of molecules
(ATP is the energy currency used by these reactions)
Metabolism
7.1 Metabolism
• Catabolism
– Food contains three nutrients that are used as energy
sources
– These nutrients can be broken down into smaller
molecules
• Carbohydrates
Glucose
• Fats
Glycerol and Fatty Acids
• Proteins
Amino Acids
7.1 Metabolism
• Anabolism
– Many of the building blocks of larger molecules come
directly from our food.
• Glucose
Glycogen
• Amino Acids
Proteins
7.1 Metabolism
• Cellular Respiration
– Release of energy from glucose (usually) coupled to
ATP synthesis
– An aerobic process that requires O2 and releases
CO2
Cellular Respiration
7.2 Overview of Cellular
Respiration
• This is hard. You must learn it. So –
• Get it done
7.2 Overview of Cellular
Respiration
• Metabolic pathways allow energy within glucose
to be released
• Release of energy does happen all at once
• As glucose is broken down, ATP is built up
• Breakdown of glucose results in 36 or 38 ATP
molecules
• The energy released is by the removal of a
phosphate group
7.2 Overview of Cellular
Respiration
• NAD+ and FAD
• Two coenzymes of oxidation and reduction that are active
during cellular respiration
• They carry electrons from the cytoplasm or the mitochondrial
matrix and carry them to the cristae of the mitochondria
• NAD+ and FAD each carry two electrons and two hydrogen
atoms
The NAD+ Cycle
7.2 Overview of Cellular
Respiration
• Phases of Cellular Respiration
– Glycolysis
– Preparatory Reaction
– Citric Acid Cycle
– Electron Transport Chain
– We will simplify: Glycolysis, Krebs
cycle, electron transport
Phases of Glucose Breakdown
7.2 Overview of Cellular
Respiration
• Glycolysis
– Breakdown of glucose to 2 molecules of pyruvate
– Oxidation by removal of hydrogens releases enough
energy to make 2 ATP
7.2 Overview of Cellular
Respiration
• Glycolysis
– Breakdown of glucose to 2 molecules of pyruvate
– Oxidation by removal of hydrogens releases enough
energy to make 2 ATP
7.2 Overview of Cellular
Respiration
• Glycolysis
– Breakdown of glucose to 2 molecules of pyruvate
– Oxidation by removal of hydrogens releases enough
energy to make 2 ATP
7.2 Overview of Cellular
Respiration
• Preparatory Reaction
– Pyruvate oxidized to acetyl CoA and carbon dioxide is
removed
– Prep reaction occurs twice because glycolysis
produces 2 pyruvates
7.2 Overview of Cellular
Respiration
• Citric Acid Cycle
– Acetyl CoA is converted to citric acid and enters the
cycle
– Cyclical series of oxidation reactions that produces 1
ATP and carbon dioxide
– Citric acid cycle turns twice because 2 acetyl CoA’s
are produced per glucose
7.2 Overview of Cellular
Respiration
• Electron Transport Chain
– Series of electron carrier molecules
– Electrons passed from one carrier to another
– As the electrons move from a higher energy state to a
lower one, energy is released to make ATP
– Under aerobic conditions 32-34 ATP per glucose
molecule can be produced
7.2 Overview of Cellular
Respiration
• Electron Transport Chain
– Series of electron carrier molecules
– Electrons passed from one carrier to another
– As the electrons move from a higher energy state to a
lower one, energy is released to make ATP
– Under aerobic conditions 32-34 ATP per glucose
molecule can be produced
7.2 Overview of Cellular
Respiration
• Pyruvate
– Pivotal metabolite in cellular respiration
– If no oxygen is available, pyruvate is reduced to
lactate (in animals) or alcohol and carbon dioxide (in
plants) in a process called fermentation
– Fermentation results in a net gain of 2 ATP/glucose
7.3 Outside the Mitochondria:
Gycolysis
7.3 Outside the Mitochondria:
Gycolysis
• Energy-Investment Steps
– Energy from 2 ATP is used to activate glucose
– Glucose is split into two 3-carbon G3P molecules
7.3 Outside the Mitochondria:
Gycolysis
• Energy-Harvesting Steps
– Oxidation of G3P by removal of hydrogens
– Hydrogen’s are picked up by NAD+ to form NADH
– Oxidation of G3P and further substrates yields
enough energy to produce 4 ATP by direct substrate
phosphorylation
Glycolysis: Inputs and Outputs
7.4 Inside the Mitochondria
• Preparatory Reaction
– Produces the molecule that will enter the citric acid
cycle
– 3C pyruvate is converted to 2C acetyl CoA
– Carbon dioxide is produced
– Hydrogen atoms are removed from pyruvate and
picked up to form NADH
– This reaction occurs twice per glucose
The Preparatory Reaction
7.4 Inside the Mitochondria
• Citric Acid Cycle
– C2 acetyl group from prep reaction combines with a
C4 molecule to produce C6 citrate
– Oxidation of citrate by removal of hydrogens
– Produces 3 NADH and 1 FADH2
– Produces 1 ATP by direct substrate phosphorylation
– Cycle turns twice per glucose
Citric Acid Cycle:
Inputs and Outputs
Citric Acid Cycle
7.4 Inside the Mitochondria
• Electron Transport Chain
– 2 electrons per NADH and FADH2 enter the electron
transport chain
– Electrons are passed to series of electron carriers
called cytochromes
– Energy is captured and stored as a hydrogen ion
concentration gradient
– For each NADH enough energy is released to form 3
ATP
– For each FADH2 there are 2 ATP produced
7.4 Inside the Mitochondria
• Electron Transport Chain
– The final electron acceptor is oxygen
– After receiving electrons oxygen combines with
hydrogen ions to form water as an end product
• ½ O2+ 2 e- + 2H+  H2O
– NAD+ and FAD recycle back to pick up more
electrons from glycolysis, prep reaction, and citric
acid cycle
Electron Transport Chain
7.4 Inside the Mitochondria
• Organization of Cristae
– Electron carriers are arranged along the cristae
• As electrons are passed, energy is used to pump
H+ into the intermembrane space of mitochondrion
• As H+ moves back into matrix energy is released
and captured to form ATP by ATP synthase
complexes
– Process is called chemiosmosis
Organization of Cristae
Energy Yield per
Glucose Molecule
7.4 Inside the Mitochondria
7.4 Inside the Mitochondria
• Efficiency of Cellular Respiration
– The difference in energy content of reactants (glucose
and oxygen) and products (carbon dioxide and water)
is 686 kcal
– ATP phosphate bond has 7.3 kcal of energy
– 36 ATP are produced in respiration 36 X 7.3 = 263
kcal
– 263/686 = 39% efficiency of energy capture
– The rest of the energy is lost as heat
7.5 Fermentation
• Fermentation
–
–
–
–
Occurs when O2 is not available
Animal cells convert pyruvate to lactate
Other organisms convert pyruvate to alcohol and CO2
Fermentation regenerates NAD+ which keeps
glycolysis going
7.5 Fermentation
• Advantages and Disadvantages of Fermentation
– Provides a rapid burst of ATP
– Provides a low but continuous supply of ATP when
oxygen is limited and only glycolysis can function
– Lactate is potentially toxic to muscles, lowering pH
and causing fatigue
Fermentation:
Inputs and Outputs
Fermentation