Transcript Cellular Respiration

Inquiry into Life
Eleventh Edition
Sylvia S. Mader
Chapter 7
Lecture Outline
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Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
7.1 Overview of cellular
respiration
• Overall process
– Oxidation of glucose to carbon dioxide,
water, and energy. This is an Exergonic
reaction used to drive ATP synthesis
which is endergonic
– 4 phases of respiration are required for
complete oxidation of glucose
– Oxidation involves the removal of hydrogen
atoms from substrates by redox coenzymes
NAD+ and FAD
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Cellular respiration
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Overview of cellular respiration
cont’d.
• NAD+ and FAD
– Redox coenzymes active in respiration
– NAD+ is reduced to NADH
– FAD is reduced to FADH2
– FADH2 and NADH carry electrons to the
electron transport chain
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The NAD+ cycle
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Overview of cellular respiration
cont’d.
• Phases of cellular respiration
– Glycolysis (Takes place in the Cytoplasm)
• Use Energy from 2 ATP’s to activate glucose
• Breakdown of glucose to 2 molecules of
pyruvate
• Oxidation by removal of hydrogens releases
enough energy to make 2 ATP’s from each
pyruvate results in a Net Gain of 2 ATP’s in this
Phase per Glucose Molecule.
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•Phases of cellular respiration, cont’d.
–Preparatory reaction (Takes place in
Matrix of Mitochondria)
–Pyruvate oxidized to acetyl CoA and carbon dioxide
is removed
•Prep reaction occurs twice per Glucose
molecule because glycolysis produces 2
pyruvates
•No ATP’s produced in this phase
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•Phases of cellular respiration, cont’d.
–Citric acid cycle (Takes place in Matrix of
Mitochondria)
–Each Pyruvate was oxidized to acetyl CoA in
Preparatory Reaction.
•Now Acetyl CoA is converted to citric acid and
enters the cycle
•Cyclical series of oxidation reactions that
produces 1 ATP and carbon dioxide per cycle
turn
•Citric acid cycle turns twice per Glucose
Molecule because 2 acetyl CoA’s are produced
per glucose
•2 ATP’s produced per Glucose Molecule in this
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phase
Overview of cellular respiration
cont’d.
• Phases of cellular respiration, cont’d.
– Electron transport chain (Takes place in
Cristae of Mitochondria)
• Series of electron carrier molecules
which pass Electrons from one carrier to
another releasing energy to make ATP
• 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
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•Phases of cellular respiration, cont’d.
–In Anaerobic Conditions (No Oxygen
Present)
–Glycolysis produces Pyruvate
•Pivotal metabolite in cellular respiration
•If no oxygen is available, pyruvate is
reduced to lactate (in animals) or
ethanol and carbon dioxide (in plants)
in a process called fermentation
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Cellular respiration
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7.2 Outside the mitochondria:
Glycolysis
• Energy-investment steps
– Energy from 2 ATP is used to activate glucose
– Glucose is split into 2 3-carbon G3P molecules
• Energy-harvesting steps
– Oxidation of G3P by removal of hydrogens
– Hydrogens 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, so there’s a net gain of 2 ATP’s.
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Outside the mitochondria:
glycolysis cont’d.
• Glycolysis yields:
– 4 ATP by direct substrate phosphorylation
• 2 ATP were consumed in the investments steps
• Net gain of ATP from glycolysis is therefore 2 ATP
– 2 NADH which will carry electrons to the electron transport chain
•
No Oxygen is required for Glycolysis to
produce pyruvate.
• When oxygen is available pyruvate will enter
the mitochondria for further oxidation
• If no oxygen is available, pyruvate will enter
the fermentation pathway
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Glycolysis
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7.3 Inside the mitochondria
• Breathing, eating, and cellular
respiration
– Oxygen is taken in by breathing
– Digested food contains glucose
– Oxygen and glucose are carried to cells by
the bloodstream
– Glucose and oxygen enter cells where
respiration occurs
– Carbon dioxide is taken by the bloodstream to
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the lungs
Relationship between breathing,
eating, and cell respiration
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Inside the mitochondria cont’d.
• 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
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Inside the mitochondria cont’d.
• Citric acid cycle
– 2C acetyl group from prep reaction combines
with a 4C molecule to produce 6C citrate
– Oxidation of citrate by removal of hydrogens
– Produces 3 NADH and 1 FADH2
– Produces 1 ATP per cycle by direct
substrate phosphorylation
– Cycle turns twice per glucose
– Total yield: 6 NADH, 2 FADH2, 2 ATP, 4 CO2
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Citric acid cycle
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Inside the mitochondria cont’d.
• Electron transport chain (ETC)
– 2 electrons per NADH and FADH2 enter ETC
– Electrons are passed to series of electron
carriers called cytochromes
– Energy is captured and stored as a
hydrogen ion concentration gradient. This
process is called chemiosmosis
– For each NADH enough energy is released
to form 3 ATP
– For each FADH2 there are 2 ATP produced
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Overview of the electron transport
chain
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Inside the mitochondria cont’d.
• Electron transport chain cont’d.
– 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
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Inside the mitochondria cont’d.
• 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
– This builds an electro-chemical gradient that stores
energy
– As H+ moves back into matrix energy is released and
captured to form ATP by ATP synthase complexes
– Process is called chemiosmosis
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Organization of cristae in the
mitochondria
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Inside the mitochondria cont’d.
• Energy yield from cellular respiration is
36 – 38 ATP’s per Glucose Molecule
– From direct phosphorylation
• Net of 2 ATP from glycolysis
• 2 ATP from citric acid cycle
– From chemiosmosis
• Electron transport chain produces 32 –
34 ATP per Glucose Molecule
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Accounting of energy yield per
glucose molecule breakdown
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Inside the mitochondria cont’d.
• 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
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7.4 Fermentation
• Fermentation
– Occurs when O2 is not available
– Animal cells convert pyruvate to lactate
– Plant cells, yeasts convert pyruvate to ethanol
and CO2
– Fermentation regenerates NAD+ which keeps
glycolysis going
– Produces only a net of 2 ATP per glucose
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Fermentation
• Fig
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Fermentation cont’d.
• Advantages and Disadvantages of fermentation
– Provides a low but continuous supply of ATP when
oxygen is limited and only glycolysis can function
– Can provide a rapid burst of ATP in muscle cells,
even when oxygen is in limited supply.
– Lactate is potentially toxic to muscles, lowering
pH and causing fatigue
– Transported to liver where it is converted to pyruvate
• This process requires oxygen
• During exercise an oxygen debt is built up
• Oxygen debt is the amount of oxygen “owed” to
the liver to convert accumulated lactic acid to
pyruvate
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Fermentation , cont’d.
• Energy yield of fermentation
– Produces only a net of 2 ATP per glucose through
direct substrate phosphorylation by allowing
glycolysis to continue. MUCH LESS efficient than
Aerobic Cellular Respiration.
– Following fermentation most of the potential energy
from glucose is still waiting to be released
– Fermentation is a way to continue an ATP supply
to cells when oxygen is in short supply
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7.5 Metabolism
• Catabolism-break down reactions
– Carbohydrates-digested to glucose for cell
respiration
– Fats-digested to glycerol and fatty acids
• Glycerol can enter glycolytic pathway
• Fatty acids metabolized to acetyl CoA
which enters citric acid cycle
– Proteins- deamination
• Amino acids can enter pathway at different
points
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Metabolism
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Metabolism cont’d.
• Anabolism- synthesis reactions
– Substrates of glycolysis and citric acid cycle can be
substrates for synthesis of macromolecules
• G3P can be converted to glycerol
• Acetyl groups can be converted to fatty acids
• Some citric acid intermediates can be converted to
amino acids
– Anabolic reactions require the input of energy in
the form of ATP generated in catabolic reactions
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