objectives contrast the roles of glycolysis and aerobic respiration in cellular respiration. relate...
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Objectives
• Contrast the roles of glycolysis and aerobic respiration in cellular respiration.
• Relate aerobic respiration to the structure of a mitochondrion.
• Summarize the events of the Krebs cycle.
• Summarize the events of the electron transport chain and H+/ ATP synthase pump.
• Calculate the efficiency of aerobic respiration.
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Light energy
ECOSYSTEM
CO2 + H2O
Photosynthesis
in chloroplasts
Cellular respiration
in mitochondria
Organic
molecules+ O2
ATP
powers most cellular work
Heat
energy
PhotosynthesisCell Respiration Cycle
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Life Is Work
• Living cells– Require
transfusions of energy (a.k.a., food) from outside sources to perform their many tasks
– The giant panda obtains energy for its cells by eating plants
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Harvesting Chemical Energy
• Cellular respiration is the process by which cells break down organic compounds to produce ATP.
• Both autotrophs and heterotrophs use cellular respiration to make CO2 and water from organic compounds and O2.
• The products of cellular respiration are the reactants in photosynthesis; conversely, the products of photosynthesis are reactants in cellular respiration.
• Cellular respiration can be divided into two stages: glycolysis and aerobic respiration.
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• An overview of cellular respiration…
Electrons
carried
via NADH
Glycolsis
Glucose Pyruvate
ATP
Substrate-level
phosphorylation
Electrons carried
via NADH and
FADH2
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
ATPATP
Substrate-level
phosphorylation
Oxidative
phosphorylation
Mitochondrion
Cytosol
AEROBIC RESPIRATIONAEROBIC RESPIRATION
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Cellular Respiration
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CELLULAR RESPIRATION (Figure 5.4, p. 133)
• ALL organisms do respiration!!!
• energy in glucose released to produce ATP
• two types of respiration– AEROBIC (requires oxygen) – ANAEROBIC (does not require oxygen)
• both types start with glycolysis
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GLYCOLYSIS (Figure 5.6, p. 135)
• glycolysis is the first step of respiration• occurs in ALL cells!!!• occurs in cytoplasm and is anaerobic (no O2)
• glucose is converted to pyruvic acid– produces 2 ATP (~2% of energy in 1 glucose)– pyruvic acid then used in…
• fermentation or• aerobic respiration
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Summary of Cellular Respiration
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FERMENTATION (ANAEROBIC)
• occurs in cytoplasm– consumes pyruvic acid with no ATP production!!!
• LACTIC ACID FERMENTATION – creates lactic acid– example overworked muscles with low O2 – feels like cramp or soreness
• ALCOHOLIC FERMENTATION - produces ethyl alcohol and CO2
– used to make beer; wine; dough
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• In alcohol fermentation– Pyruvate is
converted to ethanol in two steps, one of which releases CO2
• During lactic acid fermentation
– Pyruvate is reduced directly to NADH to form lactate as a waste product
2 ADP + 2 P1 2 ATP
GlycolysisGlucose
2 NAD+ 2 NADH2 Pyruvate
2 Acetaldehyde 2 Ethanol(a) Alcohol fermentation
2 ADP + 2 P1 2 ATP
GlycolysisGlucose
2 NAD+ 2 NADH
2 Lactate(b) Lactic acid fermentation
HH OH
CH3
C
O –
OCC O
CH3
HC O
CH3
O–
C OC OCH3O
C OC OHH
CH3
CO22
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Overview of Aerobic Respiration • In eukaryotic cells, the processes of
aerobic respiration occur in the mitochondria. Aerobic respiration only occurs if oxygen is present in the cell.
• The Krebs cycle occurs in the mitochondrial matrix. The electron transport chain (which is associated with the production of ATPs) is located in the inner membrane.
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Mitochondria, the super-energy harvesters
• Mitochondria
– are the sites of aerobic cellular respiration
– are found in nearly all eukaryotic cells
– are enclosed by two membranes• smooth outer membrane• an inner membrane folded into cristae (i.e.,
higher surface area for chemical reactions)
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Mitochondrion
Intermembrane space
Outer
membrane
Free
ribosomes
in the
mitochondrial
matrix
Mitochondrial
DNA
Inner
membrane
Cristae
Matrix
100 µm
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AEROBIC RESPIRATION (requires O2)
• Net reaction…
C6H12O6 + 6O2 6CO2 + 6H2O + ATPmitochondria
enzymes
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The Krebs Cycle
• In the mitochondrial matrix, pyruvic acid produced in glycolysis reacts with coenzyme A to form acetyl CoA. Then, acetyl CoA enters the Krebs cycle.
• One glucose molecule is completely broken down in two turns of the Krebs cycle. These two turns produce four CO2 molecules, two ATP molecules, and hydrogen atoms* that are used to make six NADH* and two FADH2* molecules.
• * The energy released by the breakdown of glucose is about to be transferred to ATP!!!
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Summary of Cellular Respiration
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AEROBIC RESPIRATION (requires O2)
• occurs ONLY in mitochondria (Figure 5.10, p.138)• pyruvic acid from glycolysis is metabolized in
the KREB’S CYCLE– occurs in the matrix– two turns of cycle (1 glucose molecule) yields 4 CO2,
2 ATP, and several energy rich molecules (NADH and FADH2 )
– the energy rich molecules NADH and FADH2 are used to make a lot of ATP energy rich (using electron transport chains and ATP synthase)
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KREB’S CYCLE (in the matrix)
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• Enzymes in the Kreb’s (or citric acid) cycle…pyruvate
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Summary of Kreb’s (Citric Acid) Cycle
X 2
X 2
X 2
X 2
X 2
diffuse out
used in e- transport chain
used in e- transport chain
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Electron Transport Chain and ATP Synthesis
• High-energy electrons from from NADH and FADH2 are passed from molecule to molecule in the electron transport chain along the inner mitochondrial membrane.
• Hydrogen ions, H+, are also given up by NADH and FADH2.
• As the electrons move through the electron transport chain, they lose energy. This energy is used to pump protons from the matrix into the intermembrane space.
• The resulting concentration gradient of hydrogen ions drives ATP synthase and ATP production!
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Electron Transport Chain, H+, & ATP synthesis• H+ move through ATP synthase to make ATP from ADP+Pi • Oxygen combines with the electrons and protons to form water.
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Electron Transport Chain and ATP synthase
• The Importance of Oxygen– ATP can be synthesized using the diffusion of
H+ ions from the outer compartment to the inner compartment only if electrons continue to move along the electron transport chain.
– Oxygen is the final electron acceptor
– As a result, ATP can continue to be made through the ATP pump.
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ATP Synthase
makes ATP !!!
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An Accounting of ATP Production by Cellular Respiration
• During respiration, most energy flows in this sequence
glucose NADH e- transport chain H+ gradient ATP
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Energy Summary of Cellular Respiration
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AEROBIC RESPIRATION• Electron Transport Chains & ATP synthesis
– uses membrane bound proteins– O2 molecules are consumed
– this produces 32 more ATP• SO... total yield of ATP (1 glucose molecule) from
aerobic respiration AND glycolysis = 38 ATP• 19-times more ATP than from anaerobic
respiration alone !!! (~40% of the energy in a glucose molecule is converted to ATP)
• WHAT HAPPENS TO THE OTHER 60%?
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Summary of Cellular Respiration
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A Summary of Cellular Respiration
• Another Role of Cellular Respiration
– Providing cells with ATP is not the only important function of cellular respiration.
– Molecules formed at different steps in glycolysis and the Krebs cycle are often used by cells to make compounds that are missing in food.
• fatty acids, glycerol, amino acids
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Comparing Aerobic and Anaerobic Respiration
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• (REVIEW) Glycolysis
– Can produce ATP with or without oxygen, in aerobic or anaerobic conditions
– Glycolysis is often coupled with fermentation to produce a few more ATP, especially in prokaryotes
• Fermentation consists of
– Glycolysis plus either alcohol or lactic acid fermentation
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Fermentation and Cellular Respiration Compared
• Both fermentation and cellular respiration
– Use glycolysis to oxidize glucose and other organic fuels to pyruvate
• Cellular respiration (i.e., complete oxidation) is more efficient than anaerobic respiration pathways
– Produces more 19x more ATP (38 versus 2 ATP)
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• Pyruvate is a key juncture in catabolism
Glucose
CYTOSOL
Pyruvate
No O2 presentFermentation
O2 present Cellular respiration
Ethanolor
lactate
Acetyl CoA
MITOCHONDRION
Citricacidcycle
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The Evolutionary Significance of Glycolysis
• Glycolysis
– Occurs in nearly all organisms
– Probably evolved in ancient prokaryotes before there was oxygen in the atmosphere
– The pathways are similar (or conserved) across nearly all kingdoms (i.e., they are physiologically important and have not changed very much)