10 Cellular Respiration
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Transcript of 10 Cellular Respiration
Chapter 9
Cellular Respiration
Some intermediates “feed into” other pathways Catabolic pathways provide building block
molecules and energy for anabolic pathways
Metabolic Pathways
energy
energy
Participants in Metabolic Pathways
NAD+
hexokinase
phosphoglucose isomerase
phosphofructokinase
Reactant (substrate)
Intermediates
Product
Participants in Metabolic Pathways
NAD+
hexokinase
phosphoglucose isomerase
phosphofructokinase
Enzymes…
CofactorsCoenzymes
Cellular Respiration & Photosynthesis
PHOTOSYNTHESIS“energy-capturing”
CELLULAR RESPIRATION“energy-releasing”
6O2 + 6CO2 + 6H2O
SOLARENERGY
C6H12O6
ATPchemical energy
glucose
Which process is exergonic?
Which process is anabolic?
Glucose:Hub of Energy Processing in Cells
Glucose production (anabolism) and
storage
Glucose:Hub of Energy Processing in Cells
Breakdown of glucose (catabolism) for energy
Cellular Respiration
Cellular Respiration – process by which cells produce ATP from a nutrient molecule (usually glucose) with high potential energy
Step-wise release of energy from glucose Requires O2
Glucose is broken down (catabolized) to CO2 and H2O
Glucose is oxidized to CO2
Exergonic process (net) Released energy is used to make ATP (from ADP + Pi)
• 4 connected pathways– Glycolysis– Pyruvate processing
(prep rxn)– Citric acid (Krebs)
cycle– Electron transport
chain/chemiosmosis
• 2 types of electron carriers
• 2 compartments• 2 types of ATP synthesis
Cell Respiration…
ATP Cycle: Renewing Supplies of ATP
Energy from EXERGONIC
reactions(e.g. cellular respiration)
Energy for ENDERGONIC
reactions(e.g. protein
synthesis, muscle contraction)
Making ATP
ATP is produced using the energy stored in organic molecules (chemical energy; potential energy) such as glucose
One way of transferring
energy is through the transfer of electrons
Electrons and
energy transferred to molecule
B
Methods of Producing ATP
Substrate-Level Phosphorylation – enzyme catalyzes transfer of phosphate group from phosphorylated substrate to ADP (to make ATP)
Oxidative Phosphorylation (Electron Transport & Chemiosmosis) – oxidation of NADH and FADH2 and electron transport produces proton gradient, which drives ATP synthesis (phosphorylation of ADP)
Enzyme
ADPATP
Phosphorylatedsubstrate
Methods of Producing ATP
substrate-level phosphorylation
oxidative phosphorylation
Cytosol
Electrons
Electron transport chain
Glycolysis
Steps 1-3 (energy investment) Start with one glucose (hexose
sugar) Rearrange structure Add phosphate groups
Steps 4 & 5 (sugar splitting) Split hexose in half Both halves used in subsequent
rxns Steps 6-10 (energy harvest)
Rearrange structure & remove phosphates
End with two pyruvates (3-carbon organic acid)
Glycolysis – What goes in and what comes out
What comes out:
What goes in:
All 10 reactionsof glycolysisoccur in cytosol
Glycolysis begins with anenergy-investment
phase: 2 ATP 2 ADP
Enzyme Glucose-6-phosphate
Fructose-6-phosphate
Fructose-1,6-bisphosphate
Glucose
Pyruvate
The “2” indicates that glucosehas been split into two 3-carbonsugars (only one is shown)
During the energy payoff phase, 4 ATPare produced for a net gain of 2 ATP
Substrate-level phosphorylations
Glycolysis – What goes in and what comes out
GlycolysisTracking Carbon and Energy Carbon
Inputs: 1 glucose (6-C) Outputs: 2 pyruvate (3-C each)
Energy Inputs:
potential energy contained in chemical bonds in glucose 2 ATP
Outputs: potential energy in bonds in pyruvate (less than in glucose) 4 ATP (Net: 2 ATP) 2 NADH (carry electrons/energy)
Regulation of Glycolysis
Glucose Glucose-6-phosphate
Fructose-6-phosphate
Fructose-1,6-bisphosphate
PFK
Committed Step• catalyzed by phosphofructokinase (PFK)• PFK is inhibited by ATP
ATP
Feedback Inhibition
Feedback Inhibition – an enzyme in a metabolic pathway is inhibited by the product of the reaction sequence
Why is feedback inhibition beneficial?
Allostericsite
Fructose-1,6-bisphosphateat active site
ATP/ADP atactive site
Regulation of Glycolysis: PFK
Fructose-6-phosphate
Fructose-1,6-bisphosphate
PFK
ATP
PFK has two binding sites for ATP… Active site – ATP as substrate Allosteric site – ATP as allosteric
inhibitor
Cellular Respiration or Fermentation?
glucose
2 pyruvate
6 CO2 + 6 H2O 2 ethanol + 2 CO2 or 2 lactate
glycolysis 2 ATP
No O2O2cellular respiration fermentation
~25 ATP
Cellular Respiration or Fermentation?
Cellular respiration
If electron acceptor(such as oxygen)
is present
If electron acceptor(such as oxygen)is NOT present
Inefficient! Do not completely oxidize glucose Only utilize glycolysis Only make 2 ATP per glucose Regenerate NAD+
Do not produce enough energy to sustain large, active, multicelled organisms
Fermentation Pathways
Fermentation Pathways
First step - Glycolysis Glucose 2 pyruvate Generates 2 ATP and 2 NADH
Lactic Acid Fermentation 2 Pyruvate 2 Lactate Regenerates 2 NAD+
Alcoholic Fermentation 2 Pyruvate 2 Ethanol (Ethyl
Alcohol) + 2 CO2
Regenerates 2 NAD+
No intermediate;pyruvate acceptselectrons from NADH
2 Acetylaldehyde
2 Pyruvate
2 Pyruvate
2 Lactate
2 Ethanol
Pyruvate Processing
Inputs: 2 Pyruvate 2 Coenzyme A 2 NAD+
Outputs: 2 Acetyl CoA 2 NADH 2 CO2
Location: mitochondiral matrix
Pyruvate Processing
Coenzyme A – enzyme cofactor that acts as acetyl group “carrier” when acetyl group has bound CoA, it is “activated” (easily
transferred to acceptor molecule)
acetyl group“activated”
Coenzyme A
Pyruvate ProcessingTracking Carbon and Energy Carbon:
Inputs: 2 pyruvate (3-C each)
Outputs: 2 acetyl groups (carried by Coenzyme A) (2-C each) 2 CO2
Energy Inputs:
potential energy contained in bonds in pyruvate Outputs:
potential energy in bonds in acetyl groups (carried by Coenzyme A)
2 NADH (carry electrons/energy)
Regulation of Pyruvate Processing
Pyruvate conversion to Acetyl CoA is catalyzed by the pyruvate dehydrogenase complex; key regulatory point in glucose oxidation
Inhibited by: (feedback inhibition) ATP Acetyl CoA NADH
Activated by: AMP CoA NAD+
pyruvate dehydrogenase
complex
Citric Acid Cycle Citrate is
oxidized in a step-wise manner
Electrons (energy) transferred to NAD+ and FAD
Citric Acid CycleTracking Carbon and Energy Carbon:
Inputs: 2 Acetyl groups (carried by Coenzyme A) (2-C each)
Outputs: 4 CO2
Energy Inputs:
potential energy contained in bonds of acetyl groups Outputs:
2 ATP (substrate-level ATP synthesis) 6 NADH (carry electrons/energy) 2 FADH2 (carry electrons/energy)
So Far…summary of steps 1-3
Glucose has been fully oxidized to 6 CO2
Potential energy released from glucose has been used to generate 4 ATP (substrate-level ATP synthesis) and…
Electrons (energy) released from glucose during oxidation have been used to reduce: 2 FAD 2 FADH2
10 NAD+ 10 NADH Glucose(reduced)
6 CO2
(oxidized)
NAD+ and FADH(oxidized)
NADH and FADH2
(reduced)
This is were the energy is!
Cellular Respiration: Overview
Electron Transport Chain and Chemiosmosis: Summary
Electrons (carried by NADH and FADH2) are delivered to the electron transport chain (ETC)
Electrons are passed down the ETC to oxygen – undergo redox reactions; release energy
Released energy is used to pump protons (H+) across inner mitochondrial membrane; generates a proton gradient
Energy in gradient (proton-motive force) is used to drive synthesis of ATP (via chemiosmosis) by ATP synthase
Electron Transport Chain - Overview
Membraneof cristae
ComplexI
Intermembranespace
ComplexII
Mitochondrialmatrix
Complex I Complex II Complex III Complex IV
ComplexIII
ComplexIV
The electron transportchain occurs in theinner membrane of themitochondrion(membranes of cristae)
Chemiosmosis- Overview
Intermembranespace
Mitochondrialmatrix
Fo unit
Stator Rotor
F1 unit
Electron Transport Chain
Electrons from NADH and FADH2 are passed down ETC to O2 (final electron acceptor); generates H+ gradient
http://www.youtube.com/watch?v=xbJ0nbzt5Kw&feature=related
Chemiosmosis
Proton (H+) electrochemical gradient drives ATP synthesis via ATP synthase
Proton-Motive Force – Energy associated with movement of H+ ions down their concentration gradient across the IMM
Chemiosmosis – production of ATP via a proton gradient
Cellular Respiration: Overview
Glycolysis Pyruvate Processing and Citric Acid Cycle
Glucose
Acetyl CoA
Pyruvate
Oxaloacetate
In each of these drops,energy is transferred toenergy-storing moleculesATP, NADH, and FADH2
Series of chemical reactions,
each catalyzed by
a specific enzyme
Cellular respiration is a step-wise release of
energy from glucose
Disruption of Chemiosmosis by Poisons
Electron Transport Blockers Cyanide CO (carbon monoxide)
Uncoupler DNP (dinitrophenol)
Disruption of Chemiosmosis by Poisons
Electron Transport Blockers Cyanide CO (carbon monoxide)
Uncoupler DNP (dinitrophenol)
Anaerobic Respiration
What is the difference between anaerobic fermentation (previous slides) and anaerobic respiration? Anaerobic respiration involves the citric acid cycle and an
electron transport chain, but this ETC uses a different final electron acceptor – e.g. NO3
- , SO42-, S, or Fe3+.
Most species that perform anaerobic respiration are prokaryotes that live in environments devoid of O2.
For more information, including the ecological and economic significance of these organisms, see Wikipedia: anaerobic respiration.
Big Picture