lecture #4date _________ chapter 9~ cellular respiration: harvesting chemical energy
TRANSCRIPT
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Lecture #4 Date _________
• Chapter 9~Cellular
Respiration: Harvesting Chemical Energy
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Things to Know• The difference between fermentation and cellular respiration
• The role of glycolysis in oxidizing glucose to 2 molecules of pyruvate
• The process that brings pyruvate from cytosol into the mitochondria and introduces it into the citric acid cycle
• How the process of chemiosis utilizes the electrons from NADH and FADH2 to produce ATP
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Catabolic Pathways• Catabolic pathways – molecules are broken down and
their energy is released
2 Types of Catabolic Pathways
- fermentation – partial degradation of sugar without the use of oxygen
- cellular respiration – the most efficient catabolic pathway, where oxygen is used as a reactant with organic fuel (called aerobic respiration because it uses oxygen)
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Some Background• Carbohydrates, fats and protein can all be broken down to
release energy in cell. resp., but glucose is the primary molecule used in cell. resp.
Here’s the equation:
C6H12O6 + 6 O6 6 CO2 + 6 H2O + Energy
The energy released from this is stored by phosphorylating (adding phosphate) ADP into ATP
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Redox Reactions• The reactions in cell. resp. are a type called oxidation-
reduction (redox), where electrons are transferred from one reaction to another
- loss of electrons from reactant are called oxidation
- gain of electrons is
reduction
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Redox in Cell. Resp.
C6H12O6 + 6 O6 6 CO2 + 6 H2O + Energy
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NAD+ and NADH• NAD+ is an electron carrier• NAD+ accepts 2 electrons to form NADH
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Cellular Respiration
• There are 3 steps to cellular respiration:- Glycolysis
- Citric Acid Cycle
- Oxidative Phosphorylation: electron transport & chemiosis
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Glycolysis• Glycolysis occurs in the cytosol
(cytoplasm)• Glucose is broken down into 2
pyruvate acid molecules• In the “Energy Investment phase” 2
ATP are used• In the “Energy Payoff phase” 4 ATP
are produced• The Results: 2 ATP, 2 pyruvate acid,
2 NADH
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Citric Acid Cycle (aka Kreb’s Cycle)
• Pyruvate acids use transport protein to enter the mitochondria
• In the process, pyruvate acid is converted by Coenzyme A to make Acetyl CoA
• Now this Acetyl CoA enters the citric acid cycle
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Citric Acid Cycle (aka Kreb’s Cycle)• 2 Acetyl CoA enters the cycle and each
go into the cycle• Results (from 2 rounds): 4 CO2, 6
NADH, 2 FADH2, and 2 ATP produced• * note 1 glucose molecule (C6H12O6)
makes 2 rounds • **note CO2 released is what you
breathe out• *** note NADH and FADH2 are electron
carriers and will produce a bunch of ATP in Oxidative Phosphorylation
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Oxidative PhosphorylationElectron Transport Chain
- embedded in the inner membrane of the mitochondria- 3 proteins work as hydrogen pumps- step by step process that pumps H+ that is powered by the electron carriers NADH and FADH2
- H2O is produced in Electron Transport Chain (NO ATP produced!!)
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Oxidative PhosphorylationChemiosmosis
- the H+ ions are pumped back in chemiosmosis through a protein called the ATP Synthase
- ATP is produced from ADP in chemiosmosis
IN TOTAL
- Oxidative Phosphorylation produced 32-24 ATP- which means cellular respiration makes a total of 36-38 ATP (2 from Glycolysis and 2 from Kreb’s Cycle)
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Review: Cellular Respiration
• Glycolysis: 2 ATP (substrate-level phosphorylation)
• Kreb’s Cycle: 2 ATP (substrate-level phosphorylation)
• Electron transport & oxidative phosphorylation: 2 NADH (glycolysis) = 6ATP 2 NADH (acetyl CoA) = 6ATP 6 NADH (Kreb’s) = 18 ATP 2 FADH2 (Kreb’s) = 4 ATP
• 38 TOTAL ATP/glucose
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Fermentation• Fermentation is a process to make ATP without the presence of
oxygen• Glycolysis still occurs, but that’s the only similarity with cell. resp.• After glycolysis there’s 2 options:
- alcohol fermentation – pyruvate is converted to ethanol (alcohol), releasing CO2 and NADH- lactic acid fermentation – pyruvate is reduced by NADH and lactic acid is waste product
• Facultative anaerobes are organisms that prefer cell resp., but can do fermentation if no oxygen available