Lecture 7
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Transcript of Lecture 7
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Lecture 7: Harvesting Energy – Glycolysis & Cell Respiration
COVERS CHAPTER 8
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How do we get energy from food?*
• Glucose + O2 >> CO2 + H2O + ATP
• We breathe O2 and eat food (glucose), and convert that to CO2, water and ATP (energy for our cells to function)
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The Big Picture*
• Glycolysis and Cell Respiration are both part of a larger CYCLE of life:
• Plants (and other autotrophs) take sunlight and water and CO2 and make glucose from it via photosynthesis. Oxygen is a byproduct of this reaction.
• Humans (and other animals-heterotrophs) take the glucose in (by eating plant material and other foods) and break it down. Water and CO2 are by products.
• In this way, plants give us what we need (O2 and glucose) and we supply the plants with water and CO2.
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Photosynthesis Provides the Energy Released by Glycolysis and Cellular Respiration
Fig. 8-1
ATP
H2O O2CO2C6H12O6
glycolysis
photosynthesis
energy from sunlight
cellularrespiration
66 6
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What do we use energy for?*
• Most cellular energy in the body is stored in the chemical bonds of ATP
• Cells require a continuous supply of energy to– Run chemical reactions– Grow– Reproduce– Move the body
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More big picture*• This lecture describes the reactions that move the energy from energy
STORAGE molecules (like glucose and fat) to energy CARRYING molecules (like ATP, NADH and FADH2)
• About 40% of the energy in glucose can be transferred to ATP, the rest is released as heat.
• Cells break down glucose (the most common energy storage molecule) and give it to energy carrying molecules (ATP) via 2 separate reactions:– Glycolysis (2 steps)
• Glucose activation• Energy Harvest
– Cellular Respiration (3 steps)• Creation of Acetyl CoA• Krebs Cycle• Oxidative Phosphorylation
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A Summary of Glucose Breakdown
Fig. 8-2
cellularrespiration
glucose
glycolysis
fermentation2 pyruvate
lactate
ethanol+
CO2
(cytoplasmicfluid)
mitochondrion
ATP
CO2
34or36
ATP2
6 H2O
O2
6
6
If no O2 is availableIf O2 is available
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Glycolysis: 2 parts• Takes place in cytoplasm• Starts with a molecule of glucose, ends with PYRUVATE• Is an anaerobic reaction: can happen even in the absence of oxygen• 2 parts
– Glucose activation: a glucose molecule is energized by the addition of TWO high energy phosphates FROM TWO ATP molecules, leaving ADP. (Yes, you have to spend ATP to make it!)
– Energy Harvest: The products of these reactions give high energy phosphates back to 4 ADP molecules, resulting in the creation of 4 ATP molecules (but only a NET production of 2 ATPs.) Also, 2 high energy electrons and a hydrogen ion are added to “empty” electron carrier NAD+ to make NADH. Pyruvate is the end product of glycolysis.
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The Essentials of Glycolysis
Fig. 8-3
glucosefructose
bisphosphate
G3P pyruvate
NAD+
ADPATP
2
2 2
22
4 4
2
ADP
NADH
ATP
Energy harvestGlucose activation
CC CCCC CC CC C CC C CCCC
PPP
1 2
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Glycolysis*
• One molecule of glucose is transformed into 2 molecules of pyruvate
• Pyruvate then moves into the mitochondrial matrix
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Anatomy of a mitochondrion*
• Outer membrane: most small molecules can freely diffuse across
• Intermembrane Space: space between inner and outer membrane
• Inner Membrane: high ratio of proteins to lipids-most molecules must pass through protein channels
• Cristae: internal compartments formed by the inner membrane
• Matrix: space inside inner membrane
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Cell Respiration: Big Picture*
• Pyruvate (from glycolysis) is broken down (for every molecule of glucose entering glycolysis, keep in mind TWO pyruvates are made.)
• Energy is extracted (given to energy carrying molecules)• CO2 and H2O are released• Happens in mitochondria• 3 reactions make up cellular respiration:
– Creation of Acetyl CoA (matrix)– Kreb’s Cycle (AKA TCA Cycle, Citric Acid Cycle) (matrix)– Oxidative Phosphorylation (across inner mito membrane from matrix to
intermembrane space)
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Creation of Acetyl CoA & Kreb’s Cycle
• Pyruvate >> Acetyl CoA (intermediate) + CO2
• Acetyl CoA >> H2O + 2 ATP + more CO2 + NADH + FADH2 + H ions
• CO2 LEAVES THE MITOCHONDRIA• 2 ATP are made• **High energy electrons and hydrogen ions are
transferred to energy carrying molecules NAD+ (10) and FAD (2), turning them into 10 NADH and 2 FADH2. **follow the NADH, FADH2 and H ions!
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Creation of Acetyl CoA
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Kreb’s Cycle
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Oxidative Phosphorylation• 4 high energy electrons are transferred from NADH and
FADH2 to the ELECTRON TRANSPORT CHAIN, embedded in the inner mito membrane.
• The electrons “jump” from molecule to molecule along the chain, losing small amounts of energy each time. SOME OF THIS ENERGY is used to pump H atoms across inner membrane and into intermembrane space.
• Result is HIGH H+ concentration inside the intermembrane space.
• Electrons reach the “end” of the transport chain and are transferred to oxygen.
• H atoms and oxygen combine to form WATER.
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Oxidative Phsophorylation
• FINALLY, H atoms flow DOWN their gradient from intermembrane space BACK to the matrix
• ADP and free phosphate are waiting there, and they combine to form ATP.
• ATP leaves matrix and mitochondria and enter cytoplasm to fuel cell’s processes. (and more ADP moves into matrix to make more ATP.
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Oxidative Phosphorylation
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Another pic of Oxidative Phosphorylation
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ATP Yield*
• One molecule of glucose going through glycolysis can generate TWO molecules of ATP. If the material continues through cell respiration, another 34-36 molecules of ATP can be generated.
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Aerobic vs anaerobic reactions
• Glycolysis is an anaerobic reaction: it can happen even in the absence of oxygen
• Cellular Respiration requires oxygen to happen: it is an aerobic reaction.
• (If there is no oxygen available, a cell cannot do cell respiration, and instead performs a fermentation reaction. Lactate-lactic acid- is a byproduct of fermentation.)
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Fig. 8-2
cellularrespiration
glucose
glycolysis
fermentation2 pyruvate
lactate
ethanol+
CO2
(cytoplasmicfluid)
mitochondrion
ATP
CO2
34or36
ATP2
6 H2O
O2
6
6
If no O2 is availableIf O2 is available
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Can we get energy from other molecules besides glucose?
• Keep in mind that most animals can harvest ATP from a number of different molecules (like glycogen-storage form of glucose- and fats and proteins), but glucose is the PRIMARY source of our ATP.
• (We would have to break down these other molecules and they can enter the cell respiration pathway at different points.)
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Proteins and Fats can give us energy!