chapter 7: how cells harvest energy how our food becomes energy for our cells (atp)
TRANSCRIPT
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Chapter 7: How Cells Harvest Energy
• How our food becomes energy for our cells (ATP)
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How to make ATP from glucose
Can be aerobic (with oxygen) or anaerobic (without oxygen
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ATP Review
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Requires coenzymes NADH and FADH2
Need to collect electrons from the food and use them to drive the machine that synthesizes
ATP
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Redox Reactions
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Redox with NAD and FAD
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Aerobic RespirationHow cells harvest energy from glucose
Glucose + 6OGlucose + 6O22 6CO 6CO22 + 6H + 6H22O + Energy O + Energy
ATP + Heat
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4 Steps of Aerobic respiration1.Glycolysis2.Oxidation of pyruvate3.Kreb’s cycle (aka Citric Acid Cycle)4.Electron transport chain
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Glycolysis: 6 carbon glucose to two 3 carbon pyruvates
Occurs in Cytoplasm
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Glycolysis• 6 carbon molecule broken into two 3 carbon molecules• Glucose has to be activated. This uses up 2 ATP
molecules, but kick-starts the whole thing off. • 4 ATPs are made during glycolysis, so a net gain of 2
ATPs
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Glycolysis• Uses an electron carrier called NADH• Each NADH molecule carries 2 electrons that it
has removed from glucose• These electrons will be very important later!!!!!
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Over-all Glycolysis• End products are 2 pyruvates (2 carbon
molecules), 2 ATPs, and 4 electrons stored on 2 NADH’s
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Oxidation of Pyruvate(Breaking 3 carbon pyruvate into a 2
carbon molecule and CO2)
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Oxidation of Pyruvate
• Pyruvate is transported into the mitochondrial matrix
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Oxidation of Pyruvate• The 3 carbon pyruvate is
broken down into a 2 carbon molecule called AcetylCoA and a CO2
• The CO2 bubbles out of the mitochondria, then the cell
• The AcetylCoA will be further broken down in the next step
• 2 NADH’s are made in this step (stealing electrons from the organic pyruvate)
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Summary: Oxidation of Pyruvate• Carbon backbone has been broken from 3 to 2
carbons
• CO2 has been made and released
• 2 NADH’s made (one per pyruvate)• No ATP made
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Stage 3: Kreb’s Cycle (aka Citric Acid Cycle)
• Occurs in the matrix
• AcetylCoA is broken apart into CO2
• Final breakdown of the carbon backbone
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Kreb’s Cycle(In mitochondrial matrix)
• The last electrons are removed from the organic molecules and put on electron carriers.
• FADH2 is an electron carrier like NADH. It can carry 2 electrons on each molecule.
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Summary Kreb’s Cycle• No more carbon-carbon bonds or electrons from
glucose
• 6 NADH’s and 2 FADH2 created (16 electrons stored and carried)
• CO2 given off
• 2 ATPs made
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Summary so far:• Glucose carbon-backbone is totally
demolished. Carbons have been released in CO2 molecules.
• All available electrons have been stripped from glucose and are now carried on 10 NADH’s and 2 FADH2’s
• Only net gain of 4 ATP’s
What to do with the electrons?
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Electron Transport Chain• NADH and FADH2 drop off electrons on
the inner membrane proteins– This results in recycling NAD+ and FAD,
which will go back and participate in earlier events
– The electrons jump from one protein to the next creating something like an electric current
– This “electricity” runs something called the H+ pump. This protein moves H+ from the matrix into the inter-membrane space.
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Electron Transport ChainThe H+ build up in the inter-membrane space and create a
big potential energy called the proton motive force
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Electron Transport Chain• The H+ can move back into the matrix, but only through
a channel attached to an enzyme called ATP Synthase, This is called chemiosmosis.
• Like water running over a water-wheel, the H+ moving across the membrane powers the ATP Synthase to build ATP
• Approximately 32 ATPs are made in the ETC for every glucose
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Summary: Electron Transport Chain•NADH and FADH2 are
used to power the proton pump•Protons (H+) are pumped from mitochondrial matrix into intermembrane space•These protons push through the ATP synthase making its “motor work”•ADP and Phosphate are put together to make ATP in the matrix
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One last thing about the Electron Transport Chain
• The electrons moving through the ETC will finally bind to a oxygen with 2 H+, making water
• THIS IS THE REASON YOU BREATHE IN OXYGEN! To keep the electron chain moving
• If no oxygen, no ATP, and you die
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• Cyanide blocks the last step of the electron transport chain, so electrons are blocked from oxygen
• The whole thing gets backed up and no electrons move through.
• Without “electric current”, the H+ pumps don’t build up the concentration gradient.
• The ATP synthase has no H+ to drive it.• You die within minutes without the new ATP!
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Summary of Glycolysis and Aerobic Respiration
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Aerobic –vs- Anaerobic RespirationIf no oxygen available, the glucose molecule can’t be broken down all the way.The results are 2 ATPs and either:
•2 Lactic acids (3 carbon molecules)
Or
•2 Ethanosl (2 carbon molecule) and 2 CO2
(Fermentation)
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Lactate Fermentation• Uses glycolysis
• Makes 2 ATPs
• Recycles 2 NAD+
Occurs in the muscles when not enough oxygen available to make ATP neededHurts!
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Alcohol Fermentation• Uses glycolysis
• Makes 2 ATPs
• Recycles 2 NAD+
• Makes carbonated ethanol (beer?)
We use yeast to do this when making alcohol. Lots of money & research goes done on this metabolic pathway.
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Anaerobic vs Aerobic
Anaerobic fermentation Aerobic respiration
No oxygenNo mitochondria neededOnly net gain of 2 ATPs
Oxygen is requiredOccurs in cytoplasm and inside mitochondriaMakes about 36 ATPs
Begins with glucoseUses glycolysisIn cytoplasmUses coenzymesFAD and NAD