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Cellular Respiration
Jolyon Johnson
Dartmoor School, Issaquah
Goal
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Cells need energy to survive.
We eat food to get its energy.
This energy comes in the form of ATP.
Lets look at the conversion of glucose to ATP.
Three Simple Steps
• Glycolysis – Break down of glucose to pyruvate
– Glucose is C6H12O6
– Pyruvate is C3H4O3
• Krebs Cycle – Break down pyruvate to energy storing
molecules
– NADH - Nicotinamide Adenine Dinucleotide (NAD+) plus
Hydrogen
– FADH2 - Flavin adenine dinucleotide (FAD) plus 2 Hydrogen
• Electron Transport Chain – Take energy from storing
molecules and convert it to ATP
– Most ATP made here
Where does glucose come from?
Sun
Plants
Glucose
(C6H12O6)
Animals
Cells
Quiz!
What is the purpose of cellular respiration?
• Turn energy stored in glucose into ATP
• Bring oxygen into and out of the cell
• Reproduce lung cells
Where is glucose made?
• In the sun
• In plants
• In animals
In which of the three parts of cellular respiration are
most ATPs created?
• Glycolysis
• Krebs Cycle
• Electron Transport Chain
Glycolysis – Step 1
• Glucose enters the cytoplasm
• Two ATPs leave a phosphate on the ends of
the six-carbon chain molecule, becoming ADP
• Thus, it costs two ATPs to begin the process
• We will soon gain those back, and many more
glucose
fructose biphosphate
Glycolysis – Step 2
• The six-carbon chain is split into two threecarbon chains
• Their atoms rearrange to be identical
• No ATP has been produced
fructose biphosphate
glyceraldehyde 3-phosphate
Glycolysis – Step 3
• From each three-carbon chain, an NAD+
molecule steals a hydrogen atom
– This makes two NADH, which will be important
• They leave behind an extra phosphate on each
three-carbon chain
• Still no ATP was formed
glyceraldehyde 3-phosphate
bisphosphoglycerate
Glycolysis – Step 4
• From each three-carbon chain, two ADP
molecule steal the phosphates
• This creates four ATPs
• The two spent ATPs were replaced and two
extra ATP’s were produced
• The resulting three carbon chain is called
pyruvate
bisphosphoglycerate
pyruvate
Glycolysis Review
• 2 NADH created
• 4 ATP created (but it took 2 to start)
Quiz!
What does it take to begin glycolysis?
• The Krebs Cycle
• 2 ATP’s
• 2 Pyruvates
Once glycolysis has begun, how many ATP’s are made?
• 4 ATP’s
• 27 ATP’s
• No ATP’s
What is the resultant molecule after Glycolysis?
• Glucose
• Protein
• Pyruvate
Aerobic vs Anaerobic
• An aerobic process occurs in the presence of
oxygen (O2)
• If oxygen is present in the cell, the pyruvate
molecule enters the Krebs Cycle
• An anaerobic process occurs in the absence of
oxygen
• If no oxygen is present, the pyruvate molecule
begins the process of fermentation
Alcoholic Fermentation
• A CO2 molecule leaves each pyruvate
– This leaves just two two-carbon chains
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NADH leaves an H+, becoming NAD+
NAD+ returns to glycolysis
The two carbon chains become ethanol
Bread, cheese, and yogurt are made by
fermenting bacteria, yeast, and mold
Lactic Acid Fermentation
• Pyruvate reacts with NADH to make NAD+
– NAD+ returns to glycolysis
• Pyruvate becomes lactic acid
• Animals also use a fermentation process when
they are not getting enough oxygen
– The lactic acid is what makes your muscles burn
when you exercise
Before the Krebs Cycle
• Each pyruvate loses a CO2 molecule and an H+
• A free NAD+ bonds with the H+ to make NADH
• The remaining acetat (C2OH3) bonds with a
coenzime (CoA) to make acetyl CoA
– CoA makes reactions happen more quickly
acetate
CoA
Krebs Cycle – Step 1
• Acetate drops the CoA
• Water and oxaloacetate (C4H4O5) join acetate
• Citrate molecule (C6H8O7) forms
acetate
oxaloacetate
• Atoms of citrate rearrange
citrate
Krebs Cycle – Step 2
• NAD+ steals an H+ to make NADH
• An extra H+ is released
• Citrate loses a CO2 to make ketoglutarate
(C5H6O5)
ketoglutarate
Krebs Cycle – Step 3
• NAD+ takes an H+ to make NADH
• Ketoglutarate loses a CO2 to make succinate
(C4H5O3)
• CoA comes back to speed up the process
Succinate
Krebs Cycle – Step 4
• GDP and a Phosphate make GTP by losing an
OH-, which replaces the CoA
• ADP takes the phosphate from GTP to make ATP
GTP
ATP
Krebs Cycle – Step 5
• Succinyl OH loses H2 to FAD to make FADH2
• Succinyl OH becomes fumarate (C4H4O4)
Succinyle OH
Fumarate
Krebs Cycle – Step 6
• Water joins fumarate to make malate (C4O5H6)
• NAD+ steals H+ to make NADH
• Malate becomes oxaloacetate
Fumarate
Malate
Krebs Cycle – Summary
• 3 NADH, 1 FADH2, 1 ATP produced per cycle
• Fats are “stored energy” because they break
down into acetate and enter the Krebs cycle
• Ketoglutarate, succinate, fumarate, and
malate form into amino acids to build proteins
• There are two cycles for one glucose molecule
Krebs Cycle Review
Krebs Cycle
Quiz!
What 2 molecules begin the Krebs Cycle?
• Acetyl CoA and Oxaloacetate
• ATP and a Phosphate
• Mitochondria and Glycolysis
How many times does the Krebs Cycle occur for every glucose?
• It only occurs when there is no oxygen available
• Infinite, it never stops
• Twice because there are two pyruvates for every glucose
What is the most important thing made in the Krebs Cycle?
• Lots of ATP
• Electron Carriers: NADH and FADH2
• Glucose
Only 4 ATP? What about the NADH
and FADH2? What’s going on???
Electron Transport Chain Anatomy
• Mitochondrial Matrix
– Negatively charged
• Intermembrane Space
– Positively charged
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Complex I
Complex II
Complex III
Complex IV
ATP Synthase
Krebs
Cycle
Electron Transport Chain – Complex I
• NADH gives 2 electrons to carrier Q (loses
energy)
• 1 H+ moves to the intermembrane space,
using the lost electron energy
• NAD+ returns to Krebs Cycle
Electron Transport Chain – Complex II
• FADH2 gives 2 electrons to carrier Q (loses
energy)
• 1 H+ move to the intermembrane space, using
the lost electron energy
• FAD+ returns to Krebs Cycle
Electron Transport Chain – Complex III
• Carrier Q gives 4 electrons to carrier C (loses
energy)
• 2 H+ moves to the intermembrane space,
using the lost electron energy
• Carrier C gains two electrons from a carrier in
the intermembrane space
– These came from the NADH produced in glycolysis
• Carrier Q stars over
Electron Transport Chain – Complex IV
• Carrier C gives 6 electrons to 3 oxygen (loses energy)
– 2 electrons from NADH made in glycolysis
– 2 electrons from NADH made in the Krebs Cycle
– 2 electrons from FADH2 made in the Krebs Cycle
• 2 H+ move to the intermembrane space, using the lost
electron energy
• Each oxygen bonds with 2H+ (created during Krebs
Cycle and at ATP synthase) in the matrix
– 3 water molecules are formed
• Carrier C stars over
• Water goes to the Krebs Cycle
How many hydrogens?
• H+ is undergoing active transport to move
from the matrix to the intermembrane space
• 3 hydrogens for every NADH moved to the
intermembrane space
• 2 hydrogens for every FADH2 moved to the
intermembrane space
ATP Synthase
• This enzyme moves H+ back into the matrix
• H+ then bonds with oxygen to make water or
goes back to the intermembrane space
• ADP and a phosphate in the matrix bond with
the ATP synthase enzyme
• The H+ gives ATP synthase the energy needed
to bind the ADP and phosphate into ATP
• ATP Synthase Video
– Stop at 2:55
Electron Transport Chain Review
Quiz!
What does each complex do?
• Move electrons and use the energy to move H+
• Make ATP’s and glucose
• Convert CO2 into oxygen for the brain
What is wasted in the electron transport chain?
• Many ATP’s and electron carriers
• Two of the four complexes
• Nothing. Everything is used and recycled
Where are all of the ATP’s made?
• Each complex makes a few of them
• ATP Synthase
• The electron carriers are turned into ATP
Total ATP/Glucose
• Glycolysis: -2 ATP (to start the process)
• Glycolysis: 4 ATP
• Glycolysis: 2 ATP/NADH * 2 NADH = 4 ATP
– Electrons enter electron transport chain at complex 3
• Pyruvate: 0 ATP/NADH * 2 NADH = 0 ATP
– These NADH are not used in ATP production
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Krebs Cycle: 2 ATP
Krebs Cycle: 3 ATP/NADH * 6 NADH = 18 ATP
Krebs Cycle: 2 ATP/ FADH2 * 2 FADH2 = 4 ATP
Total: 30 ATP
Review of Cellular Respiration