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CHAPTER 7: Cellular Respiration and Fermentation - Coggle Diagram
CHAPTER 7: Cellular Respiration and Fermentation
Overview of Cellular Respiration
A process by which living cells obtain energy from organic molecules
Primary aim is to make Adenosine Triphosphate (ATP) and NADH
Aerobic Respiration uses oxygen
O2 consumed and CO2 released
Primarily uses glucose but other organic molecules can also be used
Glucose Metabolism
Four Metabolic Pathways:
Breakdown of Pyruvate
Stage 2 of cellular respiration
In eukaryotes, pyruvate is transported into the mitochondrial matrix
Broken down by an enzyme called pyruvate dehydrogenase
Molecule of CO2 removed from each pyruvate
Remaining acetyl group attached to CoA to make acetyl CoA
Citric Acid Cycle
Stage 3 of cellular respiration
A metabolic cycle
Some molecules enter while other leave
Series of organic molecules regenerated in each cycle
Acetyl is removed from acetyl CoA and attached to oxaloacetate to form citrate (aka citric acid)
Series of steps releases 2 CO2, 1 ATP, 3 NADH, and 1 FADH2
Oxaloacetate is regenerated to start the cycle again
Glycolysis
Stage 1 of cellular respiration
Can occur with or without oxygen
Steps in glycolysis are nearly identical in all living species
Ten steps in three phases:
Energy Investment
Steps 1-3
2 ATP hydrolyzed to create fructose-1,6 bisphosphate
Cleavage
Steps 4-5
6 carbon molecules broken into two 3 carbon molecules of glyceraldehyde-3-phosphate (G3P)
Energy Liberation
Steps 6-10
Two glyceraldehyde-3-phosphate molecules broken down into two pyruvate molecules - produce 2 NADH and 4 ATP
Oxidative Phosphorylation
Stage 4 of cellular respiration
High energy electrons removed from NADH and FADH2 to make ATP
Typically requires oxygen
Oxidative process involves the electron transport chain (ETC)
Phosphorylation occurs by ATP synthase
Oxidation by the Electron Transport Chain (ETC)
Protein complexes and small organic molecules embedded in the inner mitochondrial membrane
Accept and donate electrons in a linear manner in a series of redox reactions
Movement of electrons generates an H+ electrochemical gradient (proton-motive force)
This provides energy for the next step, which is synthesizing ATP
Phosphorylation by ATP synthase
Lipid bilayer of inner mitochondrial membrane is relatively impermeable to H+
Protons can only pass through ATP synthase
Harnesses free energy to synthesize ATP from ADP
Chemiosmosis - chemical synthesis of ATP as a result of pushing H+ across a membrane
NADH oxidation makes most of the cell's ATP
NADH oxidation creates the H+ electrochemical gradient used to synthesize ATP
Yield = up to 30-34 ATP molecules / glucose
But rarely achieve maximal amount because:
NADH also used in anabolic pathways
H+ gradient used for other purposes
ATP synthase
captures free energy as H+ ions flow through
The enzyme converts energy from the proton motive force of the H+ gradient to chemical bond energy in ATP
ATP synthase is a rotary machine that makes ATP as it spins
Connections Among Carbohydrate, Protein, and Fat Metabolism
Besides glucose, other molecules are also used for energy: carbohydrates, proteins, and fats
Metabolism can be used to make molecules (anabolism)
Enter into glycolysis or citric acid cycle at different points
Utilizing the same pathways for breakdown increases efficiency
Anaerobic Respiration and Fermentation
For environments that lack oxygen or during oxygen deficient times
Can be of two strategies:
Use substance other than O2 as final electron acceptor in electron transport chain
Produce ATP only via substrate-level phosphorylation
Fermentation
But glycolysis uses up NAD+ and makes too much NADH under anaerobic conditions (which is a dangerous situation)
Muscle cells solve the problem by reducing pyruvate into lactate
Many organisms can only use O2 as final electron acceptor, so under anaerobic conditions, they need a different way to produce ATP, like using glycolysis
Yeast solve problem by making ethanol
Fermentation is the breakdown of organic molecules without net oxidation
Fermentation produces far less ATP than oxidative phosphorylation