Pathways that reduce NAD+ to NADH How do cells transfer electrons from food to NAD+ to make NADH?...
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Transcript of Pathways that reduce NAD+ to NADH How do cells transfer electrons from food to NAD+ to make NADH?...
Pathways that reduce NAD+ to NADH
• How do cells transfer electrons from food to NAD+ to make NADH?– From sugars– From proteins– From fatty acids
Images are from Wikimedia Commons unless otherwise indicated
Oxidation of glucose to CO2
http://www.biologie.uni-hamburg.de/b-online/e19/19d.htm
Glycolysis Pyruvate oxidation
Citric acid cycle
Glycolysis: partial oxidation of glucose to pyruvate
Glycolysis – in cytoplasm of all cells
1. Uses 2 ATPs to “activate” glucose
2. Splits glucose into two 3-carbon sugars
3. Partially oxidizes the sugars, yielding 2 NADH per glucose
4. Substrate-level phosphorylation of ADP to make 4 molecules of ATP
5. Nets 2 pyruvates, 2 ATP, 2 NADH
In respiring cells, pyruvate is oxidized to CO2 + acetyl CoA
Two molecules of pyruvate are oxidized to 2 acetyl CoA + 2CO2, generating 2 NADH per molecule of glucose.
http://www.micro.siu.edu/micr201/chapter8N.html
Citric acid cycle generates ATP, reduced electron carriers and oxidizes acetate to CO2
Campbell & Reece Biology 8th ed.
Fats and proteins
http://www.life.umd.edu/classroom/bsci424/BSCI223WebSiteFiles/GeneralCatabolism.gif
http://www.ruf.rice.edu/~bioslabs/studies/mitochondria/mitokrebs.html
Locations of eukaryotic energy pathways
Campbell & Reece Biology 8th ed.
Respiring cells make most of their ATP via oxidative phosphorylation. What happens in the absence of respiration (no electron transport chain function)?
Fermentation reduces pyruvate to lactic acid or ethanol, to regenerate NAD+ from NADH
2 ADP + 2 Pi 2 ATP
Glucose Glycolysis
2 NAD+ 2 NADH
2 Pyruvate
+ 2 H+
2 Acetaldehyde2 Ethanol
(a) Alcohol fermentation
2 ADP + 2 Pi2 ATP
Glucose Glycolysis
2 NAD+ 2 NADH+ 2 H+
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation
2 CO2
In the absence of respiration
• Cells can make ATP through glycolysis and fermentation of glucose
• Cells cannot run pyruvate oxidation or citric acid cycle (no mitochondrial function in eukaryotes)