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Alternate Pathways

Alternate Pathways. 2.3. Carbohydrates are the first nutrients most organisms catabolize for energy. What if there is no food? Most organisms possess alternate metabolic pathways. Proteins, lipids, and nucleic acids can be used for cellular respiration. Protein Catabolism.

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Alternate Pathways

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  1. Alternate Pathways 2.3

  2. Carbohydrates are the first nutrients most organisms catabolize for energy.. • What if there is no food? • Most organisms possess alternate metabolic pathways. • Proteins, lipids, and nucleic acids can be used for cellular respiration.

  3. Protein Catabolism • Deamination: amino groups removed from amino acids. • Converted to ammonia, a __________ product in animals and a useful byproduct in plants. • Other parts of amino acids converted to components of glycolysis or the Krebs cycle • Depends on the amino acid • Leucine: acetyl-CoA • Alanine: pyruvate • Proline: alpha-ketoglutarate

  4. Lipid Catabolism (1) • Triglycerides first digested into glycerol and Fas. • Gluconeogenesis: glycerol converted into glucose, or DHAP  G3P. • Fatty acids transported into the matrix • Beta-oxidation: 2C acetyl groups removed from fatty acids and then added to coenzyme A  acetyl CoA

  5. Lipid Catabolism (2) • c • Lipids are harder to break down than carbohydrates • Requires energy input • Yields more energy (about 2x as much)

  6. Anaerobic Pathways • There are some organisms are anaerobic: ______________________. How do they acquire ATP? • Some organisms only carry out glycolysis: ______ ATP/glucose molecule. • Think about this: in aerobic respiration, NAD+  NADH in glycolysis. NADH eventually donates its electrons to the ETC in which oxygen is the final electron acceptor. • If no oxygen  NADH has nowhere to donate electrons to  NAD+ not recycled  no NAD+ to oxidize G3P in glycolysis  glycolysis would ____________.

  7. Anaerobic Pathways • Glycolysis can occur in the absence of oxygen • Fermentation: transfer of hydrogen atoms of NADH to organic molecules instead of ETC • Ethanol fermentation • Lactate Fermentation

  8. Ethanol Fermentation • NADH passes hydrogen atoms to acetaldehyde ethanol. • Used in alcoholic beverages • NAD+ can be recycled and glycolysis can continue. • 2 ATP molecules may satisfy the organism’s energy needs. • Yeast: single-celled fungi • Breads, pastries, wine, beer, liquor, soy sauce.

  9. Bread: • Yeast + starch + water • Yeast ferment glucose from Starch and release CO2 and Ethanol. • CO2 makes bread rise • Ethanol evaporated • Wine: • Yeast ferments grape & fruit sugars • Fermentation ends when concentration of ethanol reaches approx. 12%  yeast cells die. • Flooded Plants • Undergo ethanol fermentation in the roots. • Do not overwater Sally!

  10. FAS Read the section on page 120 on fetal alcohol syndrome. What do you think?

  11. Lactate (Lactic Acid) Fermentation • Used during strenuous exercise. • Muscle cells used glucose faster than oxygen can be supplied. • NADH transfers hydrogen atoms to pyruvate in the cytoplasm  lactate (NAD+ is regenerated) • Allows glycolysis to continue. • Accumulation of lactate: stiffness, soreness, and fatigue. • Lactate  bloodstream  liver. • When strenuous exercise ceases, lactate  pyruvate  Krebs Cycle

  12. Seatwork/Homework • PPs page 124 • #1,2,3,7,8,9,10.

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