Metabolic Pathways

1. Metabolic Pathways • A metabolic pathway or biochemical pathway is where a substrate will convert to a product, and that product will turn into a substrate for a different enzyme • Exergonic Reaction is a reaction where energy is released • Endergonic Reaction is where a reaction will need to take in energy to occur

2. Endergonic and ExergonicRxns

3. Catabolic and Anabolic Pathways • Chemical reactions which break larger molecules into smaller ones are catabolic pathways. • aerobic respiration, anaerobic respiration, dehydration reaction • These reactions are typically exergonic

4. Catabolic and Anabolic Pathways • Chemical reactions which synthesize larger molecules from smaller ones are anabolic pathways. • Protein synthesis, photosynthesis, condensation reaction • These reactions are typically endergonic.

5. Central Role of ATP • ATP stands for adenosine triphospate, which means that it has three phosphate groups attached to it. • ADP stands for adenosine diphospate • AMP stands for adenosine monophosphate

6. Central Role of ATP • High-energy phosphate bonds are the bonds of the last 2 phosphate groups, which are easily broken to release energy for cellular processes. • ATP → ADP + P + energy

7. Electron Transport • Electron transport is where electrons give up their energy as they move through a series of electron transport reactions. • Oxidation-reductionreaction is where molecules either gain or lose electrons. • Oxidation is where a molecule loses electrons • Reduction is where a molecule gains electrons • Three important electron acceptors (carriers) are NAD+, NADP+, and FAD

8. Proton Pump • One major way to generate ATP is via a proton pump. • The energy from high energy electrons is used to pump H+ across a membrane, like pumping water behind a dam.

9. Biology 100Chapter 6Biochemical Pathways-Cellular Respiration

10. Autotrophs • Autotrophs are able to take basic energy sources to make energy-containing organic molecules from inorganic molecules • (auto-self, troph-feeding) • Two types of autotrophs • Chemosynthetic autotrophs are prokaryotic organisms that use inorganic chemical reactions as a source of energy to make larger, organic molecules • Photosynthetic autotrophs use sunlight to create the organic molecules used for energy

11. Heterotrophs • Heterotrophs do not make their own organic molecules, so they must intake their energy source through food • (hetero-other, troph-feeding) • In eukaryotic cells, certain biochemical processes are carried out in certain organelles • Chloroplasts are sites of photosynthesis • Mitochondria are the sites of most cellular respiration • Prokaryotes lack both chloroplasts and mitochondria, so many biochemical processes occur in the cytoplasm

12. Cellular Respiration • Cellular Respiration is where organisms control the release of chemical-bond energy from large, organic molecules and use the energy to sustain life • Aerobic cellular respiration requires oxygen to occur • Anaerobic cellular respiration do not require oxygen to occur

13. Aerobic Cellular Respiration • In aerobic cellular respiration, ATP forms as electrons are harvested, transferred along the electron transport chain, and eventually donated to oxygen gas. • C6H12O6 + 6O2 → 6CO2 + 6H20 + Energy • In glucose, the covalent bonds has chemical potential energy. The easiest ones to get to are the C-H and O-H bonds

14. Aerobic Cellular Respiration • When the bonds from glucose are broken, two things happen: • The energy of electrons will phosphylate ADP to make ATP • Hydrogen ions (protons) are released • Oxygen will be the final electron acceptor • Glucose will be oxidized, while oxygen will be reduced.

15. Overview of Aerobic Respiration • Aerobic respiration is divided into three processes: • Glycolysis • Krebs Cycle • Electron Transport System

16. Glycolysis • Glycolysis (glyco-sugar,lysis-split) • Glucose + 2 ATP + NAD+ → 4 ATP + 2 NADH + 2 pyruvic acid • Anaerobic • Occurs in cytoplasm • Requires 2 ATP to start glycolysis • Has a net gain of 2 ATP

17. Glycolysis • An inorganic phosphate group is added to each 3C molecule. • This leaves each 3C molecule with phosphate groups at either end Pi – C –C –C –Pi • Other enzymes pull off a pair of high energy electrons (and H+) and pass them to our electron delivery truck, NAD+, producing NADH.

18. Kreb’s Cycle • Takes place in mitochondrian • One carbon, in the form of CO2, is pulled off the 3C molecules, leaving 2C. • And a pair of high energy electrons are loaded onto NAD+ to produce NADH.

19. Kreb’s Cycle • A phosphate group is added to each 2C molecule and then transferred to ADP, forming ATP. • Enough high energy electrons are pulled off the 2C fragments to load up 3 more NAD+, forming 3 NADH. • A pair of slightly less energetic electrons are passed to another carrier, FAD, producing FADH2

20. Kreb’s Cycle • Pyruvic Acid + ADP + 4NAD+ + FAD → 3CO2 + 4NADH + FADH2 + ATP (for each pyruvic acid) Also known as the Citric Acid Cycle

21. Electron Transport System • Both glycolysis and the Krebs cycle pass electrons to the electron carriers, NADH and FADH2. • The carriers pass their electrons to transport molecules in the inner mitochondrial membrane. • NAD+ and FAD leave to pick up another load. • As electrons are passed from transport molecule to transport molecule, H+ ions are pumped across the membrane. • Finally, the electrons are passed to O2, which combines with 2H+ to form H2O.

22. Electron Transport System • The energy in the electrons carried by each NADH can be cashed in for 3 ATPs • 10 NADH x 3 ATP = 30 ATP. • The energy in the electrons carried by FADH2 can be cashed in for 2 ATPs. • 2 FADH2 x 2 ATP = 4 ATP. • Total: 34 ATP from the ETS. • 6 O2 are consumed to produce H2O.

23. Aerobic Respiration • Starting with glucose (C6H12O6) and 6 O2 • Produce 6 CO2 and 6 H2O and up to 36 ATP • However, 1/3 of energy is wasted in heat release, yet still incredibly efficient source of energy • The NAD+ and FAD are released to be used over again • Since oxygen is the final electron acceptor, H2O is formed

24. Anaerobic Respiration • Fermentation is the term used to describe anaerobic pathways that oxidize glucose to generate ATP energy by using an organic molecule as ultimate hydrogen acceptor • Incomplete oxidation of glucose • Lower amount of ATP produced • The pyruvic acid may be turned into lactic acid, ethyl alcohol or other molecules

25. Anaerobic Respiration

26. Alcoholic Fermentation • Alcoholic fermentation is the anaerobic respiration pathway that yeast cells follow when there is no oxygen in the environment • Pyruvic Acid is converted into ethanol and carbon dioxide • In bread-making, the carbon dioxide is trapped in the bread dough and called leavened

27. Lactic Acid Fermentation • Lactic Acid Fermentation is where pyruvic acid is converted into lactic acid. • Lactic Acid is considered a waste product to the human body • However, lactic acid is used to make yogurts, sour cream and cheese • When exercising, the skeletal muscle cells may have to function anaerobically. The lactic acid will ultimately be metabolized, which requires oxygen. After finishing working out, our body will start to metabolize the lactic acid.

28. Respiration • Both proteins and fats can be catabolized via aerobic respiration (but not anaerobic respiration). • The glycerol (3C) from fats enters glycolysis near the end and then continues through the Krebs cycle. • Fatty acids are split into 2C fragments by the peroxisomes. • The 2C fragments are passed to the Krebs cycle for conversion into CO2 and generation of lots of ATP.

29. Respiration • Proteins are first split into their amino acids. • The amine groups are split off each amino acid, forming NH3, ammonia. • Some organisms excrete the toxic NH3 immediately, while others convert it to urea. • The rest of the C skeleton pass into various spots in the Krebs cycle where they are converted to CO2.