Metabolic Pathways

1. Metabolic Pathways Related to Cellular Respiration

3. Cell Starvation http://www.imgenex.com/emarketing/Autophagy_landingpage/autophagy_regulation1.jpg • In some cases carbohydrates (the first nutrient most organisms catabolize for energy) are unavailable and the cell must metabolize other energy rich nutrients • Most organisms have metabolic pathways that can break down the cells proteins, lipids and nucleic acids

4. Autophagy (intro)http://www.helsinki.fi/bioscience/biochemistry/pictures/Eskelinen2.jpghttp://www.nature.com/scitable/topicpage/the-discovery-of-lysosomes-and-autophagy-14199828 • Eukaryotic cells have evolved a way to resist eating for long periods of time by digesting their own components. • When starving conditions are prolonged, cells digest part of their own cytoplasmic components to recycle metabolites needed to synthesize essential molecules

5. Autophagy (continued)http://www.helsinki.fi/bioscience/biochemistry/pictures/Eskelinen2.jpghttp://www.nature.com/scitable/topicpage/the-discovery-of-lysosomes-and-autophagy-14199828 • Autophagy (a Greek word that means "self-eating") is a catabolic process in eukaryotic cells where cytoplasmic components are surrounded in membranes to form autophagosomes • autophagosomes fuse to the lysosomal membrane to form a structure known as the autolysosome • Then, depending on the stimuli that initiated the autophagy process, the cargo is either degraded or recycled.

6. Protein Catabolism • Proteins can be used for energy. • Polypeptide chains are broken down via hydrolysis into individual amino acids. • Amino acids are generated by the digestion of proteins in the intestine or by the degradation of proteins within the cell.

7. Deaminationwww.elmhurst.edu/~chm/vchembook/632oxdeam.html • The first stage of protein metabolism is deamination • Deamination is an oxidative reaction that occurs under aerobic conditions in all tissues but especially the liver. • The ammonia eventually goes into the urea cycle.

8. Protein Components enter Cellular Respiration http://upload.wikimedia.org/wikipedia/commons/8/85/Aerobic_pathways.png • Other chemical reactions convert the remaining parts of the amino acids into various components of cellular respiration • The point of entry depends on the identity of the amino acid

9. Lipid Catabolism http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/fatcatab.htm • Triacylglycerols (triglycerides) are the most abundant dietary lipids. • They are the form in which we store reduced carbon for energy

10. Lipid CatabolismGlycerolhttp://themedicalbiochemistrypage.org/gluconeogenesis.html • Glycerol arising from hydrolysis of triacylglycerols is converted to the Glycolysis intermediate dihydroxyacetone phosphate (DHAP) • The glycerol backbone of lipids can be used for gluconeogenesisis {the biosynthesis of new glucose, (i.e. not glucose from glycogen)}

11. Lipid CatabolismFatty Acid Chains1http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/fatcatab.htm • Fatty acids are degraded in the mitochondrial matrix via the b-Oxidation Pathway. • For most steps of the pathway there are multiple enzymes specific for particular fatty acid chain lengths

12. Lipid CatabolismFatty Acid Chains2http://neuromuscular.wustl.edu/pics/diagrams/functional/mitofcn3c.gif • Each round of β-oxidation produces one mole of NADH, one mole of FADH2 and one mole of acetyl-CoA. • The acetyl-CoA, the end product of each round of β-oxidation, then enters the TCA cycle, where it is further oxidized to CO2 with the concomitant generation of three moles of NADH, one mole of FADH2 and one mole of ATP. • The NADH and FADH2 generated during the fat oxidation and acetyl-CoA oxidation in the TCA cycle then can enter the respiratory pathway for the production of ATP.

13. Anaerobic Pathwayshttp://www2.bakersfieldcollege.edu/bio16/images/05-23_repfermprod_1.jpg

14. Why Anaerobic? • Prokaryotic organisms do not have mitochondria, thus no use for oxygen • Oxygen is not always available for Eukaryotic organisms

15. Fermentation1http://www.mr-damon.com/experiments/2sp/projects/images/fermentation.jpgFermentation1http://www.mr-damon.com/experiments/2sp/projects/images/fermentation.jpg • Glycolysis allows organisms to obtain energy from nutrients in the absence of oxygen • Cell possess a limited supply of NAD+

16. Fermentation2http://www.strombergtanks.com/Amend/images/photo_gallery/Fermentation%20Tanks-tn.jpgFermentation2http://www.strombergtanks.com/Amend/images/photo_gallery/Fermentation%20Tanks-tn.jpg • If glycolysis continues without a pathway to oxidize NADH back into NAD+ step 6 will be blocked and glycolysis will stop • One method of recycling NAD+ involves transferring the hydrogen atoms of NADH to certain organic molecules instead of the ETC

17. Fermentation3http://preuniversity.grkraj.org/html/2_CELL_DIVISION_files/image001.jpgFermentation3http://preuniversity.grkraj.org/html/2_CELL_DIVISION_files/image001.jpg • Prokaryotic organisms have evolved many forms of fermentation • Eukaryotic organisms primarily use two methods: ethanol fermentation and lactate fermentation

18. Ethanol Fermentation1http://www.studentsguide.in/microbiology/microbial-photosynthesis/images/ethanol-fermentation.jpg • This fermentation is carried out by many yeasts, such as Saccharomycescerevisiae (Baker's yeast),but by relatively few bacteria. • This pathway is quite important in food and industrial microbiology and is used to produce beer, wine and distilled spirits. The carbon dioxide produced during this fermentation causes the rise of the bread.

19. Ethanol Fermentation2http://chemwiki.ucdavis.edu/Biological_Chemistry/Metabolism/Glycolysis/Fermentation • Alcoholic fermentation consists of pyruvate being first converted into acetaldehyde by the enzyme pyruvate decarboxylase and releasing CO2.  • In the second step acetaldehyde is converted into ethanol using alcohol dehydrogenase and producing NAD+ in the process.  It is this recycled NAD+ that can be used to continue on with glycolysis.

20. Lactate Fermentation1http://www.science.siu.edu/microbiology/micr201/chapter8N.html • In lactic acid fermentation, NADH produced in glycolysis transfers its hydrogen atoms to pyruvate in the cytoplasm of the cell, regenerating NAD+ and allowing glycolysis to continue

21. Lactate Fermentation2http://www2.ufp.pt/~pedros/bq/lactate_cycle.gif • During intense physical exercise, lactate produced in the muscles is sent to the bloodstream, and can be used by the liver as a gluconeogenic substrate. • this "lactate cycle" is advantageous to the organism, since it allows the maintenance of the anaerobic exercise for a little longer (and this can be crucial for survival, e.g., by allowing a prey to outrun its predator, or a predator to keep chasing its prey).

22. Lactate Fermentation3http://rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/glycolysis.htm • Lactate released to the blood may also be taken up by other tissues, or by skeletal muscle after exercise, and converted via Lactate Dehydrogenase back to pyruvate, which may be oxidized in Krebs Cycle • Extra oxygen is required to catabolize the lactate, this is refered to as oxygen debt

23. Lactic Acid Bacteriahttp://www.biotech-weblog.com/50226711/lactic_acid_bacteria_as_vehicle_for_anthrax_vaccine.php • Lactic acid bacteria are a group of related bacteria that produce lactic acid as a result of carbohydrate fermentation. These microbes are broadly used by us in the production of fermented food products, such as yogurt (Streptococcus spp. and Lactobacillus spp.), cheeses (Lactococcus spp.), sauerkraut (Leuconostoc spp.) and sausage. http://www.waksmanfoundation.org/labs/mbl/lactic.html

24. Lactic Acid Yeasthttp://www.jstor.org/pss/3757638 http://www.jstor.org/pss/3757638 • The vast majority of fungi are considered to be obligate aerobic and obtain energy from respiration • Many higher fungi are known to ferment sugars to ethanol and carbon dioxide • A small number of lower fungi carry out lactic acid fermentation

25. THE END