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Cellular Respiration

Cellular Respiration. Chapter 4.4 & 4.5. Overview of Cellular Respiration. Cellular Respiration occurs in mitochondria of ALL eukaryotic cells (plants, animals, fungus, protists)

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Cellular Respiration

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  1. Cellular Respiration Chapter 4.4 & 4.5

  2. Overview of Cellular Respiration • Cellular Respiration occurs in mitochondria of ALL eukaryotic cells (plants, animals, fungus, protists) • When you eat food, you do not get the energy directly from the food – instead, you break down the food molecules to produce ATP • Cellular respiration releases chemical energy from sugars to make ATP when oxygen is present

  3. Overview of Cellular Respiration • Cellular Respiration is an aerobic process – it requires oxygen (O2) • Mitochondria are often called the “powerhouses” of the cell because they are where ATP is made • Food must first be broken down into glucose • Then glucose is broken down in a process called glycolysis

  4. Overview of Cellular Respiration • Glycolysis is an anaerobic process because it doesn’t use oxygen • It occurs in the cell’s cytoplasm • Glucose is broken down into smaller molecules and ATP is made • Glycolysis is necessary for cellular respiration – the products of glycolysis are broken down in the mitochondria to make many more ATP

  5. Overview of Cellular Respiration • Cellular Respiration is like a mirror image of photosynthesis • The products of photosynthesis are the reactants of cellular respiration (Glucose and Oxygen) • The structure of the mitochondria is similar to the chloroplast – it has a double membrane • The fluid inside is called the matrix

  6. Overview of Cellular Respiration • Cellular Respiration occurs in 2 stages • The first stage takes place in the mitochondrial matrix and is called the Krebs Cycle • The second stage is the Electron Transport Chain that takes place across and in the mitochondrial membrane • A total of up to 38 ATP molecules are made in the whole process, including glycolysis

  7. Glycolysis • Glycolysis is an ongoing process in all cells • It occurs in the cytoplasm of the cell • It does not require oxygen • A small amount of ATP is made • The other products are even more important for cellular respiration

  8. Glycolysis • Two ATP molecules are used to energize a glucose molecule • The glucose is split into 2 smaller molecules (3 carbons each) • A series of enzymes & reactions changes those molecules into 2 molecules of pyruvate • 4 ATP are made & 2 NADH are made

  9. Glycolysis • NADH is similar to NADPH in photosynthesis – it is an electron carrier • The net ATP production is 2 (remember, 2 molecules of ATP were used to break down glucose at the start of the process) • Pyruvate (pyruvic acid) and NADH are used in cellular respiration

  10. Krebs Cycle • Pyruvate is broken down into CO2 and acetyl CoA. NADH is made. • Citric Acid is formed • Citric Acid is broken down. NADH is made. CO2 is made and given off as waste • ATP, NADH and CO2 are produced, as well as another Carbon molecule • Carbon molecule is rearranged, NADH is made.

  11. Krebs (Citric Acid) Cycle • Pyruvate (3C) is converted into Acetyl-CoA (2C) and a CO2 is released • Acetyl-CoA combines with OAA (4C) to produce Citric Acid (6C) [citrate] • Citric Acid is converted in a-KG (5C). CO2 is released and NADH is made • a-KG is converted in Succinate (4C). CO2 is released and ATP is made • Succinate (4C) is converted into OAA (4C) & NADH is made. Repeat!

  12. Pyruvate CO2 Acetyl CoA Citrate OAA CO2 Succinate a-KG CO2

  13. Electron Transport Chain • The electron transport chain occurs in and through the mitochondrial inner membrane • The chain is made of proteins • The proteins use energy from electrons supplied by NADH (& FADH2) to pump hydrogen ions across the inner membrane, against the concentration gradient.

  14. Electron Transport Chain • The hydrogen ions later flow back through the membrane to produce ATP (recall photosynthesis!) • Oxygen is needed at the end of the chain to accept the electrons (final electron acceptor)

  15. Electron Transport - Details • 1. Electrons are removed – proteins in the membrane take electrons from NADH (& FADH2) – 2 NADH are used • 2. Hydrogen Transported – The electrons travel through the proteins. Energy is used to pump the H+ through the membrane • 3. ATP produced – H+ ions diffuse through ATP synthase (protein channel) & ATP is produced – each pair of electrons makes 3 ATP!

  16. Electron Transport - Details • 4. Water is Formed – oxygen picks up the electrons and hydrogen ions to form water (H2O). The water is given off as waste. • Up to 34 ATP molecules are formed from the electron transport chain • 2 ATP from glycolysis, 2 ATP from the Krebs Cycle – so that totals up to 38 ATP molecules for EACH glucose!

  17. Fermentation (4.6) • Your body cells get enough oxygen from breathing during normal activities, but during high levels of activity, like exercise, your cells do not get enough oxygen, even if you are breathing faster. • When there is not enough oxygen present for your cells to undergo cellular respiration, fermentation will occur.

  18. Fermentation (4.6) • Recall that glycolysis produces 2 ATP • If O2 is present, cellular respiration will come next to produce more ATP • If O2 is not present, fermentation will allow glycolysis to continue • Fermentation does not produce any ATP • Fermentation is an anaerobic process (lack of oxygen)

  19. Fermentation (4.6) • Fermentation removes electrons from NADH and recycles the NAD+ molecules back to glycolysis • Glycolysis needs the NAD+ molecules • If NAD+ molecules are present, glycolysis will continue to break down glucose and make ATP • In your muscle cells, lactic acid fermentation occurs

  20. Fermentation (4.6) • Lactic acid fermentation produces lactic acid, C3H6O3 – this is what makes your muscles “burn” during exercise • Step 1 – pyruvate is converted into lactic acid using NADH molecules • Step 2 – the NAD+ molecules go back to glycolysis

  21. Fermentation (4.6) • Once oxygen is present again, your cells break down the lactic acid that has built up in your cells, and cellular respiration starts again • There is another type of fermentation that occurs in cells other than your muscle cells – alcoholic fermentation • Yeast and certain types of plants undergo alcoholic fermentation

  22. Fermentation (4.6) • Alcoholic fermentation starts at the same place as lactic acid fermentation - pyruvate • Step 1 - Pyruvate is broken down using NADH into an alcohol and carbon dioxide • Step 2 - The NAD+ is recycled back to glycolysis

  23. Fermentation (4.6) • The process of fermentation is very important for many reasons • Cheese, bread and yogurt are all foods made by the products of fermentation • Bacteria that undergo fermentation also help animals fully digest foods

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