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Chapter 7: Cellular Respiration

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1 Chapter 7: Cellular Respiration
Cellular (aerobic) respiration (red arrows) is the main means by which both fungi and plants utilize energy in the form of organic compounds that were previously created through photosynthesis (green arrow). ( wikipedia)

2 Cellular respiration is
the process by which cells break down organic compounds to produce ATP. Products of cellular respiration are the reactants in photosynthesis; they are opposites!

3 Plants & Animals: Both autotrophs and heterotrophs use cellular respiration to get energy from organic compounds and O2 & produce waste products CO2 and water

4 Cellular Respiration Refers to the biochemical pathway by which cells release energy from the chemical bonds of food molecules and provide that energy for the essential processes of life.

5 Cellular respiration can be divided into 2 stages:
glycolysis aerobic respiration.

6 During glycolysis One six-carbon glucose molecule is oxidized to form two three-carbon pyruvic acid molecules. A net yield of two ATP molecules is produced for every molecule of glucose that undergoes glycolysis

7 Glycolysis takes a 6-carbon sugar & breaks it into 2 3-carbon sugars

8 Remember: Lysis means to break up
Breaking up the glucose molecule into 2 smaller sugars (pyruvic acid) provides energy to make ATP which is the principle energy 'currency' in the cell

9 Glycolysis occurs in the cytoplasm (cytosol) and does not require oxygen. There are 10 steps in glycolysis and each one is catalyzed by a specific enzyme

10 In more detail ( you do not need to know this:
Glycolysis is a definite sequence of ten reactions involving ten intermediate compounds (one of the steps involves two intermediates). The intermediates provide entry points to glycolysis. For example, most monosaccharides, such as fructose, glucose, and galactose, can be converted to one of these intermediates.

11 (you do not need to memorize these.)
Steps in glycolysis (you do not need to memorize these.)

12 So- What happens after glycolysis?
(Anaerobic) - If no oxygen is available- fermentation occurs (Aerobic) If oxygen is available- the krebs cycle

13 Glycolysis - in the cytoplasm
Glycolysis - in the cytoplasm. The next step is aerobic Respiration in the Krebs (TCA) cycle. Unless there is no Oxygen, in which case Anaerobic Fermentation occurs.

14 1. Fermentation (anaerobic).
Occurs if oxygen is not present convert pyruvic acid into other compounds For example: Lactic Acid Fermentation an enzyme converts pyruvic acid into another three-carbon compound, called lactic acid. 2. Alcoholic Fermentation Some plants and unicellular organisms, (like yeast) convert pyruvic acid to ethyl alcohol & CO2.

15 2. Aerobic Respiration Called the Krebs cycle
occurs in the mitochondria. occurs only if oxygen is present in the cell. Called the Krebs cycle

16 The Krebs cycle Also known as the: tricarboxylic acid cycle (TCA)
was first recognized in 1937 by the man for whom it is named, German biochemist Hans Adolph Krebs

17 Krebs happens in the mitochondria
After the glycolysis takes place in the cell's cytoplasm, the pyruvic acid molecules travel into the interior of the mitochondria.

18 The Krebs Cycle: Each turn produces 1 ATP 2 CO2 3 NADH 1 FADH2
In this simplified cycle diagram you can see that Each turn produces 1 ATP 2 CO2 3 NADH 1 FADH2

19 The Krebs Cycle. 2 turns produce:
First, pyruvic acid (produced in glycolysis) reacts with coenzyme A to form acetyl CoA. Then, acetyl CoA enters the Krebs cycle. The original glucose becomes completely broken down after 2 turns of the Krebs cycle. 2 turns produce: four CO2 molecules, two ATP molecules, and hydrogen atoms that are used to make six NADH and two FADH2 molecules.

20 The Krebs or Citric Acid (TCA) Cycle
Note that there are 8 steps

21 Finally: Electron Transport Chain
High-energy electrons in hydrogen atoms from NADH and FADH2 are then passed from molecule to molecule in the electron transport chain along the inner mitochondrial membrane

22 Electron Transport Chain
In eukaryotes, oxidative phosphorylation occurs in the mitochondrial cristae. It comprises the electron transport chain that establishes a proton gradient (chemiosmotic potential) across the inner membrane by oxidizing the NADH produced from the Krebs cycle. A by-product of oxidative phosphorylation is hydrogen peroxide. (a toxin) Remember the liver lab. What enzyme in liver broke down the H2O2? What were the products? Catalase, O2, H2O

23 Electron Transport Chain

24 Efficiency of Cellular Respiration
Cellular respiration can produce up to 38 ATP molecules from the oxidation of a single molecule of glucose. Most eukaryotic cells produce about 36 ATP molecules per molecule of glucose. Thus, cellular respiration is nearly 20 times more efficient than glycolysis alone.

25 Summary of Cellular Respiration
Providing cells with energy : ATP is an important function of cellular respiration. Also: Molecules formed at different steps in glycolysis and the Krebs cycle are often used by cells to make compounds that are missing in food.

26 Summary of Glycolysis and Cellular Respiration

27 Remember Homeostasis? Cellular respiration produces CO2 as a metabolic waste. This CO2 binds with water to form carbonic acid, helping to maintain the blood's pH. Since too much CO2 would lower the blood's pH too much, the removal of the excess CO2 must be accomplished on an ongoing basis- or homeostasis is disturbed.

28 Usefulness of Fermentation- Anaerobic exercise
During vigorous exercise, oxygen is consumed faster than breathed in. Additional ATP energy is provided to the muscles by glycolysis and the result is a buildup of lactate in the muscles. When lactate builds up, the blood pH drops and the muscles fatigue. At rest, lactate is converted back to pyruvate (the oxygen debt is repaid). This is why you continue to breathe hard after you have finished running or rapid stair climbing.


30 Summary diagram- cellular respiration:

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