6.1 Energy and organisms Organisms are classified based on the kind of energy they use. – Autotrophs Use the energy from sunlight to make organic molecules (sugar) called photosynthetic autotroph Use the energy from inorganic chemical reaction to make larger organic molecules called chemosynthetic autotroph – Heterotrophs Obtain their energy from the chemical bonds of food molecules, such as carbohydrates, fats, and proteins, which they must obtain from their surroundings All organisms use cellular respiration. – To harvest the energy from organic molecules and use it to make ATP
4 6.2 Aerobic respiration: An overview A series of enzyme controlled reactions – Oxygen is used to oxidize glucose. – Glucose is oxidized to form carbon dioxide. – Oxygen is reduced to form water. During the oxidation of glucose – The C-H and O-H bonds will be broken. – The electrons will be transferred to electron carriers, NAD and FAD. Glycolysis and Kreb’s cycle – The electrons will be passed through an electron transport chain. The energy from the electrons will be used to pump protons. The energy from the diffusion of protons will be used to make ATP.
5 Aerobic respiration and oxidation- reduction reactions
7 Glycolysis The breakdown of glucose into pyruvic acid Two ATP molecules are used to energize glucose. As glucose is metabolized enough energy is released to – make 4 ATP molecules. 4 ATP made -2 ATP used = net production of 2 ATP – reduce 2 NAD+ to make 2 NADH. Occurs in the cytoplasm
8 Krebs cycle Also known as the citric acid cycle or the tricarboxylic acid (TCA) cycle The breakdown of pyruvic acid – Released as carbon dioxide Enough energy is released as one pyruvic acid molecules is metabolized to – make 1 ATP. – reduce 4 NAD+ to form 4 NADH. – reduce 1 FAD to form 1 FADH 2. Occurs in the mitochondrial matrix
9 Electron-transport system NADH and FADH 2 release the electrons they received during glycolysis and the Kreb’s cycle to the electron transport chain (ETC). The proteins of the ETC transfer the electrons and use the energy released to pump protons. – Protons are pumped from the matrix to the intermembrane space. – Creates a concentration gradient
10 Electron-transport system Oxygen is the final electron acceptor at the end of the ETC. – Oxygen accepts the electrons, combines with protons and become water. The accumulated protons diffuse back into the matrix through ATPase The energy released from the diffusion fuels the formation of ATP.
11 6.4 Aerobic respiration in prokaryotes Very similar to aerobic respiration in eukaryotes. Since prokaryotes have no mitochondria, it all occurs in the cytoplasm. Make 2 more ATP because there is a cost to the eukaryotic cell of getting the electrons into the mitochondrion
12 6.5 Anaerobic cellular respiration Some organisms do not have the enzymes for Kreb’s cycle or the electron transport system. Some organisms can metabolize glucose in the absence of oxygen. Metabolizing glucose in the absence of oxygen is called anaerobic respiration. – Involves the incomplete oxidation of glucose. – Fermentation is an anaerobic pathway that uses an organic molecule as the final electron acceptor.
13 Anaerobic cellular respiration Anaerobic respiration usually starts with glycolysis. – Glucose is metabolized into pyruvic acid. – 2 ATP are made. The fermentation reactions oxidize NADH to regenerate the NAD+ that is needed in glycolysis. – In the process, pyruvic acid is reduced to either lactic acid or ethanol or another organic molecule.
15 Alcoholic fermentation Starts with glycolysis – Glucose is metabolized to pyruvic acid. – A net of 2 ATP is made. During alcoholic fermentation – Pyruvic acid is reduced to form ethanol. – Carbon dioxide is released. Yeast do this – Leavened bread (p. 122) – Sparkling wine (p. 123)
16 Lactic acid fermentation Starts with glycolysis – Glucose is metabolized to pyruvic acid. – A net of 2 ATP is made. During lactic acid fermentation – Pyruvic acid is reduced to form lactic acid. (p. 123) – No carbon dioxide is released. Muscle cells have the enzymes to do this, but brain cells do not. (p. 123) – Muscle cells can survive brief periods of oxygen deprivation, but brain cells cannot. – Lactic acid “burn” in muscles.
18 Metabolizing other molecules Cells will use the energy in carbohydrates first. – Complex carbohydrates are metabolized into simple sugars. Cells can use the energy in fats and proteins as well. – Fats are digested into fatty acids and glycerol. – Proteins are digested into amino acids. Cells must convert fats and proteins into molecules that can enter and be metabolized by the enzymes of glycolysis or the Kreb’s cycle.
19 Fat respiration (See p. 124) Fats are broken down into – Glycerol – Fatty acids Glycerol – Converted to glyceraldehyde-3-phosphate – Enters glycolysis Fatty acids – Converted to acetylCoA – Enter the Kreb’s cycle Each molecule of fat fuels the formation of many more ATP than glucose. (p. 124) – This makes it a good energy storage molecule.
21 Protein respiration (p. 125) Proteins are digested into amino acids. Then amino acids have the amino group removed. – Generates a keto acid (acetic acid, pyruvic acid, etc) – Enter the Kreb’s cycle at the appropriate place
The interconversion of fats, carbohydrates and proteins
23 The bottom line Carbohydrates, fats and proteins can all be used for energy. – Glycolysis and the Kreb’s cycle allow these types of molecules to be interchanged. If more calories are consumed than used – The excess food will be stored. – Once the organism has all of the proteins it needs And its carbohydrate stores are full The remainder will be converted to and stored as fat.
How Science works 6.1 Applying Knowledge of Biochemical Pathways