Ch 6 Cellular respiration

Cells use energy in food to make ATP No ATP=dead ATP powers all life processes All living things use the potential energy in food to generate ATP

Aerobic respiration is the reverse of photosynthesis C6H12O6 + O2  CO2 + H2O + ATP(36) Producers still use the food they produce! They use about half the oxygen they produce to do cell respiration for their own needs.

6.2 Cellular respiration includes three main pathways Basic overview- an enzyme adds a phosphate group to ADP, yielding ATP. ATP synthesis requires an input of energy. Cell respiration is a redox reaction Cell respiration cannot happen all at once, because it would burn up the cell

3 main categories of organization for biochemical pathways of cell respiration 1. glycolysis-breaking sugar to make pyruvate, NADH and ATP 2. Krebs cycle- oxidize pyruvate and reduce CO2 Makes NADH and FADH2 3. Electron transport chain- transfers NADH and FADH2 through a series of proteins making a proton gradient for ATP synthase to work.

6.3 In Eukaryotes, Mitochondria produce most ATP Glycolysis always occurs in the cytoplasm, but in eukaryotes mitochondria house the other reactions of cell respiration.

Anatomy of a mitochondrion Outer membrane surrounds a highly folded inner membrane- cristae are the folds The intermembrane compartment is the area between the two membranes and the matrix is the space enclosed within the inner membrane.

Mitochondria contain their own DNA that codes for ATP synthase and most of the proteins of the ETC. Muscle and nervous tissue cells can contain as many as 10,000 mitochondria

6.4 Glycolysis breaks down glucose to pyruvate Glycolysis is a universal pathway- it splits 6 carbon glucose into 2 three carbon pyruvate molecules. It happens in the cytoplasm- doesn’t require oxygen

10 step process- Steps 1-5 Glucose activation requires 2 ATP Phosphate transfer- glucose has a phosphate attached to become glucose 6 phosphate(requires 1 ATP) rearrangement into fructose-6-phosphate A second phosphate is transferred from ATP producing fructose-1, 6 bisphosphate

4. This is split into 2 different three carbon intermediates- 1 PGAL and dihydroxyacetone phosphate 5. The second one from above is converted into PGAL Steps 6-10 energy extraction- 6. Oxidation and phosphorylation-PGAL has a phosphate added to each molecules producing 2 molecules of NADH and 2 molecules of 1,3-bisphosphoglycerate

7. Substrate level phosphorylation yields ATP- One of the phosphates from each molecule is pulled off to convert ADP into ATP, leaving 2 molecules of 3-PGA. 8. These are rearranged into 2 PGA 9. water is removed leaving 2 molecules of PEP(phosphophenyl pyruvate 10. substrate level phosphorylation yields ATP and two molecules of pyruvate per glucose molecule.

6.5 Aerobic respiration yields much more ATP than glycolysis After glycolysis- pyruvate moves into the mitochondrial matrix A preliminary chemical reaction oxidizes each pyruvate CO2 is removed and NAD+ is reduced to NADH The remaining 2 carbon molecule is transferred to form Acetyl CoA which enters the Kreb’s cycle

Acetyl CoA loses the coenzyme and combines with a four carbon molecule(oxaloacetate) to become a six carbon molecule called citrate(sometimes the Kreb’s cycle is also called the citric acid cycle)

The citrate molecule is rearranged and oxidized through several intermediates. CO2 molecules are released, NADH and FADH2 are produced, ATP is phosphorylated, and oxaloacetate is again formed to continue the cycle. Overview- 4 CO2 released, 2 ATP, 6 NADH, and 2 FADH2 Parts of the Krebs cycle are also used to make amino acids or fats. These can also be used to get energy.

Electron transport chain The NADH and FADH2 produced by the Krebs cycle are used in an ETC. The final electron acceptor is O2 which combines with hydrogen to form water. The energy from NADH and FADH2 is used to maintain a proton gradient so that ATP synthase can make ATP by chemiosmotic phosphorylation.

6.6 How many ATP’s can one glucose molecule yield? The theoretical net yield from a molecule of glucose is 36 ATP per molecule. In reality, the yield is about 30 ATP because some energy is spent when protons leak across the membrane and it takes energy to move pyruvate into the mitochondria. Potential energy is also lost as heat due to laws of thermodynamics.

6.7 Other Food Molecules Energy the energy extracting pathways. Polysaccharides are broken down to glucose to enter glycolysis. Proteins are broken down into amino acids. Most of these are rearranged to form new proteins, but when carbohydrate supplies are low, they can be used for energy.

Ammonia is stripped from the amino acid and the remainder of the molecule energy the pathway as pyruvate, acetyl CoA, or some other intermediate. Lipids are broken down into glycerol and fatty acids. The glycerol is converted to pyruvate to be used in the Krebs cycle. The fatty acids enter the mitochondria where they are converted to acetyl CoA.

Organisms can also store extra energy by converting acetyl CoA away from the Krebs cycle and building fats out of it.

6.8 Some energy pathways do not require oxygen A. anaerobic respiration uses an electron acceptor other than O2 Alternative acceptors include NO3-, SO42-, and CO2 The amounts of ATP generated varies, but it’s always less than with aerobic respiration. Many Archaea and Bacteria get energy this way. This is important to nutrient cycles.

B. Fermenters acquire ATP only from glycolysis Fermenters can do glycolysis- still get the same products (pyruvate, NADH, and ATP’s) The electrons from the NADH reduce pyruvate. Leaving NAD+ for glycolysis to continue, but no additional ATP is generated. Fermentation is common among organisms that live in a high sugar environment, so they don’t run out of food.

Some organisms only do fermentation, for example, Entamoeba histolytica (causes dysentery) Escherichia coli (lives in your gut) can use O2 when available or fermentation when it’s not. Multicellular organisms need too much energy to rely on fermentation alone.

Many fermentation pathways exist. You need to know 2 1. alcoholic fermentation- pyruvate is converted to acetyl aldehyde and CO2, and then NADH reduces the acetyl aldehyde to produce NAD+ and ethanol. Used to make wine, mead, hard cider, beer, whisky, etc. depending on what is fermented.

2. Lactic acid fermentation- a cell uses NADH to reduce pyruvate, but the products are NAD+ and lactic acid. Ex. Lactobacillus ferments milk to make yogurt. This type of fermentation can also happen in human muscles when O2 supplies are low. Buildup of lactic acid causes muscles to burn.