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Cellular Respiration Part V:Fermentation and other details1Figure 9.16

Electron shuttlesspan membraneMITOCHONDRION2 NADH2 NADH2 NADH6 NADH2 FADH22 FADH2or 2 ATP 2 ATP about 26 or 28 ATPGlycolysisGlucose2 PyruvatePyruvate oxidation2 Acetyl CoACitricacidcycleOxidativephosphorylation:electron transportandchemiosmosisCYTOSOLMaximum per glucose:About30 or 32 ATP2What was oxygens role in cellular respiration?Without OxygenMost cellular respiration requires O2 to produce ATPWithout O2, the electron transport chain will cease to operateIn that case, glycolysis couples with fermentation or anaerobic respiration to produce ATP

3Emphasize that last bullet! Students think only in terms of oxygen-based respiration. They may not even be aware that respiration is possible anaerobically! Anaerobic respiration uses an electron transport chain with a final electron acceptor other than O2, for example sulfateFermentation uses substrate-level phosphorylation instead of an electron transport chain to generate ATP

4Also emphasize that anaerobic respiration simply occurs when a different chemical accepts the electrons instead of oxygen. Many substances can function as final electron acceptors. These include sulfate (SO42-), nitrate (NO3-), sulfur (S), or fumarate. Often organisms that utilize the molecules are obligate anaerobes.Types of FermentationFermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis

Two common types are alcohol fermentation and lactic acid fermentation5Emphasize to student that there are many, many types of alcohols and not all are safe for human consumption! Alcoholic FermentationIn alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2

Alcohol fermentation by yeast is used in brewing, winemaking, and baking

6We are indeed referring to ethanol when we say alcohol fermentation.Figure 9.17

2 ADP2 ATPGlucoseGlycolysis2 Pyruvate2 CO222 NADH2 Ethanol2 Acetaldehyde(a) Alcohol fermentation(b) Lactic acid fermentation2 Lactate2 Pyruvate2 NADHGlucoseGlycolysis2 ATP2 ADP2PiNAD2 H2Pi2NAD2 H7Figure 9.17 Fermentation. Emphasize the similarities and differences between two different types of fermentation. Animations of each follow.

2 ADP 2 P i2 ATPGlucoseGlycolysis2 Pyruvate2 CO22 NAD2 NADH2 Ethanol2 Acetaldehyde(a) Alcohol fermentation2 HFigure 9.17a8Note end product is ethanol and NAD is regeneratedAlcoholic Fermentation9

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(b) Lactic acid fermentation2 Lactate2 Pyruvate2 NADHGlucoseGlycolysis2 ADP 2 P i2 ATP2 NAD2 HFigure 9.17b10Figure 9.17 Fermentation.Lactic Acid FermentationIn lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO2Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurtHuman muscle cells use lactic acid fermentation to generate ATP when O2 is scarce

11Lactate Fermentation

12Fermentation compared to Anaerobic & Aerobic RespirationAll use glycolysis (net ATP = 2) to oxidize glucose and harvest chemical energy of foodIn all three, NAD+ is the oxidizing agent that accepts electrons during glycolysisThe processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respirationCellular respiration produces 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule 13Anaerobic RespirationObligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O2Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respirationIn a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes14Figure 9.18

GlucoseCYTOSOLGlycolysisPyruvateNo O2 present:FermentationO2 present: Aerobic cellular respirationEthanol,lactate, orother productsAcetyl CoAMITOCHONDRIONCitricacidcycle15 Pyruvate as a key juncture in catabolism.Evolutionary Significance of GlycolysisAncient prokaryotes are thought to have used glycolysis long before there was oxygen in the atmosphere

Very little O2 was available in the atmosphere until about 2.7 billion years ago, so early prokaryotes likely used only glycolysis to generate ATP

Glycolysis is a very ancient process16Never pass up an opportunity to connect a unit back to evolution! But I eat more than sugar..Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration

Glycolysis accepts a wide range of carbohydrates

Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle

17Emphasize the literal meaning of carbohydrate, carbon-waters which have a generic formula of CH2O. Multiply that by 6 and you have glucose! Add bunches of those together through bunches of dehydration synthesis reactions and you have a starch.Figure 9.19

CarbohydratesProteinsFattyacidsAminoacidsSugarsFatsGlycerolGlycolysisGlucoseGlyceraldehyde 3- PNH3PyruvateAcetyl CoACitricacidcycleOxidativephosphorylation18Figure 9.19 The catabolism of various molecules from food.Regulation of RespirationFeedback inhibition is the most common mechanism for control

If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down

Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway19Emphasize one last time that METABOLISM is the sum of CATABOLISM (breaking down or deconstructing) + ANABOLISM (synthesizing or building up)It sounds simple butWhy do you have to eat?What does it have to do with entropy?Why do you have to breathe?

Can you give an AP Biology level answer to these questions?20

20Energy use in different animals

In both endothermic and ectothermic animals, the normal metabolic rate is inversely related to body sizeWhy is this so? Recall that temperature is an important factor in enzyme activity.Why then is there and inverse relationship then between metabolic rate and body size?

21There is also an inverse relationship between size and relative metabolic rate in ectothermic animals but it doesnt work the same way.

Energy use in different animals22

Energy use in different animals23