Glycolysis and Fermentation Chapter 8

Cellular Respiration and Photosynthesis Things to know in these chapters Names and order of the processes Reactants and products of each process How do they relate to the overall equations? What environmental factors are needed to run the process? Where will these processes occur? (organisms and organelles) The occasional important “step” within the process

Cellular Respiration Cellular respiration is the process of breaking down sugars to provide cells with energy Cellular Respiration Equation: C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy Cellular respiration allows for a molecule of glucose to be broken down as slowly as possible If glucose was broken down quickly, much of the energy it holds would be lost as heat Cellular respiration is able to harness 39% of the energy available in a glucose molecule Photosynthesis is 55% efficient The average gasoline automobile is 25% efficient

Cellular Respiration Cellular respiration is 3 separate processes that combine to maximize the energy output in various conditions 1. Glycolysis. Slowly convert glucose into pyruvic acid. Obtain small quantity of energy; very little wasted though Designed to maximize energy production later 2. Aerobic Respiration Takes place when cell has access to oxygen Citric Acid Cycle and Electron Transport Chain Large amounts of ATP produced 3. Anaerobic Respiration (Fermentation) Takes place when cell has no access to oxygen Alcohol or lactic acid produced Maintains life temporarily until oxygen can be maintained

Glycolysis Summary Each process in photosynthesis and respiration is a machine. The machine takes a reactant and, throughout a series of steps, builds products. Like man-made machines, each of these steps creates waste material Unlike man-made machines, the waste materials just happen to be molecules the cell needs Sometimes, the products also are needed. Sometimes they aren’t. As long as the cell keeps these machines working, the machines will keep churning out these “waste” products

Glycolysis Summary Glycolysis takes place in the cytoplasm Glycolysis is ten steps long Glycolysis requires an input of energy “Glyco” = glucose; “lysis” = “to split” For the processes in these chapters, I will provide all the information so you know what is happening. The essential info for memorizing will be underlined

Glycolysis Step 1 Begins with a molecule of glucose Energy from an ATP is consumed At this point, the cell has used energy and hasn’t harnessed any. It’s in debt. By spending energy now, it can invest the energy and get MUCH more energy later. The cell forms a molecule of glucose-6-phosphate

Glycolysis Step 2 Glucose-6-phosphate is rearranged to form a molecule of fructose-6-phosphate

Glycolysis Step 3 Another input of ATP is required At this point the cell has spent two high-energy molecules and has made none. The cell is even more in debt now. Fructose-6-Phosphate is rearranged to form Fructose-1,6-Bisphosphate

Glycolysis Step 4 and Step 5 The glucose molecule is split from one 6-carbon molecule into two 3-carbon molecules The amount of carbon, hydrogen, oxygen and phosphorus hasn’t changed. But now there’s two molecules instead of one. One molecule immediately forms a glyceraldehyde-3-phosphate (PGAL, or G3P) The other forms a different molecule temporarily, then immediately forms a second PGAL From this point on, there are two identical molecules that enter each step of cell respiration, which means we will double the products we make from here on out. Without the input of energy at the beginning, we couldn’t have done this.

Glycolysis Step 6 The PGAL is phosphorylated (a free-floating phosphate is attached) This phosphate will eventually be attached to an ADP to form an ATP PGAL also donates a Hydrogen to an NAD+ to become an NADH NADH is a waste product in glycolysis, but NADH will be used later in the electron transport chain as a reactant The PGAL rearranges to form a molecule of 1,3-bisphosphoglycerate (PGAP)

Glycolysis Step 7 The PGAP donates one of it’s phosphates to an ADP to form ATP The ATP is a “waste” product in glycolysis—but the cell can use it somewhere else *Remember: we’ve actually made TWO ATP’s (one for each PGAL we made earlier) PGAP is rearranged to form a 3-phosphoglycerate (PGA)

Glycolysis Step 8 PGA is rearranged to form a 2-phosphoglycerate

Glycolysis Step 9 2-phosphoglycerate loses a water molecule 2-phosphoglycerate is rearranged to form Phosphoenolpyruvate (PEP)

Glycolysis Step 10 PEP donates a phosphate to form an ATP The final molecule of glycolysis is a 3-carbon pyruvate.

Glycolysis Summary Inputs Outputs Net Gain 1 glucose molecule 2 ATP 2 pyruvate molecules 2 NADH 4 ATP Net Gain

Fermentation After glycolysis, the pyruvic acid will enter either aerobic or anaerobic respiration Aerobic respiration: if oxygen is available Anaerobic respiration: if oxygen is not available Anaerobic respiration, or fermentation, comes in two forms Alcoholic fermentation: Yeasts and other microorganisms Pyruvic acid + NADH  Alcohol + CO2 + NAD+ Lactic Acid fermentation: muscle cells Pyruvic acid + NADH  Lactic Acid + NAD +

Fermentation Fermentation for humans is not ideal at all. It’s a life-support system. Without oxygen, the only process for cells to obtain energy from is glycolysis. In order for glycolysis to occur, it needs three reactants Glucose, which is obtained from food. This is not a problem ADP, to form ATP. This is not a problem NAD+ to form NADH. NADH is consumed and transformed back to NAD+ during aerobic respiration But…we can’t go through aerobic respiration right now. So we can’t turn the NADH back to NAD+. So we don’t have any NAD+ to use in glycolysis. So we can’t run glycolysis. THIS is the problem.

Fermentation The sole purpose of fermentation is to remove the “H” off of the NADH and turn it back to NAD+. The NAD+ can then re-enter glycolysis, and the cell can get another net gain of 2 ATP. 2 ATP is pathetic, but it is something. So why do we do it? Fermentation gives the organism a few extra precious minutes to find some oxygen again Without it, organisms would die the instant their cells are without oxygen.

Cell Respiration Summary C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy C6H12O6 : For glycolysis 6 O2 : To collect the electron in the ETC 6 CO2 : Given off in intermediate step and Citric Acid Cycle 6 H2O : Given off in the ETC Energy : In the form of ATP