2 Cellular Respiration Produces ATP Before you can use the energy you obtain from food, it has to be transferred to ATP.Glucose’s energy (and other organic compounds) is transferred to ATP through cellular respiration.Oxygen makes the production of ATP more efficient, but some ATP is produced without oxygen.
3 Aerobic Respiration – metabolic processes that require oxygen Anaerobic respiration – metabolic processes that do not require oxygen
4 Overview of Cellular Respiration C6H12O6 + 6O2 → 6CO2 + 6H2O + energyFigure 5-10 p. 104STAGE 1: Glucose is converted to pyruvate, producing a small amount of ATP and NADH.STAGE 2: When oxygen is present, pyruvate and NADH are used to make a large amount of ATP (aerobic respiration). Aerobic respiration occurs in the mitochondria in eukaryotic cells and in the cell membrane of prokaryotic cells. When oxygen is not present, pyruvate is converted to either lactate or ethanol and CO2 (anaerobic respiration).
6 STAGE 1: Glycolysis Glycolysis – the breakdown of glucose The primary fuel for cellular respiration is glucose.Glucose formed when carbohydrates (starch and sucrose) are broken down.If too few carbohydrates are available, other molecules such as fats can be broken down to make ATP. (1 gram of fat = 2 grams carbohydrates)
7 STAGE 1: GlycolysisGlycolysis – glucose is being broken down in the cytoplasm. It is an enzyme-assisted anaerobic process that breaks down one 6-carbon molecule of glucose to two 3-carbon pyruvates.Pyruvate – the ion of a 3-carbon organic acid called pyruvic acidAs glucose is broken down, some of its hydrogen atoms are transferred to an electron acceptor called NAD+. This forms the electron carrier called NADH.
9 STAGE 1: GlycolysisFor cellular respiration to continue, the electrons carried by NADH are eventually donated to other organic compounds. This recycles NAD+ making it available to accept more electrons.
10 STAGE 1: Glycolysis Summary of Glycolysis Figure 5-11 p. 105 Step 1: Phosphate groups from 2 ATP molecules transferred to a glucose moleculeStep 2: Resulting 6-carbon compound broken down to 2 3-carbon compounds, each with a phosphate group.Step 3: 2 NADH molecules produced. 1 more phosphate group transferred to each 3-carbon compound.Step 4: Each 3-carbon compound is converted to a 3-carbon pyruvate. Produces 4 ATP molecules.Process uses 2 ATP, produces 4 ATP, so… NET GAIN OF 2 ATP.
11 Glycolysis is followed by another set of reactions that use the energy temporarily stored in NADH to make more ATP.
14 STAGE 2: Aerobic Respiration When oxygen is present, pyruvate produced during glycolysis enters a mitochondrion. Then pyruvate is converted to a 2-carbon compound.When pyruvate is converted to a 2-carbon compound – 1 CO2, 1 NADH, and 2-carbon acetyl group is produced.Acetyl group is attached to a molecule called coenzyme A (CoA) – forms acetyl-CoA
16 STAGE 2: Aerobic Respiration – Kreb’s Cycle Acetyl-CoA enters a series of enzyme-assisted reactions – Kreb’s cycleStep 1: Acetyl-CoA combines with a 4-carbon compound, forming a 6-carbon compound and releasing coenzyme-AStep 2: CO2 released from 6-carbon compound, forming 5-carbon compound. Electrons transferred to NAD+, making a molecule of NADH.
17 STAGE 2: Aerobic Respiration – Kreb’s Cycle Step 3: CO2 released from 5-carbon compound, forming a 4-carbon compound. 1 ATP and 1 NADH made.Step 4: 4-carbon compund converted to a new 4-carbon compound. Electrons transferred to an electron acceptor FAD, making a molecule of FADH2 (another type of electron carrier).Step 5: New 4-carbon compound then converted to the 4-carbon compound that began cycle. Another NADH is produced.
18 STAGE 2: Aerobic Respiration – Kreb’s Cycle NADH and FADH2 now contain much of the energy that was previously stored in glucose and pyruvate.Recycles the 4-carbon compound.
21 STAGE 2: Aerobic Respiration – Electron Transport Chain The electrons donated by NADH and FADH2 pass through an electron transport chain.Figure 5-13 p. 107Occurs in the inner membranes of mitochondriaEnergy of the electrons used to pump H+ out of inner mitochondrial compartmentsH+ accumulates in outer compartment – produces a concentration gradient across the inner membrane
22 STAGE 2: Aerobic Respiration – Electron Transport Chain H+ diffuses back into inner compartment through a carrier protein that adds a phosphate group to ADP to make ATP.At end of electron transport chain, H+ and spent electrons combine with O2 to form H2O – oxygen is final electron acceptor.
25 FermentationFermentation follows glycolysis in the absence of oxygen. – anaerobic respirationWhen enough oxygen is not present for aerobic respiration to occur, electron transport chain does not function. Why? Oxygen is not able to serve as final electron acceptor. Also, NADH electrons not transferred, so NAD+ cannot be recycled.
26 FermentationAnaerobic Respiration – NAD+ recycled in a different way. Electrons carried by NADH are transferred to pyruvate that is produced in glycolysis. This recycles NAD+ so it can continue making ATP through glycolysis.Fermentation – recycling NAD+ using an organic hydrogen acceptor
27 Lactic Acid Fermentation 3-carbon pyruvate converted to a 3-carbon lactate. NAD+ recycled.Lactate – ion of organic acid called lactic acidDuring vigorous exercise, pyruvate in muscles converted to lactate when muscles operate without enough oxygen.Causes soreness because it builds up in muscles – blood does not remove it fast enough
29 Alcoholic Fermentation 3-carbon pyruvate converted to a 2-carbon ethanol molcule. CO2 is released.2 Step Process:1. Pyruvate converted to a 2-carboncompound – CO2 released.2. Electrons transferred from NADH tothe 2-carbon compound producing ethanol.NAD+ recycledYeast or fungi – foods and beverages (wine, beer, rising of bread dough)