Chapter 6: How Cells Harvest Chemical Energy

Muscle Fibers Fast-twitch Slow-twitch Performs best for sprints Contract quickly but tire quickly Make ATP anaerobically (not using oxygen Perform best for endurance Can sustain repeated contractions Make ATP aerobically (using oxygen)

Photosynthesis vs. Cell Respiration Photosynthesis uses carbon dioxide to produce high energy carbon molecules and oxygen Cellular respiration uses carbon molecules and oxygen to produce energy and carbon dioxide The products of photosynthesis are the reactants of cellular respiration

Cellular respiration Function: generate ATP to be used for cellular functions Can produce up to 38 ATP molecules which is 40% of energy from a glucose molecule, the rest is lost in heat energy

Energy consumption of the body The human brain burn about 120 g (1/4 lb.) of glucose per day and uses 15% of oxygen consumption a day The average human needs to take in 2200 kcal per day about 1.25 lb. of glucose per day

Reduction vs. oxidation Reduction reactions The addition of electrons from a substance Oxidation reactions The loss of electrons from a substance

2 key players in oxidizing glucose Dehydrogenase: an enzyme that takes hydrogens from molecules NAD+ : Nicotinamide adenine dinucleotide, an organic molecule that cells make from the vitamin niacin and use to shuttle electrons in redox reactions

Stages of cellular respiration Stage 1: Glycolysis: cytoplasm: breaks glucose into 2 pyruvates Stage 2: Citric Acid Cycle: Mitochondria: Stroma: makes small amounts of ATP and provides ETS with electrons Stage 3: oxidative phosphorylation (ETS and chemiosmosis: cristae: makes most ATP

Overview of cell respiration

Glycolysis Begins with glucose and ends with 2 pyruvates Substrate-level phosphorylation: an enzyme transfers a phosphate group from a molecule directly to an ADP to form ATP. This is used in both glycolysis and citric acid cycle to produce small amounts of ATP At the end the molecules of pyruvate still hold most of the energy from glucose and will be oxidized in the citric acid cycle The 2 molecules of ATP produced here are only 5% of the glucose molecule

Glycolysis

Pyruvate for the citric acid cycle Pyruvate loses the carboxyl group in the for of carbon dioxide (released during respiration) 2 C-compound is oxidized and NAD+ becomes NADH Coenzyme A joins the 2 C-compound and becomes Acetyl coenzyme A

Citric Acid Cycle AKA the Kreb’s Cycle named for Hans Krebs Takes place in the matrix of the mitochondria Starts with acetyl Coenzyme A and ends with 2 CO2, 6 NADH and 2 FADH2

Citric Acid Cycle

Oxidative Phosphorylation Includes the electron transport chain and chemiosmosis Takes place in the cristae (folds in the inner membrane of the mitochondria). The cristae increase the surface area of the membrane so that more reactions can take place Exergonic reaction Chemiosmosis the energy of H+ drives the synthesis of ATP

Poisons that interrupt Cell Respiration Rotenone: binds with an electron carrier at the first protein complex and blocks the movement of electrons through the ETS Cyanide and carbon monoxide: bind with an electron carrier at the 4th protein complex blocking the passage of oxygen ceasing the flow of H so no ATP can be formed Oligomycin (an antibiotic): used for fungal infections: prevents the flow of H

More poisons Uncouplers: causes the mitochondria to leak H DNP (DiNitrophenol): produces an enomrous increase in metabolic rate, profuse sweating as the body tries to cope with the excess heat energy produced, collapse and death

Totals Stage where Start With ATP Dir. ATP Indir. FADH2 NADH CO2 Other glycolysis Cyto-plasm Glucose 2 ATP 2 2 pyruvates Pyruvate to Citric Acid Cycle Cyto to mito. pyruvate 2 (goes to the atm. None Citric Acid Cycle (goes through 2x) Matrix of mito. Acetyl CoA 6 4 (goes to the atm.) none Oxidative Phosphorylation cristae NADH, FADH2 O2 2x2=4 3X10= 30 Total 38 4 34

Totals

Lactic Acid Fermentation Can be used by muscle cells to generate NAD+ Lactate builds up in muscles during strenuous activity, carried back to the liver and converted to pyruvate Used in the dairy industry to make cheese

Alcoholic fermentation Used in the winemaking industry

Anaerobes obligate aerobes: must have oxygen to survive Obligate anaerobes: must have no oxygen to survive Facultative anaerobe: can survive with or without oxygen

Organic molecules into cell respiration