A biochemist wanted to study how various substances were used in cellular respiration

Photosynthesis and cellular respiration provide energy for life. Photosynthesis uses solar energy to produce glucose and O2 from CO2 and H2O. In cellular respiration, O2 is consumed during the breakdown of glucose to CO2 and H2O, and energy is released.

Breathing supplies O2 for use in cellular respiration and removes CO2.

Cellular respiration banks energy in ATP molecules. The summary equation for cellular respiration is C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP + Heat).

The human body uses energy from ATP for all its activities.

Cells tap energy from electrons falling from organic fuels to oxygen. Electrons removed from fuel molecules (oxidation) are transferred to NAD+ (reduction). NADH passes electrons to an electron transport chain. As electrons fall from carrier to carrier and finally to O2, energy is released.

Overview: Cellular respiration occurs in three main stages.

Glycolysis harvests chemical energy by oxidizing glucose to pyruvate. ATP is used to prime a glucose molecule, which is split in two. These three-carbon intermediates are oxidized to two molecules of pyruvate, yielding a net of 2 ATP and 2 NADH. ATP is formed by substrate-level phosphorylation, in which a phosphate group is transferred from an organic molecule to ADP.

Pyruvate is oxidized prior to the citric acid cycle. In the oxidation of pyruvate to acetyl CoA, CO2 and NADH are produced.

The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH2 molecules. For each turn of the cycle, two carbons from acetyl CoA are added and 2 CO2 are released; the energy yield is 1 ATP, 3 NADH, and 1 FADH2.

Most ATP production occurs by oxidative phosphorylation. In mitochondria, electrons from NADH and FADH2 travel down the electron transport chain to O2, which picks up H+ to form water. Energy released by these redox reactions is used to pump H+ from the mitochondrial matrix into the intermembrane space. In chemiosmosis, the H+ diffuses back across the inner membrane through ATP synthase complexes, driving the synthesis of ATP.

Interrupting cellular respiration can have both harmful and beneficial effects. Poisons can block electron flow, block the movement of H+ through ATP synthase, or allow H+ to leak through the membrane. Uncouplers in brown fat produce body heat.

Review: Each molecule of glucose yields many molecules of ATP. Substrate-level phosphorylation and oxidative phosphorylation produce up to 32 ATP molecules for every glucose molecule oxidized in cellular respiration.

Fermentation enables cells to produce ATP without oxygen. Under anaerobic conditions, muscle cells, yeasts, and certain bacteria produce ATP by glycolysis. NAD+ is recycled from NADH as pyruvate is reduced to lactate (lactic acid fermentation) or, in microbes, alcohol and CO2 (alcohol fermentation).

Glycolysis evolved early in the history of life on Earth. Glycolysis occurs in the cytoplasm of nearly all organisms and is thought to have evolved in ancient prokaryotes.

Cells use many kinds of organic molecules as fuel for cellular respiration. Carbohydrates, fats, and proteins can all fuel cellular respiration.

Food molecules provide raw materials for biosynthesis. Cells use intermediates from cellular respiration and ATP for biosynthesis of other organic molecules. Metabolic pathways are often regulated by feedback inhibition.

Fill in the blanks in this summary map to help you review the key concepts of cellular respiration.

What is the role of oxygen in cellular respiration? a. It is reduced in glycolysis as glucose is oxidized. b. It provides electrons to the electron transport chain. c. It combines with the carbon removed during the citric acid cycle to form CO2. d. It is required for the production of heat and light. e. It accepts electrons from the electron transport chain.

When the poison cyanide blocks the electron transport chain, glycolysis and the citric acid cycle soon grind to a halt as well. Why do you think they stop? a. They both run out of ATP. b. Unused O2 interferes with cellular respiration. c. They run out of NAD+ and FAD. d. Electrons are no longer available. e. They run out of ADP.

A biochemist wanted to study how various substances were used in cellular respiration. In one experiment, he allowed a mouse to breathe air containing O2 labeled by a particular isotope. In the mouse, the labeled oxygen first showed up in a. ATP. b. glucose (C6H12O6). c. NADH. d. CO2. e. H2O.

In glycolysis, ______ is oxidized and ______ is reduced. a. NAD+ . . . glucose b. glucose . . . oxygen c. ATP . . . ADP d. glucose . . . NAD+ e. ADP . . . ATP

Which of the following is the most immediate source of energy for making most of the ATP in your cells? a. the reduction of oxygen b. the transfer of from intermediate substrates to ADP c. the movement of H+ across a membrane down its concentration gradient d. the splitting of glucose into two molecules of pyruvate e. electrons moving through the electron transport chain

In which of the following is the first molecule becoming reduced to the second molecule? a. pyruvate acetyl CoA b. pyruvate lactate c. glucose pyruvate d. NADH + H+ NAD+ + 2 H e. C6H12O6 6 CO2

Which of the following is a true distinction between cellular respiration and fermentation? a. NADH is oxidized by the electron transport chain in respiration only. b. Only respiration oxidizes glucose. c. Fermentation is an example of an endergonic reaction; cellular respiration is an exergonic reaction. d. Substrate-level phosphorylation is unique to fermentation; cellular respiration uses oxidative phosphorylation. e. Fermentation is the metabolic pathway found in prokaryotes; cellular respiration is unique to eukaryotes.

Which of the three stages of cellular respiration is considered the most ancient? Explain your answer. 1

Explain in terms of cellular respiration why you need oxygen and why you exhale carbon dioxide. 1

Compare and contrast fermentation as it occurs in your muscle cells and as it occurs in yeast cells. 1

Explain how your body can convert excess carbohydrates in the diet to fats. Can excess carbohydrates be converted to protein? What else must be supplied? 1

An average adult human requires 2,200 kcal of energy per day. Suppose your diet provides an average of 2,300 kcal per day. How many hours per week would you have to walk to burn off the extra calories? Swim? Run? (See Figure 6.4.) 1

Your body makes NAD+ and FAD from two B vitamins, niacin and riboflavin. The Recommended Dietary Allowance for niacin is 20 mg and for riboflavin, 1.7 mg. These amounts are thousands of times less than the amount of glucose your body needs each day to fuel its energy needs. Why is the daily requirement for these vitamins so small? 1

In a detail of the citric acid cycle not shown in Figure 6.9B, an enzyme converts succinate to a compound called fumarate, with the release of H+. You are studying this reaction using a suspension of bean cell mitochondria and a blue dye that loses its color as it takes up H+. You know that the higher the concentration of succinate, the more rapid the decolorization of the dye. You set up reaction mixtures with mitochondria, dye, and three different concentrations of succinate (0.1 mg/L, 0.2 mg/L, and 0.3 mg/L). Which of the following graphs represents the results you would expect, and why? 1

ATP synthase enzymes are found in the prokaryotic plasma membrane and in the inner membrane of a mitochondrion. What does this suggest about the evolutionary relationship of this eukaryotic organelle to prokaryotes? 1

Excess consumption of alcohol by a pregnant woman can cause a complex of birth defects called fetal alcohol syndrome (FAS). Symptoms of FAS include head and facial irregularities, heart defects, mental retardation, and behavioral problems. The U.S. Surgeon Generals Office recommends that pregnant women abstain from drinking alcohol, and the government has mandated a warning label on liquor bottles: Women should not drink alcoholic beverages during pregnancy because of the risk of birth defects. Imagine you are a server in a restaurant. An obviously pregnant woman orders several alcoholic drinks. How would you respond? Is it the womans right to make those decisions about her unborn childs health? Do you bear any responsibility in the matter? Is a restaurant responsible for monitoring the health habits of its customers?