Cellular Respiration Biology

Glucose:

- is a high-energy molecule; CO2 and H2O are low-energy molecules; cellular respiration is thus exergonic because it releases energy. - Electrons are removed from substrates and received by oxygen, which combines with H+ to become water. - Glucose is oxidized and O2 is reduced.

Glycolysis

- is the breakdown of glucose in the cytoplasm into two molecules of pyruvate. i. Enough energy is released for an immediate yield of two ATP. ii. Glycolysis takes place outside the mitochondria and does not utilize oxygen; it is therefore an anaerobic process. All the other phases require oxygen and are therefore aerobic.

Citric Acid Cycle Steps

-The citric acid cycle occurs in the matrix of mitochondria. 1. The cycle begins by the addition of a two-carbon acetyl group to a four-carbon molecule, forming a six-carbon citrate (citric acid) molecule. 2. In the subsequent reactions, at three different times two electrons and one hydrogen ion are accepted by NAD+, forming NADH. 3. At one time, two electrons and two hydrogen ions are accepted by FAD, forming FADH2. 4. NADH and FADH2 carry these electrons to the electron transport chain. 5. Some energy is released and is used to synthesize ATP by substrate-level ATP synthesis. 6. One high-energy metabolite accepts a phosphate group and transfers it to convert ADP to ATP. 7. The citric acid cycle turns twice for each original glucose molecule. 8. The products of the citric acid cycle (per glucose molecule) are 4 CO2, 2 ATP, 6 NADH, and 2 FADH2. 9. Production of CO2: a. The six carbon atoms in the glucose molecule have become the carbon atoms of six CO2 molecules, two from the prep reaction and four from the citric acid cycle

Anabolism

1. ATP produced during catabolism drives anabolism. 2. Substrates making up pathways can be used as starting materials for synthetic reactions. 3. The molecules used for biosynthesis constitute the cell's metabolic pool. 4. Carbohydrates can result in fat synthesis: G3P converts to glycerol; acetyl groups join to form fatty acids. 5. Some metabolites can be converted to amino acids by transamination, the transfer of an amino acid group to an organic acid. 6. Plants synthesize all the amino acids they need; animals lack some enzymes needed to make some amino acids. 7. Humans synthesize 11 of 20 amino acids; the remaining nine essential amino acids must be provided by the diet.

NAD+

1. As a metabolite is oxidized, NAD+ (nicotinamide adenine dinucleotide) accepts two electrons and a hydrogen ion (H+); this results in NADH. 2. Electrons received by NAD+ and FAD are high-energy electrons and are usually carried to the electron transport chain. 3. NAD+ is a coenzyme of oxidationreduction since it both accepts and gives up electrons; thus, NAD+ is sometimes called a redox coenzyme. 4. Only a small amount of NAD+ is needed in cells because each NAD+ molecule is used repeatedly.

Advantages and Disadvantages of Fermentation

1. Despite a low yield of two ATP molecules, fermentation provides a quick burst of ATP energy for muscular activity. 2. Fermentation products are toxic to cells. a. When blood cannot remove all lactate from muscles, lactate changes pH and causes muscles to fatigue. b. The individual is in oxygen debt because oxygen is needed to restore ATP levels and rid the body of lactate. c. Recovery occurs after lactate is sent to the liver where it is converted into pyruvate; some pyruvate is then respired or converted back into glucose.

Catabolism Examples

1. Fat breaks down into glycerol and three fatty acids. 2. Amino acids break down into carbon chains and amino groups

Outside the Mitochondria: Fermentation

1. Fermentation is an anaerobic (i.e., occurs in the absence of oxygen) process which consists of glycolysis plus reduction of pyruvate to either lactate or to alcohol and CO2 (depending on the organism). 2. Animal cell fermentation results in lactate. 3. Bacteria can produce an organic acid like lactate, or an alcohol and CO2. 4. Yeasts produce ethyl alcohol and CO2. 5. NADH passes its electrons to pyruvate instead of to an electron transport chain; NAD+ is then free to return and pick up more electrons during earlier reactions of glycolysis.

Phases of Cellular Respirations

1. Glycolysis 2. Preparatory Reaction 3. Citric Acid Cycle 4. Electric Transport Chain

Energy-Investment Steps

1. Glycolysis begins with the activation of glucose with two ATP; the glucose splits into two C3 molecules known as G3P, each of which carries a phosphate group.

Outside the Mitochondria: Glycolysis

1. Glycolysis occurs in the cytoplasm outside the mitochondria. 2. Glycolysis is the breakdown of glucose into two pyruvate molecules. 3. Glycolysis is universally found in organisms; therefore, it likely evolved before the citric acid cycle and electron transport chain. 4. Glycolysis can be divided into the energy-investment steps where ATP is used to "jump start" glycolysis, and the energy-harvesting steps, where more ATP is made than used.

Metabolic Pool

1. In a metabolic pool, substrates serve as entry points for degeneration or synthesis of larger molecules. 2. Degradative reactions (catabolism) break down molecules; they tend to be exergonic. 3. Synthetic reactions (anabolism) build molecules; they tend to be endergonic.

Energy-Harvesting Steps

1. Oxidation of G3P occurs by removal of electrons and hydrogen ions. 2. Four electrons and two hydrogen ions are accepted by two NAD+, resulting in two NADH; later, when the NADH molecules pass two electrons to the electron transport chain, they become NAD+ again. 3. The oxidation of G3P and subsequent substrates results in a high-energy phosphate group on each C3 molecule, which are used to synthesize four total ATP molecules; this process is called substrate-level ATP synthesis. 4. Two of the four ATP molecules produced are required to replace two ATP molecules used in the initial phosphorylation of glucose; therefore there is a net gain of two ATP from glycolysis. 5. Pyruvate enters a mitochondrion (if oxygen is available) and cellular respiration ensues. 6. If oxygen is not available, fermentation occurs and pyruvate undergoes reduction.

Electron Transport Chain Steps

1. The electron transport chain (ETC) is located in the cristae of the mitochondria and consists of carriers that pass electrons successively from one to another. 2. NADH and FADH2 carry the electrons to the ETC. 3. Members of the Chain a. NADH gives up its electrons and becomes NAD+; the next carrier then gains electrons and is thereby reduced. b. At each sequential redox reaction, energy is released to form ATP molecules. c. Some of the protein carriers are cytochrome molecules, a protein with a tightly bound heme group with a central atom of iron.

Inside the Mitochondria

1. The next reactions of cellular respiration involve the preparatory (prep) reaction, the citric acid cycle, and the electron transport chain. 2. These reactions occur in the mitochondria. 3. A mitochondrion has a double membrane with an intermembrane space (between the outer and inner membrane). 4. Cristae are the inner folds of membrane that jut into the matrix, the innermost compartment of a mitochondrion that is filled with a gel-like fluid. 5. The prep reaction and citric acid cycle enzymes are in the matrix; the electron transport chain is in the cristae. 6. Most of the ATP produced in cellular respiration is produced in the mitochondria; therefore, mitochondria are often called the "powerhouses" of the cell.

Preparatory Reaction Steps

1. The preparatory (prep) reaction connects glycolysis to the citric acid cycle. 2. In this reaction, pyruvate is converted to a two-carbon acetyl group, and is attached to coenzyme A, resulting in the compound acetyl-CoA. 3. This reaction occurs twice for each glucose molecule. 4. CoA carries the acetyl group to the citric acid cycle. 5. The two NADH carry electrons to the electron transport chain. 6. The CO2 diffuses out of animal cells into blood, is transported to lungs, and exhaled.

Efficiency of Fermentation

1. Two ATP produced per glucose molecule during fermentation is equivalent to 14.6 kcal. 2. Complete glucose breakdown to CO2 and H2O during cellular respiration represents a potential yield of 686 kcal per molecule. 3. Efficiency of fermentation is 14.6/686 or about 2.1%, far less efficient than complete breakdown of glucose.

The breakdown of glucose yields to how many ATP?

36 or 38 ATP

The net equation for glucose breakdown is:

C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + energy.

Cycling of Carriers

a. By the time electrons are received by O2, three ATP have been made. b. When FADH2 delivers electrons to the electron transport system, two ATP are produced. c. Oxygen serves as the terminal electron acceptor and combines with hydrogen ions to form water.

Flow of Energy

a. Energy flows through organisms. For example, the sun is the energy source for producing carbohydrates in chloroplasts. In the mitochondria, the carbohydrate energy is converted into ATP molecules during cellular respiration. b. Chemicals cycle throughout cells. Mitochondria use carbohydrates and oxygen produced in chloroplasts, and chloroplasts use carbon dioxide and water produced in the mitochondria.

ETC and Chemiosmosis

a. Most of the ATP is produced by the electron transport chain and chemiosmosis. b. Per glucose, ten NADH and two FADH2 molecules provide electrons and H+ ions to the electron transport chain. c. For each NADH formed within the mitochondrion, three ATP are produced. d. For each FADH2 formed by the citric acid cycle, two ATP are produced. e. For each NADH formed outside the mitochondria by glycolysis, electrons are shuttled across the mitochondrial membrane by an organic molecule, reducing the ATP produced to four instead of six in some cells.

Substrate-Level ATP Synthesis

a. Per glucose molecule, there is a net gain of two ATP from glycolysis in cytoplasm. b. The citric acid cycle in the matrix of the mitochondria produces two ATP per glucose. c. A total of four ATP are formed by substrate-level ATP synthesis outside of the electron transport chain.

The Cristae of a Mitochondrion and Chemiosmosis

a. The ETC consists of three protein complexes and two carriers that transport electrons. b. The three protein complexes include NADH-Q reductase complex, the cytochrome reductase complex, and the cytochrome oxidase complex; the two protein mobile carriers are coenzyme Q and cytochrome c. c. Energy released from the flow of electrons down the ETC is used to pump H+ ions, which are carried by NADH and FADH2, into the intermembrane space. d. Accumulation of H+ ions in this intermembrane space creates a strong electrochemical gradient. e. ATP synthase complexes are channel proteins that serve as enzymes for ATP synthesis. f. As H+ ions flow from high to low concentration, ATP synthase synthesizes ATP by the reaction: ADP + P = ATP. g. Chemiosmosis is the term used for ATP production tied to an electrochemical (H+) gradient across a membrane. h. Once formed, ATP molecules diffuse out of the mitochondrial matrix through channel proteins. i. ATP is the energy currency for all living things; all organisms must continuously produce high levels of ATP to survive. j. Active tissues require greater amounts of ATP and therefore have more mitochondria than less active cells. **** I DO NOT KNOW IF WE NEED TO KNOW THIS SINCE ONLY CHEMIOSMOSIS IS BOLDED BUT IT WOULD BE GOOD TO STUDY IT JUST IN CASE****

Efficiency of Cellular Respiration

a. The energy difference between total reactants (glucose and O2) and products (CO2 and H2O) is 686 kcal. b. An ATP phosphate bond has an energy content of 7.3 kcal; 36 to 38 ATP are produced during glucose breakdown for a total of at least 263 kcal. c. This efficiency is 263/686, or 39% of the available energy in glucose is transferred to ATP; the rest of the energy is lost as heat.

FAD

another coenzyme of oxidationreduction, which can replace NAD+; FAD accepts two electrons and two hydrogen ions to become FADH2.

The reactions of Cellular respiration allow

energy in glucose to be released slowly; therefore ATP is produced gradually.

Electron Transport Chain

i. Is a series of carriers in the inner mitochondrial membrane that accept electrons from glucose; electrons are passed from carrier to carrier until received by oxygen; ii. Passes electrons from higher to lower energy states, allowing energy to be released and stored for ATP production;

Citric Acid Cycle

i. Occurs in the matrix of the mitochondrion and produces NADH and FADH2; ii. Is a series of reactions that gives off CO2 and produces one ATP; iii. Turns twice because two acetyl-CoA molecules enter the cycle per glucose molecule; iv. Produces two immediate ATP molecules per glucose molecule.

Cellular respiration

involves various metabolic pathways that break down carbohydrates and other metabolites with the concomitant buildup of ATP

Cellular respiration consumes

oxygen and produces CO2; because oxygen is required, cellular respiration is aerobic.

Preparatory Reaction

pyruvate enters a mitochondrion and is oxidized to a two-carbon acetyl group and CO2 is removed; this reaction occurs twice per glucose molecule.

Cellular respiration usually involves

the complete breakdown of glucose into CO2 and H2O.