Chapter 6 Outline and Terms
6.1. Energy (p. 100)
A. Energy
1. Capacity to do work; cells must continually use energy to do biological work.
2. Kinetic energy is energy of motion; all moving objects have kinetic energy.
3. Potential energy is stored energy.
a. Water behind a dam has potential energy that can be converted to kinetic energy.
b. Energy within an atom lies in arrangement of its atoms in molecule; glucose has more energy than its breakdown components, carbon dioxide and water.
B. Two Laws of Thermodynamics
1. First law of thermodynamics (also called the law of conservation of energy)
a. Energy cannot be created or destroyed; it can be changed from one form to another.
b. In an engine, chemical energy of coal converts to heat; heat energy converts to kinetic energy.
c. In human body, chemical energy in food is converted to chemical energy in ATP and then converted to mechanical energy of muscle contraction. (Fig. 6.1)
2. Second law of thermodynamics
a. Energy cannot be changed from one form into another without a loss of usable energy.
b. 25% of chemical energy of gasoline is converted to move a car; rest is lost as heat.
c. When muscles convert chemical energy in ATP to mechanical energy, some is lost as heat.
d. Heat is form of energy but quickly dissipates into the environment; because heat dissipates, it can never be converted back to the form of potential energy.
B. Entropy
1. Measure of randomness or disorder
2. Organized/usable forms of energy have low entropy; unorganized/less stable forms have high entropy.
3. Energy conversions result in heat and therefore the entropy of the universe is always increasing.
4. It takes a constant input of usable energy from the food you eat to keep you organized.
6.2. Metabolic Reactions and Energy Transformations (p. 101)
A. Metabolism
1. Sum of all the biochemical pathways of a cell.
2. In a reaction A + B 
C + D, A and B are reactants and C and D are products.
3. Free energy (G) is the amount of energy that is free to do work after a chemical reaction.
4. Change in free energy is noted as 
G; a negative G means that products have less free energy than reactants; the reaction occurs spontaneously.
5. Exergonic reactions have a negative G and energy is released.
6. Endergonic reactions have a negative G; products have more energy than reactants; such reactions can only occur with an input of energy.
7. Reversible reactions have a free energy difference near zero; such a reaction is at equilibrium.
8. Cells use product of a first reaction as reactant in second reaction; such a process pulls first reaction in one direction.
B. Coupling Reactions
1. Occur when energy released by exergonic reaction is used to drive an endergonic reaction.
2. Energy released from ATP ADP + 
is used to fuel many biological reactions.
3. ATP breakdown is coupled to a reaction that requires energy; both reactions take place at same time in same place.
4. When ATP breaks down to drive reactions, some energy is lost as heat; overall reaction becomes exergonic. (Fig. 6.2)
C. ATP: Energy for Cells
1. ATP (adenosine triphosphate) is the energy currency of cells.
a. When cells require energy, they "spend" ATP.
b. Great demand for ATP requires body to constantly produce ATP.
c. Small amount of ATP is constantly recycled from ADP and :it is continually made, broken down, and remade in cells. (Fig. 6.3) [transp. 36]
d. The energy released from ATP ADP + is just about enough for most biological reactions.
D. Function of ATP
1. Chemical work: ATP supplies energy to synthesize macromolecules that make up the cell.
2. Transport work: ATP supplies energy needed to pump substances across the plasma membrane.
3. Mechanical work: ATP supplies energy to move muscles, cilia and flagella, chromosomes, etc.
E. Structure of ATP
1. ATP is a nucleotide made of base adenine, sugar ribose, and three phosphate groups. [transp. 36]
2. ATP is called a "high-energy" compound because a phosphate group is easily removed.
3. In cells, about 7.3 kcal per mole is released when ATP is hydrolyzed to ADP + .
6.3. Metabolic Pathways and Enzymes (p. 103)
A. Reactions in Cells Are Orderly
1. Metabolic pathways are orderly sequence of chemical reactions; each step is catalyzed by a specific enzyme.
2. Metabolic pathways begin with particular reactant, end with end product; have many intermediate steps.
3. One pathway leads to next; since pathways use same molecules, a pathway can lead to several others.
4. Metabolic energy is captured more easily if it is released in small increments.
5. A reactant is substance that participates in reaction; a product is substance formed by reaction.
6. Each step in a series of chemical reactions is assisted by an enzyme.
7. Enzymes are catalysts that speed chemical reactions without the enzyme being changed.
8. Every enzyme is specific in its action and catalyzes only one reaction or one type of reaction.
9. A substrate is a reactant in an enzymatic reaction.
B. Enzymes Lower the Energy of Activation
1. Almost no metabolic reaction occurs in a cell unless its own enzyme is present.
2. Without enzymes, activation is achieved by heating reaction flask to increase molecular collisions.
3. Energy of activation (Ea) is energy that must be added to cause molecules to react. (Fig. 6.4)
[transp. 37]
C. Enzyme-Substrate Complexes
1. Enzymes speed chemical reactions by lowering the energy of activation (Ea) by forming a complex with their substrate(s) at the active site. (Fig. 6.5) [transp. 38]
a. Active site is small region on surface of enzyme where the substrate(s) bind.
b. When substrate binds to enzyme, active site undergoes a slight change in shape that facilitates the reaction---this is called the induced-fit model.
2. Only a small amount of enzyme is needed in a cell because enzymes are not used up.
3. Some enzymes actually participate in the reaction (e.g., trypsin).
4. Sometimes a particular reactant(s) produces more than one type of product(s).
a. Presence or absence of an enzyme determines which reaction takes place.
b. If reactants can form more than one product, enzymes present determine product produced.
5. Every cell reaction requires its specific enzyme; therefore, they are named for substrates by adding the ending "-ase."
D. Factors That Affect Enzymatic Speed
1. Enzymatic reactions are rapid (e.g., 2H2O2 H2O + O2 occurs 600,000 times/sec with catalase).
a. To achieve maximum product per unit time, need enough substrate to fill active sites.
b. Optimal temperature and pH also increase rates of enzymatic reaction.
2. Moderate Temperature and Optimal pH is Best
a. As temperature rises, there is increase in enzyme activity. (Fig. 6.6a) [transp. 39]
b. As temperature rises, enzyme activity increases because there are more molecular collisions.
c. Enzyme activity declines rapidly when enzyme is denatured at a certain temperature; results in change in shape of enzyme.
d. Each enzyme has optimal pH that maintains its normal configuration. (Fig. 6.6b) [transp. 39]
e. A change in pH alters ionization of side chains, eventually resulting in denaturation.
3. Amount of Active Enzyme Affects Speed
a. Enzyme concentration varies when genes coding for the enzyme are turned on or off.
b. Enzymes regulated by phosphorylation; molecules received by membrane receptors turn on kinases, which activate enzymes by phosphorylating them.
c. Other enzymes called phosphatases remove phosphate groups from enzymes.
d. Phosphorylation and dephosphorylation regulate protein synthesis, cell division, activity of motor molecules, nuclear envelope breakdown, and development.
4. Enzymes Can Be Inhibited
a. Cyanide inhibits an essential enzyme (cytochrome oxidase) found in all cells.
b.. Inhibition is common means by which cells regulate enzyme activity.
c. In competitive inhibition, another molecule is similar to enzyme's substrate, competes with true substrate for enzyme's active site, resulting in decreased product formation.
d. In noncompetitive inhibition, a molecule binds to allosteric site, a site other than active site, hereby changing the three-dimensional structure of enzyme and ability to bind to its substrate.
e. Feedback inhibition regulates activity of most enzymes; product produced by an enzyme binds to enzyme's active site. (Fig. 6.7) [transp. 40]
1) When product is abundant, active sites are full and enzyme activity drops.
2) When product is used up, inhibition is reduced and more product is produced.
3) Concentrations of products can be kept within narrow ranges.
4) Pathways can be regulated by feedback inhibition; end product of pathway binds at an allosteric site on the first enzyme of the pathway, shutting down the pathway.
5. Cofactors Help Enzymes
a. Many enzymes require an inorganic ion or nonprotein cofactor to function.
b. The ions are metals; the organic cofactors are coenzymes (e.g., vitamins) that assist enzymes or accept or contribute atoms to the reaction.
c. Vitamins required in trace amounts for synthesis of coenzymes; become part of coenzyme's molecular structure; vitamin deficiency causes lack of coenzyme and lack of enzymatic action.
6.4. Metabolic Pathways and Living Things (p. 107)
A. Energy Flows Through Systems
1. Pathways of photosynthesis and aerobic respiration transform one form of energy into another.
2. Energy released by breakdown of ATP is used for biological work; eventually it is converted to nonusable heat.
3. Without a constant input of solar energy, life could not exist.
B. Photosynthesis and Aerobic Respiration: Opposing Processes
1. Photosynthesis uses energy to combine carbon dioxide and water to produce glucose.
2. Aerobic respiration releases energy by breakdown of glucose to carbon dioxide and water.
C. Electron Transport System
1. Both photosynthesis and respiration are metabolic pathways that use an electron transport system consisting of membrane-bound carriers to pass electrons from one carrier to another.
2. High-energy electrons are delivered to the system and low-energy electrons leave it. (Fig. 6.8)
[transp. 41]
3. Each time electrons transfer to a new carrier, energy is released; ultimately used to produce ATP.
D. NADP+ and NAD+
1. Photosynthesis uses NADP+ and aerobic respiration uses NAD+, both coenzymes of reduction/oxidation.
2. NADP+ contains a phosphate group that is lacking in NAD+.
3. When NADP+ (nicotinamide adenine dinucleotide phosphate) donates hydrogen atoms (H+ + e- ) to a substrate during photosynthesis, substrate has accepted electrons and is reduced.
4. When NAD removes hydrogen atoms (H+ + e- ) during cell respiration, the substrate has lost electrons and is oxidized.
5. In chloroplasts
a. Electrons that enter the electron transport system are taken from water.
b. Solar energy has energized electrons that transfer from carrier to carrier and release energy.
c. In the end, NADP+ accepts energized electrons and an H+ to become NADPH.
d. NADPH supplies electrons; ATP supplies energy to reduce carbon dioxide to a carbohydrate.
6. In mitochondria
a. High energy electrons entering electron transport system have been removed from carbohydrate substrates by coenzyme NAD.
b. At end of aerobic respiration, glucose has been oxidized to carbon dioxide and water and ATP have been produced.
E. ATP Production
1. ATP synthesis was known to be coupled to the electron transport system.
2. Peter Mitchell received 1978 Nobel prize for chemiosmotic theory of ATP production.
3. In mitochondria and chloroplasts, carriers of electron transport systems are located within a membrane.
4. In chemiosmotic theory, H+ ions collect on one side of membrane because they are pumped there by certain carriers.
5. The electrochemical gradient across the membrane is used to provide energy for ATP production.
6. Particles called ATP synthase complexes span the membrane; each complex contains a channel that allows H+ ions to flow down their electrochemical gradient. (Fig. 6.9) [transp. 42]
7. Flow of H+ ions through the channel provides the energy to drive ADP + ATP. (Fig. 6.9)
F. Energy Flows Through Systems
1. Energy released by ATP breakdown is used by the cell to do work; eventually it is lost as heat.
2. Expended energy cannot be used to reform ATP; energy does not cycle but flows through cells.
3. As solar energy is collected by plants and converted to ATP, inner mitochondrial membrane acts as a dam to maintain energy gradient; formation of ATP resembles the turbines in a dam that couple water flow to formation of electricity.
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