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CHAPTER 6 METABOLISM: ENERGY AND ENZYMES
I. Cells and the Flow of Energy
A. Forms of Energy
1. Energy is capacity to do work; cells continually use energy to develop, grow, repair,
reproduce, etc.
2. Kinetic energy is energy of motion; all moving objects have kinetic energy.
3. Potential energy is stored energy.
4. Food is chemical energy; it contains potential energy.
5. Chemical energy can be converted into mechanical energy, e.g., muscle movement.
B. Two Laws of Thermodynamics
1. First law of thermodynamics (also called the law of conservation of energy)
a. Energy is not created nor destroyed.
a. Energy can change from one energy form to another.
b. Energy could be in forms of electrical, chemical, kinetic, or potential energy forms as example.
2. Second law of thermodynamics
a. Some useful energy is lost as heat whenever an energy transfer occurs.
b. In all natural processes, the entropy of the universe increases.
c. Spontaneous processes are ones that represent changes from state of higher energy
level to lower energy level.
d. A change from a state order to a state of chaos is spontaneous.
C. The flow of energy on earth
1.
Sunlight is the ultimate source of metabolic energy. Sunlight is absorbed by plants
(autotrophs). The energy then was consumed by animals (heterotrophs), becomes
heat in the end and dissipated into environment.
2.
The conversion of energy is less than 100%.
II. Metabolic Reactions and Energy Transformations
1. Metabolism is the sum of all the biochemical reactions in a cell.
2. In the 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. So G is the parameter
to judge the direction of a reaction.
5. Exergonic reactions have a negative G and energy is released.
6. Endergonic reactions have a positive G; products have more energy than reactants;
such reactions can only occur with an input of energy.
A. ATP: Energy for Cells
1. Adenosine triphosphate (ATP) is the energy currency of cells; when cells need
energy, they “spend” ATP.
2. When ATP is converted into ADP + P, the energy released is sufficient for biological
reactions with little wasted.
3. When one phosphate group is removed, about 7.3 kcal of energy is released per mole.
4. Only 39% of the chemical energy of glucose is transformed into ATP; 61% is lost as
heat.
B. ATP can have any of three functions.
1. Chemical Work: ATP supplies energy to synthesize molecules that make up the cell.
2. Transport Work: ATP supplies energy to pump substances across the plasma
membrane.
3. Mechanical Work: ATP supplies energy needed to perform mechanical processes
(e.g., muscle contraction, propel cilia, etc.).
III. Metabolic Pathways and Enzymes
A metabolic pathway is an orderly sequence of linked reactions; each step is catalyzed
by a specific enzyme. A coenzyme (ot cofactor) is an organic cofactor, often vitamins.
A. Energy of Activation
The energy of activation (Ea) is the energy that must be added to cause molecules to
react; without an enzyme (i.e., in a reaction vessel in the laboratory) this energy may be
provided by heat, which causes an increase in the number of molecular collisions.
B. An active site is a small region on the surface of the enzyme where the substrate(s) bind.
Only a small amount of enzyme is needed in a cell because enzymes are not consumed
during catalysis.
C. Factors Affecting Enzymatic Speed
1. Substrate concentration.
2. Temperature and pH. Enzymes are proteins that can be denatured and lose activity.
3. Enzyme concentration:
4. Enzyme inhibitors:
1)
In competitive inhibition, the substrate and the inhibitor are both able to
bind to the enzyme’s active site.
2) In noncompetitive inhibition, the inhibitor binds to the enzyme at a location
other than the active site (the allosteric site), changing the shape of the
enzyme and rendering it unable to bind to its substrate.
IV. Oxidation-Reduction and the Flow of Energy
1. In oxidation-reduction (redox) reactions, electrons pass from one molecule to another.
Oxidation is the loss of electrons. Reduction is the gain of electrons.
2. Both reactions occur at the same time because one molecule accepts electrons given
up by another molecule.
A. Photosynthesis
1. Photosynthesis uses energy to combine carbon dioxide and water to produce glucose
in the formula:
6 CO2 + 6 H2O + energy = C6H12O6 + 6 O2
2. When hydrogen atoms are transferred to carbon dioxide from water, water has been
oxidized and carbon dioxide has been reduced.
3. Chloroplasts capture solar energy and convert it by way of an electron transport
system into the chemical energy of ATP.
4. The reaction that reduces NADP+ is:
NADP+ + 2e + H+ = NADPH
B. Cellular Respiration
1. The overall equation for cellular respiration is opposite that of photosynthesis:
C6H12O6 + 6 O2 = 6 CO2 + 6 H2O + energy
2. When NAD removes hydrogen atoms (H+ + e-) during cellular respiration, the
substrate has lost electrons and is therefore oxidized.
3. At the end of cellular respiration, glucose has been oxidized to carbon dioxide and
water and ATP molecules have been produced.
2. In metabolic pathways, most oxidations involve the coenzyme NAD+ the molecule
accepts two electrons but only one hydrogen ion: NAD+ + 2e + H+ = NADH
C. Electron Transport Chain
1. Both photosynthesis and respiration use an electron transport chain consisting of
membrane-bound carriers that pass electrons from one carrier to another.
2. High-energy electrons are delivered to the system and low-energy electrons leave it.
3. The overall effect is a series of redox reactions; every time electrons transfer to a new
carrier, energy is released for the production of ATP.
D. ATP Production
1. There are four sources of ATP production from glucose to CO2 in the presence of O2.
2. There is an initial ATP investment.
3. Direct ATP production that is more than invested.
4. Energy harvested as forms of e- carriers, NADH or FAD2. The electrochemical
gradient thus established across the membrane of mitochondrion is used to provide
energy for ATP production. This is the most efficient way and it needs O2.
5. GTP generated can be converted into ATP.
CHAPTER 7 PHOTOSYNTHESIS
I. Photosynthetic Organisms
Algae, plants, and cyanobacteria (photosynthetic bacteria)
Only 42% of the solar radiation that hits the Earth’s atmosphere reaches surface; most is
visible light.
II. Photosynthetic Pigments
1. Pigments found in chlorophyll absorb specific wavelengths of light in their absorption
spectra. Their absorption spectra analyzed using a spectrophotometer. It is called
their absorption spectrum.
2. Two major photosynthetic pigments are chlorophyll a and chlorophyll b.
3. Both chlorophylls absorb violet, blue, and red wavelengths best. Very little green
light is absorbed; most is reflected (this is why leaves appear green).
4. Carotenoids are yellow-orange pigments that absorb light in violet, blue, and green
regions.
5. When chlorophyll breaks down in the fall, the yellow-orange pigments in leaves show
through.
III. Photosynthetic Reaction
1. In 1930, van Niel showed that O2 given off by photosynthesis comes from water and
not from CO2.
2. The net equation of photosynthesis reads: 6CO2 + 6H2O = C6 H12O6 + 6O2.
3. In 1905, Blackman proposed two sets of reactions for photosynthesis. Light
reactions take place only in the presence of light.
a. Light reactions are the energy-capturing reactions.
b. Chlorophyl within thylakoid membranes absorbs solar energy and energizes
electrons.
c. When energized electrons move down an electron transport chain, energy is
captured and used for ATP production.
d. Energized electrons are also taken up by NADP+, converting it to NADPH.
IV. ATP Production
1.
The thylakoid space acts as a reservoir for H+ ions; each time H2O is split, two
H+ remain.
2.
Flow of H+ from high to low concentration across thylakoid membrane
provides energy to produce ATP from ADP + P by using an ATP synthase enzyme.
CHAPTER 8 CELLULAR RESPIRATION
I. . Phases of Cellular Respiration
1. Glycolysis is the breakdown of glucose in the cytoplasm into two molecules of pyruvate, an
anaerobic process.
2. The citric acid cycle:
3. The electron transport chain:
II. The Electron Transport Chain
1. The electron transport chain is located in the cristae of mitochondria and chloroplasts
and consists of carriers that pass electrons successively from one to another.
3. NADH and FADH2 carry the electrons to the electron transport system.
4. At each sequential redox reaction, energy is released to form ATP molecules. ATP
synthase complexes are channel proteins that serve as enzymes for ATP synthesis;
ADP + P = ATP.
5. Because O2 must be present for the proteins to work, this process is also called
oxidative phosphorylation.
6. Oxygen serves as the terminal electron acceptor and combines with hydrogen ions to
form water.
7. By the time electrons are received by O2, three ATP have been made.
8. When FADH2 delivers electrons to the electron transport system, two ATP are formed
by the time the electrons are received by O2.
III. Mitochondion would be the only cellular fraction that would
A.
B.
C.
form an electrochemical gradient of H+ across a membrane.
use significant amounts of oxygen.
use a chemiosmotic complex to produce ATP.
IV. Fermentation
Fermentation is an anaerobic process as alternative energy source in absence of O2,
which consists of glycolysis plus reduction of pyruvate to either lactate or to alcohol and
CO2 (depending on the organism).
Review Qs:
1. If enzymes could not be used during a reaction, would a thermodynamically favorable
reaction still occur?
2. If enzymes could not be used during a reaction, what could be added to a system to make the
reaction occur faster?
3. What measure can be used to judge the direction of a reaction?
4. Describes the first law and the second law of thermodynamics.
5. What has happened to the sunlight energy after being absorbed on earth?
6. A living organism represents stored energy in the form of chemical compounds. When an
organism dies, what happens to this stored energy?
7. What are the characteristics of enzymes?
8. What is ATP? Its three parts?
9. ATP is considered a high-energy compound because under cellular conditions, 7.3 kcal per
mole of energy is released when a bond is broken between ____ ____.
10. If there are twelve different intermediate products produced in the stages for production of a
molecule in a cell, we can expect that there are ______?______ enzyme(s).
11. Factors that influence enzyme activities:
12. How do inhibitors of enzymes work?
13. A coenzyme is ______. Examples:
14. Which organelles contain functioning ATP synthase complexes in their membranes?
15. If a reaction results in one molecule losing an electron and a second molecule gaining that
electron, the reaction is said to be _________. It is typical of co-enzymes do during the
metabolic pathway.
16. Features of the electron transport chain:
17. Potential energy is best described as _______________. Chemical energy is a form of
_______________ energy.
18. Some bacteria are strict aerobes and others are strict anaerobes. Some bacteria, however, are
facultative anaerobes and can live with or without oxygen. If given the choice of using oxygen or
not, which should a facultative anaerobe perform?
19. What molecules are oxidized and reduced during the citric acid cycle?
20. Locations of the three major metabolic processes: glycolysis, citric acid cycle and the
electron transfer?
21. What molecule is the ultimate electron recipient in metabolism?
22. Cellular respiration yields about ______ of the energy from glucose in ATP molecules.
23. The process based on the Greek root words for "sugar" and "lysis" is _______.
24. What is the first process in breaking down glucose? Which process produces alcohol or
lactate? Which process produces both NADH and FADH2? Which process reduces molecular
oxygen to water? Where are the largest amounts of ATPs produced?
Choices:
Glycolysis
Fermentation
Preparatory Reaction
Citric Acid Cycle (Kreb’s Cycle)
Electron Transfer in Mitochondrion
25. The enzymes of the electron transport chain are bound to the surface of the cristae. The
cristae are folded inward in order to
26.
Compared with other cell components (organelles, cell membrane or nucleus), the
mitochondria would be the only cellular fraction that would __________________
27. The primary energy carrier between the citric acid cycle and the electron transport system is
28. What are the products of photosynthesis? What organisms are capable of photosynthesis?
What wave lengths are more effective?
29. Why are plants green?
30. An early experiment by Van Helmont (1600s) describes how he "grew a tree in a large pot
and found that after five years, the amount of soil in the pot had not changed. He concluded that
the increase in weight was due to the addition of water." At that time, the compounds in the air
had not yet been identified. Today, you know that he only discovered half the story. Which
additional experiment would provide evidence for the rest of the story?
31. What are the properties of photosynthetic pigments?
32. The ultimate source of energy for all organisms is the sun and the main source of the oxygen
we breathe from our environment is water.
True / False
33. Fossil fuels are full of energy stored from photosynthesis millions of years ago.
True / False
34. The ultimate driving force of metabolism is _________________.
True / False