Chapter 15 (Metabolism: Basic Concepts and Design)
What are the two criteria that must be satisfied by a biochemical pathway?
1) The reactions must be specific, in that only one set of products is formed from a specific set of reagents. 2) As a whole, the pathway must be spontaneous; that is, it must be thermodynamically favored.
In the cell, the hydrolysis of an ATP molecule in a coupled reaction changes the equilibrium ratio of products to reactants by a factor of _________________.
10^8
The metabolic pathways that require energy and are often biosynthetic processes are: A) anabolic. B) catabolic/ C) ametabolic. D) All of the above. E) None of the above.
A
Which energy source is used to regenerate ATP from ADP and Pi? A) oxidation of carbon to CO2 B) electrochemical potential of stored glycogen C) reduction of pyruvate to lactate D) All of the above. E) None of the above.
A
How much ATP is used daily by a typical human? How is it regenerated?
A human uses 40 kg of ATP per day. There are only about 100 g ATP available; thus the ATP is used and regenerated rapidly. ATP is regenerated from ADP and Pi, using the energy from catabolic processes.
The ____________ is the "chemical currency" of metabolism.
ATP
List five activated carriers in metabolism, and give the vitamins that are the precursors of these carriers.
Activated carrier NADH and NADPH FADH2 acetyl-coenzyme A biotin tetrahydrofolate Vitamin niacin riboflavin pantothenate biotin folic acid
What is an activated carrier? Provide two examples.
Activated carriers are molecules that are used as the carrier molecules of a particular molecule, atom, electron, or of protons. One example would be ATP, which is the activated carrier of phosphoryl groups. Flavin derivatives (FAD) and nicotinamide derivatives (NAD+) are examples of activated carriers of electrons.
_________________ is the process of building larger molecules from smaller ones.
Anabolism
The reaction pathways that transform fuels into cellular energy are: A) anabolic. B) catabolic. C) ametabolic. D) All of the above. E) None of the above.
B
Which of the following is the electron donor used for reductive biosynthesis? A) NADH B) NADPH C) FADH2 D) CoA-SH E) ATP
B
Compare ATP to acetyl CoA.
Both are activated carriers: Acetyl CoA carries acetyl groups, with high acetyl-ransfer potential, whereas ATP carries phosphate groups with high phosphoryl-transfer potential. Both molecules are common to several pathways.
What is the standard-state free energy (ΔG°′) for the hydrolysis of ATP to ADP? A) +45.6 kJ/mol B) −45.6 kJ/mol C) −30.5 kJ/mol D) −14.6 kJ/mol E) +30.5 kJ/mol
C
Which is the correct coenzyme-carrier pair? A) NADH: acyl B) tetrahydrofolate: electrons C) coenzyme A: acyl D) lipoamide: aldehyde E) thiamine pyrophosphate: glucose
C
In aerobic metabolism, the product of oxidation of carbon containing fuels is/are ____________.
CO2
_________________ is the type of metabolism where useful energy is harvested.
Catabolism
How are metabolic processes unified? How can you use this to help learn and understand biochemistry?
Common molecules and mechanisms are evident in motifs and patterns throughout metabolic pathways. Understanding the logic of catabolic and anabolic paths, and knowing common molecules (such as ATP) and mechanisms (oxidation reduction) make it simpler to understand the myriad paths of metabolism.
Pantothenate kinase associated degeneration: A) is a predominantly neurological disorder. B) can cause anemia. C) effects tissues that are dependent on aerobic metabolism. D) A and C. E) A, B, and C.
D
The electron carrier(s) that include(s) ATP is/are: A) NAD+ B) FAD C) FMN D) A and B E) A, B, and C
D
The reduced form of flavin adenine dinucleotide is: A) FADH B) FAD C) FADH++ D) FADH2 E) None of the above
D
Metabolic processes are regulated by: A) transcriptional regulation of the amount of enzyme. B) allosteric control of enzyme activity. C) the accessibility of substrates by compartmentalization. D) AandB. E) A,B,andC.
E
Some of the mechanisms by which enzyme catalytic activity is controlled are: A) allosteric control. B) feedback inhibition. C) covalent modification. D) AandC. E) A,B,andC.
E
What are the major purpose(s) for which organisms require energy? A) the performance of mechanical work B) active transport C) the synthesis of biomolecules D) A and C E) A, B, and C
E
Which activated carrier(s) contain(s) adenosine phosphate units? A) NADH B) FADH2 C) coenzyme A D) A and B E) A, B, and C
E
Which of the following molecules has a higher phosphoryl-transfer potential than ATP? A) phosphoenolpyruvate B) creatine phosphate C) 1,3-bisphosphoglycerate D) A and B E) A, B, and C
E
The electron donor in most reductive biosyntheses is ____________.
NADPH
In aerobic organisms, the ultimate acceptor of electrons is/are ____________.
O2
What general factors contribute to the high phosphoryl-transfer potential of ATP?
Resonance stabilization, electrostatic repulsion, and stabilization due to hydration are important.
How is metabolism controlled?
The amounts of enzymes and their catalytic activity are two controllable aspects of metabolism. Substrate accessibility is also important.
Draw the resonance structures of orthophosphate and explain why these structures are not significant in ATP.
The answer would be as shown in Figure 15.5 in the textbook. Each resonance structure would have an overall −2 charge. These structures do not contribute to the stabilization of ATP because the positively charged oxygen is next to a positively charged phosphorus.
If many compounds are common to both anabolic and catabolic paths, how can metabolism be controlled?
The enzymes and their activities can be controlled by the energy charge in the cell. The biosynthetic and catabolic paths are different from each other and may even be located in different compartments in the cell. Thus the two opposing processes can be controlled independently.
Explain how a metabolic pathway can contain an energetically unfavorable reaction yet still occur.
The free-energy changes of the individual steps in a pathway are summed to determine the overall free-energy change. Thus, a step that might not normally occur can be driven if it is coupled to a thermodynamically stable reaction.
What is oxidative phosphorylation?
The process by which ATP is formed by the phosphorylation of ADP using the energy of the proton gradient that was generated by the transfer of electrons from reduced coenzymes to oxygen.
Why are fats a more efficient fuel source than carbohydrates?
When any fuel molecule is oxidized, the free energy released is used to generate ATP. In that carbohydrates are already more oxidized than fats, less energy is released in the complete oxidation to CO2
What is the relationship between the energy charge of a cell and control of the ATP-generating pathway?
When the energy charge is high, ATP-generating pathways are inhibited and visa versa.
____________ pathways can be either anabolic or catabolic, depending on the energy conditions of the cell.
amphibolic
____________ are organisms that obtain chemical energy from the oxidation of foodstuffs.
chemotrophs
____________: This compound serves as an acyl carrier in metabolism.
coensyme A
A thermodynamically unfavorable reaction can be driven by a thermodynamically favorable reaction to which it is _________________.
coupled
In vertebrate muscle, _________________ serves as a reservoir of high-potential phosphoryl groups that can be readily transferred to ADP to regenerate ATP.
creatine phosphate
ATP-generating (catabolic) pathways are inhibited by a _________________ energy charge.
high
The electron carrier, NADH, is derived from the ____________ vitamin.
niacin
ATP is considered an "energy rich" compound because it contains two ______________ bonds.
phosphoanhydride
____________ are organisms that use energy from sunlight and convert it to chemical energy.
phototrophs
FAD is an electron carrier that is derived from the vitamin _________________.
riboflavin
One way that metabolism is regulated is through control of the accessibility of _________________.
substrates
The acetyl group is attached to coenzyme A by a(n) _________________ bond.
thioester
The small organic compounds, ____________, are required in the diet of higher organisms and are components of coenzymes.
vitamins
