Concept explainers
Problem Set
QUANTITATIVE Succinate Oxidation. The oxidation of succinate to fumarate is an important cellular reaction because it is one of the steps in the citric acid cycle (see Figure 10-9). The two hydrogen atoms that are removed from succinate are accepted by a coenzyme molecule called flavin adenine dinucleotide (FAD), which is thereby reduced to FADH2:
ΔG°′ for Reaction 5-32 is 0 cal/mol.
(a) If you start with a solution containing 0.01 M each of succinate and FAD and add an appropriate amount of the enzyme that catalyzes this reaction, will any fumarate be formed? If so, calculate the resulting equilibrium concentrations of all four species. If not, explain why not.
(b) Answer part a assuming that 0.01 M FADH2 is also present initially.
(c) If the steady-state conditions in a cell are such that the FADH2/FAD ratio is 5 and the fumarate concentration is 2.5 μM, what steady-state concentration of succinate is needed to maintain ΔG′ for succinate oxidation at –1.5 kcal/mol?
Figure 10-9 The Citric Acid Cycle. The two carbon atoms of pyruvate that enter the cycle via acetyl CoA are shown in pink in citrate and subsequent molecules until they are randomized by the symmetry of the fumarate molecule. The carboxyl group of pyruvate that is lost as CO2 is shaded, as are the two carboxyl groups of oxaloacetate that give rise to CO2 in reactions CAC-3 and CAC-4. Five of the reactions are oxidations, with NAD+ as the electron acceptor in four reactions (PDH, CAC-3, CAC-4, and CAC-8) and FAD as the electron acceptor in one reaction (CAC-6). The reduced form of the coenzyme is shown in purple in each case. Note that when CO2 is released, no H+ is given off during NAD+ reduction, thereby maintaining the charge balance of these reactions. The generation of GTP shown in reaction CAC-5 is characteristic of animal mitochondria. In bacterial cells and plant mitochondria, ATP is formed directly.
Want to see the full answer?
Check out a sample textbook solutionChapter 5 Solutions
Becker's World of the Cell (9th Edition)
- Biochemical events in the synthesis of ATP: I. Subunits of ATP synthase chages in conformation and twists/rotates as H+ moves through it II. H+ gradient is the driving force (through the ATP synthase) to form ATP from ADP + Pi. III. H+ moving across the membrane through ATP synthase rotates its ring of c subunits II and III only I, II, III I and II only I and III onlyarrow_forward70 gram lactose working under aerobic conditions. First calculate the total amount of energy units (ATP, GTP, FADH2, NADH) obtained from its degradation to CO2 and H2O. Convert this value to total ATP units.Show your work in detail at each reaction step. Which energy units are obtained after each reaction step.arrow_forwardO BIOCHEMISTRY Understanding major biochemical energy storage and release. A certain anabolic biochemical reaction A has AG- 17.8 kJ mol , and is always coupled to another reaction B, which has two reactants and two products, I this: R + R2 P + P2 The molecule in the drawing area below is either R, or P. • If it's R, change it into P. But if it's P, change it into R. • In either case, draw the molecule as it would exist at physiological pH. • Also please answer the questions about Reaction B in the table below. OR, Was the molecule in the drawing area R, or P, before you changed it? What is R? Enter its common name, usual symbol, or chemical formula: What is P2? Enter its common name, usual symbol, or chemical formula: O BIOCHEMISTRY Understanding major biochemical energy storage and release.. ODO its common name, usual symbol, or chemical formula: NH, -CH N. H OH OH ...... to IIIarrow_forward
- Modified TRUE or FALSE. Write the word TRUE if the statement is correct. If the statement is false, write the incorrect underlined word/s and indicate the correct word/s to make the statement true. The Michaelis-Menten Constant (Km) of an enzyme is equal to the enzyme concentration at which the initial velocity of the reaction is one half of maximum velocity (Vmax).arrow_forwardM-CSA Mechanism and Catalytic Site Atlas (ebi.ac.uk) (ii) Acyl Carrier Protein S-acetyltransferase (EC 2.3.1.38) is a transferase enzyme that catalyzes the first biosynthetic pathway for fatty acid synthase. It transfers the acyl group (CH3CO) first from coenzyme A to a cysteine residue in the active site. This is similar to what happens in Chymotrypsin, however utilizing a sulfur instead of an oxygen. The acyl group is then transferred to the molecule ACP. Provide the enzyme- catalyzed mechanism for the reaction below, making sure to identify the roles of all key amino acids: i H3C SCOA acetyl COA enzyme + HS i H3C SACP acetyl ACParrow_forwardSelect all that apply. What is true about the conformational aspects of coupling? O The proton gradient is involved in the release of bound ATP from the synthase as a result of conformational change. O The conformational states interconvert as a result of proton flux through the synthase. There are two sites for substrate on the synthase and two possible conformational states: open (0) and tight-binding (T). Dinitrophenol binds to and inhibits ATP synthase conformational changes, thus inhibiting ATP synthesis. The Fo portion of ATP synthase acts as a rotary motor.arrow_forward
- Chemical labeling of chymotrypsin by the compound tosylphenylalanine chloromethyl ketone (TPCK) modifies the His 57 in the enzyme's active site. The structure of this derivative is shown below. TPCK inactivates the enzyme because the bulky addition prevents it from cleaving nearby covalent bonds. HCI + CH, C-O Chymotrypsin-His 57 TPCK Modified enzyme True O Falsearrow_forwardNeed help ASAP. Describe the steps by which the F0 portion of the ATP synthase harnesses the proton-motive force to help synthesize ATP. What would you expect to observe if the proton gradient were reversed? Explain your answer.arrow_forward. Pyruvate can be processed under anaerobic conditions to ethanol (in yeast) or to lactate (in mammals), as shown. Explain the primary purpose of these reactions. Describe the major biochemical features of each reactionarrow_forward
- Question #1: Choanoflagelletes are a unicellular ancestor to animals. One observation to support this hypothesis is the appearance of adhesion molecules that are key to the development of multiceullarity. Bulk transport Gap junctions Animals. Adhesion, cell signaling Single-celled :} Insects, mammals, and other animals with bilateral symmetry (~10,000,000) Jellyfish and their relatives (10,000) } Sponges (10,000) Choanoflagellates (150) Despite their simple unicellular lifestyle they express adhesion molecules including cadherins and lectins (King et al., 2003) but don't seem to have molecules that are typically found in the extracellular matrix such as integrins or laminins (Williams et al., 2014). Design a microscopy experiment to test the assertion that choanoflagellates have (some) adhesion molecules and those molecules play a similar role in a closely related animal like sponges.arrow_forwardHigh potential. What is the equilibrium ratio of phosphoenolpyruvate to pyruvate under standard conditions when [ATP ]/[ ADP ]=10? [ATP]/[ADP] = 10?arrow_forwardBiochemical Reactions Using good details, compare and contrast the pairs of different biochemical reactions. Create your own comparing and contrasting map similar to the one below to show your understanding. Anabolism Catabolism First Pair of Describe Describe differences here différences here Reaction Types Describe similarities here Second Describe Pair of differences here Reaction Types Describe similarties here Describe differences here Pair of Reaction Describe sampar lus heru Types Describe Par of 110 Describe differences here Describe différences here Describe differences herearrow_forward
- BiochemistryBiochemistryISBN:9781305577206Author:Reginald H. Garrett, Charles M. GrishamPublisher:Cengage Learning