Biochem Exam 3

Choose all the true statements about the electron transport chain.

The electron transport chain (ETC), or respiratory chain, is linked to proton movement and ATP synthesis. Select the statements that accurately describe the electron transport chain. Choose all that apply.

Without using a textbook, predict the sequence of electron transport carriers (the sequence of participants in the redox reactions) in the electron transport chain. A table of standard reduction potentials is given for reference.

Determine which complex of the electron transport chain (respiratory chain) each phrase describes.

When considering free energy change, biochemists define a biochemical standard state, ΔG°', which differs from the chemical standard state, ΔG°. A similar distinction must be made with reduction potentials. In contrast to the chemical reduction potential, ΔE°, the biochemical standard reduction potential, ΔE°'. Why might the standard reduction potential for a reaction differ from the reduction potential found in a cell?

ΔG°' = -nFΔE°

As part of the malate-aspartate shuttle, the malate-α-ketoglutarate transporter transfers malate formed in the cytosol to the mitochondrion. The malate-α-ketoglutarate transporter is inhibited by n-butylmalonate. When n-butylmalonate is added to an aerobic suspension of kidney cells using glucose as the primary source of energy, ATP synthesis drastically decreases. Select the statements that explain why the addition of n-butylmalonate causes a decrease in ATP synthesis.

Although some citric acid cycle enzymes operate primarily in the mitochondria, malate dehydrogenase operates in both the cytosol and the mitochondria. Match each function to cytosolic malate dehydrogenase or mitochondrial malate dehydrogenase.

The following statements concern the relationship between mitochondrial hydrogen ion concentration and energy storage as ATP during oxidative phosphorylation. Classify each statement as either accurate or inaccurate.

ATP synthase, shown below, uses the proton (H ) gradient to drive ATP synthesis. Put the following steps of ATP synthesis in order from proton transport to the synthesis of ATP:

The adenine nucleotide translocase (ADP-ATP translocase), a transporter located in the inner mitochondrial membrane, transports ADP and ATP across the membrane. It is an antiporter. (Recall that these adenine nucleotides are negatively charged: ADP3- and ATP4-.) Phosphate translocase is also located in the inner mitochondrial membrane. It transports H and phosphate (H2PO4-) across the membrane. It is a symporter. Answer parts (a), (b), (c), and (d) below. (a) Which direction is ATP4- transported during times of active oxidative phosphorylation? (b) What drives the transport of adenine nucleotides? (c) What is the ratio of ADP to ATP transported by the adenine nucleotide translocase? That is, how many ADP are transported for each ATP transported? (d) What drives the transport of H2PO4- across the membrane? Which direction is it transported during oxidative phosphorylation?

The energy derived from the movement of H ions down an electrochemical gradient from the intermembrane space into the matrix is used to drive the synthesis of ATP. How many H ions must be moved into the matrix for the synthesis of 1 ATP?

Which of the following regulate oxidative phosphorylation under hypoxic conditions?

Louis Pasteur observed that when oxygen is introduced to cells consuming glucose at a high rate in an anaerobic environment, fermentation ceases and the rate of glucose consumption decreases. This phenomenon is called the Pasteur effect. The basis of this effect is the shift from fermentation to oxidative phosphorylation to regenerate NAD . Additionally, the cells also synthesize ATP through oxidative phosphorylation. In respiration-deficient yeast mutants that lack cytochrome oxidase, the Pasteur effect is not seen. Select the reasons why the absence of cytochrome oxidase eliminates the Pasteur effect?

Which of the following is the major regulator of oxygen consumption during oxidative phosphorylation?

n mitochondria the rate of electron transfer is tightly coupled to the demand for ATP. When the rate of use of ATP is relatively low, the rate of electron transfer is low; when demand for ATP increases, electron-transfer rate increases. Under these conditions of tight coupling, the number of ATP molecules produced per atom of oxygen consumed when NADH is the electron donor, the P/O ratio, is about 2.5. Predict what would happen when an uncoupling agent, such as 2,4-dinitrophenol, is added to an actively respiring tissue preparation. Ingestion of uncouplers causes profuse sweating and an increase in body temperature. Explain this phenomenon in molecular terms.

The reduced coenzymes generated by the citric acid cycle donate electrons in a series of reactions called the electron transport chain. The energy from the electron transport chain is used for oxidative phosphorylation. For each part, select all that apply. (a) Which compounds donate electrons to the electron transport chain? (b) Which of the following is the final electron acceptor? (c) Which of the following are the final products of the electron transport chain and oxidative phosphorylation?

Which of the following options shows the correct order that each electron carrier first appears in the electron transport system?

The citric acid cycle occurs in the: The electron transport chain is located in the: Oxidative phosphorylation takes place in the:

Identify the statements that accurately describe how hydrogen ion concentration relates to energy production in oxidative phosphorylation.

Reactive oxygen species (ROS) are unstable, or reactive, compounds that result from the partial reduction of oxygen. ROS can cause damage to molecules, including membrane lipids and nucleic acids, and may be associated with some diseases. Which of the following compounds are reactive oxygen species? Choose all that apply.

Place three sentences from the list into the correct order to describe the synthesis of ATP by ATP synthase. Only three sentences are accurate; four are inaccurate. Scroll down to see all the phrases. (O is the open site, L is the loose site, and T is the tight site.)

Select the true statements regarding non-shivering thermogenesis.

Choose all the true statements about the oxidative phosphorylation.

Cytochromes are critical participants in the electron transport chains used in photosynthesis and cellular respiration. How do cytochromes donate and accept electrons?

The yield of ATP by the mitochondrial ATP synthase can be estimated by the number of protons pumped out of the matrix during the oxidation of NADH and FADH2, and the number of protons moved into the matrix as ATP is formed. Mitochondrial oxidation of NADH by O2 results in the transport of ten protons from the matrix to the intermembrane space, while oxidation of FADH2 results in the transport of six protons. ATP synthase utilizes three protons from the intermembrane space to form one ATP. Use the information given above to make the following calculations. Note: Recent data on ATP synthase suggests that the number of protons required per ATP varies with the number of c subunits. Here, an approximate value of 3 protons/ATP is used. How many ATP are formed per NADH oxidized? How many ATP are formed per FADH2 oxidized? The ATP yields calculated above do not consider other mitochondrial components that affect the proton gradient during ATP synthesis. When these other components are considered, the number of ATP produced per FADH2 oxidized is lowered to 1.5. Choose the statement(s) that correctly describe the reason for the lower yield of ATP.

Do fatty acid synthesis and degradation occur in the same location of the cell? Where does fatty acid degradation occur in the cell?

Complete the sentences to correctly describe steps in fatty acid synthesis. Move the terms to the appropriate blanks. Some terms will not be used, and some will be used more than once. Scroll down to see all the terms. Note that a single red X will appear if you answer any of the blanks incorrectly. Feedback will be placed next to a blank that is incorrectly filled.

Which of the following are components of animal fatty acid synthase (FAS)? Select all that apply.

Lipogenesis, or fatty acid synthesis, occurs in several cycles. A diagram of the reactions of the first cycle of fatty acid synthesis is shown below. Which of the following statements are true? Select all the true statements.

A diagram of the reactions of the first round of fatty acid synthesis (lipogenesis) is shown below. How many cycles of the synthesis pathway are needed to produce myristic acid, C13H27COOH? (14 carbons)

Sort the following phrases as they pertain to fatty acid synthesis or fatty acid oxidation. Note: If you answer any part of this question incorrectly, a single red X will appear indicating that one or more of the terms are placed incorrectly.

A nutrition researcher finds that placing young rats on a completely fat-free diet results in abnormal growth, unhealthy skin and fur, and a shortened lifespan. However, if the fat-free diet is supplemented with plant material, then the young rats show none of these symptoms. Which of the following statements explain why plant material prevents the symptoms?

Which of the following molecules regulate the enzyme that catalyzes malonyl-CoA synthesis? Which of the following enzymes does malonyl-CoA regulate? Inhibits fatty acid synthesis? Inhibits beta oxidation?

The acetyl group of acetyl-CoA, produced by oxidative decarboxylation of pyruvate in the mitochondrion, is transferred to the cytosol by the acetyl group shuttle. Similarly, the acyl group shuttle (the carnitine shuttle) transfers the fatty acyl group from the cytosol to the mitochondrion in preparation for β oxidation. Select the statements that describe the similarities or differences between the acetyl group shuttle and the acyl group shuttle.

After digestion of a large carbohydrate meal, monosaccharides that exceed caloric requirements are diverted into the synthesis of fatty acids and triacylglycerol. Fatty acid synthesis consumes acetyl-CoA, ATP, and NADPH. These three compounds can be made from glucose at the same time that glucose is being processed for fatty acid synthesis. Complete the statements below by moving terms to the appropriate blanks.

In what organelle or membrane are triacylglycerols synthesized and fatty acids elongated?

Phosphatidate (phosphatidic acid), shown below, is a precursor in the synthesis of some lipids. Identify the lipids that have phosphatidate as a precursor.

The synthesis of phosphatidylcholine has alternate pathways. In mammals, for example, phosphatidylcholine (PC) can be synthesized by two pathways -a pathway that begins with choline and a pathway that includes phosphatidylethanolamine. Determine whether each of the following describes PC synthesis from choline or from phosphatidylethanolamine.

A young rat maintained on a diet deficient in methionine fails to thrive unless choline is included in the diet. Choose the best explanation.

Which of the following are true about the synthesis of various lipids? Select all the true statements.

Cholesterol synthesis

The synthesis of cholesterol is a process that involves over 30 different steps. Which step is the rate-determining step of cholesterol synthesis?

The HMG-CoA reductase reaction (the rate-limiting step) is a major feedback control point for cholesterol synthesis. Which of the following stimulate the degradation of HMG-CoA reductase enzyme by proteolysis? Select all that apply.

Determine the order of the intermediates in the biosynthesis of cholesterol.

Four major serum lipoproteins are listed below. Identify the primary function of each and the major apoproteins found in each by dragging the labels to the appropriate bins.

Chylomicrons, VLDL, and LDL transport triacylglycerols (TAGs) and cholesterol in the blood. All three of these lipoproteins contain an apoC-II component. Identify one reason this is significant.

Lipoproteins are globular structures that are responsible for transporting lipids through the blood stream. Two types of lipoproteins are LDL and HDL. Sort each statement as applying to LDL, HDL, or both.

Lipids are transported in the blood in complexes with proteins. These water-soluble complexes are called lipoproteins. Complete the sentences below by selecting the lipoprotein that transports each lipid.

Sort each of the phrases as describing exogenous cholesterol transport, endogenous cholesterol transport, or reverse cholesterol transport.

The percent composition by mass is given for each of several plasma lipoproteins. Which is the most soluble and most dense? Which is the least soluble and least dense?

Which two of the following phrases describing the synthesis of amino acids are accurate? Select all the true statements.

Non-essential amino acids

Two of the 20 commonly occurring amino acids contain a sulfur atom. Identify the most direct source of the sulfur atom in these amino acids in humans.

Glyphosphate binds noncovalently to the S3P-EPSP synthase complex, preventing PEP from binding. In mutants that do not bind glyphosphate, the affinity for the substrate S3P is also reduced. What type of inhibition is this? There is more than one correct answer. Glyphosate kills plants, but is considered nontoxic, or of low toxicity, to animals. Why?

Individuals with a genetic defect in phenylalanine hydroxylase require an additional amino acid in their diet which is not an essential amino acid in the ordinary human diet. Which nonessential amino acid has become essential because of the lack of phenylalanine hydroxylase?

The table below lists several neurotransmitters, some neurotransmitter functions, and amino acid precursors. Complete the tabe by moving the labels to the appropriate targets. Click here to view a table of amino acids. Not all labels will be used. Some labels may be used more than once.

Classify the following statements based on whether they represent true or false statements about heme.

Inosine monophosphate (IMP), product of the de novo purine biosynthetic pathway, can serve as a precursor of both GMP and AMP. Complete the pathways for the synthesis of GMP and AMP by filling in the blanks with the appropriate item from the list at the right. Which cofactor inhibits the first step of the GMP pathway? Which cofactor inhibits the first step of the AMP pathway?

A flow chart for the de novo synthesis of pyrimidine nucleotides is shown below. (a) Add intermediates to show the general outline for the synthesis of a pyrimidine nucleotide. (PRPP is the abbreviation for 5-phosphoribosyl-1-pyrophosphate.) (b) Which of the intermediates are also intermediates in at least one other pathway? Both the intermediate and the pathway must be correct.

In humans, the multifunctional enzyme uridine 5'-monophosphate (UMP) synthase has orotate phosphoribosyltransferase (OPRT) and orotidylate decarboxylase (ODC) activity. Both enzyme functions are impaired in persons with orotic aciduria. Which of the following is present at high levels in the urine of patients with orotic aciduria?

Compare and contrast the de novo synthesis of purine and pyrimidine ribonucleotides. Move each item to the appropriate bin. If a phrase does not describe either purine or pyrimidine ribonucleotide synthesis, move it to the "Neither" bin.

The diazo compound O-(2-diazoacetyl)-L-serine, known also as azaserine, is a powerful inhibitor of glutamine amidotransferases. If growing cells are treated with azaserine, what intermediates of nucleotide biosynthesis will accumulate?

Under starvation conditions cells deaminate amino acids to produce carbon skeletons that enter the glycolytic pathway and the citric acid cycle to generate ATP. Nucleotides, on the other hand, are not broken down to yield energy. Select the statements that describe how cells metabolize nucleotides.

Ribonucleotide reductase is one of the best-characterized examples of an enzyme involving free radicals. The enzyme from E. coli has a stable tyrosyl radical that is generated and stabilized by a nearby binuclear iron-oxygen center. Which of the following statements describes the role of this tyrosine radical in the mechanism of the reaction that conerts a nucleotide to a deoxynucleotide?

Identify the correct statements about Lesch-Nyhan syndrome.

Amino acid precursors for purines and pyrimidines?

When amino acids bind a transaminase enzyme, their amino group is transferred to ___________ associated with the transaminase before it is transferred to an alpha-keto acid.

Select the statements that correctly describe pyridoxal phosphate (PLP).

Allopurinol is a drug used to treat gout, which is caused by a buildup of sodium urate crystals. Allopurinol has a structure similar to hypoxanthine, and can bind the enzyme that acts on hypoxanthine as a suicide inhibitor (a type of irreversible inhibitor). What enzyme does allopurinol inhibit? In what form are the waste products of purine catabolism excreted under this treatment? Choose two answers.

S-Adenosylmethionine (abbreviated adoMet or SAM) is a methyl group donor in numerous metabolic pathways, including the metabolism of lipids and amino acids. Which of the following descriptions of S-adenosylmethionine are accurate? Check all that apply.

The synthesis of deoxyribonucleotides is controlled by the regulation of ribonucleotide reductase. There are two regulatory allosteric sites on the R1 subunit. One regulates the overall activity of the enzyme, and the other regulates the substrate specificity of the enzyme. Which statement about the site regulating overall activity is true?