Multiple choice questions- Biological Oxidation

Q.1-Out of the following respiratory chain components indicate which  one is a mobile carriers of electrons?

a)Cytochrome oxidase

b)NADH-Q reductase

c)Ubiquinone

d)Succinate dehydrogenase                                              (c)

Q.2-Choose the incorrect statement about redox potential

a)The redox potential of a system (E₀) is usually compared with the potential of the hydrogen electrode

b)The components of electron transport chain are organized in terms of their redox potential.

c)NADH/NAD⁺ redox pair has the least redox potential of -0.42 volts

d)Oxygen/H₂O redox pair has the highest redox potential of +.82 volts

                                                                                           (c)

Q.3-All are flavoproteins except one, choose the odd one out

a)Xanthine oxidase

b)NADH dehydrogenase –Q reductase

c)Succinate dehydrogenase

d)Cytochrome c                                                                 (d)

Q.4-All except one are incorrect about oxidases-

a)Oxidases catalyze reactions involving hydrogen peroxide.

b)Oxidases catalyze reaction using oxygen as a hydrogen acceptor

c)Oxidases catalyze  reactions using Niacin as coenzyme

d)Oxidases catalyze reactions of direct incorporation of oxygen in to the substrate

                                                                                          (b)

Q.5-All of the followings are NAD⁺ requiring enzymes except one -

a)Acyl co A dehydrogenase

b)Glyceraldehyde-3-P dehydrogenase

c)Pyruvate dehydrogenase complex

d)Malate dehydrogenase

                                                                                          (a)

Q.6-One out of the following enzymes can utilize both NAD⁺ and NADP⁺as a coenzyme

a)Aldehyde dehydrogenase

b)Alcohol dehydrogenase

c)Glutamate dehydrogenase

d)Glycerol-3-P dehydrogenase

                                                                                      (c)

Q.7-Which out of the following components is not a haemo protein?

a)Catalase

b)Peroxidase

c)Ubiquinone

d)Cytochrome c                                                               (c)

Q.8-Dioxygenasescatalyze the incorporation of both atoms of oxygen in to the substrate. Which out of the following is a dioxygenase?

a)Tryptophan pyrrolase

b)Lactate dehydrogenase

c)Cytochrome oxidase

d)L- amino acid oxidase                                                   (a)

Q.9-Which of the components of electron transport chain does not contain Iron sulfur center?

a)NADH dehydrogenase complex

b)Cytochrome a-a3 oxidase

c)Succinate dehydrogenase

d)Cytochrome bc₁-c reductase                                          (b)

Q.10-A child has accidentally ingested a chemical and has presented with high fever.The chemical is known to affect ATP formation in electron transport chain,which out of the followings could cause the similar manifestations

a)Cyanide

b)Malonate

c)2,4 dinitrophenol

d)Rotenone                                                                     (c)

Q.11-A 32- year female working in a laboratory consumed cyanide and was rushed to hospital .She was declared dead upon reaching the hospital. Cyanide is a known inhibitor of Electron Transport chain (ETC). Which complex of ETC might have been inhibited?

a)Complex I

b)Complex II

c)Complex III

d)Complex IV        

                                                                                      (d)

Q.12-The enzymes of mitochondrial matrix include all except

a)Enzymes of fatty acid oxidation

b)Creatine kinase

c)Enzymes of TCA cycle

d)Pyruvate dehydrogenase complex

                                                                                      (b)

Q.13-Patients with inherited defects of mitochondria involving components of the respiratory chain and oxidative phosphorylation present with all except

a)Myopathy

b)Lactic acidosis

c)Encephalopathy

d)Hepatomegaly

                                                                                      (d)

Q.14-The inner mitochondrial membrane is rich in which of the following phospholipids?

a)Cardiolipin

b)Lecithin

c)Cephalin

d)None of the above                                                        (a)

Q.15-All are true about ATP synthase complex, except

a) F₁projects into the inter membranous space

b) F₀spans the membrane and forms a proton channel.

c) F₀is inhibited by Oligomycin

d) F₁containsthe phosphorylation mechanism                     (a)

Q.16-The energy yield during the conversion of succinate to Fumarate is-

a) 2ATP

b) 1ATP

c) 3ATP

d) No ATP                                                                        (a)

Q.17-Which of the following best describes the biochemical basis of hyperthermia associated with Aspirin toxicity

a)Increased fatty acid oxidation

b)Increased muscular activity

c)Elevated consumption of ATP to support muscle contraction

d)Uncoupling of oxidative phosphorylation                       

                                                                                      (d)

Q.18-The electron flow from complex I to complex III is through

a)Cytochrome c

b)Ubiquinone

c)Complex II

d)Complex IV

                                                                                      (b)

Q.19-Which of the followings best describes the toxicity associated with Atractyloside

a)Acts as an inhibitor of ETC

b)Acts as an uncoupler

c)Acts as an inhibitor of ATP/ADP transporter

d)Inactivates ATP synthase complex

                                                                                      (c)

Q.20- For each H₂O molecule formed in ETC around ———– protons are pumped into

inter membranous space

a) 4

b) 2

c) 10

d) None of the above

                                                                                      (c)

Q.21- Which one of the following enzymes catalyzes substrate level phosphorylation in TCA cycle

a) Malate dehydrogenase

b) Succinate Thiokinase

c) Succinate dehydrogenase

d) Alpha keto glutarate dehydrogenase complex

                                                                                        (b)

Q.22- Which of the following occurs in non shivering thermogenesis?

a) Glucose is oxidized to lactate

b) Fatty acids uncouple oxidative phosphorylation

c) ATP is spent for heat production

d) Glycogen is excessively degraded

                                                                                          (b)

Q.23- One out of the following is an inhibitor of complex I

a) Rotenone

b) H₂S

c) BAL

d) CN

                                                                                            (a)

Q.24- Which out of the following statements concerning the components of electron transport chain is true?

a) Oxygen directly oxidizes Cytochrome c

b) Succinate dehydrogenase directly reduces Cytochrome c

c) All of the components are embedded in the inner mitochondrial membrane

d) Cyanide does not inhibit proton pumping but inhibits ETC

                                                                                              (d)

Q.25- The free energy released during the transport of a pair of electrons in electron transport chain is

a) 7.3 Kcal/mol

b) 52.6 Kcal/mol

c) 21.9 Kcal/mol

d) None of the above

                                                                                               (b)

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Multiple Choice Questions- Amino acid metabolism

Q.1- Which of the following is a common compound shared by the TCA cycle and the Urea cycle?

a) α- Keto glutarate

b) Succinyl co A

c) Oxalo acetate

d) Fumarate

Q.2-Which of the followings is a common nitrogen acceptor for all reactions involving transaminases?

a) α- Keto glutarate

b) Pyruvate

c) Oxaloacetate

d) Acetoacetate

Q.3- In a 55- year-old man, who has been diagnosed with cirrhosis of liver, Ammonia is not getting detoxified and can damage brain. Which of the following amino acids can covalently bind ammonia, transport and store in a non toxic form?

a) Aspartate

b) Glutamate

c) Serine

d) Cysteine

Q.4- In a new born presenting with refusal to feeds and irritability, a deficiency of Cystathionine –β- synthase has been diagnosed, which of the following compounds is expected to be elevated in blood?

a) Serine

b) Glutamate

c) Homocysteine

d) Valine

Q.5 -A 3- month-old child is being evaluated for vomiting and an episode of convulsions, Laboratory results show hyperammonemia and Orotic aciduria. Which of the following enzyme defect is likely to be there?

a) Glutaminase

b) Arginase

c) Argino succinic acid synthase

d) Ornithine Transcarbamoylase

Q.6- Which out of the following amino acids is not converted to Succinyl co A?

a) Methionine

b) Valine

c) Isoleucine

d) Histidine

Q.7-All of the following compounds are synthesized by transmethylation reactions, except-

a) Choline

b) Epinephrine

c) Creatine

d) Ethanolamine

Q.8- A patient diagnosed with Hart Nup disease, (due to deficiency of transporter required for the absorption of amino acid tryptophan), has been brought with skin rashes and suicidal tendencies. Tryptophan is a precursor for many compounds, the deficiencies of which can cause the said symptoms. Which out of the following compounds is not synthesized by tryptophan?

a) Serotonin

b) Epinephrine

c) Melatonin

d) Niacin

Q.9- Histamine, a chemical mediator of allergies and anaphylaxis, is synthesized from amino acid Histidine by which of the following processes?

a) Deamination

b) Decarboxylation

c) Transamination

d) Dehydrogenation

Q.10- The synthesis of all of the following compounds except one is deficient in a patient suffering from Phenylketonuria-

a) Melanin

b) Melatonin

c) Catecholamines

d) Thyroid hormone

Q.11- The diet of a child suffering from Maple syrup urine disease (an amino acid disorder), should be low, in which out of the following amino acids content?

a) Branched chain amino acids

b) Phenylalanine Alanine

c) Methionine

d) Tryptophan

Q.12- Which out of the following amino acids in not required for creatine synthesis?

a) Methionine

b) Serine

c) Glycine

d) Arginine

Q.13- All of the following substances are synthesized from Cysteine, except-

a) Taurine

b) Mercaptoethanolamine

c) Melanin

d) Pyruvate

Q.14- Urea is synthesized in -

a) Cytoplasm

b) Mitochondria

c) Both cytoplasm and mitochondria

d) In lysosomes

Q.15-Blood urea decreases in all of the following conditions, except-

a) Liver cirrhosis

b) Pregnancy

c) Renal failure

d) Urea cycle disorders

Q.16- All of the following amino acids are donors of one carbon compounds except-

a) Histidine

b) Tyrosine

c) Tryptophan

d) Serine

Q.17- The two nitrogen of urea are derived from-

a) Aspartate and Ammonia

b) Glutamate and ammonia

c) Argino succinate and ammonia

d) Alanine and ammonia

Q.18- Which out of the following amino acids is not required for the synthesis of Glutathione?

a) Serine

b) Cysteine

c) Glutamic acid

d) Glycine

Q.19- The first line of defence in brain in conditions of hyperammonemia is-

a) Urea formation

b) Glutamine synthesis

c) Glutamate synthesis

d) Asparagine formation

Q.20- Which coenzyme out of the followings is required for the oxidative deamination of most of amino acids?

a) Folic acid

b) Pyridoxal- P

c) FMN

d) FAD

Q.21-Chose the incorrect statement about amino acid Glycine-

a) One carbon donor

b) Required for the synthesis of haem

c) Forms oxalates upon catabolism

d) Both glucogenic as well as ketogenic

Q.22- Which out of the followings is required as a coenzyme for the transamination reactions?

a) Coenzyme A

b) Pyridoxal-P

c) Folic acid

d) Cobalamine

Q.23- A patient diagnosed with Homocystinuria should be supplemented with all of the following vitamins except-

a) Vitamin C

b) Folic acid

c) Vitamin B12

d) Pyridoxal- P

Q.24- In a patient suffering from Cystinuria, which out of the following amino acids is not seen in urine of affected patients?

a) Arginine

b) Methionine

c) Lysine

d) Ornithine

Q.25- Positive nitrogen balance is seen in all of the following conditions except-

a) Pregnancy

b) Growth

c) Fever

d) Convalescence

Q.26- The L-amino acids are absorbed from intestine by-

a) Active transport

b) Passive diffusion

c) Pinocytosis

d) Facilitated diffusion

Q.27- A child presented with increased frequency of urination, photophobia and impairment of vision. Which out of the following defects could be responsible for the said symptoms?

a) Tyrosinosis

b) Cystinosis

c) Alkaptonuria

d) Albinism

Q.28- Which out of the following statements about Glutamate dehydrogenase is correct?

a) Required for transamination reactions

b) Universally present in all the cells of the body

c) Can utilize either of NAD⁺ /NADP⁺

d) Catalyzes conversion of glutamate to glutamine

Q.-29-A child was brought to paediatric OPD with complaint of passage of black colored urine. A disorder of Phenylalanine metabolism was diagnosed. A low phenylalanine diet and a supplementation of vitamin C were recommended. Which enzyme defect is expected in this child?

a) Phenyl alanine hydroxylase

b) Tyrosine transaminase

c) Homogentisic acid oxidase

d) Hydrolase

Q.30- Dopamine is synthesized from which of the following amino acids?

a) Tyrosine

b) Tryptophan

c) Histidine

d) Methionine

Q.31- In mammalian tissue serine can be a biosynthetic precursor for which amino acid?

a) Methionine

b) Glycine

c) Arginine

d) Lysine

Q.32- Hydroxylation of Phenyl Alanine to Tyrosine requires all except-

a) Glutathione

b) Tetra hydrobiopterin

c) Molecular oxygen

d) NADPH

Q.33- The amino acid that undergoes oxidative deamination at a highest rate is-

a) Glutamine

b) Glutamate

c) Aspartate

d) Alanine

Q.34- All of the following statements regarding serotonin are true except-

a) Causes vasodilatation

b) Causes broncho constriction

c) Metabolized to 5-hydroxy Indole acetic acid

d) Causes diarrhoea

Q.35- Choose the incorrect statement about cysteine-

a) Carbon skeleton is provided by serine

b) Sulfur group is provided by Methionine

c) Forms Hippuric acid for detoxification of xenobiotics

d) Required for Bile salt formation

 Answers-

1)-d, 2)-a, 3)- b, 4) -c, 5)-d, 6) -d, 7)-d, 8)-b, 9) -b, 10)-b, 

11)-a), 12)-b, 13)-c, 14)-c, 15)-c,16)-b, 17)-a, 18)-a, 19)-b, 20)-c

21)-d, 22)-b,23)-a,24)-b, 25)-c, 26)-a, 27)-b,28)-c, 29)-c, 30)-a

31)-b,32)-a,33)-b, 34)-a,35)-c

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Fatty acid synthesis versus fatty acid oxidation

“Although chemical processes involved are the same but Fatty acid synthesis is not simply a reversal of fatty acid oxidation”.             

Fatty acid synthesis seems simply a reversal of the degradative pathway, but it consists of a new set of reactions, exemplifying the principle that synthetic and degradative pathways are almost always distinct.Some important differences between the pathways are:

1. Synthesis takes place in the cytosol, in contrast with degradation, which takes place primarily in the mitochondrial matrix.

2. Intermediates in fatty acid synthesis are covalently linked to the sulfhydryl groups of an acyl carrier protein (ACP), whereas intermediates in fatty acid breakdown are covalently attached to the sulfhydryl group of coenzyme A.

3. The enzymes of fatty acid synthesis in higher organisms are joined in a single polypeptide chain called fatty acid synthase. In contrast, the degradative enzymes do not seem to be associated.

4. The growing fatty acid chain is elongated by the sequential addition of two-carbon units derived from acetyl CoA. The activated donor of two carbon units in the elongation step is malonylACP. The elongation reaction is driven by the release of CO2.

5. The reductant in fatty acid synthesis is NADPH, whereas the oxidants in fattyacid degradation are NAD ⁺ and FAD.

6. Elongation by the fatty acid synthase complex stops on formation of Palmitate(C16). Further elongation and the insertion of double bonds are carried out by other enzyme systems.

Over view of fatty acid oxidation- The process of degradation converts an aliphatic compound into a set of activated acetyl units (acetyl CoA) that can be processed by the citric acid cycle. An activated fatty acid is oxidized to introduce a double bond; the double bond is hydrated to introduce oxygen; the alcohol is oxidized to a ketone; and,finally, the four carbon fragment is cleaved by coenzyme A to yield acetyl CoA and a fatty acid chain two carbons shorter. If the fatty acid has an even number of carbon atoms and is saturated, the process is simply repeated until the fatty acid is completely converted into acetyl CoA units. (Figure)

Overview of fatty acid synthesis- Fatty acid synthesis is essentially the reverse of this process. Because the result is a polymer, the process starts with monomers in this case with activated acyl group (most simply, an acetyl unit) and malonyl units (see Figure). The malonyl unit is condensed with the acetyl unit to form a four-carbon fragment. To produce the required hydrocarbon chain, the carbonyl must be reduced. The fragment is reduced, dehydrated, and reduced again, exactly the opposite of degradation, to bring the carbonyl group to the level of a methylene group with the formation of butyryl CoA. Another activated malonyl group condenses with the butyryl unit and the process is repeated until a C16 fatty acid is synthesized. (See figure)

 

Figure-Showing the chemical processes involved in fatty acid synthesis and oxidation

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General structure and classification of lipoproteins

Lipids absorbed from the diet and synthesized by the liver and adipose tissue must be transported between various cells and organs for utilization and storage. Since lipids are insoluble in water, the problem of transportation in the aqueous plasma is solved by associating nonpolar lipids (triacylglycerols and cholesteryl esters) with amphipathic lipids(phospholipids and cholesterol) and proteins to make water-miscible Lipoproteins.

General Structure of Lipo protein

 Lipoproteins Consist of a Nonpolar Core & a Single Surface Layer of Amphipathic Lipids

The nonpolar lipid core consists of mainly triacylglycerol and cholesteryl ester and is surrounded by a single surface layer of amphipathic phospholipid and cholesterol molecules (Figure-1). These are oriented so that their polar groups face outward to the aqueous medium. The protein moiety of a lipoprotein is known as an apolipoprotein or apoprotein,constituting nearly 70% of some HDL and as little as 1% of Chylomicons. Some apolipoproteins are integral and cannot be removed, whereas others can be freely transferred to other lipoproteins.

 

Figure-1- showing general structure of lipoprotein

 Classification of Lipoproteins

 Lipoproteins can be classified in three ways-

 1) Based on density

Because fat is less dense than water, the density of a lipoprotein decreases as the proportion of lipid to protein increases.  Lipoproteins with high lipid content will have low density and so float on centrifugation. Those with high protein content sediment easily and have a high density. They are separated by Ultracentrifugation. Depending upon the floatation constant (Sf), Five major groups of lipoproteins have been identified that are important physiologically and in clinical diagnosis. These are

 (i) Chylomicons, derived from intestinal absorption of triacylglycerol and other lipids; Density is generally less than0.95 while the mean diameter lies between 100- 500 nm

 (ii) Very low density lipoproteins(VLDL), derived from the liver for the export of triacylglycerol; density lies between 0.95- 1.006 and the mean diameter lies between 30-80 nm.

 (iii) Intermediate density lipoproteins (IDL) are  derived from the catabolism of VLDL,with a density  ranging intermediate between Very low densityand Low density lipoproteins i.e. ranging between 1.006-1.019 and the meandiameter ranges between 25-50nm.

 (iv)Low-density lipoproteins (LDL), representing a final stage in thecatabolism of VLDL; density lies between 1.019-1.063 and mean diameter lies between 18-28 nm

 (iv) High-density lipoproteins (HDL),involved in cholesterol transport and also in VLDL and chylomicron metabolism. Density ranges between 1.063-1.121 and the mean diameter varies between 5-15 nm. (Table)

Figure- 2-showing the relationship of density and mean diameter of lipoproteins

Triacylglycerol is the predominant lipid in chylomicron and VLDL, whereas cholesterol and phospholipid are the predominant lipids in LDL and HDL, respectively. (Table)

 2) Based on electrophoretic mobilities

Lipoproteins may be separated according to their electrophoretic properties into alpha , beta, pre-beta,and broad beta lipoproteins. The mobility of a  lipoprotein is mainly dependent upon protein content. Those with higher protein content will move faster towards the anode and those with minimum protein content will have minimum mobility.

 HDL are alpha , LDLbeta, VLDL pre-beta, and IDL are broad beta lipoproteins. Free fattyacids and albumin complex although not a lipoprotein is an important lipid fraction in serum and is the fastest moving fraction. Chylomicons remain at the origin since they have more lipid content. VLDL with less protein content than LDL move faster than LDL, this is due to nature of apoprotein present.

Table- showing the composition of lipoproteins. As the lipid content increases, density decreases and size increases, that is why Chylomicons are least dense but biggest in size, while HDL are rich in proteins , hence most dense but smallest in size.

 3)Based on nature of Apo- protein content

 One or more apolipoproteins (proteins or polypeptides) are present in each lipoprotein. The major apolipoproteins of HDL Alpha Lipoproteins) are designated A.The main apolipoprotein of LDL (beta -lipoprotein) is apolipoprotein B(B-100), which is found also in VLDL. Chylomicons contain a truncated form of apo B (B-48) that is synthesized in the intestine, while B-100 is synthesized in the liver. Apo B-100 is one of the longest single polypeptide chains known,having 4536 amino acids and a molecular mass of 550,000 Da. Apo B-48 (48% ofB-100) is formed from the same mRNA as apo B-100 after the introduction of a stop signal by an RNA editing enzyme. Apo C-I, C-II, and C-III are smaller polypeptides (molecular mass 7000–9000 Da) freely transferable between several different lipoproteins. Apo E is found in VLDL, HDL, Chylomicons, andchylomicron remnants; it accounts for 5–10% of total VLDL apolipoproteins in normal subjects.

 Functions of Apoproteins- Apolipoproteins carry out several roles: 

 (1) They can form part of the structure of the lipoprotein, eg, apo B is a structural component of VLDL and Chylomicons

 (2)They are enzyme cofactors, e.g. C-II for lipoprotein lipase, A-I for lecithin: cholesterolacyl transferase (LCAT), 

 (3) They act as enzyme inhibitors, eg, apo A-II and apo C-III for lipoprotein lipase, apo C-I for cholesteryl ester transfer protein;

 (4)They act as ligands for interaction with lipoprotein receptors in tissues, eg,apo B-100 and apo E for the LDL receptor, apo A-I for the HDL receptor. The functions of apo A-IV and apo D, however, are not yet clearly defined, although apo D is believed to be an important factor in human neuro degenerative disorders and acts as cholesteryl ester transfer protein required for the exchange of triglycerides and cholesteryl esters between VLDL,chylomicron remnants and HDL.

 All apoproteins are synthesized mainly in liver but small amounts can be synthesized in almost all organs.

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