Biochemistry Flashcards
The following can inhibit ATP synthesis by increasing the permeability of the inner mitochondrial membrane to protons, resulting in the loss of the proton gradient, EXCEPT:
A. 2, 4 dinitrophenol B. Aspirin C. Dimercarpol D. Thermogenin E. None of the above
C. Dimercarpol
Dimercarpol inhibits complex III of the Electron Transport Chain (ETC).
Uncouplers increase the permeability of the of the inner mitochondrial memebrane, the proton gradient is then lost without passing through the ATP synthase complex (complex V). Examples of uncouplers include aspirin & 2,4 dinitrophenol, which are synthetic, and the uncoupling protein thermogenin.
Which of the following pairs are examples of enantiomers?
A. D-Glucose and L-Glucose B. Glucose and Galactose C. Glucose and Mannose D. D-Glucose and D-Galactose E. α-D-Glucopyranose and β-D-Glucopyranose
A. D-Glucose and L-Glucose
Enantiomers are MIRROR IMAGES of each other, they are designated as a D-sugar and L-sugar, D-sugars are the major sugars in humans.
Epimers are compounds that differ in configuration around only one specific carbon atom, with exception of the carbonyl carbon. Glucose and Galactose differ at carbon 4, while Glucose and Mannose differ at carbon 2.
Anomers are designated as α and β, and are cyclic saccharide epimers that differ in configuration, specifically at the hemiacetal/acetal carbon, also called the anomeric carbon.
What is the rate limiting step of glycolysis?
A. Phosphorylation of Glucose
B. Phosphorylation of Fructose-6-Phosphate
C. Phosphorylation of Fructose-1,6-Biphosphate
D. Formation of Pyruvate
E. Dephosphorylation of Fructose-1,6-Biphosphate
B. Phosphorylation of Fructose-6-Phosphate
The rate limiting step in GLYCOLYSIS is the PHOSPHORYLATION OF FRUCTOSE-6-PHOSPHATE, catalyzed by the enzyme PHOSPHOFRUCTOKINASE-1
Which of the following if true of hexokinase, but not of glucokinase?
A. Present only in liver parenchymal cells and islet cells of pancreas
B. Can phosphorylate glucose and other hexoses
C. Inhibited by glucose 6-phophate
D. High Km
E. High Vmax
C. Inhibited by glucose 6-phophate
Hexokinase is inhibited by glucose-6-phosphate. Glucokinase is inhibited by fructose-6-phosphate.
Hexokinase is present in most tissues. Glucokinase is present only in liver parenchymal cells and islet cells of the pancreas.
Both can phosphorylate glucose and other hexoses.
Hexokinase has a low Km (high affinity) and low Vmax, wherease glucokinase has a high Km (low affinity) and high Vmax.
Which enzyme is NOT part of the citric acid cycle?
A. Pyruvate dehydrogenase B. Fumarase C. Succinate dehydrogenase D. α-Ketoglutarate dehydrogenase E. Isocitrate dehydrogenase
A. Pyruvate dehydrogenase
Pyruvate dehydrogenase catalyzes the conversion of pyruvate into acetyl CoA + NADH + CO2, (not part of the CAC).
Acetyl CoA then enters the Kreb cycle (CAC).
Which of the following is NOT true regarding the citric acid cycle?
A. It is the final common pathway for aerobic oxidation of all nutrients.
B. It is an amphibolic process
C. It occurs in all cells with mitochondria
D. Complex I of the electron transport chain is also part of the citric acid cycle
E. Isocitrate dehydrogenase is the rate limiting enzyme
D. Complex I of the electron transport chain is also part of the citric acid cycle
Complex II (succinate dehydrogenase) is both a part of the ETC and the CAC/TCAC, not complex I.
The citric acid cycle (or the Kreb cycle, or the tricarboxylic acid cycle) is amphibolic (both catabolic and anabolic).
Right after a large meal, which of the following is expected?
A. Glycogen synthase is phosphrylated B. Phosphofructokinase-1 is inactivated C. Hormone sensitive lipase is activated D. Glycogen Phosphorylase in phosphorylated E. Debranching enzyme is inactivated
E. Debranching enzyme is inactivated
In the WELL-FED state DEPHOSPHORYLATION OF ENZYMES BY INSULIN occurs.
Dephosphorylated enzymes involved, in GLYCOLYSIS, GLYCOGENESIS, and FATTY ACID SYNTHESIS are ACTIVATED; dephosphorylated enzymes involved in GLUCONEOGENESIS, GLYCOGENOLYSIS, and LIPOLYSIS are INACTIVATED.
In the FASTING state, PHOSPHORYLATION OF ENZYMES BY GLUCAGON occurs.
Phosphorylated enzymes involved in GLUCONEOGENESIS, GLYCOGENOLYSIS, and LIPOLYSIS are ACTIVATED; phosphorylated enzymes involved in GLYCOLYSIS, GLYCOGENESIS, and FATTY ACID SYNTHESIS are INACTIVATED.
A 30-year old male complained of muscle pain, and early fatigue every time he would try to engage in any physical activity, which he also noticed since he was a child. Patient also complained of tea-colored urine. What is the most likely diagnosis?
A. Von Gierke's disease B. Pompe's disease C. Cori's disease D. Andersen's disease E. McArdle's disease
E. McArdle’s disease
McArdle’s disease (glycogen storage diseaes V) is the deficiency of skeletal muscle glycogen phosphorylase.
Von Gierke’s disease (GSD I) is the deficiency of the enzyme glucose-6-phosphatase.
Pompe’s disease (GSD II) is caused by an accumulation of glycogen in the lysosome due to deficiency of the lysosomal enzyme acid α-glucosidase. It is the only glycogen storage disease with a defect in lysosomal metabolism.
Cori’s disease (GSD III) is the deficiency in glycogen debranching enzymes.
Andersen’s disease is caused by a mutation in the GBE1 gene, which causes a defect in the glycogen branching enzyme.
The transketolases involved in the pentose phosphate pathway require which co-factor(s):
A. Thiamine B. NAD+ C. FAD D. Coenzyme A E. All of the above
A. Thiamine
Thiamine (vitamin B1) is a necessary co-factor in transketolases. RBC transketolase activity can be used to diagnose thiamine deficiency.
The following are true of phase 1 in of the pentose phosphate pathway, EXCEPT in adipose tissue lipolysis:
A. Oxidative B. Irreversible C. Key enzymes are the transketolases D. Main product is NADPH E. None of the above
C. Key enzymes are the transketolases
The key enzyme in phase 1 of the pentose phosphate pathway is glucose-6-phosphate dehydrogenase.
Which fatty acid is also known as an omega-3-fatty acid?
A. Linoleic acid B. Linolenic Acid C. Arachidonic Acid D. Palmitic Acid E. Stearicc Acid
B. Linolenia
Both linolenic and linoleic have 18 carbons.
Linoleic has double bonds at carbon 9 and 12, while linolenic has double bonds at carbon 9, 12 and 15.
Omega fatty acid numbering indicates the location of the first double bond starting from the last carbon.
Linoleic acid also known as omega-6 fatty acid, while linolenic is also known as omega-3 fatty acid; both are correlated with decrease risk of cardiovascular disease.
Which of the following occur both in the cystoplasm and mitochondria?
A. Heme synthesis B. Urea cycle C. Glycogenesis D. Only A and B E. All of the above
D. Only A and B
Processes that occur BOTH IN THE CYTOPLASM AND THE MITOCHONDRIUM:
- heme synthesis
- urea cycle
- gluconeogenesis (NOT glycogenesis)
Cerebrohepatorenal syndrome, which occurs in individuals with a rare inherited absence of peroxisomes in all tissues:
A. Jamaican vomiting sickness B. Methylmalonic acidemia C. Zellweger's syndrome D. Refsum's disease E. X-linked adrenoleukodystrophy
C. Zellweger’s syndrome
ZELLWEGER SYNDROME is the inhereted absence/decrease of peroxisomes in ALL TISSUES.
JAMAICAN VOMITING SICKNESS is caused by eating unripe AKEE FRUIT which contains HYPOGLYCIN, a toxin that inactivates medium- and short-chain ACYL-COA DEHYDROGENASE.
REFSUM DISEASE is a rare neurologic disorder due to the accumulation of PHYTANIC ACID.
X-LINKED ADRENOLEUKODYSTROPHY is a defect in peroxisomal activation of very long-chain fatty acids.
METHYLMALONIC ACIDEMIA is a defect in the conversion of METHYLMALONYL COA to SUCCINYL COA.
The following are associated with increased risk of developing coronary artery disease, EXCEPT:
A. Familial lipoprotein lipase deficiency B. Familial hypercholesterolemia C. Familial dysbetalipoproteinemia D. Familial hypertriglyceridemia E. None of the above
A. Familial lipoprotein lipase deficiency
Type 1 familial lipoprotein lipase deficiency result in findings of HIGH VLDL and HIGH CHYLOMIRCRON with LOW LDL and LOW HDL.
This is associated with pancreatitis and xanthomas, but NO INCREASE RISK of coronary heart disease.
What is the enzyme involved in the conversion of cholesterol to pregnenolone?
A.HMG CoA reductase B.HMG CoA synthase C.Carnitine acyltransferase D.Desmolase E.Aromatase
D. Desmolase
Desmolase it the rate limiting enzyme in STEROID HORMONE SYNTHESIS.
HMG CoA reductase is the rate limiting enzyme in CHOLESTEROL SYNTHESIS.
HMG CoA synthase is the rate limiting enzyme in KETOGENESIS.
Aromatase converts testosterone to estradiol.
