Please be aware that these questions do not represent all topics that can be asked in the Unified Quiz and that they are just meant for practice! It is suggested to take all 40 questions in a row with a time limit of 60 min.The answer key at the end will point out the correct answers and explain why the others are incorrect. Please feel free to contact me when you do not agree with the best correct answer and I will be glad to discuss the question with you. My e-mail is mtrotz@sgu.edu

Q#1 Dependent on the polarity, we separate polar lipids and neutral lipids. Neutral lipids, like triacylglycerols (TAGs), are cleaved by lipases. One of the lipases that digest dietary TAGs is lingual lipase which

a. needs colipase for its activityb. is acid-stable at the stomach proton concentration c. needs conjugated bile salts for its activityd. is deficient in patients with cystic fibrosise. cleaves both, TAGs and phospholipids

Q#2 A 56-year old man was seriously injured in an accident. He needs parenteral nutrition, which should include dietary essential fatty acids. Which of the following fatty acids is a dietary essential fatty acid of the -6 family?

a. Palmitoleic acidb. Oleic acidc. Linoleic acidd. -linolenic acide. Arachidonic acid

Q # 3 What is a characteristic indication that a child with common long bone fractures could have defective collagen as found in osteogenesis imperfecta tarda (OI Type I)?

a. hypermobility of jointsb. bleeding of gumsc. stretchy skind. blue scleraee. long limbs

Q#4 Our knowledge about enzymes has increased immensely since the first description of a protein acting as a catalyst. Enzymatic catalysis

a. changes the thermodynamics of the reaction b. works without a transition statec. is independent of the pHd. can involve a prosthetic group like FADe. involves binding of the substrate to its huge active site

Q#5 A 52-year-old man is brought to the emergency room by his wife. He had suffered a mild heart attack two years ago and experienced similar pain during the last night. His ECG does not indicate an acute MI and blood samples are taken. His blood plasma is used to test for both, total serum creatine kinase (CK) and serum CK-MB. What is the reasoning behind this?

a. Total serum CK alone is an injury marker for the liver b. Increase of serum CK-MB but not of total CK indicates rhabdomyolosis

c. Serum CK-MB larger than about 5% of total serum CK can indicate an acute MId. Serum cTnT is also a marker for MI, but accumulates only after 2 days in bloode. Serum levels of CK-MB but not total serum CK are increased after an acute MI

Q#6Pharmaceutical companies investigate the possible inhibition of enzymes by drugs. Which graph is obtained when the data are expressed in the Lineweaver-Burk plot? It results in data presentation that

a. shows a sigmoidal curve that reaches Vmax at high [S]b. is plotted as initial velocity (Vo) versus 1/[S]c. results in a reciprocal value of Vmax to be found at the intercept with the x-axisd. shows a hyperbolic curve that reaches Vmax at high [S]e. results in a straight line due to plotting 1/Vo to 1/[S]

Q#7In many graphs that investigate the action of enzymes, the data are shown as velocity in response to increased substrate concentrations. The velocity

a. reaches Vmax at the substrate concentration at Kmb. represents product formation (mol) over time (min) c. is independent of the amount of enzyme d. increases for human enzymes at temperatures above 400 Ce. is proportional to substrate concentrations at very high [S]

Q#8Lipids are a major component of our normal diet and we have several digestive lipases. What is special of pancreatic lipase, often just named lipase? Pancreatic lipase

a. cleaves dietary triacylglycerols to mainly free glycerol and fatty acidsb. in serum can be an injury marker for pancreatitis c. cleaves mainly triacylglycerols with medium-chain fatty acidsd. is proteolytically activated by trypsine. is released as zymogen from the pancreas

Q#9 The fibrous proteins collagen and elastin have a specific amino acid composition. Which amino acid represents about one third of amino acids in collagen and also in elastin?

a. Serineb. Alaninec. Glycined. Hydroxyprolinee. Hydroxylysine

Q#10The digestion of dietary carbohydrates is very much watched in programs that promote weight loss. One could target the enzymes that degrade complex sugars or one could target the uptake of glucose and galactose into intestinal mucosal cells. This uptake is performed by

a. facilitated transportb. GLUT-4c. GLUT-2d. primary active transport e. co- transport with sodium ions

Q#11During your clinical rotations, you come to learn about a family with a child who suffers from Cystic Fibrosis. Not only is the child treated with physical clearing of the lungs from the accumulating mucus, but also a special nutrition is of importance and part of the treatment. What is special about the digestion in cystic fibrosis patients? Patients with cystic fibrosis

a. lack the glucose transporter SGLTb. are deficient in the digestion performed by pepsinc. should eat a diet low in lactosed. can digest TAGs with medium-chain fatty acids e. should eat a diet low in purine nucleotides

Q#12Digestion of food starts in the mouth and after swallowing it continues in the stomach. The stomach performs the digestion of

a. sucrose and lactoseb. TAGs with long-chain fatty acidsc. proteins to mainly peptides d. nucleic acids to bases and sugarse. phospholipids to fatty acids and lysophospholipids

Q#13There are several hormones involved with the digestion of our normal food intake. Amongst them are gastrin, secretin and cholecystokinin (CCK). What is special about CCK? Cholecystokinin

a. is a hormone formed in the pancreasb. activates trypsinogen to trypsinc. leads to release of bicarbonate from the pancreasd. leads to release of protons into the stomach lumene. leads to release of bile from the gallbladder

Q#14A 54-year-old woman complains to her physician of feeling night-blind while driving home late at night. It happened to her only recently, and she is worried about her health. Upon questioning, she tells her physician that she is since last month very strict with her diet, which is mostly fat-free. There is no change in her feces. What could most likely be the reason for her problems?

a. Less uptake of the lipid-soluble vitamin A b. Lack of conjugated bile salts c. The deficiency of dietary cholesterol d. A diet that is too high in proteins e. A diet too high in purine nucleotides

Q#15 Cholesterol is released by the liver into the bile. The solubility of cholesterol in bile is achieved by conjugated bile salts and phosphatidylcholine. Taurocholic acid is formed from cholic acid and taurine. This conjugated bile salt is

a. synthesized in the gallbladderb. the main component of gallstonesc. able to prevent gallstone formation d. grouped as secondary conjugated bile salte. mainly released and excreted in feces

Q#16 Digestive enzymes are very powerful enzymes that cannot only digest dietary proteins or phospholipids, but also cell components which are not meant to be digested. Proteolytic activation of digestive zymogens is often used. A key player in that respect is trypsin which proteolytically activates in the duodenum

a. pepsinogenb. enteropeptidasec. chymotrypsinogend. -amylasee. pancreatic lipase

Q#17 Digestive proteases have specific cleavage sites and work all together in the intestinal lumen in order to efficiently digest proteins to amino acids. Which amino acid side chain contains a positive charge and is (besides lysyl residues) the cleavage site for trypsin?

a. Asparagineb. Argininec. Glutamined. Tryptophane. Histidine

Q#18 The plasma membrane separates the cell from its neighbor cells and the extracellular or interstitional fluid. The correct fluidity of the plasma membrane is regulated by

a. free cholesterol which buffers the fluidity changes of fatty acids during temperature changesb. by the amounts of glucose transporters and other proteinsc. arachidonic acid in phospholipids which will reduce the fluidityd. palmitic acid which is more fluid than oleic acide. free cholesterol which increases the fluidity at the area of the polar head groups

Q#19A 19-year-old Danish female developed severe diarrhea on a hiking trip. After her return, she consults a physician as she still suffers from continued abdominal pain with bloating and painful cramping. This takes place especially after eating sweets and drinking milk. What could be most likely the reason for her problems?

a. Deficiency of disaccharidases due to her severe diarrheab. A strong genetic predisposition for primary lactose intolerancec. Congenital lactase deficiencyd. Deficiency of secretin and cholecystokinine. Inability to cleave lactose in the stomach

Q#20 You might have seen on cans of diet soft drinks the warning that phenylketonurics should not consume drinks containing aspartame. Aspartame is an artificial dipeptide sweetener that contains phenylalanine. What can you say about the structure and grouping of this amino acid? Phenylalanine

a. contains a hydroxyl groupb. is an aromatic amino acidc. contains a sulfhydryl groupd. is a dietary nonessential amino acide. is grouped as a branched-chain amino acid

Q#21 The neurotransmitter GABA can be formed by the decarboxylation of the -carboxyl group of a specific amino acid. Which amino acid is decarboxylated to GABA?

a. Glycineb. Tryptophanc. Glutamated. Aspartatee. Glutamine

Q#22 Proteins consist of amino acids linked together by peptide bonds. The sequence is represented in the primary structure. Some proteins form the secondary structure of an -helix. The -helix

a. can bend inside of the peptide bonds involved in the protein structureb. cannot be changed into a -pleated sheet once it is formed as -helixc. contains amino acids with their side chains to the outside of the helixd. is a structure favored by a high amount of proline residuese. is a structure found in myoglobin but not in hemoglobin

Q# 23 Creatine kinase is an enzyme that is named after the fact that it phosphorylates creatine. What is special about this enzyme? Creatine kinase a. catalyses an irreversible reaction b. is a serum injury marker for bone damage c. can be used to form ATP d. has two different subunits and consists of a tetramer e. is a serum injury marker of MI which peaks after 2 days

Q #24 Covalent bonds and noncovalent bonds are found in the tertiary structure of proteins. Which of the following bonds is a covalent bond formed by side chains of amino acids?

a. ionic bonds between aspartate and lysineb. hydrogen bonds between serine and glutamatec. van der Waals forces found in the -helixd. disulfide bonds between two cysteine residuese. hydrophobic forces between valine and isoleucine

Q#25Shown are the Lineweaver-Burk plots for the uninhibited reaction (no inhibitor added) and also two data plots for a high and a low concentration of the same specific inhibitor added to the assays.

Which statement best describes the data shown in line 2?

a. no inhibitor addedb. high concentration of a competitive inhibitor c. high concentration of a non-competitive inhibitord. low concentration of a competitive inhibitore. low concentration of a non-competitive inhibitor

Q#26 Defective fibrous proteins can lead to serious illness due to defects related to the synthesis of collagen or elastin. Some enzymes are needed for intracellular post-translational modifications or extracellular for preparation of covalent cross-linking. The enzyme lysyl oxidase

a. is needed for both, collagen and elastin synthesisb. needs zinc as cofactorc. is mainly found inside fibroblastsd. is defective in osteogenesis imperfectae. acts on pro--chains of procollagen

Q#27 The fibril forming collagens show a staggered arrangement of collagen molecules. These collagen fibrils need covalent bonds to link them together. The cross-linking of collagen molecules

a. is performed inside fibroblastsb. involves disulfide bonds c. uses desmosined. is performed by collagenasee. involves lysine and allysine-residues

Q#28 Which of the following enzymes are in the serum injury marker for liver damage?a. Creatine kinase MBb. Creatine kinase MMc. Amylased. Alanine aminotransferasee. Lactate dehydrogenase -1

Q#29 Collagen and elastin contain an amino acid which is needed for eventual covalent cross-linking. This amino acid is

a. Glycineb. Lysinec. Proline

d. Alaninee. Cysteine

Q#30 A low-dose of aspirin (81 mg) is used toa. Inhibit acetylcholine esteraseb. Reversibly inhibit cyclooxygenasec. Reduce the activity of prostacyclind. Chemically modify thromboxanee. Reduce the amount of thromboxane

Q#31Phospholipids are components of polar lipids that often can be used to form biomembranes due to their amphipathic character. The group includes cardiolipin which contains totally four esterified fatty acids. What else is special about cardiolipin? Cardiolipin is

a. exclusively found in the heartb. found in high concentration in mitochondria c. a major component of all biomembranesd. part of the glycocalyxe. a sphingophospholipid

Q#32 Human enzymes allow the regulation of their catalysis dependent on the changing needs of the cells or the total human body. Which of the following regulations is used in humans when insulin is ruling?

a. Increased synthesis of key enzymes for gluconeogenesisb. Induction of key enzymes for fatty acid de-novo synthesis c. Increased degradation of the key enzyme for cholesterol synthesisd. Phosphorylation of key enzymes of pathways by protein kinase Ae. Inhibition of protein phosphatases

Q#33 Allosteric enzymes do not follow Michaelis-Menten kinetics. What is special about the graph plotted with the velocity at the y-axis and the substrate concentration at the x-axis? The curve for allosteric enzymes

a. Would not lead to a Vmaxb. Is sigmoidal due to a cooperative effect of the substratec. Is shifted to the right when a feed-forward activator is addedd. Cannot be used to determine K 0.5e. Shows only first order kinetics

Q#34 The enzyme lactate dehydrogenase a. contains FAD as prosthetic groupb. is a protein dimer with the compostition HMc. in serum is an early MI markerd. needs vitamin C for its reactione. cannot form pyruvate at high NADH levels

Q#35 Most phospholipases are found inside of cells and are membrane-bound and tightly regulated.

One of the exceptions is a soluble phospholipase A2 that cleaves dietary phospholipids. This enzyme

a. is the result of proteolytic activation by enteropeptidaseb. has a pH optimum of 2c. is synthesized as prophospholipase in the stomachd. is eventually degraded by digestive proteasese. is released in its active form by the pancreas

Q#36 Membranes contain different transporters. Which of the following is an example of an ABC-transporter?

a. SGLTb. GLUT-1c. CFTRd. GLUT-5e. Na+/K+-ATPase

Q#37 Hepatocytes contain a specific glucose transporter. This transporter isa. insulin-dependentb. a low-affinity transporter c. only found in hepatocytesd. also found in RBCe. only used for uptake of glucose but not for release of glucose

Q#38 Premature babies are often treated with lung surfactant whicha. is a glycosphingolipidb. is a plasmalogenc. lines the alveoli of the lungs and prevents collapsed. contains mainly protein and some phospholipidse. contains two arachidonic acids in its structure

Q#39 Glucagon is released by the -cells of the pancreas and signals low blood glucose levels. The glucagon receptor

a. is found in the liver and kidneyb. allows the cAMP second messenger systemc. activates phospholipase Cd. is found in the nucleus of hepatocytese. binds both, glucagon and epinephrine

Q#40 Creatine phosphatea. is formed in the heart by cytochrome C oxidaseb. contains two phosphoanhydride bondsc. is grouped as a high-energy compoundd. is formed by creatine kinase in cytosol at low ATP levelse. is formed using creatine and inorganic phosphate as substrates

Short answer key:

1B, 2C, 3D, 4D, 5C, 6E, 7B, 8B, 9C, 10E, 11D, 12C, 13E, 14A, 15C, 16C, 17B, 18A, 19A, 20B, 21C, 22C, 23C, 24D, 25E, 26A, 27E, 28D, 29B, 30E, 31B, 32B, 33B, 34E, 35D, 36C, 37B, 38C, 39B, 40C

Answers and explanations for the practice exam: Unified Quiz

Q#1B is correct: Lipid digestion can be performed by lingual lipase in the stomach. The enzyme is acid-stable at the stomach proton concentration

a. incorrect: not lingual lipase, but pancreatic lipase needs colipase for its activityb. correct:, lingual lipase cleaves preferably TAGs with medium-chain fatty acids

c. incorrect: lingual lipase does not need conjugated bile salts for its activity d incorrect: it is pancreatic lipase that is deficient in CF patients e incorrect: lingual lipase does not cleave phospholipids, it cleaves only neutral lipids

Q#2 C is correct: Linoleic acid is dietary essential and is of the -6 family (18:2,6).

a. incorrect: palmitoleic acid (16:1) can be formed in humans from palmitic acid (16:0) b incorrect: oleic acid (18:1) can be formed in humans from stearic acid (18:0) c correct, it can then be used to form arachidonic acid of the same family d. incorrect: -linolenic acid (18:33) is a dietary essential fatty acid of the -3 family. e incorrect: arachidonic acid (20:4,6) is normally not dietary essential

Q#3 D is correct: blue sclerae are an indication that a child with common long bone fractures could have osteogenesis imperfecta tarda (OI Type I).

a. incorrect: hypermobility of joints is mostly an indication of EDSb. incorrect: bleeding of gums is mostly an indication of vitamin C deficiencyc. incorrect: stretchy skin is mostly an indication of EDSd. correct, it is also found in other diseases, but used mostly as indicator for OIe. incorrect: long limbs can be a sign of Marfan’s disease

Q#4D is correct: enzymatic catalysis can involve a prosthetic group like FAD

a. incorrect: enzymes do not change the thermodynamics of the reaction b. incorrect: enzymatic catalysis does not work without a transition state c. incorrect: enzymatic catalysis shows a respective pH optimum d correct, FAD is a bound coenzyme for some oxidoreductases e incorrect: the active site is small, not large

Q#5 C is correct: serum CK-MB/total CK larger than about 5% can indicate a MI

a. incorrect: total CK is not an injury marker for the liver, CK is not found in the liver b. incorrect: rhabdomyolosis leads to increase of mainly total CK and little CK-MB

c. correct, CK-MB alone can be used, but the % related to total CK is better d. incorrect: serum cTnT and cTnI accumulate already several hours after MI e. incorrect: both, total CK and CK-MB increase in plasma as indication for a MI

Q#6E is correct: the Lineweaver-Burk plot leads to a graph with a straight line due to plotting 1/V0 to 1/[S] (double reciprocal)

a. incorrect: a sigmoidal curve, velocity versus [S] is found for allosteric enzymes b. incorrect: it does not show V0 data versus 1/[S] but instead 1/V0 versus 1/[S]c. incorrect: 1/Vmax is at the intercept with the y-axis and not the x-axisd. incorrect: a hyperbolic curve is found when plotted in the Michaelis-Menten plot e correct, less experimental data are needed in comparison to Michaelis-Menten plot

Q#7 B is correct: the velocity of a reaction represents product formation (mol) over time

a. incorrect: Km is the substrate concentration at half Vmaxb. correct, velocity describes formation of product in concentration/min, not total amount

c. incorrect: the velocity is dependent on the amount of the enzyme. d. incorrect: human enzymes start to denature above 40 C (high fever) e. incorrect: the velocity is proportional to the substrate at low [S], not large [S]

Q#8B. is correct: pancreatic lipase in serum can be a used as injury marker for pancreatitis

a. incorrect: pancreatic lipase cleaves TAG to MAG and two fatty acids b correct, often just named lipase as injury marker in serum c. incorrect: it cleaves TAGs with long-chain fatty acids (majority of food) d incorrect: pancreatic lipase is not activated by trypsin e. incorrect: pancreatic lipase does not need to be synthesized as zymogen

Q#9 C. is correct: glycine represents about one third of amino acids in collagen and also in elastin.

All other choices are incorrect: no other amino acid represents one third of amino acids in both collagen and also in elastin.

Alanine and serine are found in elastin and are besides glycine cleavage sites of elastase. Hydroxyproline and hydroxylysine are found in collagen and mostly absent in elastin.

Q#10E is correct: dietary glucose or galactose are taken up into the intestinal mucosal cells by co-transport with sodium ions

a. incorrect: dietary glucose and galactose are taken up by secondary active transportb. incorrect: GLUT-4 is found in fat and muscle cellsc. incorrect: GLUT-2 is used for release into the portal circulation

d incorrect: it is not primary but secondary active transport e correct, either glucose or galactose is transported by SGLT into mucosal cells

Q#11D. is correct: cystic fibrosis patients can digest triacylglycerols with medium-chain fatty acids (using lingual and gastric lipase)

a. incorrect: CF patients have a defect related to CFTR ( specific chloride ion channel) b. incorrect: CF patients are not deficient in the digestion performed by pepsin.

c. incorrect: CF patients are not lactose intolerant and can eat a diet containing lactosed. correct, some milk TAGs can be digested in the stomach (medium-chain fatty acids)

e. incorrect: CF does not lead to gout.

Q#12 C. is correct: the stomach performs digestion of proteins to mainly peptides

a. incorrect: sucrose and lactose are not digested in the stomach b. incorrect: TAGs with long-chain fatty acids are mainly digested in the duodenum c.correct, pepsin is an endopeptidase and leads mainly to peptides d. incorrect: nucleic acids are denatured in the stomach but not degraded e. incorrect: phospholipids are digested by pancreatic phospholipase A2 in the duodenum

Q#13 E. is correct: cholecystokinin (CCK) leads to release of bile from the gallbladder

a. incorrect: CCK is a hormone formed in endocrine cells of the duodenumb. incorrect: CCK does not activate trypsinogen, enteropeptidase activates trypsinogenc. incorrect: it is mainly secretin, that leads to release of bicarbonate from the pancreas

d incorrect: it is gastrin that leads to release of protons into the stomach lumene. correct, CCK has its name from the fact that it contracts the gallbladder

Q#14 A is correct: the most likely reason for her night blindness is less uptake of the lipid-soluble vitamin A. Retinol leads to cis-retinal for the vision cycle.

b incorrect: lack of conjugated bile salts would lead to change in her feces (steatorrhea) c incorrect: night blindness is not related to deficiency of dietary cholesterol d incorrect: a diet that is too high in proteins does not lead to night-blindness e incorrect: the diet too high in purine nucleotides can lead to a gout attack

Q# 15 C. is correct: Taurocholic acid is able to prevent gallstone formation

a. incorrect: conjugated bile salts are only synthesized in the liver b. incorrect: cholesterol is the main component of gallstones. c. correct, conjugated bile salts are negatively charged and favor cholesterol solubility d. incorrect: cholic acid is a primary bile acid synthesized in the liver e incorrect: conjugated bile salts are cleaved to bile acids which are 95% taken up again

Q#16 C. is correct: trypsin activates in the small intestine chymotrypsinogen to chymotrypsin.

a. incorrect: pepsinogen is not activated by trypsin b. incorrect: enteropeptidase is activated by CCK.

c. correct, trypsin is an endopeptidase that proteolytical cleaves chymotrypsinogen d. incorrect: -amylase is not synthesized as zymogen

e incorrect: pancreatic lipase is not synthesized as zymogen

Q#17 B. is correct: the amino acid arginine contains a positive charge in its side chain and is (besides lysine) the cleavage site in proteins for trypsin

a. incorrect: asparagine side chain is not charged b. correct, cleavage at the carboxyl site of the long, positively charged side chain c. incorrect: glutamine side chain is not charged d. incorrect: tryptophan has a bulky, aromatic side chain

e incorrect: histidine side chains can be positively charged but do not fit into trypsin pocket

Q#18 a. A is correct: the fluidity of the plasma membrane is controlled by free cholesterol, which buffers fluidity changes of fatty acids during temperature changes

b. incorrect: glucose transporters do not regulate the fluidity of the plasma membranec. incorrect: arachidonic acid in phospholipids will increase the fluidity.d. incorrect: palmitic acid is less fluid than oleic acide. incorrect: cholesterol stiffens the plasma membrane at the polar head groups

Q#19 a. A is the correct answer: the deficiency of sucrase and lactase due to severe diarrhea are most likely the reason for her problems

b. incorrect: Northern Europeans do not have a strong genetic pre-disposition c. incorrect: congenital lactase deficiency exists at birth and can lead to early death d. incorrect: this is not a defect related to secretin or CCK deficiencye. incorrect: lactose is cleaved by lactase bound to the outside of intestinal mucosal cells

Q#20 B is correct: phenylalanine is an aromatic amino acid

a incorrect: a hydroxyl group is found in serine, threonine or tyrosineb. correct, phenylalanine is used to form tyrosine in humans (hydroxylation)c. incorrect: a sulfhydryl group is found in cysteined. incorrect: phenylalanine is a dietary essential fatty acide. incorrect: branched-chain amino acids are valine, leucine and isoleucine

Q#21 C is correct: glutamate is decarboxylated to GABA (-aminobutyric acid)

a. incorrect: glycine is not decarboxylatedb. incorrect: tryptophan is first hydroxylated, and then serotonin is formedc. correct: renaming as the former carboxyl group is now carbon #1d. incorrect: aspartate is not used to form GABA, does not have carboxyl groupe. incorrect: glutamine needs first to be deaminated to form glutamate

Q#22 C is correct: the amino acid side chains are outside of the structure of an -helix

a incorrect: the peptide bond cannot bend, it has partial double-bond characterb incorrect: an-helix can change into a -pleated sheet, as shown in the prion diseasec. correct, side-chains can be used for tertiary structure d incorrect: proline residues disrupt the formation of an -helix and force a bend e incorrect: the -helix is found in both myoglobin and hemoglobin

Q#23 C is correct: creatine kinase can be used to form ATP when it uses CrP and ADP

a incorrect: creatine kinase catalyzes a reversible reaction (unususal for a kinase)b incorrect: it is not a serum injury marker for bone disease, ALP is c. correct, at low ATP levels, CrP and ADP are used to form ATP by creatine kinased incorrect: CK has two different subunits (M and B) and it consists of a dimer. e incorrect: it is an early injury marker and back to baseline after 2 days

Q#24 D is correct: disulfide bonds between two cysteine side chains are covalent bonds. In proteins they stabilize the tertiary structure.

a incorrect: the bonds between aspartate and lysine are noncovalent ionic bondsb incorrect: hydrogen bonds between serine and glutamate are noncovalent bondsc incorrect: van der Waals forces found in the -helix are very weak noncovalent bondsd. correct, disulfide bonds are not meant to be broken during conformational changee incorrect, hydrophobic forces between valine and isoleucine side chains are noncovalent

Q#25 E. is correct: Line 2 is the line for a low concentration of a non-competitive inhibitor.

Type of inhibition? A noncompetitive inhibition shows the same Km but apparent Vmax is smaller. Line 2 shows the same -1/Km for all lines, and it shows a changed 1/Vmax. The next question is, whether Line 2 represents a low or high concentration of the inhibitor. The uninhibited reaction shows the largest Vmax which means a small number for 1/Vmax on the y-axis and is represented by Line 3. Line 1 represents the highest concentration of the inhibitor as the apparent Vmax is the smallest, shown by a large number of 1/Vmax on the y-axis.

a. incorrect: if no inhibitor is added, then 1/Vmax should be the smallestb. incorrect: Line 2 is not the line for a competitive inhibitor. c. incorrect: Line 2 is not the line of a high concentration of a noncompetitive inhibitord. incorrect: line 2 does not represent a competitive inhibition

Q#26 a. A is correct: the enzyme lysyl oxidase is needed for both, collagen and elastin synthesis. It forms allysine residues and prepares covalent cross-linking

b. incorrect: lysyl oxidase, contains copper as cofactor, not zincc. incorrect: it is an extracellular enzyme not found in fibroblastsd. incorrect: lysyl oxidase can be defective in Ehlers-Danlos syndromes

e. incorrect: it does not act on pro--chains of procollagen

Q#27 E. is correct: cross-linking of collagen molecules uses lysine and allysine residues

a. incorrect: cross-linking takes place outside of fibroblastsb. incorrect: disulfide bonds link propeptides of procollagenc. incorrect: desmosine is used to cross-link elastind. incorrect: collagenase cleaves collagen molecules, and does not cross-link collagene. Correct, cross-linking leads to tensile strength in fibril forming collagens

Q#28 D. is correct: alanine aminotransferase in the serum is a marker for liver damage

a. incorrect: Creatine kinase MB is characteristic for heart infarctionb. incorrect: Creatine kinase MM is characteristic for skeletal muscle damagec. incorrect: Amylase is characteristic for pancreatic diseased. correct, high concentration in liver cytosol, used with other markerse. incorrect: LDH-1 is found in heart and RBC, liver contains LDH-5

Q#29 B. is correct: Collagen and elastin contain lysine which is needed for eventual covalent cross-linking.

a. incorrect: both contain glycine but it is not used for covalent cross-linksb. correct, both need lysyl oxidase to form allysine residuesc. incorrect: both contain proline but it forms hydrogen bonds in collagen-triple-helixd. incorrect: alanine is mainly found in elastin and is not used for cross-linkse. incorrect: cysteine is only used for cross-links in procollagen propeptides

Q#30 E. is correct: A low-dose of aspirin is used to reduce the amount of thromboxane

a. incorrect: acetylcholine esterase is inhibited by DFPb. incorrect: the inhibition of COX is irreversible, even at low dosec. incorrect: the activity of prostacyclin is not reducedd. incorrect: thromboxane is not chemically modifiede. correct: mature platelets cannot synthesize new COX

Q#31B. is correct: cardiolipin is found in high concentration in mitochondria

a. incorrect: cardiolipin is found in all mitochondrial membranes b. correct, it is necessary in the inner mitochondrial membrane c. incorrect: cardiolipin is not a major component of all biomembranes d. incorrect: cardiolipin is a phospholipid that is not found in the plasma membrane e. incorrect: it is a glycerophospholipid, sphingomyelin is a sphingophospholipid

Q#32 B is correct: insulin induces key enzymes for fatty acid de-novo synthesis

a incorrect: glucagon, not insulin, induces key enzymes of gluconeogenesis b. correct, insulin signals high blood glucose levels that need to be buffered

c. incorrect: the key enzyme of cholesterol synthesis is not degraded but induced insteadd. incorrect: insulin leads to dephosphorylated key enzymes of pathwayse. incorrect: protein phosphatases are active after insulin action

Q#33 B is correct: the curve is sigmoidal due to the cooperative effect of the substrate

a. incorrect: Vmax is also found for allosteric enzymesb. correct, the substrate is a homotropic effector for the allosteric enzymec. incorrect: it is shifted to the leftd. incorrect: K0.5 [S] can be determined from the graph at half Vmaxe. incorrect: it shows first order and zero order kinetics

Q#34 E is correct: The enzyme lactate dehydrogenase cannot form pyruvate at high NADH levels, as it needs for this direction NAD+ as coenzyme

a. incorrect: it does not contain FAD as prosthetic groupb. incorrect: it is a tetramer with H and M subunitsc. incorrect: it is in serum not an early MI marker, it accumulates laterd. incorrect: prolyl hydroxylase and lysyl hydroxylase need vitamin C e. correct, at high NADH levels lactate cannot be used for gluconeogenesis

Q#35 D is correct: pancreatic phospholipase A2 is eventually degraded by digestive proteases

a. incorrect: trypsin performs the proteolytic activation of prophospholipase A2b. incorrect: pepsin has a pH optimum of 2, phospholipase acts at duodenal pHc. incorrect; it is synthesized as zymogen in the pancreas, not in the stomachd. correct: digestive proteases will eventual degrade all digestive enzymese. incorrect: it is released in its zymogen form by the pancreas

Q#36 C is correct: CFTR is an example of an ABC-transporter (chloride ion channel)

a. incorrect: SGLT is involved with secondary active transportb. incorrect: GLUT-1 performs facilitative diffusionc. correct: CFTR is an epithelial chloride ion channel in the plasma membraned. incorrect: GLUT-5 performs facilitated diffusion of fructosee. incorrect: Na+/K+-ATPase performs primary active transport

Q#37 B is correct: Hepatocytes contain a specific glucose transporter. This transporter is a low-affinity transporter

a. incorrect: GLUT-4 is insulin-dependent and found in fat cells and muscleb. correct, it is GLUT-2, a low-affinity transporter with a large Ktc. incorrect: it is GLUT-2 which is also found e.g. in kidney, -cells of pancreasd. incorrect: GLUT-2 is not found in RBCe. incorrect: it is used in liver for uptake of glucose and also for release of glucose

Q#38 C is correct: Premature babies are often treated with lung surfactant which lines the alveoli of the lungs and prevents collapse

a. incorrect: it is a glycerophospholipidb. incorrect: it is a specific phosphatidylcholine, not a plasmalogenc. correct, it is mainly DPPC released by Type II alveolar cellsd. incorrect: it is the other way round, mainly phospholipids and some proteinse. incorrect: it does not contain arachidonic acid in its structure

Q#39 B is correct: The glucagon receptor allows the cAMP messenger system

a. incorrect: the receptor is found in the liver but not in the kidneyb. correct, it stimulates adenylate cyclasec. incorrect: it does not activate phospholipase C d. incorrect, it is found in the cell membrane of hepatocytese. incorrect: it binds only glucagon and not epinephrine

Q#40 C is correct: Creatine phosphate is grouped as a high-energy compound

a. incorrect: it is not formed in the electron transport chain by cyt C oxidaseb. incorrect: creatine phosphate contains one energy-rich phosphoamide bond c. Correct, it can be used to form ATP from ADPd. incorrect: at high ATP levels, it can be formed by creatine kinase in cytosol e. incorrect: it is formed from creatine and ATP, inorganic phosphate is not used