front 1 Approximately what fraction of total body solids is normally composed
of proteins? | back 1 B. About three quarters of solids |
front 2 Which structural feature is shared by essentially all proteinogenic
amino acids? | back 2 D. One carboxyl and one amino group |
front 3 A gastric protease cleaves the covalent bonds that connect amino
acids into a polypeptide. Which bond is directly hydrolyzed? | back 3 A. Peptide (amide) linkage between residues |
front 4 During ribosomal peptide bond formation between two amino acids,
which immediate event accounts for water production? | back 4 C. H+ from amino, OH− from carboxyl |
front 5 Hemoglobin consists of multiple polypeptide chains that associate
noncovalently. Which interaction most directly links different chains
via backbone C=O and N–H groups? | back 5 B. Hydrogen bonds between peptide groups |
front 6 Because free amino acids are relatively strong acids at physiological
pH, how do they predominantly exist in plasma? | back 6 A. As ionized species in solution |
front 7 In a healthy individual, which form accounts for almost all
nitrogenous products absorbed across the small-intestinal
mucosa? | back 7 D. Individual amino acids |
front 8 A healthy volunteer ingests a high-protein meal. Serial measurements
of plasma amino acid concentration are obtained. Which pattern best
describes the normal postprandial response over the next 2–3
hours? | back 8 B. Small rise of only a few mg/dL |
front 9 In a normal adult, small quantities of amino acids continue to be
absorbed from the gut for how long after a protein-rich meal? | back 9 C. Approximately 2–3 hours |
front 10 Following a rapid intravenous amino acid load in a healthy subject,
plasma amino acid levels initially rise slightly. Within what
approximate time are most of these excess amino acids taken up by
tissues, especially the liver, so that large accumulations rarely
occur? | back 10 A. Within 5–10 minutes |
front 11 Free amino acids are much too large to diffuse through aqueous pores
of cell membranes. How do they primarily cross most plasma
membranes? | back 11 D. Carrier-mediated facilitative or active transport |
front 12 In normal individuals, how are filtered amino acids reabsorbed in the
proximal tubule? | back 12 B. Secondary active transport coupled to Na+ |
front 13 Which statement best describes intracellular handling of amino acids
in most tissues? | back 13 C. Incorporated into proteins; free pool kept low |
front 14 During a brief fast, plasma amino acid levels fall slightly below
normal. Which tissues preferentially release stored amino acids to
stabilize plasma levels? | back 14 A. Liver, kidneys, and intestinal mucosa |
front 15 A researcher infuses a massive amino acid load intravenously into a
healthy volunteer. Plasma amino acid concentration rises far above
normal, and significant aminoaciduria develops despite normal GFR and
intact tubules. Which mechanism best explains the urinary loss? | back 15 D. Saturation of secondary active transporters |
front 16 Which hormone combination most directly increases formation of tissue
proteins? | back 16 B. Growth hormone and insulin |
front 17 Which hormone class primarily causes the increased plasma amino
acids? | back 17 A. Adrenocortical glucocorticoids |
front 18 Which cells are most prolific users of amino acids, depleting
proteins in other tissues? | back 18 C. Cancer cells |
front 19 Each cell type has what property regarding protein storage? | back 19 B. Fixed upper limit for proteins |
front 20 After a high-protein meal, a healthy adult has mild, transient
elevation of plasma amino acids. Any amino acids not used for tissue
protein synthesis are primarily: | back 20 D. Degraded, used for energy, or stored |
front 21 Which combination best represents the major classes of plasma
proteins in human blood? | back 21 C. Albumin, globulins, fibrinogen |
front 22 A patient with severe hypoalbuminemia develops generalized edema and
ascites. Which primary function of albumin explains these
findings? | back 22 D. Maintains plasma colloid osmotic pressure |
front 23 Which plasma protein class is most directly responsible for natural
and acquired immunity? | back 23 C. Globulin fraction |
front 24 Which plasma protein normally polymerizes into fibrin threads during
coagulation? | back 24 A. Fibrinogen |
front 25 Which site normally forms essentially all albumin, all fibrinogen,
and most globulins? | back 25 C. Liver parenchyma |
front 26 In healthy individuals, most gamma globulins are synthesized
in: | back 26 C. Lymphoid tissues |
front 27 Gamma globulins are best described as: | back 27 C. Immunoglobulin antibody molecules |
front 28 In a healthy adult, what is the approximate daily rate of plasma
protein formation by the liver? | back 28 D. 30 grams per day |
front 29 A patient with long-standing nephrotic syndrome has massive
proteinuria but preserved GFR. Over months, daily urinary losses of
plasma protein may reach approximately: | back 29 A. 20 grams per day |
front 30 Which process in the liver reduces plasma protein synthesis? | back 30 B. Cirrhosis with fibrous replacement |
front 31 During prolonged fasting, tissue protein breakdown supplies amino
acids, yet plasma proteins serve as a rapidly mobilizable reserve.
Plasma proteins function as what type of protein storage medium? | back 31 C. Labile storage |
front 32 A child with acute, life-threatening protein deficiency and severe
edema presents to the emergency department. Which intervention most
rapidly supplies amino acids and restores colloid osmotic
pressure? | back 32 D. Intravenous plasma protein infusion |
front 33 A patient on total parenteral nutrition receives a mixture of amino
acids. Those that cannot be synthesized by human tissues and must be
supplied in the diet are called: | back 33 B. Essential amino acids |
front 34 A deficiency in synthesis of certain amino acids is traced to
impaired formation of their carbon skeletons. Synthesis of
nonessential amino acids depends mainly on formation of: | back 34 B. Alpha-keto acids |
front 35 The alpha-keto acid precursor of alanine is: | back 35 A. Pyruvic acid |
front 36 A metabolic reaction moves an amino group from glutamate to pyruvate,
forming alanine and alpha-ketoglutarate, while exchanging the keto
oxygen. This reaction type is best described as: | back 36 D. Transamination |
front 37 In rapidly dividing lymphocytes, a particular amino acid shuttles
amino groups between tissues and serves as a major nitrogen reservoir.
Which amino acid principally functions as an “amino radical
storehouse”? | back 37 A. Glutamine |
front 38 A hepatocyte uses a pool of amino donors to transaminate various
alpha-keto acids. Amino radicals are most commonly transferred
from: | back 38 C. Asparagine, glutamic, aspartic acids |
front 39 A patient begins catabolizing amino acids during prolonged exercise
to generate ATP. The degradation of amino acids for energy generally
begins with which biochemical step? | back 39 A. Deamination of the amino group |
front 40 In hepatocytes, removal of nitrogen from most amino acids occurs
primarily through which mechanism? | back 40 C. Transamination to an acceptor keto acid |
front 41 Transamination, the key reaction initiating deamination of many amino
acids, is catalyzed by which group of enzymes? | back 41 A. Aminotransferases |
front 42 Ammonia liberated during deamination of amino acids is rapidly
detoxified in humans by conversion mainly into: | back 42 B. Urea |
front 43 Essentially all urea produced in the human body is synthesized in
which organ? | back 43 D. Liver |
front 44 A patient with fulminant hepatic failure develops confusion,
asterixis, and then unresponsiveness. Massive accumulation of ammonia
in this setting most classically leads to: | back 44 B. Hepatic coma |
front 45 After amino acids are deaminated, their carbon skeletons remain as
alpha-keto acids. What is a major general fate of these keto acids in
energy metabolism? | back 45 D. Oxidation to release usable energy |
front 46 Which intermediate was formed directly when alanine is
deaminated? | back 46 C. Pyruvic acid |
front 47 Which term best describes the metabolic process by which amino acid
carbon skeletons are converted into glucose? | back 47 C. Gluconeogenesis |
front 48 Conversion of deaminated amino acid carbon skeletons predominantly
into keto acids and fatty acids is referred to as: | back 48 D. Ketogenesis |
front 49 Even when a person consumes no dietary protein, some body proteins
are continually degraded to amino acids and oxidized. This is
termed: | back 49 A. Obligatory loss of proteins |
front 50 A patient’s diet is severely deficient in one essential amino acid,
while all others are abundant. What happens to the use of the other
amino acids for protein synthesis? | back 50 D. They cannot form complete proteins |
front 51 A dietary protein has an amino acid pattern markedly different from
that of average body proteins and is deficient in one or more
essential amino acids. Such a protein is best described as a: | back 51 A. Partial (incomplete) protein |
front 52 After several weeks of starvation, when carbohydrate and fat reserves
become critically depleted, what happens to circulating amino
acids? | back 52 C. Rapidly deaminated and oxidized |
front 53 Because carbohydrate and fat are normally used preferentially for
energy before protein, they are often referred to as: | back 53 A. Protein sparers |
front 54 In an untreated type 1 diabetic with absolute insulin deficiency,
what is the expected effect on protein synthesis in tissues? | back 54 B. Reduced to almost zero |
front 55 Which statement best describes the direct effects of insulin on amino
acid and protein metabolism in most tissues? | back 55 B. Increases amino acid uptake, lowers breakdown |
front 56 How do glucocorticoids primarily affect protein metabolism? | back 56 C. Increase breakdown of extrahepatic proteins |
front 57 Increased deposition of contractile proteins in skeletal muscle in
normal males: | back 57 B. Testosterone |
front 58 In contrast to testosterone, which enlarges protein tissues for only
several months, which hormone can cause tissues to continue growing
almost indefinitely if secreted in excess? | back 58 B. Growth hormone |
front 59 Which hormone most indirectly alters protein metabolism by increasing
cellular metabolic activity? | back 59 D. Thyroxine |
front 60 Which best explains thyroxine’s effect when carbohydrates and fats
are insufficient? | back 60 B. Rapid degradation of proteins for energy |
front 61 Which mechanism best explains the growth inhibition in thyroxine
deficiency? | back 61 C. Impaired protein synthesis due to low thyroxine |
front 62 Which statement best describes thyroxine’s overall effect on protein
metabolism in most tissues? | back 62 A. Increases both anabolic and catabolic protein reactions |
front 63 During ribosomal peptide bond formation between two amino acids, what
is directly lost from the amino and carboxyl groups,
respectively? | back 63 A. Proton from amino, hydroxyl from carboxyl |
front 64 The covalent linkage formed between amino acids in a growing
polypeptide chain is produced by which type of reaction? | back 64 C. Dehydration (condensation) between amino acids |
front 65 A severely malnourished child with edema and muscle wasting receives
an intravenous infusion of concentrated plasma proteins. Why does this
therapy help restore both plasma and tissue protein levels? | back 65 B. Plasma proteins form a labile protein reservoir |
front 66 Nonessential amino acids can be synthesized endogenously. Their
synthesis depends mainly on formation of which type of
precursor? | back 66 C. Appropriate alpha-keto acid skeletons |
front 67 A hepatocyte transfers an amino group from glutamine to pyruvate,
forming alanine, using an aminotransferase enzyme. Which statement
best describes this transamination reaction? | back 67 A. Transfer amino group to an alpha-keto acid |
front 68 A young woman starts estrogen therapy. Compared with testosterone,
what is estrogen’s effect on protein deposition in tissues? | back 68 A. Causes some protein deposition, but much less |
front 69 Which statement best describes the deamination step that initiates
amino acid catabolism in the liver? | back 69 D. Transfer amino group to acceptor keto acid |
front 70 A man with acute fulminant hepatitis rapidly develops confusion,
asterixis, and then coma. Which mechanism best explains this
neurologic decline? | back 70 B. Ammonia accumulation |
front 71 Which statement best compares ATP yield from complete oxidation of
protein versus glucose on a per-gram basis? | back 71 C. Protein yields slightly less ATP per gram |
front 72 Oxidation of a deaminated amino acid to produce ATP typically
proceeds in two major steps. Which option best reflects these
sequential processes? | back 72 D. Conversion to TCA intermediate, then cycle oxidation |
front 73 Which direct effect on cellular protein metabolism is most
characteristic of growth hormone? | back 73 B. Increases synthesis of cellular proteins |
front 74 Why is insulin considered necessary for effective net protein
synthesis in most tissues? | back 74 C. It reduces degradation by improving glucose availability |
front 75 Which tissue shows especially marked protein deposition in response
to testosterone excess? | back 75 A. Contractile proteins of skeletal muscle |