Phys 70 Flashcards

Approximately what fraction of total body solids is normally composed of proteins?
A. About one quarter of solids
B. About three quarters of solids
C. Almost all body solids
D. Less than half of solids

Which structural feature is shared by essentially all proteinogenic amino acids?
A. Sulfhydryl and basic guanidinium groups
B. Two carboxyl groups on alpha carbon
C. Aromatic ring and hydroxyl group
D. One carboxyl and one amino group

A gastric protease cleaves the covalent bonds that connect amino acids into a polypeptide. Which bond is directly hydrolyzed?
A. Peptide (amide) linkage between residues
B. Disulfide bond between cysteine residues
C. Hydrogen bond between peptide backbones
D. Ionic bond between charged side chains

During ribosomal peptide bond formation between two amino acids, which immediate event accounts for water production?
A. Loss of two protons from carboxyl
B. Release of hydroxyl from amino group
C. H+ from amino, OH− from carboxyl
D. Oxidation of both alpha carbons

Hemoglobin consists of multiple polypeptide chains that associate noncovalently. Which interaction most directly links different chains via backbone C=O and N–H groups?
A. Covalent peptide bonds between chains
B. Hydrogen bonds between peptide groups
C. Ionic bonds between side chains
D. Hydrophobic clustering of side chains

Because free amino acids are relatively strong acids at physiological pH, how do they predominantly exist in plasma?
A. As ionized species in solution
B. As neutral uncharged molecules
C. Covalently bound to plasma lipids
D. In large insoluble protein aggregates

In a healthy individual, which form accounts for almost all nitrogenous products absorbed across the small-intestinal mucosa?
A. Intact dietary proteins
B. Large oligopeptide fragments
C. Free ammonia molecules
D. Individual amino acids

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?
A. Large sustained rise of >100 mg/dL
B. Small rise of only a few mg/dL
C. No change from fasting baseline
D. Progressive accumulation to very high levels

In a normal adult, small quantities of amino acids continue to be absorbed from the gut for how long after a protein-rich meal?
A. Only the first 15 minutes
B. About 30–45 minutes
C. Approximately 2–3 hours
D. More than 12 continuous hours

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?
A. Within 5–10 minutes
B. Within 30–60 minutes
C. Over 3–4 hours
D. Over several days

Free amino acids are much too large to diffuse through aqueous pores of cell membranes. How do they primarily cross most plasma membranes?
A. Simple diffusion through lipid bilayer
B. Pinocytosis of bulk extracellular fluid
C. Passage through large nonselective pores
D. Carrier-mediated facilitative or active transport

In normal individuals, how are filtered amino acids reabsorbed in the proximal tubule?
A. Primary active pumping via Na+/K+ ATPase
B. Secondary active transport coupled to Na+
C. Passive diffusion down concentration gradients
D. Simple filtration followed by endocytosis

Which statement best describes intracellular handling of amino acids in most tissues?
A. Stored mainly as large cytosolic crystals
B. Rapidly oxidized, with little protein synthesis
C. Incorporated into proteins; free pool kept low
D. Sequestered inside lysosomes as free amino acids

During a brief fast, plasma amino acid levels fall slightly below normal. Which tissues preferentially release stored amino acids to stabilize plasma levels?
A. Liver, kidneys, and intestinal mucosa
B. Bone marrow and splenic pulp
C. Cardiac and skeletal muscle only
D. Adipose tissue and dermis

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?
A. Failure of glomerular filtration barrier
B. Suppression of Na+/K+ ATPase activity
C. Inhibition of proximal tubular endocytosis
D. Saturation of secondary active transporters

Which hormone combination most directly increases formation of tissue proteins?
A. Cortisol and glucagon
B. Growth hormone and insulin
C. Aldosterone and vasopressin
D. Thyroxine and calcitonin

Which hormone class primarily causes the increased plasma amino acids?
A. Adrenocortical glucocorticoids
B. Pancreatic peptide hormones
C. Posterior pituitary hormones
D. Parathyroid peptide hormones

Which cells are most prolific users of amino acids, depleting proteins in other tissues?
A. Skeletal muscle cells
B. Adipose stromal cells
C. Cancer cells
D. Hepatocyte stem cells

Each cell type has what property regarding protein storage?
A. No limit on protein storage
B. Fixed upper limit for proteins
C. Expanding capacity with more amino acids
D. Unlimited expansion of endoplasmic reticulum

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:
A. Excreted unchanged in the urine
B. Stored as free plasma amino acids
C. Converted to urea and nucleic acids
D. Degraded, used for energy, or stored

Which combination best represents the major classes of plasma proteins in human blood?
A. Albumin, collagen, fibrinogen
B. Albumin, elastin, globulins
C. Albumin, globulins, fibrinogen
D. Globulins, keratin, fibrinogen

A patient with severe hypoalbuminemia develops generalized edema and ascites. Which primary function of albumin explains these findings?
A. Carrier of thyroid and steroid hormones
B. Major buffer of blood pH
C. Source of acute phase reactants
D. Maintains plasma colloid osmotic pressure

Which plasma protein class is most directly responsible for natural and acquired immunity?
A. Albumin fraction
B. Complement C3 fraction
C. Globulin fraction
D. Fibrinogen fraction

Which plasma protein normally polymerizes into fibrin threads during coagulation?
A. Fibrinogen
B. Prothrombin
C. Albumin
D. Transferrin

Which site normally forms essentially all albumin, all fibrinogen, and most globulins?
A. Bone marrow
B. Lymph nodes
C. Liver parenchyma
D. Spleen red pulp

In healthy individuals, most gamma globulins are synthesized in:
A. Renal tubular cells
B. Pancreatic acinar cells
C. Lymphoid tissues
D. Cardiac myocytes

Gamma globulins are best described as:
A. Iron transport proteins
B. Enzymes of clot stabilization
C. Immunoglobulin antibody molecules
D. Hormone-binding carrier proteins

In a healthy adult, what is the approximate daily rate of plasma protein formation by the liver?
A. 5 grams per day
B. 10 grams per day
C. 20 grams per day
D. 30 grams per day

A patient with long-standing nephrotic syndrome has massive proteinuria but preserved GFR. Over months, daily urinary losses of plasma protein may reach approximately:
A. 20 grams per day
B. 5 grams per day
C. 60 grams per day
D. 1 gram per day

Which process in the liver reduces plasma protein synthesis?
A. Steatosis of hepatocytes
B. Cirrhosis with fibrous replacement
C. Acute hepatocellular necrosis
D. Cholestasis from bile stones

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?
A. Stable storage
B. Insoluble storage
C. Labile storage
D. Structural storage

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?
A. High-carbohydrate oral feeding
B. Isotonic saline infusion
C. Whole blood transfusion
D. Intravenous plasma protein infusion

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:
A. Nonessential amino acids
B. Essential amino acids
C. Neutral amino acids
D. Branched-chain amino acids

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:
A. Beta-keto acids
B. Alpha-keto acids
C. Long-chain fatty acids
D. Aromatic carboxylic acids

The alpha-keto acid precursor of alanine is:
A. Pyruvic acid
B. Oxaloacetic acid
C. Alpha-ketoglutarate
D. Acetoacetic acid

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:
A. Deamination
B. Decarboxylation
C. Reductive amination
D. Transamination

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”?
A. Glutamine
B. Glycine
C. Tyrosine
D. Tryptophan

A hepatocyte uses a pool of amino donors to transaminate various alpha-keto acids. Amino radicals are most commonly transferred from:
A. Methionine, leucine, isoleucine
B. Lysine, arginine, histidine
C. Asparagine, glutamic, aspartic acids
D. Serine, threonine, cysteine

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?
A. Deamination of the amino group
B. Decarboxylation to release carbon dioxide
C. Oxidation of the carbon skeleton
D. Condensation with another amino acid

In hepatocytes, removal of nitrogen from most amino acids occurs primarily through which mechanism?
A. Direct hydrolysis to free ammonia
B. Lysosomal proteolysis of whole proteins
C. Transamination to an acceptor keto acid
D. Nonenzymatic decomposition in the cytosol

Transamination, the key reaction initiating deamination of many amino acids, is catalyzed by which group of enzymes?
A. Aminotransferases
B. Dehydrogenases
C. Decarboxylases
D. Carboxylases

Ammonia liberated during deamination of amino acids is rapidly detoxified in humans by conversion mainly into:
A. Ammonium chloride
B. Urea
C. Uric acid
D. Creatinine

Essentially all urea produced in the human body is synthesized in which organ?
A. Kidney cortex
B. Small intestine
C. Skeletal muscle
D. Liver

A patient with fulminant hepatic failure develops confusion, asterixis, and then unresponsiveness. Massive accumulation of ammonia in this setting most classically leads to:
A. Obstructive jaundice
B. Hepatic coma
C. Metabolic alkalosis
D. Portal hypertension

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?
A. Immediate excretion in the urine
B. Storage as cytosolic protein granules
C. Conversion only to ketone bodies
D. Oxidation to release usable energy

Which intermediate was formed directly when alanine is deaminated?
A. Acetoacetic acid
B. Oxaloacetic acid
C. Pyruvic acid
D. Alpha-ketoglutaric acid

Which term best describes the metabolic process by which amino acid carbon skeletons are converted into glucose?
A. Ketogenesis
B. Glycogenolysis
C. Gluconeogenesis
D. Glycolysis

Conversion of deaminated amino acid carbon skeletons predominantly into keto acids and fatty acids is referred to as:
A. Proteolysis
B. Lipolysis
C. Gluconeogenesis
D. Ketogenesis

Even when a person consumes no dietary protein, some body proteins are continually degraded to amino acids and oxidized. This is termed:
A. Obligatory loss of proteins
B. Adaptive protein sparing
C. Essential amino acid turnover
D. Basal nitrogen equilibrium

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?
A. Protein synthesis continues at reduced rate
B. Other amino acids fully compensate
C. Excess amino acids are stored unchanged
D. They cannot form complete proteins

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:
A. Partial (incomplete) protein
B. Complete body protein
C. Storage structural protein
D. High-biologic-value protein

After several weeks of starvation, when carbohydrate and fat reserves become critically depleted, what happens to circulating amino acids?
A. Stored as plasma transport proteins
B. Excreted unchanged in the urine
C. Rapidly deaminated and oxidized
D. Converted mainly into triacylglycerol

Because carbohydrate and fat are normally used preferentially for energy before protein, they are often referred to as:
A. Protein sparers
B. Nitrogen donors
C. Nonessential fuels
D. Obligatory substrates

In an untreated type 1 diabetic with absolute insulin deficiency, what is the expected effect on protein synthesis in tissues?
A. Increased synthesis above normal
B. Reduced to almost zero
C. Mildly reduced but still adequate
D. Unchanged from normal

Which statement best describes the direct effects of insulin on amino acid and protein metabolism in most tissues?
A. Decreases amino acid uptake, increases breakdown
B. Increases amino acid uptake, lowers breakdown
C. Lowers amino acid uptake and breakdown
D. No significant effect on proteins

How do glucocorticoids primarily affect protein metabolism?
A. Decrease hepatic protein synthesis
B. Increase breakdown of hepatic proteins
C. Increase breakdown of extrahepatic proteins
D. Decrease breakdown of muscle proteins

Increased deposition of contractile proteins in skeletal muscle in normal males:
A. Growth hormone
B. Testosterone
C. Cortisol
D. Thyroxine

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?
A. Glucagon
B. Growth hormone
C. Insulin
D. Aldosterone

Which hormone most indirectly alters protein metabolism by increasing cellular metabolic activity?
A. Insulin
B. Glucagon
C. Testosterone
D. Thyroxine

Which best explains thyroxine’s effect when carbohydrates and fats are insufficient?
A. Stimulates hepatic glycogen storage from protein
B. Rapid degradation of proteins for energy
C. Inhibits mitochondrial ATP generation in muscle
D. Promotes exclusive use of dietary carbohydrate

Which mechanism best explains the growth inhibition in thyroxine deficiency?
A. Reduced intestinal absorption of essential amino acids
B. Increased renal loss of plasma proteins
C. Impaired protein synthesis due to low thyroxine
D. Complete suppression of growth hormone secretion

Which statement best describes thyroxine’s overall effect on protein metabolism in most tissues?
A. Increases both anabolic and catabolic protein reactions
B. Selectively inhibits all catabolic protein reactions
C. Stimulates protein synthesis while blocking degradation
D. Has minimal impact on protein metabolism

During ribosomal peptide bond formation between two amino acids, what is directly lost from the amino and carboxyl groups, respectively?
A. Proton from amino, hydroxyl from carboxyl
B. Hydroxyl from amino, proton from carboxyl
C. Only water lost from both groups
D. Loss of carbon dioxide from carboxyl group

The covalent linkage formed between amino acids in a growing polypeptide chain is produced by which type of reaction?
A. Hydrolysis of an amide bond
B. Oxidation of adjacent alpha carbons
C. Dehydration (condensation) between amino acids
D. Isomerization of amino acid side chains

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?
A. Plasma proteins are inert structural molecules
B. Plasma proteins form a labile protein reservoir
C. Plasma proteins cannot equilibrate with tissues
D. Plasma proteins only provide oncotic pressure

Nonessential amino acids can be synthesized endogenously. Their synthesis depends mainly on formation of which type of precursor?
A. Dietary essential amino acid backbones
B. Long-chain fatty acyl intermediates
C. Appropriate alpha-keto acid skeletons
D. Simple ammonia plus carbon dioxide

A hepatocyte transfers an amino group from glutamine to pyruvate, forming alanine, using an aminotransferase enzyme. Which statement best describes this transamination reaction?
A. Transfer amino group to an alpha-keto acid
B. Release ammonia directly into the bloodstream
C. Attach carboxyl groups to amino sugars
D. Decarboxylate amino acids to form amines

A young woman starts estrogen therapy. Compared with testosterone, what is estrogen’s effect on protein deposition in tissues?
A. Causes some protein deposition, but much less
B. Causes identical anabolic effects as testosterone
C. Has no measurable effect on protein stores
D. Causes rapid loss of contractile proteins

Which statement best describes the deamination step that initiates amino acid catabolism in the liver?
A. Direct hydrolysis releasing free ammonia only
B. Oxidative decarboxylation producing carbon dioxide only
C. Nonenzymatic loss of amino group in cytosol
D. Transfer amino group to acceptor keto acid

A man with acute fulminant hepatitis rapidly develops confusion, asterixis, and then coma. Which mechanism best explains this neurologic decline?
A. Failure to form bilirubin from heme
B. Ammonia accumulation
C. Excess formation of ketone bodies in liver
D. Massive loss of plasma proteins through kidneys

Which statement best compares ATP yield from complete oxidation of protein versus glucose on a per-gram basis?
A. Protein yields much more ATP per gram
B. Protein yields no usable ATP at all
C. Protein yields slightly less ATP per gram
D. Protein yields identical ATP per gram

Oxidation of a deaminated amino acid to produce ATP typically proceeds in two major steps. Which option best reflects these sequential processes?
A. Direct entry as acetyl-CoA, no modification
B. Conversion to glucose then direct ATP generation
C. Oxidation to lactate followed by Cori cycling
D. Conversion to TCA intermediate, then cycle oxidation

Which direct effect on cellular protein metabolism is most characteristic of growth hormone?
A. Decreases synthesis, increases protein breakdown
B. Increases synthesis of cellular proteins
C. Decreases both synthesis and degradation
D. Inhibits amino acid uptake by tissues

Why is insulin considered necessary for effective net protein synthesis in most tissues?
A. It directly forms peptide bonds in ribosomes
B. It replaces essential amino acids in diet
C. It reduces degradation by improving glucose availability
D. It blocks amino acid entry into mitochondria

Which tissue shows especially marked protein deposition in response to testosterone excess?
A. Contractile proteins of skeletal muscle
B. Hepatic parenchymal cells
C. Renal tubular epithelial cells
D. Adipocytes of subcutaneous tissue