Biochem 35 Flashcards

A pancreatic enzyme deficiency prevents activation of chymotrypsinogen, proelastase, and procarboxypeptidases. Which enzyme is most likely absent?

A. Pepsin
B. Enteropeptidase
C. Trypsin
D. Aminopeptidase

Trypsin, chymotrypsin, and elastase are all endopeptidases and share which catalytic classification?

A. Metalloproteases
B. Serine proteases
C. Aspartyl proteases
D. Cysteine proteases

A peptide is cleaved at internal peptide bonds rather than sequentially from a terminus. Which class of enzymes performs this function?

A. Exopeptidases
B. Carboxypeptidases
C. Aminopeptidases
D. Endopeptidases

Which one cleaves peptide bonds in which the carboxyl (carbonyl) group is provided by lysine or arginine?

A. Elastase
B. Carboxypeptidase A
C. Chymotrypsin
D. Trypsin

A researcher designs a peptide rich in phenylalanine, tyrosine, tryptophan, and leucine. Which enzyme would most strongly favor cleavage of this substrate?

A. Chymotrypsin
B. Trypsin
C. Aminopeptidase
D. Carboxypeptidase B

After pancreatic endopeptidases generate oligopeptides, which enzymes remove amino acids one at a time from peptide ends?

A. Ligases
B. Isomerases
C. Exopeptidases
D. Transaminases

A defect in an enzyme that removes residues sequentially from the carboxyl terminus of peptides would most directly impair which enzyme group?

A. Pepsins
B. Carboxypeptidases
C. Aminopeptidases
D. Enterokinases

preferentially releases hydrophobic AA:

A. Carboxypeptidase A
B. Carboxypeptidase B
C. Carboxypeptidase C
D. Carboxypeptidase D

preferentially releases basic AA:

A. Carboxypeptidase A
B. Carboxypeptidase B
C. Carboxypeptidase C
D. Carboxypeptidase D

Carboxypeptidase B most preferentially releases which amino acids?

A. Leucine and valine
B. Glycine and alanine
C. Serine and threonine
D. Arginine and lysine

Which statement best describes pepsinogen physiology?

A. Produced in pancreas, activated intestine
B. Produced in stomach, activated stomach
C. Produced in liver, activated duodenum
D. Produced in jejunum, activated colon

Which enzyme is located on the brush border and removes single amino acids from the amino terminus of peptides?

A. Aminopeptidase
B. Trypsin
C. Elastase
D. Cathepsin

Proteins can be degraded by lysosomal enzymes called:

A. Caspases
B. Cathepsins
C. Carboxypeptidases
D. Granzymes

An intracellular protein is marked for degradation by covalent attachment of a small peptide to lysine residues. Which molecule provides this targeting signal?

A. SUMO
B. Biotin
C. Ubiquitin
D. Carnitine

After polyubiquitination, a damaged cytosolic protein is most directly sent to which structure?

A. Proteasome
B. Peroxisome
C. Lysosome
D. Endosome

A regulatory protein contains regions rich in proline, glutamate, serine, and threonine. What is the most likely effect of this sequence motif?

A. Enhanced secretion
B. Mitochondrial import
C. Longer half-life
D. Shorter half-life

Amino acids enter intestinal epithelial cells from the lumen primarily through which mechanism?

A. Primary active Ca2+ pump
B. Na+-dependent cotransport
C. Cl− antiport
D. Simple diffusion only

Once concentrated within intestinal epithelial cells, amino acids typically leave across the basolateral membrane by:

A. Facilitated transport
B. Na+/K+ ATPase
C. Proton symport
D. Endocytic vesicles

In a prolonged fasting state, which statement best describes amino acid handling by intestinal epithelial cells?
A. Minimally use amino acids for energy
B. Rely mainly on luminal amino acids
C. Release amino acids into the lumen
D. Take up blood amino acids for fuel

Which kinase has an important regulatory role in autophagy?

A. AMPK
B. PKA
C. Akt
D. mTOR

In proteasomal degradation, what is used both to unfold the tagged protein and to push the protein into the core of the cylinder?

Digestive proteases are generally synthesized in inactive precursor forms best termed:

A. Isoenzymes
B. Zymogens
C. Apoenzymes
D. Holoproteins

What cells secrete hydrochloric acid (HCL)?

What cells secrete pepsinogen?

A child in a famine-stricken region has generalized edema, muscle wasting, and preserved caloric intake from starches. Which diagnosis best fits?

A. Kwashiorkor
B. Marasmus
C. Pellagra
D. Scurvy

The edema of kwashiorkor is most directly caused by decreased levels of which plasma protein?

A. Fibrinogen
B. Transferrin
C. Albumin
D. Ceruloplasmin

A toddler with protein deficiency appears swollen rather than cachectic. Which finding most specifically explains the apparent “plump” appearance?

A. Hepatic glycogen accumulation
B. Mesenteric inflammation
C. Edema with distended abdomen
D. Increased subcutaneous adipose

Why must pancreatic zymogens be activated within a short span after trypsin appears?

A. Active enzymes digest one another
B. Bile salts rapidly inactivate them
C. Luminal pH soon denatures them
D. Brush-border enzymes remove them

A congenital defect prevents conversion of trypsinogen to trypsin at the intestinal surface. Which enzyme is deficient?

A. Aminopeptidase
B. Carboxypeptidase B
C. Pepsin
D. Enteropeptidase

_____ first activates a small amount of trypsinogen into trypsin, which then triggers a rapid cascade by cleaving all other pancreatic zymogens into their _____ forms.

This immediate activation ensures that these potent proteases begin digesting dietary proteins simultaneously before they can undergo autolysis or autodigestion.

Enteropeptidase is secreted by which cells?

A. Pancreatic acinar cells
B. Small-intestinal brush-border cells
C. Gastric chief cells
D. Duodenal goblet cells

Failure of trypsin generation would most directly impair activation of all except which enzyme?

A. Chymotrypsin
B. Elastase
C. Carboxypeptidases
D. Pepsin

A child with cystic fibrosis develops protein, fat, and carbohydrate maldigestion from pancreatic insufficiency. The primary defect initially causes inspissation of which secretions?

A. Endocrine pancreatic secretions
B. Biliary canalicular secretions
C. Pancreatic exocrine secretions
D. Gastric chief-cell secretions

In cystic fibrosis, failure of pancreatic enzymes to reach the intestinal lumen is caused primarily by:

A. Zymogen overactivation
B. Ductal obstruction
C. Brush-border atrophy
D. Decreased enteropeptidase

The pancreas synthesizes a secretory trypsin inhibitor primarily to prevent:

A. Intrapancreatic zymogen activation
B. Pepsin-mediated mucosal injury
C. Renal amino acid wasting
D. Lysosomal proteolysis

Loss of pancreatic trypsin inhibitor would most likely predispose to which condition?

A. Cystinuria
B. Hartnup disease
C. Kwashiorkor
D. Pancreatitis

Hartnup disease is caused by defective transport of which class of amino acids?

A. Basic amino acids
B. Neutral amino acids
C. Acidic amino acids
D. Sulfur-containing amino acids

Hartnup disease affects transport across which epithelial sites?

A. Hepatic and alveolar
B. Gastric and colonic
C. Intestinal and renal
D. Biliary and pancreatic

In both Hartnup disease and cystinuria, impaired tubular handling causes what urinary change?

A. Increased urinary amino acids
B. Decreased urinary amino acids
C. Increased urinary glucose
D. Decreased urinary ketones

Excess amino acid carbon skeletons are primarily converted into:

A. Cholesterol and ketones
B. Lactate and pyruvate
C. Purines and porphyrins
D. Glycogen and triacylglycerols

A young adult with recurrent nephrolithiasis has stones composed of a poorly soluble amino acid. Which substance is the culprit in cystinuria?

A. Tyrosine
B. Tryptophan
C. Cystine
D. Taurine

A patient with cystinuria presents with severe flank pain radiating to the groin and gross hematuria. Which complication most likely explains this presentation?

A. Papillary necrosis
B. Bladder rupture
C. Glomerulonephritis
D. Ureteral stone obstruction

A misfolded cytosolic protein is targeted for proteasomal degradation after a small peptide is covalently attached to the ε-amino group of which residue?

A. Serine
B. Lysine
C. Arginine
D. Histidine

Proteins rich in proline, glutamate, serine, and threonine are typically degraded by which pathway?

A. Lysosomal cathepsin pathway
B. Calpain-mediated proteolysis
C. Ubiquitin–proteasome system
D. Caspase-dependent cleavage

The γ-glutamyl cycle is required for synthesis of which antioxidant compound?

A. Taurine
B. Bilirubin
C. Glutathione
D. Uric acid

Glutathione is protection against:

A. Thermal injury
B. Oxidative damage
C. Osmotic stress
D. Calcium overload

Which protease is active within the stomach lumen?

A. Trypsin
B. Elastase
C. Pepsin
D. Aminopeptidase

Which set contains only pancreatic proteases?

A. Pepsin, trypsin, aminopeptidase
B. Trypsin, chymotrypsin, elastase
C. Pepsin, elastase, carboxypeptidase
D. Aminopeptidase, trypsin, pepsin

Which enzyme is located on the intestinal brush border?

A. Chymotrypsin
B. Elastase
C. Carboxypeptidase A
D. Aminopeptidase

Cystinuria results from defective renal reabsorption of which amino acids?

A. Cysteine, arginine, lysine
B. Glycine, alanine, serine
C. Aspartate, glutamate, taurine
D. Phenylalanine, tyrosine, tryptophan

The most serious complication of cystinuria results from the poor solubility of:

A. Cysteine
B. Methionine
C. Homocysteine
D. Cystine

Neutrophil-derived elastase is normally inhibited by which molecule?

A. α-1-antitrypsin
B. Transferrin
C. Ceruloplasmin
D. Hemopexin

Alpha-1 antitrypsin deficiency (AATD) is a genetic condition causing low levels of the protective protein AAT, leading to:

A. Pulmonary fibrosis
B. Emphysema
C. Bronchiectasis
D. Pulmonary edema

The lung injury in α-1-antitrypsin deficiency is primarily due to:

A. Autoimmune alveolitis
B. Infectious necrosis
C. Proteolytic tissue destruction
D. Surfactant overproduction

Pepsinogen becomes pepsin when gastric acidity increases because:

A. HCl directly hydrolyzes proteins
B. Low pH activates pepsinogen
C. Gastrin cleaves pepsinogen
D. Bicarbonate exposes active site

Cystinuria is most directly caused by which underlying abnormality?

A. Defective glomerular filtration barrier
B. Mutated tubular amino acid transporter
C. Excess hepatic cystine synthesis
D. Deficient lysosomal cysteine export

Which statement best describes pepsin’s enzymatic action?

A. Carboxyl-terminal exopeptidase
B. Amino-terminal exopeptidase
C. Endopeptidase in stomach
D. Cytosolic ubiquitin ligase

Which group contains only endopeptidases?

A. Pepsin, trypsin, elastase
B. Aminopeptidase, pepsin, trypsin
C. Carboxypeptidase, elastase, pepsin
D. Aminopeptidase, carboxypeptidase, pepsin

Which pair contains only exopeptidases?

A. Pepsin and trypsin
B. Chymotrypsin and elastase
C. Trypsin and aminopeptidase
D. Carboxypeptidase and aminopeptidase

Which event is the key initiating step that leads to activation of the major pancreatic zymogens?

A. Pepsinogen cleavage by HCl
B. Enteropeptidase activates trypsinogen
C. Aminopeptidase activates pepsin
D. Elastase activates trypsinogen

During acute inflammation, elastase released from which cell type can contribute to tissue injury if not properly inhibited?

A. Eosinophil
B. Neutrophil
C. Macrophage
D. Fibroblast

Exopeptidases are best defined as enzymes that:

A. Cleave internal peptide bonds
B. Remove one terminal residue
C. Hydrolyze disulfide bonds
D. Deaminate free amino acids

Which kinase directly integrates nutrient and growth factor signals to inhibit autophagy when active?
A. AMPK
B. mTOR
C. Akt
D. GSK3β

During energy deprivation, which kinase is activated to initiate autophagy via mTOR inhibition?
A. Akt
B. JAK2
C. AMPK
D. ERK1/2

In the low-energy autophagy pathway, what is the direct effect of AMPK on the TSC1/TSC2 complex?
A. Phosphorylates and activates TSC1/TSC2
B. Dephosphorylates and inactivates TSC1/TSC2
C. Induces degradation of TSC1/TSC2
D. Prevents transcription of TSC1/TSC2

Under low-energy conditions, with inactive Rheb and inhibited mTOR, what happens to autophagy?
A. mTOR activated, autophagy blocked
B. mTOR unchanged, autophagy unchanged
C. mTOR inhibited, autophagy blocked
D. mTOR inhibited, autophagy proceeds

In the presence of insulin or growth factors, which kinase is activated upstream of mTOR to oppose autophagy?
A. AMPK
B. PKC
C. JNK
D. Akt

Under insulin signaling with active Rheb-GTP, what is the net effect of mTOR on cell processes?
A. Stimulates autophagy and protein synthesis
B. Stimulates autophagy and inhibits protein synthesis
C. Inhibits autophagy and stimulates protein synthesis
D. Inhibits both autophagy and protein synthesis

A patient presents with diarrhea, dermatitis, and dementia. Pellagra is suspected. This syndrome most commonly results from deficiency of:
A. Niacin or dietary tryptophan
B. Riboflavin or dietary tyrosine
C. Biotin or dietary cysteine
D. Folate or dietary glycine

In cystinuria, the abnormal transport protein normally reabsorbs amino acids from which location?

A. Blood into glomerulus
B. Kidney lumen into tubular cells
C. Tubular cells into blood
D. Liver into bile canaliculi

Which enzyme is both a pancreatic protease and an exopeptidase?

A. Chymotrypsin
B. Pepsin
C. Carboxypeptidase
D. Aminopeptidase

Which metabolic condition most directly activates AMPK in the autophagy pathway described?

A. High ATP state
B. High AMP state
C. High insulin state
D. High Rheb state

In the fed state, activation of mTOR has which additional major effect besides inhibiting autophagy?

A. Blocks peptide absorption
B. Stimulates protein synthesis
C. Activates ubiquitination
D. Suppresses Akt signaling

Which of the following proteases is primarily responsible for the execution of programmed cell death (apoptosis)?

A. Matrix metalloproteinases

B. Caspases

C. Calpains

D. Serine proteases

Which group of proteases plays a major role in physiological processes such as digestion and blood clotting?

A. Caspases

B. Calpains

C. Serine proteases

D. Matrix metalloproteinases

The remodeling of extracellular matrix components is a function primarily attributed to which of the following?

A. Proteasomes

B. Matrix metalloproteinases

C. Serine proteases

D. Caspases

Which of these cysteine proteases is described as having "many different cellular roles" that are strictly dependent on calcium levels?

A. Serine proteases

B. Caspases

C. Calpains

D. Proteasomes

A segment of dietary protein consists mainly of alanine, glycine, and serine. Which enzyme preferentially cleaves peptide bonds whose carboxyl group is contributed by these small side chains?
A. Pepsin
B. Trypsin
C. Chymotrypsin
D. Elastase

Which statement best describes the cap complexes regulating the ubiquitin–proteasome system?
A. Two calcium-dependent caps bind substrates
B. Caps detach ubiquitin using lysosomal enzymes
C. Caps inhibit ATP use during degradation
D. Four ATP-dependent caps recognize ubiquitin

In both Hartnup disease and cystinuria, how are the affected amino acids handled?
A. Tubular reabsorption increased, urinary levels decreased
B. Tubular secretion increased, reabsorption unchanged
C. Tubular reabsorption decreased, urinary levels increased
D. No filtration, so none appear in urine