PHR 912 - Block 3 Test With
Correct Solution
What statement about pepsin is correct? (3 are correct)
1. Is synthesized by a zymogen
2. In slightly basic condition (pH =7.5) pepsin is autocatalyzed to become an active
enzyme
3. It's enzymatic activity is pH-sensitive
4. It is an endopeptidase - ANSWER 1, 3 & 4 are correct
2 is incorrect because pepsin is acidic pH dependent
Which statement is wrong about protein digestion? (Two options)
1. Pepsin begins the process by breaking down proteins to smaller polypeptides
2.. Cleavage of oligopeptides is achieved by enzymes produced by intestinal epithelial
cells (aminopeptidases) at the brush border
3. Amino acid absorption occurs through the intestinal epithelium
4. Di and tripeptides are absorbed and cleaved intracellular in epithelial cels by other
peptidases
5. In the stomach, polypeptides are also transported across the plasma membrane
6. Monoamino acids are also generated by HCl produced in the stomach - ANSWER 5 is
wrong because polypeptides will only exit the stomach into the small intestine
6 is wrong because the HCl does not generate amino acids, nor are monoamino acids
produced in the stomach
Which statement is wrong about diseases associated with digestion/absorption? (Two
options)
1. A person with cystinuria shows abnormal excretion of cystine, Arg and Lys
2. A person with cystinuria shows abnormal excretion of Trp
3.. The concentrated cysteine in kidney leads to the formation of kidney stones
4. Hartnup disease is caused by defective transport of neutral amino acids
,5. Hartnup disease is routinely treated with supplemental nicotinamide
6. Kwashiorkor is caused by the deficiency of protein diet
7. Celiac disease is caused by genetic defects of amino acid transporters - ANSWER 2 is
wrong because 1 is correct
7 is wrong because celiac disease is caused by an autoimmune response to eating
gluten
Which statement is wrong about the gamma-glutamyl cycle?
1. Transports amino acids into cells in intestine and kidney
2. A transpeptidase is required to transport amino acids
3. ATP is required from amino acid transport
4. Is a Na+ dependent transport system
5. Involves covalent modification of amino acid - ANSWER 4 is wrong because the
requirements of the gamma-glutamyl cycle are Glutathione, ATP, transpeptidase and
the covalent linkage of amino acid and glutathione
In which disease does the following molecule play a dominant role?
(Di-sulfur bond) - ANSWER Cystinuria
Which statements about intracellular protein degradation?
1. Lysosomal proteases are capable of degrading proteins all the way to amino acids
2. In general, lysosomal proteases are optimal in acidic conditions
3. Proteasome degrades ubiquity-tagged proteins
4. Proteasome produce monoamino acids - ANSWER 4 is incorrect because they
generate small peptides (8-11 polymer)
Which of the following is wrong about nitrogen metabolism? (2 options)
1. About 50% of nitrogen in the body is excreted as free ammonium ion
2. Humans are totally dependent on other organisms for converting atmospheric
nitrogen into forms available to the body
3. Dietary proteins are the primary source of nitrogen metabolized by the body
4. Carbon skeletons of amino acids are oxidized for energy, converted to glucose and
stored as glycogen
5. Amino nitrogen is mainly excrete as uric acid
, 6. Amino acids are used for synthesis of purines - ANSWER 1 and 5 are both wrong
because about 90% of the nitrogen in the body is excreted as *urea*
Which statement is wrong about amino acid absorption?
1. AAs are absorbed through a single transporter
2. AAs are absorbed through semi-specific Na+-dependent transport systems
3. Na+,K+ - ATPase plays a critical role in intestinal amino acid absorption
4. Pancreatic enzymes are required to process oligopeptides - ANSWER 1 is wrong
because amino acids require a cotransporter to be absorbed
Which statement is incorrect about non-essential amino acids?
1. Non-essential amino aids are synthesized in the body if not present in the diet
2. A non-essential amino acid, tyrosine, is synthesized from an essential amino acid,
phenylalanine
3. Arginine is not synthesized in the body
4. Glutamate is a non-essential amino acid - ANSWER 3. Is incorrect because arginine is
a non-essential amino acid, meaning it is synthesized in the body
*The non-essential amino acids are:*
Alanine, Arginine, Asparagine, Aspartate, Cysteine, Glutamate, Glycine, Proline, Serine,
Tyrosine
*The essential amino acids are:*
Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine,
Tryptophan, Valine
Which of the following is wrong about trypsin?
1. Is a serine protease
2. Is an exopeptidase
3. Activates other inactive pancreatic enzymes
4. Cleaves after lys, arg residues - ANSWER 2 is wrong because trypsin is an
endopeptidase
Trypsinogen is the inactive form of trypsin that is activated by a membrane bound
enterokinase
Once active, trypsin will activate:
Correct Solution
What statement about pepsin is correct? (3 are correct)
1. Is synthesized by a zymogen
2. In slightly basic condition (pH =7.5) pepsin is autocatalyzed to become an active
enzyme
3. It's enzymatic activity is pH-sensitive
4. It is an endopeptidase - ANSWER 1, 3 & 4 are correct
2 is incorrect because pepsin is acidic pH dependent
Which statement is wrong about protein digestion? (Two options)
1. Pepsin begins the process by breaking down proteins to smaller polypeptides
2.. Cleavage of oligopeptides is achieved by enzymes produced by intestinal epithelial
cells (aminopeptidases) at the brush border
3. Amino acid absorption occurs through the intestinal epithelium
4. Di and tripeptides are absorbed and cleaved intracellular in epithelial cels by other
peptidases
5. In the stomach, polypeptides are also transported across the plasma membrane
6. Monoamino acids are also generated by HCl produced in the stomach - ANSWER 5 is
wrong because polypeptides will only exit the stomach into the small intestine
6 is wrong because the HCl does not generate amino acids, nor are monoamino acids
produced in the stomach
Which statement is wrong about diseases associated with digestion/absorption? (Two
options)
1. A person with cystinuria shows abnormal excretion of cystine, Arg and Lys
2. A person with cystinuria shows abnormal excretion of Trp
3.. The concentrated cysteine in kidney leads to the formation of kidney stones
4. Hartnup disease is caused by defective transport of neutral amino acids
,5. Hartnup disease is routinely treated with supplemental nicotinamide
6. Kwashiorkor is caused by the deficiency of protein diet
7. Celiac disease is caused by genetic defects of amino acid transporters - ANSWER 2 is
wrong because 1 is correct
7 is wrong because celiac disease is caused by an autoimmune response to eating
gluten
Which statement is wrong about the gamma-glutamyl cycle?
1. Transports amino acids into cells in intestine and kidney
2. A transpeptidase is required to transport amino acids
3. ATP is required from amino acid transport
4. Is a Na+ dependent transport system
5. Involves covalent modification of amino acid - ANSWER 4 is wrong because the
requirements of the gamma-glutamyl cycle are Glutathione, ATP, transpeptidase and
the covalent linkage of amino acid and glutathione
In which disease does the following molecule play a dominant role?
(Di-sulfur bond) - ANSWER Cystinuria
Which statements about intracellular protein degradation?
1. Lysosomal proteases are capable of degrading proteins all the way to amino acids
2. In general, lysosomal proteases are optimal in acidic conditions
3. Proteasome degrades ubiquity-tagged proteins
4. Proteasome produce monoamino acids - ANSWER 4 is incorrect because they
generate small peptides (8-11 polymer)
Which of the following is wrong about nitrogen metabolism? (2 options)
1. About 50% of nitrogen in the body is excreted as free ammonium ion
2. Humans are totally dependent on other organisms for converting atmospheric
nitrogen into forms available to the body
3. Dietary proteins are the primary source of nitrogen metabolized by the body
4. Carbon skeletons of amino acids are oxidized for energy, converted to glucose and
stored as glycogen
5. Amino nitrogen is mainly excrete as uric acid
, 6. Amino acids are used for synthesis of purines - ANSWER 1 and 5 are both wrong
because about 90% of the nitrogen in the body is excreted as *urea*
Which statement is wrong about amino acid absorption?
1. AAs are absorbed through a single transporter
2. AAs are absorbed through semi-specific Na+-dependent transport systems
3. Na+,K+ - ATPase plays a critical role in intestinal amino acid absorption
4. Pancreatic enzymes are required to process oligopeptides - ANSWER 1 is wrong
because amino acids require a cotransporter to be absorbed
Which statement is incorrect about non-essential amino acids?
1. Non-essential amino aids are synthesized in the body if not present in the diet
2. A non-essential amino acid, tyrosine, is synthesized from an essential amino acid,
phenylalanine
3. Arginine is not synthesized in the body
4. Glutamate is a non-essential amino acid - ANSWER 3. Is incorrect because arginine is
a non-essential amino acid, meaning it is synthesized in the body
*The non-essential amino acids are:*
Alanine, Arginine, Asparagine, Aspartate, Cysteine, Glutamate, Glycine, Proline, Serine,
Tyrosine
*The essential amino acids are:*
Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine,
Tryptophan, Valine
Which of the following is wrong about trypsin?
1. Is a serine protease
2. Is an exopeptidase
3. Activates other inactive pancreatic enzymes
4. Cleaves after lys, arg residues - ANSWER 2 is wrong because trypsin is an
endopeptidase
Trypsinogen is the inactive form of trypsin that is activated by a membrane bound
enterokinase
Once active, trypsin will activate:
