Protein digestion and metabolism Flashcards
Which of the following are the sources of two nitrogen that are incorporated in the urea during the urea cycle?
A. Glutamine and glutamate
B. Ammonia and arginine
C. Fumarate and aspartate
D. Aspartate and ammonia
D
A patient is brought to the hospital in a comatose state. The
family says that he was behaving in an irrational way prior to losing consciousness. You know that he is a chronic alcoholic but you can smell ammonia, not alcohol, in his breath. Which of the following will most likely explain the mental disturbance and coma?
A. Increased urea levels in blood due to liver disease
B. Increased serum pH due to NH4 OH formation from NH3
C. Increased levels in brain of glutamate, which is a toxic
compound
D. Lowered ATP in the brain due to depletion of alpha-
ketoglutarate and impaired TCA function
D
Why must essential amino acids be provided in the diet?
It is not synthesized in the body
B12 deficiency
A. decrease concentration of N5-methylfolate
B. increase serum homocysteine
C. increase production of SAM
D. decrease production of folate
B
What should be provided in the diet of patients suffering from phenylketonuria?
A. phenylalanine
B. tyrosine
C. phenylalanine and tyrosine
D. all essential amino acids
B
What amino acid is the precursor for NAD?
A. Lysine B.Tryptophan C. Phenylalamine D. Methathionine E. Arginine
B
Which of the following will explain why creatine levels in blood and urine is a kidney function test?
A. Because it is a storage form of high energy
B. Because it is a measure of muscle mass
C. Because it is produced at a constant rate
D. Because it is a precursor of phosphocreatine
C
Which of the following statements best describes why dietary proteins is essential to man?
A. High biological value protein is the essential source of energy needed for human body protein synthesis
B. High biological value protein is the source of essential amino acids needed for the human body protein synthesis.
C. High biological value proteins are less digestible source of amino acids for ATP production.
D. All of the above
B
Which pair of amino acids is LEAST likely to be transported by a common Na+ dependent transporter?
A. Lysine and aspartate B. Arginine and lysine C. Valine and leucine D. Serine and threonine E. Phenylalanine and tyrosine
A
Which product pair will be formed from the transamination of aspartate and alpha ketoglutarate?
A. Alanine + alpha-ketoglutarate
B. Oxaloacetate + glutamate
C. Pyruvate + oxaloacetate
D. Glutamate + oxaloacetate
B
Which of the following pair of compounds is utilized to transport ammonia produced in muscles and other peripheral tissues to the liver?
A. Alanine and urea
B. Alpha-ketoglutarate and glutamate
C. Alanine and glutamine
D. Pyruvate and urea
C
Which one of the following diets is probably being consumed if a person’s urine contains unusually high concentrations of urea?
A. High CHO, very low CHON B. Very high CHO, no CHON, no fat C. Very very high fat, high CHO, no CHON D. Very high fat, very low CHON E. Very low CHO, very high CHON
E
What is the classification of an amino acid that yields acetoacetyl CoA during the catabolism of its carbon skeleton?
A. Glycogenic B. Ketogenic C. Glycogenic and ketogenic D. Essential E. Non-essential
B
Which of the following will explain why arginineis considered a semi essential amino acid?
A. It can be synthesized from urea cycle pathways in other tissues.
B. The requirement for this amino acid is dependent on the health status and the stage of development.
C. The normal diet is usually deficient in arginine.
D. All of the above
E. A and B only
E
In amino acid metabolism, which of the following is NOT involved in metabolism of one-carbon compounds?
A. Tetrahydrofolate
B. S-adenosyl methionine
C. Tetrahydrobipterin
D. Methylcobalamin
C
Some of the signs and symptoms of the genetic disorder phenylketonuria include mental retardation and other neurological deficits. Physical development is below normal and hair, although dark, may contain patches of white. Which of the following reactions is defective in phenylketonuria?
A. Adenosine → Inosine
B. Phenylalanine → Tyrosine
C. Phenylalanine → Phenylpyruvate
D. Homocysteine → Methionine
B
Which of the following amino acids should be supplemented in the diet of phenylketonurics?
A. Phenylalanine
B. Tyrosine
C. Alanine
D. Glutamine
B
The mental retardation and other neurological symptoms among phenylketonurics have been related to the unavailability of which neurotransmitters derived from tyrosine?
A. Epineprine B. Norepineprine C. Dopamine D. All of the above E. A and B only
D
Which of the following conditions will be observed in a healthy adult immediately after undergoing appendectomy?
A. There will be increased excretion of nitrogenous excretory product primarily urea.
B. There will be a shift towards positive nitrogen balance.
C. The nitrogen balance will remain in equilibrium.
D. All of the above
E. A and B only
A
Which among the following about protein and amino acid
metabolism is NOT CORRECT?
A. There is a small pool of amino acids that is readily available for the body.
B. Amino acids are used for the synthesis of other nitrogenous compounds.
C. The primary function of serum albumin is the storage of proteins.
D. Amino acids are continuously despite protein uptake.
C
Which compound can’t be synthesized from tyrosine?
a. Catecholamines
b. Melanin
c. Serotonin
d. Thyroid Hormone
C
Which statement is not true about protein digestion?
A. it occurs on the stomach and intestines
B. it is initiated by the acidic gastric juices
C. it is accompanied by zymogenic gastric and pancreatic juices
C
Which of the following statements are true for both aminotransferase and glutamate dehydrogenase?
A. Both sequentially remove an amino group from the amino acid as ammonia
B. Both use α-ketoglutarate as reactant
C. Both have specific coenzymes
D. A and B
A
Which of the following are mechanisms for detoxifying ammonia?
A. Urea B. Glutamine C. Glucose-alanine cycle D. A and B E. All of the above
D
Which is true about essential amino acid?
A. cannot be synthesized by human body
B. can serve as precursor for nonessential amino acid
C. can be synthesized from glycolytic and TCA intermediates
D. All of the above
E. A & B only
E
Which of the ff a.a. is synthesized by the body but in isufficent amounts for growth?
A. asparigine
B. Arginine
C. Aspartate
D.methionine
B
Where are most amino acids metabolized?
Liver
Which amino acids are present in higher concentrations that other amino acids in most tissues?
Glu and Gln
Where does the digestion of protein begin?
Stomach
What stimulates the secretion of gastrin?
The entry of protein into the stomach
The secretion of gastrin stimulates the secretion of which gastric products?
HCl and pepsinogen
The inactive precursor of pepsin
Pepsinogen
What mediates the conversion of pepsinogen to pepsin?
Pepsinogen itself;
the conversion is by autocatalytic cleavage that occurs only at low pH
What triggers the secretion of HCl in the stomach?
Gastrin
What triggers the secretion of pepsinogen?
Gastrin
What triggers the secretion of secretin in the small intestine?
The entry of the low pH gastric contents in the intestines
The entry of amino acids and low pH gastric in the small intestines stimulate the release of which intestinal secretions?
Secretin and CCK
Upon stimulation, secretin enters the bloodstream and stimulates which organ to secrete bicarbonate?
Pancreas
The pancreas secretes this upon stimulation by secretin
Bicarbonate
How does bicarbonate from the pancreas get into the intestine to lower intestinal pH upon the entry of acidic gastric contents?
Through the pancreatic duct
How does secretin reach the pancreas to stimulate the secretion of bicarbonate?
Through the bloodstream
What function does bicarbonate serve in the instestine?
It lowers the pH upon entry of acidic gastric contents
Trypsinogen, chymotrypsinogen, and procarboxypeptidases are secreted by which tissues?
Exocrine cells of the pancreas
What are the active forms of trypsinogen, chymotrypsinogen, and procarboxypeptidase?
Trypsin, chymotrypsin and carboxypeptidase
What mediates the convesion of trypsinogen to trypsin?
Enteropeptidase begins the conversion; trypsin catalyzes the conversion of additional trypsinogen to trypsin
Where is enteropeptidase produced?
Enterocytes
What catalyzes the conversion of chymotrypsinogen to chymotrypsin?
Trypsin
What catalyzes the conversion of procarboxypeptidase to carboxypeptidase?
Trypsin
Why is there an elaborate mechanism for getting active digestive enzymes in the gastrointestinal tract?
The synthesis of enzymes as inactive precursors protects the exocrine cells from destructive proteolytic attack
What is the pancreatic trypsin inhibitor?
A protein secreted by the pancreas to protect itself from self-digestion; it prevents premature production of active proteolytic enzymes within the pancreatic cells
Where are the α-amino groups of amino acids removed?
Hepatocytes
The removal of α-amino groups of amino acids is promoted by which enzymes?
Aminotransferases/ transaminases
In transamination, the α-amino group is transferred to the α-carbon of which molecules?
α-ketoglutarate
When the α-amino group of an amino acid is transferred to α-ketoglutarate, what becomes of the amino acid?
It becomes an α-keto acid
When an α-ketoglutarate receives the α-amino group of an amino acid, what becomes of the α-ketoglutarate?
It becomes an L-Glutamate
All aminotransferases have the same prosthetic group and the same reaction mechanism. T/F
T
Which prosthetic groups do all aminotransferases have?
Pyridoxal phosphate (PLP)
PLP is the coenzyme form of which molecule?
Pyroxidine/ vitamin B6
What is the function of PLP?
It is an intermediate carrier of amino groups at the active site of aminotranferases
In hepatocytes, where does glutamate undergo oxidative deamination?
Mitochondria
Enzyme that catalyzes oxidative deamination
L-glutamate dehydrogenase
The only enzyme that can use either NAD or NADP as the acceptor of reducing equivalents
L-glutamate dehydrogenase
The combined action of an aminotransferase and glutamate dehydrogenase is referred to as what?
Transdeamination
The α-ketoglutarate formed from glutamate deamination can be used in the citric acid cycle and for glucose synthesis. T/F
T
How is toxic ammonia transported in the blood to the liver and kidney?
It is first transformed into a nontoxic substance. Free ammonia is combined with glutamate to form glutamine. Glutamine serves as the nontoxic transport of ammonia
Which enzyme catalyzes the formation of glutamine from glutamate and ammonia?
Glutamine synthetase
Excess glutamine for biosynthesis is transported to which organs for processing?
Intestines, kidneys, liver
Which enzyme cleaves glutamine into glutamate and ammonia?
Glutaminase
Ammonia from the intestines and kidneys is transported to which organ?
Liver
Where does urea synthesis occur?
Liver
How does the body dispose of ammonia?
By urea synthesis
Which amino acid do skeletal muscles use to transport α-amino groups to the liver?
Alanine
In the transdeamination of alanine, in which it transfers its α-amino group to α-ketoglutarate, which products are formed?
Pyruvate and glutamate
What is the enzyme that catalyzes transamination of alanine?
Alanine aminotransferase
Which organs uses alanine to transfer α-amino groups to the liver?
Skeletal muscle
Where in hepatocytes does the urea cycle occur?
Partly in the mitochondria, partly in the cytosol
Ammonia enters the urea cycle as what compound?
Carbamoyl phosphate
Which molecules react in order to form carbamoyl phosphate?
NH4+, HCO3, ATP
Which enzyme catalyzes the conversion of ammonia to carbamoyl phosphate?
Carbamoyl phosphate synthetase I
Carbamoyl phosphate synthetase I, the enzyme that catalyzes the production of carbamoyl phosphate is located where?
Inside the mitochondria
In the urea cycle, where does citruliine get its carbamoyl group?
From ornithine
Which urea cycle intermediate functions like oxaloacetate in the citric acid cycle?
Ornithine
Which TCA intermediate is produced in the urea cycle?
Fumarate
The second amino group in argininosiccinate is from which amino acid?
Aspartate
Carbamoyl phosphate synthase I is allosterically inhibited by which molecule?
N-acetylglutamate
How many ATP are required to produce a molecule of carbamoyl phosphate?
2
Which step of the urea cycle is reversible?
None
Ketogenic amino acids
Trp (W), Thr (T), Phe (F), Ile (I), Leu (L), Lys (K)
Glucogenic amino acids
Trp (W) Thr (T), Phe (F), Tyr (Y),
Ala (A), Asp (D), Arg (R), Asn (N),
Gly (G), Gln (Q), Glu (E),
Cys (C), S (Ser), His (H), Met (M), Pro (P)
One-carbon transfers in amino acid catabolism usually involve one of three cofactors. What are these three?
Biotin, Tetrahydrofolate, S-adenosylmethionine
Transfers one-carbon groups in immediate oxidation states and sometimes as methyl groups
A. Biotin
B. Tetrahydrofolate
C. S-adenosylmethionine
B
Transfers carbon in its most oxidized state
A. Biotin
B. Tetrahydrofolate
C. S-adenosylmethionine
A
Transfers methyl groups, the most reduced form of carbon
A. Biotin
B. Tetrahydrofolate
C. S-adenosylmethionine
C
Which of the following statements is TRUE regarding trypsin?
A. It is secreted in its catalytically active form.
B. Its catalytic triad includes a serine residue.
C. It functions optimally at acidic pH.
D. It serves primarily to hydrolyze triglycerides.
B
