Deck 6: Protein

Question 1

A function of hydrochloric acid in gastric juice during protein digestion is

A) to neutralize the acidity of the stomach.
B) to inactivate pepsinogen by suppressing pepsin formation.
C) to denature the quaternary, tertiary, and secondary structures of protein.
D) to cleave peptide bonds.

Answer 1

C

Question 2

During protein digestion, peptides are broken into free amino acids mainly

A) in the mouth.
B) in the stomach.
C) at the brush border.
D) within the enterocyte.

Answer 2

D

Question 3

What organ serves as the primary site of amino acid metabolism?

A) kidney
B) muscles
C) liver
D) neuropeptides

Answer 3

C

Question 4

What is the primary mechanism for regulation of amino acids in excess of need for synthesis of protein, providing about 50% of the liver energy needs after a meal?

A) oxidation
B) decarboxylation
C) phosphorylation
D) hydrogenation

Question 5

If you were deficient in vitamins B₆ and B₁₂ and had high blood levels of homocysteine, what dietary substance could remove some of the homocysteine by donating a methyl group to form methionine?

A) biotin
B) betaine
C) serine
D) creatine

Question 6

Serotonin is made from which amino acid?

A) tyrosine
B) niacin
C) threonine
D) tryptophan

Question 7

Three important enzymes remove ammonia from body cells. One is carbamoyl phosphate synthestase I. The other two are:

A) branched-chain alpha-keto acid dehydrogenase and phenylalanine hydroxylase.
B) alanine aminotransferase and aspartate aminotransferase.
C) glutaminase and threonine dehydratase.
D) glutamate dehydrogenase and glutamine synthetase.

Question 8

Which of the following is NOT a neurotransmitter?

A) acetylcholine
B) serotonin
C) insulin
D) epinephrine

Question 9

Which of the following amino acids is ketogenic?

A) glycine
B) alanine
C) leucine
D) aspartate

Question 10

Choose the correct order of enzyme activities in protein digestion.

A) tripeptidases, carboxypeptidasea, pepsin, free amino acids
B) trypsin, pepsin, collagenase, dipeptidases
C) pepsin, trypsin, carboxypeptidases, dipeptidases
D) trypsinogen, enteropeptisdase, dipeptidase, chymoptrypsin

Question 11

When the amino group has been removed from an amino acid, the carbon skeleton or α-keto acid may be used in many different ways. Which of the following is NOT a possible fate for the carbon skeleton?

A) conversion to glucose
B) oxidation for energy
C) production of ketone bodies
D) synthesis of creatine

Question 12

Zwitterions are amino acids that have no net electrical charge because

A) their side chains are not charged.
B) they migrate to a neutral place in an electrical field.
C) they are essential/indispensable.
D) they have an amino group in their side chain.

Question 13

Name the genetic disease associated with the lack of the liver enzyme necessary to convert phenylalanine to tyrosine.

A) maple syrup urine disease
B) phenylketonuria
C) homocystinuria
D) lactase deficiency

Question 14

When the diet is lacking in the amino acids lysine and threonine

A) proteins will be made without one amino acid.
B) the body will synthesize them.
C) protein synthesis will be limited.
D) another amino acid will be substituted so that synthesis is uninterrupted.

Question 15

Which three amino acids cannot undergo transamination to an appreciable extent, making provision of their alpha-keto acids ineffective in lowering blood nitrogen concentrations in kidney disease patients?

A) leucine, isoleucine, valine
B) lysine, threonine, histidine
C) valine, tryptophan, phenylalanine
D) methionine, cysteine, phenylalanine

Question 16

Urea synthesis occurs partly in the mitochondria and partly in the cytosol of the _____.

A) glomeruli
B) tubules
C) enterocytes
D) hepatocytes

Question 17

Which regulatory peptides in the pancreatic phase of digestion activate the release of brush-border enzymes such as enteropeptidase?

A) trypsinogen and trypsin
B) cholecystokinin and secretin
C) carboxypeptidase A and B
D) elastin and chymotrypsin

Question 18

Using, 2 high-energy bonds, arginosuccinate synthetase joins aspartate and citrulline to produce arginosuccinate in the cytosol. This is the rate-limiting step in _____ synthesis.

A) pyrimadine
B) purine
C) urea
D) creatine

Question 19

The product(s) of pepsin's action is/are _____.

A) disaccharides
B) amylose
C) short-chain fatty acids
D) hydrolyzed proteins

Question 20

In general, most amino acids are absorbed from the

A) stomach.
B) duodenum and jejunum.
C) ileum.
D) colon.

Question 21

Which of the following amino acids represent the branched-chain amino acids found in systemic circulation?

A) glycine, alanine, threonine
B) phenylalanine, tyrosine, tryptophan
C) valine, leucine, isoleucine
D) arginine, lysine, histidine

Question 22

What two major systems are used for protein degradation in most cells?

A) mitochondrial and cytosolic
B) u-calpain and m-calpain
C) GTP-requiring and GTP-independent
D) lysosomal and ubiquitin-proteosomal

Question 23

A genetic defect diminishing branched-chain alpha-keto acid dehydrogenase complex activity results in

A) phenylketonuria.
B) homocysteinuria.
C) cystathioninuria.
D) maple syrup urine disease.

Question 24

What percentage of resting energy expenditure is attributed to protein synthesis and degradation?

A) 9%
B) 10-25%
C) 30-40%
D) 45-55%

Question 25

A particular amino acid is very important for several metabolic pathways in enterocytes and so it is often added to nutritional mixtures used for hospitalized patients. The important amino acid is

A) tryptophan.
B) glutamine.
C) glycine.
D) asparagine.

Question 26

Which amino acids are metabolized mostly in skeletal muscles?

A) those with side chains containing aromatic rings
B) those with side chains that are branched
C) those with side chains containing basic groups
D) those with side chains containing sulfur atoms

Question 27

Which amino acid, when oxidized, spares the essential gluconeogenic precursors pyruvate and lactate?

A) cysteine
B) alanine
C) leucine
D) glutamine

Question 28

What is the current Tolerable Upper Intake Level established for protein and amino acids?

A) Ingestion of a diet supplying > 30% energy from protein
B) Two times the RDA
C) 42 mg/kg/d
D) No Tolerable Upper Intake Level has been established.

Question 29

Purine degradation results in the formation of xanthine and creation of _____ by xanthine oxidase.

A) polyamines
B) gout
C) citric acid
D) uric acid

Question 30

Which level of organization determines the final form of a protein molecule consisting of several polypeptide chains?

A) primary
B) secondary
C) tertiary
D) quaternary

Question 31

Legumes are limited in sulfur-containing amino acids, methionine and cysteine. What food group is considered complementary because it supplies these amino acids?

A) fruits
B) nuts
C) grains
D) starchy vegetables

Question 32

Which of the following is a nitrogen-containing, non-protein compound that performs an important function in the body?

A) glutathione
B) methionine
C) pepsin
D) actin

Question 33

Carbamoyl aspartate can only be used for _____ synthesis.

A) pyrimidine
B) purine
C) urea
D) creatine

Question 34

One of the more common ways to evaluate protein quality in a food that does not involve nitrogen balance studies is:

A) chemical score.
B) net dietary protein calories percentage.
C) biological value.
D) net protein utilization.

Question 35

When evaluating protein quality, which of the following measures represents the gain in body weight on a test protein divided by the grams of protein consumed?

A) chemical score
B) BV
C) PER
D) NPU