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AAA-MEDICAL NUTRITION > CARBOHYDRATES AND PROTEINS > Flashcards

CARBOHYDRATES AND PROTEINS Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the cheapest source of calories providing 50% or more of calories in most diets?

A

Carbohydrates

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2
Q

What is the general elemental composition of carbohydrates?

A

Cx(H2O)y

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3
Q

What is the recommended daily carbohydrate intake for males and females?

A

Males: 220-330 g/day, Females: 180-230 g/day

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4
Q

What are the principal dietary carbohydrates?

A

Polysaccharides, disaccharides, and monosaccharides

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5
Q

Which polysaccharides are primarily digested in the gastrointestinal tract?

A

Starches (glucose polymers) and their derivatives

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6
Q

What is the structure of amylopectin?

A

A branched molecule

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7
Q

What is the structure of amylose?

A

A straight chain with only α1,4 linkages

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8
Q

What are the common dietary disaccharides?

A

Lactose (milk sugar) and sucrose (table sugar)

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9
Q

What are the common dietary monosaccharides?

A

Fructose and glucose

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10
Q

What is sorbitol, and how does it affect blood sugar?

A

Sorbitol is formed when the aldehyde group of glucose is hydrogenated to an alcohol group, slowing its absorption and diminishing its effect on blood sugar concentration.

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11
Q

What is the major storage form of polysaccharides in animals?

A

Glycogen

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12
Q

What is the structural similarity between glycogen and amylose?

A

Both are straight-chain polymers.

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13
Q

What are examples of non-starch polysaccharides?

A

Cellulose, hemicellulose, pectins, gums, alginates

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14
Q

What makes cellulose indigestible by humans?

A

It is composed of beta-1,4-linked glucose molecules in straight chains.

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15
Q

What is the primary enzyme responsible for carbohydrate digestion in the mouth?

A

Salivary alpha-amylase

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16
Q

At what pH is salivary alpha-amylase deactivated?

A

pH of 4 or lower

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17
Q

Which enzyme is more efficient at digesting carbohydrates in the small intestine?

A

Pancreatic alpha-amylase

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18
Q

What are the end products of alpha-amylase digestion?

A

Maltose, maltotriose, and α-limit dextrins

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19
Q

What enzymes hydrolyze disaccharides and small glucose polymers into monosaccharides?

A

Lactase, sucrase, maltase, and α-dextrinase

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20
Q

What are the monosaccharide products of lactose digestion?

A

Glucose and galactose

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21
Q

What are the monosaccharide products of sucrose digestion?

A

Glucose and fructose

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22
Q

What is the enzyme responsible for breaking down maltose?

A

Maltase (glucoamylase)

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23
Q

What is the substrate and product of trehalase?

A

Substrate: Trehalose, Product: Glucose

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24
Q

What is the glycemic index range for ‘good’ carbohydrates?

A

≤ 55

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25
Q

What glycemic index value is considered ‘bad’?

A

> 70

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26
Q

What is the clinical importance of butyrate produced by dietary fiber fermentation?

A

Butyrate serves as a fuel for colonocytes and supports their development.

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27
Q

What receptors are involved in the transport of short-chain fatty acids in the colon?

A

GPR43, SLC5A8, SLC16A1, and GPR109A

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28
Q

What is the significance of receptors SLC5A8 and GPR109A?

A

They are critical in the development of colonocytes.

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29
Q

What is the preferred energy substrate of colonocytes?

A

Butyrate

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30
Q

What is the role of butyrate in gene transcription?

A

Inhibits histone deacetylases, modulating the epigenetic profile and transcription of selective genes in the colon

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31
Q

What is the carbon source for ketone body generation in colonocytes?

A

Butyrate

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32
Q

What is the function of dietary fiber in fecal bulk?

A

Increases mass of fecal flora, leading to increased fecal bulk

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33
Q

How does fiber affect absorption of sugars and fats?

A

Delays absorption of sugars and fats

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34
Q

What component of fiber lowers serum cholesterol by binding bile salts?

A

Lignin

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35
Q

What type of carbohydrate transport depends on sodium concentration?

A

Glucose and galactose transport via SGLT1

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36
Q

What transporter is responsible for glucose and galactose uptake from the gut?

A

SGLT1 (sodium-glucose cotransporter-1)

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37
Q

What transporter facilitates fructose entry into enterocytes?

A

GLUT5

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38
Q

How is glucose transported out of enterocytes into the interstitium?

A

Via GLUT2

39
Q

What is the most common congenital disaccharidase deficiency?

A

Congenital Sucrase-Isomaltase Deficiency

40
Q

What are common symptoms of lactose intolerance?

A

Diarrhea, bloating, and flatulence after ingestion of sugar

41
Q

What test is used to diagnose lactose intolerance?

A

Breath test detecting excessive gas

42
Q

What causes secondary lactase deficiency?

A

Mucosal injury from infectious gastroenteritis, parasitic infections, celiac disease, or Crohn’s disease

43
Q

What genetic defect causes glucose-galactose malabsorption?

A

Autosomal recessive defect in SGLT1 on chromosome 22q13

44
Q

What is the treatment for glucose-galactose malabsorption?

A

Fructose, as it is not affected by the defect

45
Q

What syndrome results from GLUT2 mutation?

A

Fanconi-Bickel syndrome

46
Q

What are complications of excessive fructose consumption?

A

Hypertriglyceridemia,
hyperuricemia, and
gout

47
Q

What is the clinical importance of butyrate in colon health?

A

It serves as a fuel for colonocytes and supports the gut-associated immune system

48
Q

What are the transporters involved in short-chain fatty acid transport into the epithelium?

A

GPR43, SLC5A8, SLC16A1, and GPR109A

49
Q

What transporter is specific to butyrate uptake?

A

GPR109A

50
Q

What is the treatment for congenital sucrase-isomaltase deficiency?

A

Sacrosidase

51
Q

What enzymes are inhibited by excessive gastric acid in ZES?

A

Pancreatic alpha-amylase and other pancreatic enzymes

52
Q

How does fructose malabsorption manifest in IBS patients?

A

Fructose is not absorbed efficiently, leading to gastrointestinal symptoms

53
Q

What happens to glucose and galactose in congenital SGLT1 defect?

A

They are not absorbed, leading to severe diarrhea and dehydration

54
Q

What is the consequence of GLUT2 mutation in carbohydrate metabolism?

A

Fasting hypoglycemia,
glycogen deposition, and
tubular nephropathy

55
Q

Why is fructose a suitable carbohydrate for patients with glucose-galactose malabsorption?

A

Fructose is absorbed via GLUT5 and is independent of SGLT1

56
Q

What short-chain fatty acid serves as a preferred energy substrate for colonocytes?

A

Butyrate

57
Q

How does fiber affect satiety?

A

Satiety is achieved more rapidly

58
Q

How is lactose intolerance treated?

A

Supplementation with lactase

59
Q

What are the clinical manifestations of congenital lactase deficiency?

A

Severe watery diarrhea upon receiving lactose-containing formula

60
Q

How does excessive gastric acid in ZES affect carbohydrate digestion?

A

Deactivates pancreatic enzymes, leading to malabsorption and diarrhea

61
Q

What happens to fructose upon entry into enterocytes?

A

It is phosphorylated, converted to glucose, and transported as glucose

62
Q

How does SGLT2 function in glucose transport?

A

It transports glucose out of the renal tubules

63
Q

What are the clinical consequences of consuming >50g of fructose?

A

Increased triglycerides, hyperuricemia, and potential for gout

64
Q

What transporter moves glucose and galactose into enterocytes?

A

SGLT1

65
Q

What is the role of GLUT5 in carbohydrate metabolism?

A

Facilitates the transport of fructose into enterocytes

66
Q

What happens to glucose in Fanconi-Bickel syndrome?

A

Glucose is stored excessively in the liver as glycogen, leading to hepatomegaly

67
Q

What is the relationship between sodium levels and glucose transport?

A

Higher sodium levels drive more glucose into cells via SGLT1

68
Q

Why does lactose intolerance cause bloating and flatulence?

A

Undigested lactose is fermented by bacteria in the colon, releasing gas

69
Q

What is the primary source of essential and non-essential amino acids for cellular metabolism?

A

Proteins

70
Q

What condition results from a deficiency of proteins due to non-availability of essential amino acids?

A

Negative nitrogen balance

71
Q

What percentage of energy in an average Western diet comes from proteins?

A

10-15%

72
Q

How much endogenous protein is secreted daily in the form of digestive secretions and desquamated cells?

A

30 g/day

73
Q

What is the difference between plant-based and animal-based proteins in terms of biological value?

A

Animal-based proteins have high biological value; plant-based proteins have low biological value.

74
Q

At what pH does pepsin optimally cleave peptide linkages in the stomach?

A

1.6 – 3.2

75
Q

Which enzymes act as endopeptidases in the small intestine?

A

Trypsin, chymotrypsin, and elastase

76
Q

What is the role of collagen in protein digestion?

A

It is a major constituent of connective tissue, and its fibers must be digested for meat protein digestion.

77
Q

Which pancreatic enzyme cleaves aromatic amino acids from the carboxy terminal end of proteins?

A

Carboxypeptidase A

78
Q

Which pancreatic enzyme cleaves arginine or lysine from the carboxy terminal end of proteins?

A

Carboxypeptidase B

79
Q

What type of peptidase cleaves amino acids from the carboxy terminal of 3-8 amino acid peptides?

A

Amino-oligopeptidase

80
Q

What transporter facilitates the absorption of dipeptides and tripeptides into intestinal cells?

A

PepT1 transporter

81
Q

Which condition is associated with defective secretion of pancreatic enzymes, causing generalized malabsorption?

A

Cystic fibrosis

82
Q

What is the genetic cause of Hartnup disease?

A

A congenital defect in the transport mechanism for neutral amino acids in the intestine and renal tubules.

83
Q

What happens in lysinuric protein intolerance due to a defect in the basolateral membrane (BLM)?

A

Impaired exit of cationic amino acids leads to protein malnutrition, hyperammonemia, and multi-organ disease.

84
Q

What is the treatment recommendation for celiac disease?

A

Gluten-free diet

85
Q

What is the most common congenital defect in amino acid transport causing renal and intestinal symptoms?

A

Cystinuria

86
Q

Which transporter system is used for sodium-independent transport of neutral amino acids?

A

System L

87
Q

What happens when PepT1 expression is induced in colon cancer?

A

It facilitates the transport of bacterially derived peptides, promoting the inflammatory process.

88
Q

How is dietary protein digested in the stomach?

A

Pepsin cleaves peptide linkages, hydrolyzing bonds between aromatic amino acids and a second amino acid.

89
Q

Which brush-border enzyme cleaves proline-containing dipeptides with a free alpha amino group?

A

Dipeptidyl aminopeptidase IV

90
Q

Why are enteral diets based solely on free amino acids hyperosmolar?

A

Free amino acids increase osmolality, unlike dipeptides and tripeptides, which improve solubility and stability.

91
Q

Which amino acid transporter is sodium-coupled and primarily transports glutamine, asparagine, and histidine?

A

System N

92
Q

Which genetic polymorphism reduces PepT1 substrate affinity?

A

Substitution of phenylalanine at position 28 with tyrosine

93
Q

What is the role of gamma-glutamyl transpeptidase in protein digestion?

A

It cleaves gamma-glutamyl bonds and transfers glutamine to amino acid or peptide acceptors.

AAA-MEDICAL NUTRITION (2 decks)

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