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GI/Nutrition > Nutritional Biochemistry > Flashcards

Nutritional Biochemistry Flashcards

1
Q

Pancreatic Secretion

  • Zymogens — Proproteases:
  • Active enzymes:
  • Ions:
A
  • Zymogens – Proproteases:
    • Trypsinogen
    • Chymotrypsinogen
    • Proelastase
    • Procarboxypeptidases
  • Active Enzymes:
    • α-Amylase
    • Lipases
    • Co-lipase
    • Phospholipases
    • Cholesterol esterases
    • RNAses
    • DNAses
  • Ions:
    • HCO3-
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2
Q

Pancreatic enzyme secretion controlled at three stages:

A
  1. Cephalic
    • Acetylcholine
  2. Gastric
    • Acetylcholine
    • Gastrin
  3. Intestinal
    • Cholecystokinin (CCK)
    • Secretin
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3
Q

What controls HCO3- secretion by pancreatic duct cells?

A
  • Acetylcholine
  • Secretin
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4
Q

List the different types of lipases:

A
  1. Lingual
  2. Gastric
  3. Pancreatic
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5
Q

Pancreatic lipase:

  1. Secreted into ….
  2. Active in ….
  3. What is required along with pancreatic lipase?
A
  1. Secreted into the duodenum
  2. Active in lumen of duodenum
  3. Requirements:
    • Bile salts required
    • Requires a colipase
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6
Q
  1. What are the lipid enzymes found in the intestinal absorptive cells?
  2. Where and how does absorption of lipids occur?
  3. How does transport of lipids occur?
A
  1. Enzymes:
    • Phospholipases
    • Cholesterol esterases
  2. Absorption
    • Direct
    • Duodenum and jejunum
    • Micelles
  3. Transport
    • Chylo-microns
    • VLDL
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7
Q

What is the function of proteases?

A

Hydrolytically cleave peptide bonds

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8
Q

What are endopeptidases?

  • Stomach:
  • Duodenum and jejunum:
A

Cleave in center of proteins and peptides

  • Stomach – Pepsinogen – Chief Cells
    • Activated by acid and auto-activated to pepsin
  • Duodenum and jejunum enzymes:
    • Synthesized and secreted by α-cells of the pancreas
    • Trypsinogen activated in the duodenum by epithelial enteropeptidase (enterokinase)
    • Chymotrypsinogen and proelastase activated by trypsin
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9
Q

What are exopeptidases?

  • Location:
  • What are the two different types?
A

Cleave from N or C terminal end of peptides and proteins

  • Location: Duodenum
  • Carboxypeptidases
    • Synthesized and secreted by α-cells of the pancreas
    • Activated in duodenum by trypsin
  • Aminopeptidases
    • Synthesized by intestinal epithelial cells
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10
Q
  1. How are proteins absorbed?
  2. What are the epithelial cell peptidases?
A
  1. Absorption
    • Amino acid transporters (class specific)
      • Dipeptide
      • Tripeptide
    • Duodenum and jejunum
  2. Epithelial cell peptidases
    • Tripeptidase
    • Dipeptidase
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11
Q

How are carbohydrates absorbed?

A
  1. Duodenum and jejunum
  2. Transporters
    • SGLT1
    • GLUT5
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12
Q

Where are macronutrients absorbed?

A

Duodenum & Jejunum

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13
Q

Vitamin B1 (Thiamine):

  • Active Form:
  • Functions:
A
  • Active Form
    • Thiamine pyrophosphate
  • Functions
    • Cofactor for pyruvate dehydrogenase –
      • Decarboxylation
    • Cofactor in pentose phosphate pathway -
      • NADPH
    • Maintains neural membranes and normal nerve conduction –
      • pH, myelin, neurotransmitters
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14
Q

What happens if there is a vitamin B1 deficiency?

A
  1. Polyneuropathy (“dry beriberi”)
  2. Dilated Cardiomyopathy (“wet beriberi”)
  3. Wernicke-Korsakoff syndrome
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15
Q

Vitamin B2 (Riboflavin):

  • Active Forms:
  • Function:
A
  • Active Forms:
    • Flavin mononucleotide (FMN)
    • Flavin adenine dinucleotide (FAD)
  • Function:
    • Electron carrier
    • Complex dehydrogenases
    • Citric Acid Cycle to Electron Transport Chain
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16
Q

What happens if there is a vitamin B2 deficiency?

A
  1. Cheilosis (scaling and fissures at the corners of the mouth)
  2. Dermatitis
  3. Corneal neovascularization
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17
Q

**Vitamin B3 (Niacin): **

  • **Sources **
  • Active forms
A
  • Sources
    • Diet
    • Synthesized from tryptophan
  • Active forms
    1. NAD+ ⇒ NADH
      • Carbohydrate, fat, amino acids and nucleic acid degradation
      • Citric acid cycle
    2. NADH ⇒ NAD+
      • Citric acid cycle - electron transport chain
    3. NADP+ ⇒ NADPH
      • Glucose-6-phosphate dehydrogenase in the pentose phosphate shunt
    4. NADPH ⇒ NADP+
      • Used in synthesis of carbohydrates, fats, amino acids and nucleic acids
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18
Q

What happens if there is a vitamin B3 deficiency?

A
  • Glossitis
  • Pellagra
19
Q

**Vitamin B5 (Pantothenic Acid): **

  • **Active Form: **
    • Function
A
  • Coenzyme A
    • Amino acid, carbohydrate, fat and nucleic acid metabolism
  • Acyl Carrier Protein
    • Fatty acid synthesis
20
Q

What happens if there is a vitamin B5 deficiency?

A
  • Dermatitis
  • Enteritis
  • Alopecia
  • Adrenal insufficiency
21
Q

**Vitamin B6 (Pyridoxine): **

  • Active Form
  • Coenzyme involved in ….​​
A
  • Active form:
    • Pyridoxal Phosphate (PLP)
  • Coenzyme involved in
    • Amino acids degradation/conversion to other important molecules
      • Aminotransferases
      • Decarboxylases – serotonin, norepinephrine
      • Serine hydroxymethyltransferase – One carbon metabolism - myelination
      • Aldolases
    • Glycogen degradation
      • Glycogen phosphorylase
    • Porphyrin synthesis
22
Q

What happens if there is a deficiency in vitamin B6?

A
  • Convulsions
  • Dermatitis
  • Peripheral neuropathy
  • Sideroblastic anemia
23
Q

Vitamin B7 (Biotin):

  • Active Form
  • Function
A
  • Active form
    • Biotin bound to carboxylases
    • Released by biotinidase in small intestine
    • Bound in cells to carboxylases
  • Function
    • Carboxylase Cofactor – Binds CO2
    • Pyruvate carboxylase
    • Acetyl CoA carboxylase
24
Q

What happens if there is a deficiency in vitamin B7 or biotinidase?

A
  • Dermatitis
  • Hair loss (Alopecia)
  • Enteritis
25
Q

**Vitamin B9 (Folate): **

  • Active Form
  • Function
A
  • Active form
    • Tetrahydrofolate (THF)
  • Function: Carrier of one carbon units for:
    • Purine synthesis
    • dTMP synthesis from dUMP
    • Conversion of homocysteine to methionine for S-adenosylmethionine (SAM) synthesis
26
Q

Vitamin B12 (Cobalamin):

  • Active Form
  • Function
A
  • Active form
    • Cobalamin
  • Function:
    • Cofactor ONLY 2 enzymes:
      • Methionine synthase
      • Methylmalonyl-CoA mutase
        • Odd Chain Fatty Acid Degradation
        • Isoleucine and Valine Degradation
    • Required for TH4Folate availability for DNA synthesis
    • Myelin Synthesis
27
Q

How is vitamin B12 absorbed?

A

Intrinsic Factor – Vitamin B12 complex

28
Q

What happens if there is a vitamin B12 deficiency?

A
  • Megaloblastic anemia
  • Fetal neural tube defects
  • Demyelination
  • Neural degeneration
29
Q

Where are the B vitamins absorbed?

A
  • Most B-vitamins
    • Duodenum
    • Jejunum
  • Vitamin B12
    • Ileum
  • Microbiota produced biotin
    • Large intestine
30
Q

Vitamin C (Ascorbate)

  • Active Form
  • Function
A
  • Active form
    • Ascorbic acid (Ascorbate)
  • Function
    • Antioxidant
      • Reactive oxygen species
      • Oxidized vitamin E
    • Cofactor of enzymes that reduce metal ions
    • Post-translational modification of proteins – collagen
      • Lysyl hydroxylase
      • Prolyl hydroxylase
    • Synthesis of neurotransmitters and hormones
31
Q

What happens if there is a deficiency in vitamin C?

A
  • Abnormal collagen crosslinking leading to bleeding
  • Scurvy
32
Q

**Vitamin E (Tocopherol): **

  • Active Form
  • Storage
  • Function
A
  • Most active form
    • α-Tocopherol
  • Storage:
    • Adipose tissue, liver, muscle
  • Function:
    • Antioxidant - scavenges free radicals
    • Recycled by Vitamin C (Ascorbate)
33
Q

**Vitamin K (Phylloquinone): **

  • **Active Form **
  • Storage
  • Function
A
  • Active form
    • Vitamin K
  • Storage
    • Liver
  • Function
    • Cofactor for Vitamin K dependent γ-carboxylase
      • Coagulation Factors 2, 7, 9, 10
      • Proteins S, C
      • Bone calcium binding proteins
    • Modified Gla residue
      • Binds calcium
      • Localizes to activated platelets
34
Q

What happens if there is a deficiency in vitamin K?

A

Bleeding

35
Q

**Vitamin A (Carotenes, Retinoids): **

  • Storage
  • Active Forms
A
  • Storage - Liver
  • Active Forms - Functions
    • β-Carotene
      • Antioxidant
      • Vitamin A precursor
    • Retinol (Vitamin A)
      • Major transport form
    • 11-cis Retinal (Retinaldehyde)
      • Vision
    • Retinoic Acid
      • Gene regulation
36
Q

**Vitamin A (Carotenes, Retinoids): **

  • Function
A
  • **Retinoic Acid **
    • all-trans, 9-cis
    • Regulation of retinoid responsive gene expression
      • Epithelial cell function
      • Mucous cell function
      • Immunity
      • Reproduction
      • Development
37
Q

What happens if there is a vitamin A deficiency?

A
  • Night blindness
  • Susceptibility to infection
  • Dry scaly skin
  • Corneal degeneration
  • Alopecia
  • Osteoporosis
38
Q

Vitamin A: Vision

  • 11-cis retinal binds ….
  • How is vitamin A used in the visual cycle?
A
  • 11-cis-retinal binds:
    • Rhodopsin in rods
    • Cone pigments in cones
  • Visual Cycle:
    • Light
      1. 11-cis-retinal ⇒ all-trans-retinal
      2. Conformational change
      3. Signal transduction
      4. Signal to the brain
      5. All-trans retinal ⇒ 11-cis-retinal in retinal pigment epithelial cells
39
Q

How is vitamin D (calciferol) expressed as:

  1. Dietary in Micelles:
  2. Hormone:
  3. Active:
A
  1. Dietary in Micelles:
    • Animals: Vitamin D3 (Cholecalciferol)
    • Plants: Vitamin D2 (Ergocalciferol)
  2. Hormone:
    • 7-Dehydrocholesterol ⇒ Vitamin D2
  3. Active:
    • 1, 25 dihydroxyvitamin D (1,25-dihydroxychole-calciferol, Calcitriol)
40
Q

How is vitamin D distributed and stored?

A
  • Distribution:
    • Chylomicrons
  • Storage:
    • Liver
41
Q

What is the function of vitamin D (calciferol)?

A
  • Controls expression of vitamin D responsive genes
    • Calcium and phosphate absorption in intestine
    • Bone formation and dissolution
    • Renal retention of calcium and phosphate
  • Other:
    • Cell cycle arrest
    • Apoptosis
    • Immune suppression
    • Anti-inflammation
    • Differentiation
  • Requires retinoic acid – binds RXR – plus 1,25 dihydroxy vitamin D – binds VDR
42
Q

Vitamin D Deficiency:

  • Children
  • Adults
A
  • Children — Rickets
  • Adults — Osteomalacia
43
Q

Where are the fat soluble vitamins absorbed?

A
  • All fat soluble vitamins
    • Duodenum
    • Jejunum
  • Vitamin D
    • Ileum
  • Microbiota produced vitamin K
    • Large intestine

GI/Nutrition (36 decks)

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