Biochemistry: Nutrition

Question 1

Fat Soluble Vitamins

Answer 1

A, D, E, K

Absorption dependant on gut and pancreas.

• Malabosorption syndromes (steatorrhea) such as cystic fibrosis and sprue or mineral oil intake can cause fat-souble vitamin deficiency
• Toxicity is more common than in water soluble vitamins

Question 2

Water soluble vitamins

Answer 2

B1,B2,B3, B5,B6,B7,B9,B12

Vitamin C

• All wash out easily from body except B12 and folate (stored in liver)
• Deficiencies result in dermatitis, glossitis, diarrhea

Question 3

Vitamin A

Answer 3

• Anti-oxidant
• constituent of visual pigments (retinal)
• Prevents squamous metaplasia
• Used to treat measles, AML and subtype M3
• Found in liver and leafy vegetables
• Deficiency
  
  • Night blindness
  • dry, scaly skin, alopecia
  • corenal degeneration
  • immune suppression
• Toxicity
  
  • Arthralgia
  • Skin changes, alopecia
  • cerebral edema
  • pseudotumor cerebi
  • osteoporosis
  • hepatic abnormalities
  • Teratogenic (cleft palate)

Question 4

Vitamin B1

Answer 4

Thiamine

• Thiamine pyrophosphate (TPP) is a co-factor for dehydrogenases
  
  • Pyruvate dehydrogenase
  • Alpha ketoglutarate dehydrogenase (TCA)
  • Transketolase (HMP shunt)
  • Branched chain ketoacid dehydrogenase
• Deficiency
  
  • impaired glucose breakdown–> ATP depletion
  • highly aerobic tissues are affected first
  • Wernicke-Korsakhoff: confusion, opthalmoplegia, ataxia, personality change, memory loss
  • Dry Beriberi: polyneuritis, symmetrical muscle wasting
  • Wet Beriberi: high-output cardiac failure (dilated cardiomyopathy), edema

Question 5

Vitamin B2

Answer 5

Riboflavin

• FAD & FMN
• used as co-factors in redox reactions
  
  • succinate dehydrogenase in TCA
• Deficiency
  
  • Cheilosis
  • Corneal vascularization

Question 6

Vitamin B3

Answer 6

Niacin

• NAD, NADP
• Used in redox reactions
• derived from tryptophan
• Used to treat dyslipidemia ( lowers VLDL and raises HDL)
• Deficiency
  
  • Glossitis
  • Pellagra ( Diarrhea, Dementia, Dermatitis)
• Excess
  
  • Facial flushing (induced by prostaglandins), hyperglycemia, hyperuricemia

Question 7

Vitamin B5

Answer 7

Pantothenate Acid

• Component of CoA
  
  • ​co-factor for acyl transfers and fatty acid synthase
• Deficiency
  
  • Dermatitis, enteritis, alopecia, adrenal insufficiency

Question 8

Vitamin B6

Answer 8

Pyridoxine

• Pyridoxal Phosphate (PLP)
  
  • transamination reactions (ALT & AST)
  • decarboxylation reactions
  • glycogen phosphorylase
  • Synthesis of cystathionine, heme, niacin, histamine, neurotransmitters (epinephrine, noreepinephrine, dopamine, GABA)
• Deficiency
  
  • Convulsions, hyperirritabiity, peripheral neuropathy, sideroblatic anemia due to impaired hemoglobin synthesis and iron excess
  • Deficiency inducible by isoniazid and oral contraceptives

Question 9

Vitamin B7

Answer 9

Biotin

• Cofactor for carboxylation enzymes ( add 1 carbon group)
  
  • Pyruvate carboxylase
  • acetyl-coA carboxylase
  • propionyl-coA carboxylase
• Deficiency rare
  
  • dermatitis, alopecia, enteritis
  • caused by antibiotic use or excessive ingestion of raw egg whites

Question 10

Vitamin B9

Answer 10

Folic Acid

• Converted to tetrahydrofolate (THF)
• co-factor for 1 carbon transfer/methylation reactions
• important for synthesis of nitrogenous bases in DNA and RNA
• Found in leafy green vegetables
• absorbed in jejunum
• small reserve pool stored in liver

Question 11

Vitamin B12

Answer 11

Cobalamin

• Cofactor for homocysteine methyltransferase and methylmalonyl Co-A
• Found in animal products
• Very large reserve pool stored in liver
• Deficiency caused by insufficient intake (vegan, malabsorption, lack of intrinsic factor, gastric bypass or absence of terminal ileum)
• Deficiency
  
  • macrocytic, megaloblastic anemia
  • Hypersegmented PMN
  • paresthesia and subacute combined degeneration due to abnormal myelin
  • associated with increased in serum homocysteine and methylmalonic acid levels

Question 12

Vitamin C

Answer 12

• Anti-oxidant
• facilitate iron absorption by reducing it to Fe2+ state
• Necessary for hydroxylation of proline & lysine in collagen synthesis
• necessary for dopamine B-hydroxylase ( Dopamine–> NE)
• Found in fruits and vegetables
• Ancillary treatment for methemoglobinemia by reducing Fe3+ to Fe2+
• Deficiency
  
  • Scurvy: swollen gums, Brusing, hemarthrosis, anemia, poor would healing, perifollicular and subperiosteal hemorrhages, corkscrew hair
  • Weakened immune response

Question 13

Vitamin D

Answer 13

D2: Ergocalciferol (plants)

D3: cholecalciferol (milk)

• formed in sun exposed skin
• 25 OH D3= storage
• 1,25 OH D3: active form
• Function:
  
  • increase intestinal absorption of calcium and phosphate
  • Increase bone mineralization
• Deficiency
  
  • Rickets (child) bone pain and deforminity
  • Osteomalacia in adults
  • Breast fed children should receive oral vitamin D
• Excess
  
  • Hypercalcemia
  • Hypercalciuria
  • loss of appetite, stupor
  • seen in sarcoidosis (increase in activation of vitamin D by epithelioid macrophages)

Question 14

Vitamin E

Answer 14

Tocopherol

• Antioxidant
• protects erythrocytes and membranes from free radical damage
• can enhace anti-coagulant effect of warfarin
• Deficiency
  
  • Hemolytic anemia
  • acanthocytosis
  • muscle weakness
  • posterior column and spinocerebellar tract demyelination

Question 15

Vitamin K

Answer 15

• Co-factor for gamm-carboxylation of glutamic acid on proteins required for clotting
  
  • Factors II, VII, IX, X
  • Protein C & S
  • Wafarin: vitamin K antagonist
• Deficiency
  
  • Neonatal hemorrage with increase PT and PTT
  • Can occur after prolonged use of antibiotics
  • Not in breast milk ( neonates are given vitamin K injection at birth)

Question 16

Zinc

Answer 16

• Essential for activity of many enzymes
  
  • Zinc finger proteins (transcription factor motifs)
• Deficiency
  
  • Delayed wound healing
  • hypogonadism
  • decreased adult hair
  • may predispose to alcoholic cirrhosis

Question 17

Ethanol Metabolism

Answer 17

• Ethanol –> Acetaldehyde
  
  • Alcohol Dehydrogenase
  • NAD+
• Acetaldehyde –> Acetate
  
  • Acetaldehyde dehydrogenase
  • NAD+
• NAD+ is the limiting reagent
• alcohol dehydrogenase= zero order kinetics

Increases NADH/NAD+ levels in liver

• Pyruvate–> lactate
  
  • lactic acidosis
• Oxaloacetate –> malate
  
  • prevents gluconeogensis
• Glyceraldehyde 3 P –> Glycerol-3-P
  
  • combines with fatty acids to made triglycerides => hepatosteatosis

Increased NADH/NAD+ decreases TCA production of NADH–> increase use of acetyl-coA for ketogenesis

• Ketoacidosis
• Lipogeneisis (hepatosteatosis)

Fomepizole: inhibits alcohol dehydrogenase

• antidote for methanol or ethylene glycol poisoning)

Disulfiram: inhibits acetaldehyde dehydrogenase

• acetaldehyde accumuates contributing to hangover symptioms

Question 18

Kwashiorkor

Answer 18

Protein malnutrition

• results in skin lesions, edema, liver malfuction (fatty change due to decreased apolipoprotein synthesis)

Question 19

Marasmus

Answer 19

Total calorie malnutrition

• resulting in tissue and muscle wasting
• loss of subQ fat
• variable edema