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Biochemistry MBBS > Vitamins > Flashcards

Vitamins Flashcards

1
Q

Vitamin present only in animal diet

A

B12

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2
Q

Marker of vitamin B2 def

A

Glutathione reductase activity

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3
Q

Vitamin syn by bacteria

A

B2,B5 , B7 ,K

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4
Q

Functions of PLP

A
  1. Transamination
  2. Decarboxylations
  3. Heme metabolism
  4. Sulphur metabolism(2 steps)
  5. Glycogenolysis ( phosphorylase)
  6. Niacin synthesis( kynureninase)
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5
Q

Vitamin B6 marker

A

Transaminase
Simple decarboxylation
Protein metabolism
Glycogen phosphorylase

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6
Q

Deficiency manifestations of B6 deficiency

A
  1. Reversible peripheral neuritis ( decarboxylation )
  2. Pellagra ( niacin deficiency)
  3. Hypochromic microcytic anaemia
  4. Homocystinuria
  5. Xanthurenic aciduria
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7
Q

B6 RDA

A

Adults 1 - 2 mg/day

Pregnancy and lactation 2.5

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8
Q

Two atypical vitamin

A

Niacin B3 and D3

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9
Q

Why is zinc important for retinol metabolism

A

Zinc is a part of alcohol dehydrogenase to convert retinal to retinol

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10
Q

Other functions of vitamin A (carotenoids)

A
  1. Like a hormone in tissue differentiation
  2. Reproduction ( retinol )
  3. Antioxidant
  4. Skin health ( against psoriasis)
  5. Against heart diseases
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11
Q

Deficiency manifestations of vitamin A

A
  1. Bitots spots in conjunctiva
  2. Keratomalacia (corneal ulcer)
  3. Preventable blindness
  4. Skin and mucous membrane lesions
  5. Night blindness and xerophthalmia

Most common vitamin deficiency

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12
Q

Daily dosage of vitamin A

A

Children 400- 600 microgram/day
Women 750
Men 750 - 1000
Pregnancy 1000

Richest sources are halibut liver oil, fish oil

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13
Q

Vitamin D requirement

A

Children 10 microgram/day or 400 IU
Adults 5 - 10
Pregnancy, lactation 10
Old age 15

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14
Q

Functions of vitamin E

A
  1. Antioxidant
  2. Against hemolysis
  3. Anti aging
  4. Against atherosclerosis
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15
Q

Vitamin E and selenium

A

Glutathione peroxidase and Vitamin E are synergistic in preventing lipid peroxidation.

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16
Q

RDA of vitamin E

A

Males 10mg/day
Females 8
Pregnancy 10
Lactation 12

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17
Q

Clotting factors activated by vitamin K

A 
2 prothrombin 
7 SPCA
9 Christmas factor
10 Stuart prower factor 
Via gamma carboxylation of glutamic acid residues
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18
Q

RDA of vitamin K

A

50 - 100 mg/day

Deficiency rare , except in preterm babies

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19
Q

Earliest manifestation of vitamin B1 or thiamine

RDA of thiamine

A

Decreased Erythrocyte transketolase activity

1 - 1.5 mg/day (depends on calorie intake)

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20
Q

Functions of FMN

A
  1. Amino acid oxidation O2 to H2O2

2. In respiratory chain in between NAD+ & CoQ

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21
Q

FAD dependent enzymes

A
  1. Succinate to fumarate by succinate dehydrogenase
  2. Acyl Co-A dehydrogenase on acyl Co-A
  3. Xanthine to uric acid by xanthine oxidase
  4. Pyruvate dehydrogenase & alpha keto glutarate dehydrogenase
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22
Q

NADPH generating reactions

A
  1. G-6-PD in HMP
  2. 6-Phosphogluconate dehydrogenase in HMP
  3. Cytoplasmic isocitrate dehydrogenase
  4. Malic enzyme
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23
Q

NADPH utilising reactions

A
  1. Beta keto acyl ACP dehydrogenase
  2. Alpha, BetaUnsaturated acyl AC to. acyl ACP
  3. HMG CoA-Reductase
  4. Folate reductase
  5. Phenylalanine hydroxylase ( to tyrosine)
  6. Meth Hb to Hb
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24
Q

Pellagra is found more in ______gender

It’s features

A

Females due to inhibitory influence of estrogen on tryptophan metabolism

  1. Dermatitis (cassals necklace)
  2. Diarrhoea
  3. Dementia
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25
Q

Daily requirement of niacin

A

20mg

5mg higher during lactation

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26
Q

Panthothenic acid(pan =>everywhere )

A

Co-A
Deficiency (rare) => Gopalan burning foot syndrome
RDA 10mg/day

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27
Q

Biotin requiring carbon fixation reactions

A
  1. Acetyl Co-A carboxylase in FA biosynthesis
  2. Propionyl Co-A carboxylase
  3. Pyruvate carboxylase for OAA synthesis(TCA) and for gluconeogenesis
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28
Q

Carboxylation reactions where biotin is NOT required

A
  1. CPS 1 and 2 for urea and pyrimidine synthesis
  2. C6 of purine
  3. Malic enzyme
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29
Q

Biotin cycle

A

Holocarboxylase synthetase + biotinidase
Deficiency
Multiple carboxylase Deficiency
CNS involvements
Tomcat urine odour
Hair and skin disorder

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30
Q

Raw eggs and biotin

A

Has Avidin which binds to B7
Pyruvate carboxylase decreases
Hypoglycaemia

Rx B7

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31
Q

RDA of biotin B7

A

200-300mg/day

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32
Q

Folic acid is absorbed in _____

A

Upper parts of jejunum ,transported through blood via beta globulins

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33
Q

Causes of folate deficiency (one of the most common )

A
  1. Pregnancy
  2. Drugs
  3. Defective absorption
  4. Haemolytic anaemia (demand increases)
  5. Dietary deficiency
  6. Folate trap(B12 deficiency)
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34
Q

Holocarboxylase

A

Bit B7(biotin ) + carboxylase

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35
Q

Manifestations of folate deficiency

A
  1. DNA synthesis Decreases (thymine synthesis decreases )
  2. Macrocytic anaemia (not megaloblastic and without neurological symptoms )
  3. Hyperhomocysteinuria which leads to
  4. Birth defects
  5. Cancer
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36
Q

Assessment of folate deficiency

A
  1. Blood level
  2. Histidine load test( FIGLU test)
  3. AICAR excretion test( pyrimidine synthesis decreases )
  4. Peripheral blood press
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37
Q

RDA of folate

A

Adults 200 mg/day
Pregnancy 400 mg/day
Lactation 300 mg/day

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38
Q

Eg of anti vitamins

A

Dicoumarol
Methotrexate (folic acid)
Isoniazid (pyridoxine)

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39
Q

Forms of B12

A 
Oral(lab) :cyano
Injections :hydroxy
Functional forms are
Storage: DeoxyAdenosyl (liver , somatic)
Transport(blood) :Methyl
40
Q

Second factor of B12 or cobalophilin is secreted from

A

Saliva

41
Q

Functions of vitamin B12

A
  1. Methyl Malonate Co-A isomerase of odd chain fatty acids
  2. Methionine synthase or homocysteine methyl transferase
  3. Demethylation of methyl THFA
42
Q

Causes of vitamin B12 deficiency

A
  1. Diet
  2. Decreased absorption
  3. Addisonian pernicious anaemia
  4. Gastric atrophy
  5. Pregnancy
  6. Fish tapeworm
43
Q

Deficiency manifestations of vitamin B12

A
  1. Folate trap
  2. Megaloblastic anaemia
  3. Homocysteinuria
  4. Demyelination due to SAM
  5. Subacute combined degeneration
  6. Achlorhydria
44
Q

Assessment of vitamin B12 deficiency

A
  1. Serum B12 levels
  2. Schilling test
  3. Methyl malonic acid
  4. Blood smear
  5. Homocysteinuria
  6. FIGLU test
45
Q

RDA of B12

A

1-2 microgram/day

2 microgram/day for pregnancy and lactation

46
Q

Functions of vitamin C

A
  1. Redox and antioxidant
  2. Hydroxylation of proline and lysine for collagen
  3. Hydroxylation of tryptophan for serotonin
  4. Tyrosine metabolism
  5. Iron absorption via reduction
  6. MetHb reduction
  7. Helping folate reductase( thus RBC maturation )
  8. Steroidogenesis
  9. Stimulates phagocytosis
  10. Cataract
47
Q

Barlow disease

A

Infantile scurvy

Vitamin C supplementation required between 6 & 12 months ( Breast milk)

48
Q

Vitamin C deficiency and anaemia ?

A

Microcytic hypochromic anaemia due to

  1. Loss of blood via haemorrhage
  2. Decreased Iron absorption
  3. Decreased THFA
  4. Increased MethHb
49
Q

RDA of vitamin C

A

75mg/day
Pregnancy and lactation 100mg/day
For smokers and those on contraceptive pills
> 100 mg/day

50
Q

Toxic water soluble vitamins are

A

Vitamin B6 and niacin

51
Q

Retinoids are found in __ sources

A

Animal

52
Q

Eg of carotenoids

A

Lutein, zeaxanthin(Rx of macular degeneration )

Lycopene (Rx of prostate cancer)

Beta carotene ( antioxidant )

53
Q

Different forms of retinoids acid

A

All trans

9 cis

13 cis
In regulation of gene expression (growth and development ,
Tissue differentiation)

54
Q

Retinol structure

A

Beta ionone ring + isoprenoid chain

55
Q

Absorption and storage of vitamin A

A

Retinol ester is split and retinol is absorbed
Deoxygenase of intestinal cells split absorbed carotenoid

These are esterified in these cells
The retinal esters are carried by chylomicron

In the liver they are stored in the peri sinusoidal cells (Ito cells)

56
Q

Vitamin A is transported in the form of a

A

Ternary complex

Retinol + RBP + Transthyretin

57
Q

Metarhodopsin II

A

It activates the signal cascade pathway

GPCR-transducin is activated
Phosphodiesterase activated
cGMP to 5’GMP
closes Na+ channel
Hyperpolarisation
58
Q

RAR

A

Retinoids acid receptor

All trans retinoids acid ligand

59
Q

RXR. Why vitamin D or thyroid deficiency causes vitamin A deficiency

A

Retinoic acid X receptor
9 cis retinoic acid

It dimerises with vitamin D receptor complex,(thyroid hormone complex,…)
Heterodimer
Then binds

60
Q

Earliest sign (not symptom)of Vitamin A deficiency

A

Loss of sensitivity to green light

Earliest symptom is nyctalopia

61
Q

Skin effects of vitamin A deficiency

A 
Follicular hyperkeratosis (phrynoderma or toad skin)  
Also caused by EFA deficiency

Squamous metaplasia( UTI & RTI)

Blockage of adnexal glands

62
Q

Toxicity of vitamin A

A

Rare
Seen in arctic explorers due to polar bear liver
Affects lysosomes

Acute
1 pseudotumor cerebri (head ache, vomitting,blurry vision)
2 exfoliating dermatitis

Chronic
Weight loss ,nausea, bony exostosis,
Joint pain, increases osteoclastic activity(hip fractures)

63
Q

Therapeutic application of vitamin A

A 
Beta carotene( cutaneous photosensitivity)
2. All trans retinoic acid( tretinoin)- mild acne, acute promylocytic leukaemia ( differentiation therapy)
64
Q

13cis retinoic acid

A

Isotretinoin
Teratogenic
Used in cystic acne(severe) , childhood neuroblastoma

65
Q

Vitamin D eg

A

Vitamin D2 ergocalciferol (plant origin)

Vitamin D3 cholecalciferol (calciol)

66
Q

Dietary source of vitamin D is

A

Fish (Halibut liver oil)
Vitamin D fortified

Rest is negligible

67
Q

Transport protein of D3 and the first hydroxylation

A

D Binding Protein(DBP)

which goes to the liver where it is hydroxylated by 25 Hydroxylase (part of cytochrome p450) to calcidiol or 25 OH D3

68
Q

Hydroxylation in the kidney of calcidiol

A

By 1 alpha hydroxylase (favoured by PTH)
it is converted to 1,25 dihydroxy cholecalciferol or calcitriol
This is the RDS

69
Q

UV. light responsible for isomerisatiom of 7 dehydrocholesterol to cholecalciferol

A

UV -B

290-315 nm

70
Q

Inactivation of calcidiol and calcitriol is by

A

24 hydroxylation to

24 calcidiol and calcitetrol

71
Q

Functions of vitamin D

A
  1. Regulation of Ca and P
  2. Immunomodulatory
  3. Antiproliferative
  4. Bone mineralization during bone development
72
Q

Phosphorus level in serum increasing substances

A

Vitamin D

73
Q

Regulation of Ca in intestine

A

Vitamin D increases

  1. Calcium transport channel TRPV6
  2. calbindin 9K
74
Q

Regulation of Ca in kidneys

A

PTH increases hydroxylation of calcidiol in DCT
Vitamin D then increases
1. TRPV 5
2. Calbindin 28K
Thus increases both Ca and P reabsorption
But PTH increases excretion of P while increasing Ca reabsorption

75
Q

Regulation of Ca in bones by vitamin D and PTH

A

Increases action of RANK ligand (receptor activator NFKB Ligand) located on osteoblasts
Whose receptor is located on proosteoclasts
Thus increases maturation of osteoclasts

76
Q

Vitamin D and tuberculosis

A

Few I alpha hydrxylation occurs in the macrophages by cytochrome p27B

Toll like receptor binds to the bacteria which increases cytochrome p27B
Calcitriol increases which increases cathelicidin which kills the bacteria

77
Q

Holy grail of cancer medicine is vitamin D

A

If vitamin D level is less than 20 no/ml it is associated with increased colon,breast and prostate cancers

It is also protective against prediabetes and metabolic syndrome

78
Q

Contrary to normal state vitamin D during bone development increases

A
  1. Osteoclastic activity
  2. Mineralisation of bone
  3. Osteocalcin (mineralization)

Thus vitamin D deficiency during infant causes poor mineralization of osteoid leading to rickets

79
Q

Rickets

A

Rachitic rosary
Wind swept deformity
Harrison’s sulcus

80
Q

Nutritional rickets

A 
Nutritional deficiency or decreased sunlight exposure
Serum Ca decreases
But,
Secondary hyperparathyroidism
1 alpha hydroxylation increases
Then vitamin D3 is normalised
Then serum Ca is normalised
But serum phosphate level will be reduced
81
Q

Toxicity of vitamin D

A

4000 IU
in infants > 50 mg/day
Deposition of Ca in soft tissues and blood vessels
(contraction of blood vessels and hypertension)
Metastatic calcification
Calcinosis

82
Q

Assay of vitamin D

A

25 hydroxy cholecalciferol
Ideal level 20-100 ng/mL

Serum osteocalcin

83
Q

Vitamin E most potent active form is

A

Alpha tocopherol

Vitamin E has chromate ring with isoprenoid unit (seen in A,E,K)

84
Q

Antioxidant Functions of vitamin E

A
  1. Chain breaking antioxidant
  2. Prevents oxidation of PUFA in the membrane
  3. Prevents oxidation of LDL
85
Q

Deficiency manifestations of Vitamin E

A
  1. Axonal degeneration (posterior column affected and hence decreased position and vibration sense)
  2. Spinocerebellar symptoms (ataxia)
  3. Peripheral neuropathy
  4. Skeletal myopathy
  5. Pigmented retinopathy
  6. Ophthalmoplegia
86
Q

Features of the least toxic fat soluble vitamin

A

Vitamin E

  1. Decreases platelet aggregation
  2. Interferes with vitamin K
87
Q

Sources of vitamin E

A

Wheat germ oil
Cotton seed oil
Sunflower oil

88
Q

High doses of vitamin E is used for

A
  1. Retrolentil fibroplasia
  2. Bronchopulmonary dysplasia
  3. Intraventricular haemorrhage
  4. Intermittent claudication
89
Q

Structure of vitamin K

A

Naphthoquinone derivative + isoprenoid chain

90
Q

Forms of vitamin K

A

K1 phylloquinone plant sources
K2 Menaquinone intestinal flora
K3 menadione synthetic - water soluble form of a fat soluble vitamin

91
Q

Action of vitamin K on clotting factors

A

Vitamin K gamma carboxylase 2,7,9,10 for Ca binding and itself is converted to vitamin K epoxide.

It is converted back by vitamin K epoxide reductase ( inhibited by warfarin, dicoumarol)

92
Q

Proteins that are affected by vitamin K (gamma carboxylation)

A
  1. Protein C, protein S
  2. Osteocalcin and nephrocalcin
  3. Product of gas 6 gene (gene arrest specific)
  4. Matrix gla protein
93
Q

ABC enzymes

A

ATP dependent Biotin Carboxylation

94
Q

Deficiency of vitamin K

A

Increases

  1. Bleeding time
  2. Prothrombin time
95
Q

Reasons why vitamin K deficiency occurs in premature infants

A
  1. Immaturity of liver
  2. Sterile gut
  3. Breast milk poor in vitamin K
  4. Poor placental transport
  5. Low body stores
96
Q

Increased vitamin K causes

A

Hemolysis ( deficiency of vitamin E causes the same)
Jaundice
Hyperbilirubinemia
Kernicterus and brain damage

Biochemistry MBBS (10 decks)

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