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Question Of Vitamins كتاب الطويل Flashcards

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1
Q

What are vitamins?

A

Organic compounds essential for many biochemical reactions, act as coenzymes, not part of tissue structure, needed in very small amounts

Vitamins are crucial for various bodily functions and must be obtained from the diet.

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2
Q

What are provitamins?

A

Precursors of vitamins converted into vitamins inside the body, e.g., carotenes are provitamin A

Provitamins serve as a source for vitamins once metabolized.

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3
Q

What are vitamers?

A

Different forms of one vitamin, e.g., Vitamin D has two vitamers: D2 and D3

Vitamers can have different biological activities.

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4
Q

How are vitamins classified based on solubility?

A

Into fat-soluble and water-soluble vitamins

Classification helps in understanding their absorption and storage in the body.

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5
Q

List the fat-soluble vitamins.

A
  • Vitamin A
  • Vitamin D
  • Vitamin E
  • Vitamin K

Fat-soluble vitamins require bile salts for absorption and can be stored in the body.

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6
Q

What are the characteristics of fat-soluble vitamins?

A

Soluble in fat solvents, require bile salts for absorption, can be stored in the body

This storage capability can lead to toxicity if consumed in excess.

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7
Q

List the water-soluble vitamins.

A
  • Vitamin C
  • B-Complex vitamins

Water-soluble vitamins are typically not stored in the body and must be consumed regularly.

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8
Q

What are the characteristics of water-soluble vitamins?

A

Soluble in water, most not stored in the body

These vitamins are often excreted in urine, necessitating regular intake.

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9
Q

What is ascorbic acid?

A

Vitamin C

Ascorbic acid is vital for collagen synthesis and antioxidant protection.

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10
Q

What is thiamine?

A

Vitamin B1

Thiamine is essential for carbohydrate metabolism and nerve function.

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11
Q

What is riboflavin?

A

Vitamin B2

Riboflavin plays a key role in energy production and cellular function.

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12
Q

What is niacin?

A

Vitamin B3

Niacin is important for DNA repair and metabolic processes.

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13
Q

What is biotin?

A

A water-soluble B vitamin

Biotin is crucial for fatty acid synthesis and metabolism of amino acids.

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14
Q

What is pantothenic acid?

A

Vitamin B5

Pantothenic acid is vital for synthesizing coenzyme A, important in fatty acid metabolism.

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15
Q

What are the hematopoietic vitamins?

A
  • Folic acid
  • Vitamin B12
  • Pyridoxine (Vitamin B6)

These vitamins are critical for blood formation and maintaining healthy red blood cells.

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16
Q

What are the forms of vitamin B6?

A
  • Pyridoxine
  • Pyridoxal
  • Pyridoxamine

These forms play various roles in amino acid metabolism and neurotransmitter synthesis.

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17
Q

What are the provitamin A compounds?

A

Carotenes

Carotenes are precursors to vitamin A found in plant sources.

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18
Q

What are the forms of vitamin A used by the body?

A

Retinol, retinal, retinoic acid

These forms are collectively referred to as vitamers.

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19
Q

What are the animal sources of vitamin A?

A
  • Liver
  • Eggs
  • Milk fat
  • Fish liver oils (e.g., shark liver oil)

These sources provide retinol directly.

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20
Q

What are the plant sources of vitamin A?

A

Carotenes

Carotenes are converted into vitamin A in the body.

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21
Q

Which vegetables are rich in carotenes?

A
  • Carrots
  • Potatoes
  • Tomatoes

Carotenes give these vegetables their yellow pigment.

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22
Q

What is the role of ß-carotene in vitamin A metabolism?

A

Converted into retinal by ß-carotene di-oxygenase enzyme

This conversion is essential for vitamin A synthesis.

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23
Q

How is retinol absorbed in the intestine?

A

Hydrolyzed from retinol esters into fatty acids and retinol

This process occurs in intestinal mucosal cells.

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24
Q

What happens to retinol in the intestinal mucosal cells?

A

Re-esterifies with fatty acid to form retinol ester

This ester is then absorbed into circulation.

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25
Where is the majority of the body's vitamin A stored?
Liver ## Footnote About 90% of the body's vitamin A is stored in the liver.
26
What is the function of retinol binding protein (RBP)?
Carries retinol to the retina and target cells ## Footnote RBP is a protein formed by the liver.
27
True or False: Retinal is converted back into retinol after being absorbed.
True ## Footnote This conversion occurs in the metabolic pathway of vitamin A.
28
Fill in the blank: Carotenes are yellow pigments containing a _______ at one end of the molecule.
ß-ionone ring ## Footnote This structure is key to the function of carotenes.
29
What are the three forms (vitamers) of vitamin K?
K1, K2, K3 ## Footnote K1 is found in plants, K2 is produced by intestinal bacteria, and K3 is synthetic.
30
What is the main source of vitamin K?
Intestinal bacteria produce Vitamin K2 ## Footnote Vitamin K1 is present in plants.
31
What is the difference between vitamin K1 and K2?
The difference lies in the side chain R ## Footnote K1 has a different R side chain compared to K2.
32
What is vitamin K3?
Synthetic, water-soluble, and more potent than K1 & K2 ## Footnote K3 has no R side chain.
33
What are the functions of vitamin K?
* Synthesis of blood clotting factors in the liver: prothrombin, factors VII, IX, X * Synthesis of osteocalcin in bones ## Footnote Osteocalcin is a calcium-binding protein.
34
What is prothrombin?
A protein formed in the liver as an inactive precursor ## Footnote It contains 10 glutamic acid residues.
35
What converts prothrombin into active thrombin?
Carboxylation of glutamic acid residues into y-carboxy glutamate ## Footnote Similar reactions occur for factors VII, IX, and X.
36
What happens in vitamin K deficiency?
Impairment of blood clotting ## Footnote Deficiency is rare due to intestinal synthesis of vitamin K.
37
In which conditions does vitamin K deficiency occur?
* Newborn infants * Prolonged use of antibiotics * Liver diseases * Prolonged use of anticoagulants (Dicumarol and Warfarin) ## Footnote Newborns have sterile intestines and liver diseases affect synthesis and absorption.
38
True or False: Vitamin K deficiency is common.
False ## Footnote It is rare due to synthesis by intestinal bacteria.
39
Fill in the blank: Vitamin K deficiency can occur in newborns because their intestines are _______.
sterile ## Footnote This lack of bacteria prevents the synthesis of vitamin K.
40
What is retinol converted into in the retina?
Retinal ## Footnote Retinal is essential for vision.
41
What does retinol get oxidized into in other target cells?
Retinoic acid ## Footnote Retinoic acid binds to nuclear receptors.
42
What does the retinoic acid receptor-complex stimulate?
Genes ## Footnote This process is similar to hormone action.
43
True or False: Retinoic acid binds to nuclear receptors.
True
44
Fill in the blank: In the retina, retinols are converted into _______.
Retinal
45
What is the mode of action of retinoic acid similar to?
Hormones
46
What is the primary function of retinal in relation to vision?
Essential for night vision ## Footnote Retinal is a derivative of vitamin A that plays a critical role in the visual cycle.
47
What role does retinol play in reproduction?
Supports sperm formation and maintains fetal life ## Footnote Retinol is crucial for spermatogenesis in males and for sustaining pregnancy in females.
48
What is the significance of retinol in growth?
Essential for normal growth and bone & teeth formation ## Footnote Retinol contributes to the development of tissues and skeletal structures.
49
How does retinol affect epithelial cells?
Essential for normal differentiation of epithelial cells ## Footnote This is important for the smoothness of skin and mucus membranes.
50
What is the function of retinoic acid in the body?
Important for glycoprotein and phospholipids synthesis ## Footnote It contributes to the production of lung surfactant and other critical cellular components.
51
What is the antioxidant action of retinoids and carotenoids?
Protect tissues from toxic oxidants and may prevent epithelial tissue cancer ## Footnote These compounds help mitigate oxidative stress in the body.
52
List therapeutic uses of retinoids.
* Treatment of promyelocytic leukemia * Treatment of psoriasis * Treatment of severe acne ## Footnote Different retinoids are utilized in various dermatological and oncological conditions.
53
What are the two types of receptor cells in the human retina?
* Cone cells * Rod cells ## Footnote Cone cells are responsible for color and day vision, while rod cells are for night vision.
54
What is the visual pigment present in cones and rods?
Rhodopsin ## Footnote Rhodopsin is crucial for the phototransduction process in the retina.
55
Fill in the blank: Retinol is essential for _______.
[normal differentiation of epithelial cells]
56
True or False: Vitamin A is only important for vision.
False ## Footnote Vitamin A has multiple roles, including reproduction, growth, and maintaining epithelial tissues.
57
What is rhodopsin composed of?
Rhodopsin consists of a protein called opsin bound to 11-cis retinal ## Footnote Opsin is a light-sensitive protein in the photoreceptor cells of the retina.
58
What happens when rhodopsin is exposed to light?
11-cis retinal is converted into all-trans retinal ## Footnote This conversion is a crucial step in the visual cycle known as photoisomerization.
59
What effect does all-trans retinal have on rod cells?
Changes the permeability of the cell membrane, allowing calcium ions to pass out ## Footnote This change initiates a nerve impulse in the optic nerve, leading to the perception of light.
60
Fill in the blank: The process of converting light into nerve impulses in the retina is called _______.
phototransduction ## Footnote Phototransduction is the process by which light is converted into electrical signals in the retina.
61
What is the role of 11-cis retinal in the visual cycle?
It is converted from all-trans retinol and is necessary for the formation of rhodopsin ## Footnote 11-cis retinal is crucial for the regeneration of rhodopsin after it has been activated by light.
62
True or False: All double bonds in all-trans retinal are in the cis form.
False ## Footnote All double bonds in all-trans retinal are in the trans form.
63
What are the two forms of retinal mentioned in the visual cycle?
11-cis retinal and all-trans retinal ## Footnote These forms are essential for the visual cycle and the function of photoreceptors.
64
What is the significance of calcium ions passing out of the rod cell membrane?
It stimulates a nerve impulse in the optic nerve ## Footnote This is a key step in transmitting visual information to the brain.
65
Fill in the blank: The conversion of 11-cis retinal to all-trans retinal occurs upon exposure to _______.
light ## Footnote Light exposure triggers the isomerization of retinal, which is essential for vision.
66
What is night blindness?
Impaired dark adaptation ## Footnote Also known as nyctalopia, it is a condition associated with vitamin A deficiency.
67
What are Bitot spots?
Dryness and roughness of cornea ## Footnote A symptom of vitamin A deficiency.
68
What is keratomalacia?
Degradation of corneal epithelium ## Footnote A severe consequence of vitamin A deficiency leading to blindness.
69
What are the effects of vitamin A deficiency on growth?
Growth retardation ## Footnote Vitamin A is essential for normal growth and development.
70
What are the skin and mucus membrane symptoms of vitamin A deficiency?
Roughness of skin and mucus membranes ## Footnote This can lead to infections in various body systems.
71
What is alopecia?
Loss of hair from the head or body ## Footnote A potential symptom of vitamin A deficiency.
72
What is the daily requirement of vitamin A?
5000 IU/day ## Footnote This is the recommended intake for adults.
73
What are the toxic effects of excess vitamin A?
Headache, nausea, bone pain, loss of hair ## Footnote These symptoms arise from vitamin A overdose.
74
What is calcitriol?
1, 25 dihydroxycholecalciferol ## Footnote It is the active form of vitamin D.
75
How is vitamin D synthesized?
Ultraviolet rays generate D vitamins from ergosterol and 7-dehydrocholesterol ## Footnote This process occurs in plants and animals.
76
What are rich dietary sources of vitamin D?
* Liver * Egg * Yeast * Fish liver oils ## Footnote These foods are high in vitamin D and help meet dietary needs.
77
What is the primary function of calcitriol?
Normalization of serum calcium levels ## Footnote Calcitriol influences calcium levels through the intestines, bones, and kidneys.
78
How does calcitriol affect the intestines?
Stimulates synthesis of calcium binding protein (calbindin) ## Footnote This protein is responsible for calcium absorption.
79
What effect does calcitriol have on bones?
Stimulates calcium resorption from bones ## Footnote This is crucial for maintaining serum calcium levels.
80
What role does calcitriol play in the kidneys?
Increases renal tubular reabsorption of calcium ## Footnote This helps conserve calcium in the body.
81
What is the effect of calcitriol in small doses on bone mineralization?
Helps bone mineralization by providing calcium and phosphate ## Footnote Essential for maintaining bone health.
82
What happens to calcium and phosphate levels in large doses of calcitriol?
They move from bone to blood ## Footnote This can lead to bone demineralization.
83
What is osteocalcin?
Calcium binding protein present in bones ## Footnote It plays a key role in bone mineralization.
84
What stimulates the synthesis of osteocalcin?
1, 25(OH)2 D3 ## Footnote This form of vitamin D promotes the production of pro-osteocalcin.
85
True or False: 24, 25 dihydroxycholecalciferol is biologically active.
False ## Footnote It is considered biologically inactive.
86
What triggers the release of parathyroid hormone in the context of vitamin D regulation?
Hypocalcemia ## Footnote Hypocalcemia is a condition characterized by low levels of calcium in the blood, which stimulates the release of parathyroid hormone.
87
What enzyme is activated by hypocalcemia to convert 25(OH)D3 into 1,25(OH)2D3?
Renal 1-hydroxylase enzyme ## Footnote The renal 1-hydroxylase enzyme is crucial for converting inactive vitamin D into its active form.
88
What is the role of 1,25(OH)2D3 in intestinal mucosal cells?
Stimulates the production of mRNA for calcium binding protein (calbindin) ## Footnote Calbindin enhances calcium absorption in the intestines.
89
What condition is characterized by bone deformities in children due to vitamin D deficiency?
Rickets ## Footnote Rickets is caused by a lack of vitamin D, leading to inadequate bone mineralization.
90
What condition occurs in adults due to vitamin D deficiency and is characterized by bone fractures?
Osteomalacia ## Footnote Osteomalacia results from poor bone mineralization, leading to increased fracture risk in adults.
91
What is renal rickets?
A condition resulting from chronic renal failure and deficient formation of active vitamin D3 ## Footnote Renal rickets occurs due to decreased 1-hydroxylation of vitamin D in the kidneys.
92
What daily requirement of vitamin D is generally recommended?
400 IU/day ## Footnote This is the standard recommendation for maintaining adequate vitamin D levels.
93
What can excessive vitamin D intake lead to?
Hypervitaminosis D ## Footnote Hypervitaminosis D can cause abnormal calcification of tissues and deposition of calcium and phosphate in various systems.
94
True or False: Absorption of phosphate occurs independently of calcium absorption.
False ## Footnote Phosphate absorption occurs secondary to calcium absorption, highlighting the interdependence of these processes.
95
Fill in the blank: The conversion of 25(OH)D3 into 1,25(OH)2D3 can be directly activated by _______.
Hypophosphatemia ## Footnote Hypophosphatemia is a condition of low phosphate levels, which also stimulates the renal 1-hydroxylase enzyme.
96
What are the four types of tocopherols?
α, β, γ, and δ ## Footnote These tocopherols differ in the number and position of -CH3 groups attached to the tocol ring.
97
What is the most active member of tocopherols?
α-tocopherol ## Footnote α-tocopherol is the most biologically active form of vitamin E.
98
Where can vitamin E be found?
Vegetables and seed oils, fish liver oils ## Footnote These sources provide dietary vitamin E.
99
What is one of the primary functions of vitamin E?
Antioxidant ## Footnote Vitamin E prevents non-enzymatic oxidation of cell components by free radicals.
100
Fill in the blank: Vitamin E prevents the non-enzymatic oxidation of _______.
cell components ## Footnote These include polyunsaturated fatty acids, DNA, and cell membranes.
101
How does vitamin E protect against free radicals?
By donating one of its electrons ## Footnote This process neutralizes free radicals, restoring stability.
102
What role does oxidized LDL play in heart disease?
It causes heart disease ## Footnote Vitamin E prevents the oxidation of LDL, reducing heart disease risk.
103
What are some symptoms of vitamin E deficiency?
Hemolysis of RBCs, anemia, muscle breakdown, acanthocytosis, peripheral neuritis, ataxia, retinitis pigmentosa ## Footnote These symptoms are particularly noted in premature infants.
104
What is the daily requirement of vitamin E?
15 IU/day ## Footnote This is the recommended dietary allowance for adults.
105
What is vitamin K commonly known as?
Anti-hemorrhagic vitamin ## Footnote Vitamin K plays a crucial role in blood clotting processes.
106
What is the chemical name for Vitamin C?
L-Ascorbic acid ## Footnote Vitamin C is crucial for various biological functions.
107
List three primary sources of Vitamin C.
* Citrus fruits (lemon, orange) * Melon * Green leafy vegetables (lettuce, tomatoes, potatoes) ## Footnote Guava is particularly rich in Vitamin C.
108
What percentage of animal tissues contain L-ascorbic acid?
90% ## Footnote The remaining 10% is dehydro L-ascorbic acid.
109
What is the inactive form produced by further oxidation of Vitamin C?
L-diketogulonic acid ## Footnote This can further oxidize to 2,3-diketogulonic acid and oxalic acid.
110
Why is ascorbic acid considered acidic?
It contains two enol groups (C-OH) ## Footnote These groups contribute to the acidic nature of Vitamin C.
111
What is the most labile vitamin in food?
Vitamin C ## Footnote Its activity is easily lost through oxidation during preparation, cooking, and storage.
112
What role does Vitamin C play in collagen formation?
Essential for the conversion of Procollagen into collagen ## Footnote Hydroxylation of proline and lysine is catalyzed by hydroxylase enzymes and Vitamin C.
113
What is the function of Vitamin C in iron absorption?
Keeps iron in ferrous state ## Footnote This enhances absorption and mobilization of iron.
114
Fill in the blank: Vitamin C acts as a co-enzyme for many hydroxylase enzymes involved in the synthesis of _______.
bile acids, osteocalcin, carnitine, epinephrine ## Footnote Each of these substances has critical roles in the body.
115
True or False: Vitamin C has antioxidant properties.
True ## Footnote It helps protect tissues from the toxic effects of some oxidants.
116
What condition is caused by Vitamin C deficiency?
Scurvy ## Footnote Scurvy is characterized by symptoms such as fatigue, inflammation of the gums, and joint pain.
117
What disease results from depleted Vitamin C stores?
Scurvy ## Footnote Scurvy is characterized by various symptoms due to decreased collagen formation and other metabolic disruptions.
118
List four manifestations of scurvy due to decreased collagen formation.
* Bleeding into gums, muscles, joints, kidneys, GIT, and pericardium * Defective formation of bone and teeth * Defective healing of wounds * Necrosis of gums and loss of teeth ## Footnote These manifestations are a direct consequence of impaired collagen synthesis.
119
What type of anemia is associated with scurvy?
Anemia due to decreased absorption of iron and bleeding ## Footnote This anemia results from the overall impact of vitamin C deficiency on iron metabolism.
120
What are the behavioral changes associated with scurvy?
* Severe emotional disturbances ## Footnote These changes are linked to decreased neurotransmitter levels, particularly epinephrine.
121
What are the symptoms of decreased carnitine and fatty acids oxidation in scurvy?
General weakness ## Footnote This weakness is a result of impaired energy metabolism.
122
What is the daily requirement of Vitamin C?
60 mg/day ## Footnote This amount is necessary to maintain adequate physiological function and prevent deficiency.
123
What condition can result from excessive intake of vitamin C?
Hyperoxaluria ## Footnote This condition is characterized by increased oxalate in urine, potentially leading to kidney stone formation.
124
What are the three main reasons the B complex vitamins are grouped together?
* All are soluble in water * All are present in the same sources * Deficiencies are often multiple rather than singular ## Footnote These factors highlight their interrelatedness in nutrition.
125
What role do B-complex vitamins play in enzymatic reactions?
They serve as coenzymes ## Footnote Coenzymes are essential for the catalytic activity of various enzymes.
126
Which B vitamins are specifically involved in hematopoiesis?
Folic acid and B12 ## Footnote These vitamins are crucial for the formation of red blood cells.
127
How are B vitamins absorbed and transported in the body?
Absorbed in the intestine and transported in the portal circulation ## Footnote This process ensures that B vitamins reach the liver and other tissues efficiently.
128
What happens to body stores of B vitamins during dietary restriction?
Depletion occurs over several weeks ## Footnote This gradual depletion highlights the minimal storage capacity of most B vitamins.
129
Are toxic effects of the B complex vitamins common?
No, they are relatively uncommon ## Footnote Excessive intake is generally excreted rapidly due to their water-soluble nature.
130
What are the primary food sources of Thiamin (vitamin B1)?
* Whole grain cereals * Legumes * Yeast * Unpolished rice * Whole wheat bread ## Footnote Thiamin is crucial for various metabolic processes and is found in a variety of dietary sources.
131
What is the active form of Thiamin?
Thiamin diphosphate (TPP) ## Footnote TPP is also known as thiamin pyrophosphate and is essential for its coenzyme functions.
132
What enzyme is required for the formation of Thiamin diphosphate?
Thiamin kinase ## Footnote This enzyme is present in the liver, red cells, and nervous tissue.
133
What are the two main reactions in carbohydrate metabolism where TPP acts as a coenzyme?
* Oxidative decarboxylation of α-ketoacids * Transketolation reactions ## Footnote These reactions are vital for energy production and metabolic pathways.
134
Which enzyme catalyzes the oxidative decarboxylation of pyruvate?
Pyruvate dehydrogenase ## Footnote This enzyme is crucial for converting pyruvate into acetyl CoA, producing energy and CO2.
135
What role does Thiamin play in nerve function?
Essential for nerve conduction and nerve membrane structure ## Footnote Thiamin triphosphate donates phosphate for the phosphorylation of sodium transport channels.
136
Fill in the blank: The structure of Thiamin consists of a substituted pyrimidine ring connected to a substituted _______ ring through a methylene bridge.
thiazole ## Footnote This structural characteristic is important for its biochemical functions.
137
True or False: Thiamin is only necessary for carbohydrate metabolism.
False ## Footnote Thiamin is also important for nerve function and the metabolism of certain amino acids.
138
What are the products of the oxidative decarboxylation reactions involving TPP?
* Energy * CO2 ## Footnote These reactions contribute to the Krebs cycle and energy production.
139
Which enzyme is responsible for transketolation reactions in the pentose phosphate pathway?
Transketolase ## Footnote This enzyme is vital for carbohydrate metabolism and nucleotide synthesis.
140
What is the function of Thiamin triphosphate in nerve cells?
Acts as a phosphate donor for phosphorylation of sodium transport channels ## Footnote This process is crucial for maintaining nerve impulse conduction.
141
What is the consequence of a deficiency in Thiamine (Vitamin B1)?
Impaired conversion of pyruvate to acetyl CoA, leading to impaired energy production and cellular functions, especially of the nervous system ## Footnote This can result in beriberi.
142
What are the types of beriberi?
* Acute beriberi (dry beriberi) * Chronic beriberi (wet beriberi) * Infantile beriberi
143
What are the characteristics of acute beriberi?
* Peripheral neuritis (numbness) * Muscle wasting (paralysis of the lower legs) * Mental confusion/speech difficulties
144
What are the characteristics of chronic beriberi?
* Heart failure * Edema * Dyspnea on exertion
145
What is a notable symptom of infantile beriberi?
Crying without tears ## Footnote Untreated, it can prove fatal within 24 hours.
146
What is the daily requirement of Thiamine (Vitamin B1)?
1.5 mg/day
147
What are the primary sources of Riboflavin (Vitamin B2)?
* Milk and milk products * Eggs * Liver * Green leafy vegetables
148
What is the structure of Riboflavin?
It is formed of a flavin ring attached to ribitol (alcohol of ribose sugar)
149
What are the active forms of Riboflavin?
* Flavin mononucleotide (FMN) * Flavin adenine dinucleotide (FAD)
150
How is FMN formed?
By phosphorylation of riboflavin by ATP (via intestinal flaviokinase enzyme)
151
How is FAD formed?
By the transfer of an AMP moiety from ATP to FMN
152
What are the functions of Riboflavin (Vitamin B2)?
* Coenzyme for flavor-enzymes * Acts as hydrogen (or electron) carriers in oxidation-reduction reactions (FMNH2 and FADH2)
153
What are the ocular disturbances caused by B2 deficiency?
* Photophobia * Vascularization of cornea ## Footnote B2 deficiency can lead to abnormal sensitivity of the eye to light and corneal vascularization.
154
What is cheilosis?
Fissuring at the corners of the mouth ## Footnote Cheilosis is a characteristic symptom of B2 deficiency.
155
What is glossitis?
Inflammation of the tongue that appears smooth and purplish ## Footnote Glossitis is another symptom associated with B2 deficiency.
156
What is the daily requirement of vitamin B2?
1.5 mg/day ## Footnote This is the recommended daily intake for vitamin B2.
157
What are the primary sources of niacin (B3)?
* Whole grain and cereals * Milk * Meat * Liver * Yeast ## Footnote These foods are rich in niacin, which is essential for human health.
158
From which amino acid can niacin be synthesized endogenously?
Tryptophan ## Footnote Each 60 mg of tryptophan can be converted to 1 mg of niacin.
159
What vitamin is required as a co-enzyme for the conversion of tryptophan to niacin?
Vitamin B6 ## Footnote Vitamin B6 is essential for the conversion process.
160
What is the structure of niacin?
A pyridine derivative ## Footnote Niacin is a nontoxic substance derived from the toxic alkaloid nicotine found in tobacco.
161
What are the active forms of niacin?
* Nicotinamide * Nicotinamide adenine dinucleotide (NAD) * Nicotinamide adenine dinucleotide phosphate (NADP) ## Footnote Niacin is converted to nicotinamide, which enters the structure of NAD and NADP.
162
Where does the synthesis of NAD and NADP occur?
In the cytosol of liver cells ## Footnote NADP has a similar structure to NAD but includes a phosphate group.
163
What forms do NAD and NADP exist in?
Oxidized and reduced forms ## Footnote They undergo reduction by accepting a hydride ion.
164
True or False: Niacin is a toxic substance.
False ## Footnote Niacin is a nontoxic substance, despite being related to the toxic alkaloid nicotine.
165
Fill in the blank: Each 60 mg of _______ can be converted to 1 mg of niacin.
tryptophan ## Footnote Tryptophan is the amino acid involved in niacin synthesis.
166
What are the functions of niacin?
* Formation of NAD and NADP * Lowering plasma cholesterol * Formation of ADP-ribose ## Footnote Niacin is essential for various biochemical processes, including metabolism and DNA repair.
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What is the role of NAD and NADP in the body?
They function as hydrogen carriers essential for biochemical oxidation-reduction reactions. ## Footnote These reactions are crucial in carbohydrate, protein, and lipid metabolism.
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How does niacin lower plasma cholesterol?
By inhibiting the flow of free fatty acids from adipose tissue. ## Footnote This inhibition reduces the availability of acetyl CoA for cholesterol and triacylglycerol synthesis.
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What is pellagra?
A disease caused by niacin deficiency characterized by diarrhea, dermatitis, dementia, and death. ## Footnote Pellagra is often referred to as the disease of the '4 Ds'.
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What are the causes of pellagra?
* Deficiency of niacin, tryptophan, or vitamin B6 * Dependence on corn as a protein source * Hartnup's disease * Argentaffinoma * Isoniazid treatment ## Footnote Each of these causes can lead to insufficient niacin levels, resulting in pellagra.
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What is the daily requirement of niacin?
20 mg/day. ## Footnote This amount is necessary to prevent deficiency and maintain health.
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What is hypervitaminosis of niacin?
A condition resulting from consuming more than 500 mg/day, potentially causing liver damage. ## Footnote Excessive intake of niacin can have toxic effects on the liver.
173
What are the sources of pyridoxine (vitamin B6)?
* Wheat * Egg yolk * Corn * Liver * Meat ## Footnote These foods are rich in vitamin B6, which is important for various bodily functions.
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What is the structure of vitamin B6?
It includes a group of vitamers derived from the pyridine ring: pyridoxine, pyridoxal, and pyridoxamine. ## Footnote These vitamers differ in the functional groups attached to the pyridine ring.
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What is the biologically active co-enzyme derived from vitamin B6?
Pyridoxal phosphate (PLP). ## Footnote PLP is crucial for many enzymatic reactions in the body.
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What is the active form of pyridoxine?
Pyridoxal phosphate ## Footnote Pyridoxal phosphate acts as a coenzyme for a large number of enzymes.
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What role does pyridoxal phosphate play in protein metabolism?
Acts as a coenzyme in various reactions ## Footnote Key reactions include transamination, trans-sulfuration, deamination, decarboxylation, heme synthesis, and tryptophan conversion.
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Fill in the blank: Pyridoxine is converted to _______ in the body.
Pyridoxal phosphate
179
What is the reaction for transamination involving glutamate and oxaloacetate?
Glutamate + Oxaloacetate <-> a-Ketoglutarate + Aspartate
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Which amino acid is involved in the trans-sulfuration reaction?
Methionine ## Footnote The reaction involves the conversion of methionine to homocysteine and cysteine.
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What is the result of the deamination reaction of serine?
Pyruvate + NH3
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What does pyridoxal phosphate produce during the decarboxylation of glutamate?
GABA + CO2
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What is the role of pyridoxal phosphate in heme synthesis?
Converts Glycine + Succinyl CoA to Aminolevulinic acid, leading to Heme formation.
184
What is the essential function of pyridoxal phosphate in the conversion of tryptophan?
Conversion of tryptophan into vitamin B3 (niacin)
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What metabolic process does pyridoxal phosphate facilitate in carbohydrate metabolism?
Glycogen breakdown into glucose (glycogenolysis)
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What role does pyridoxal phosphate play in lipid metabolism?
Important in steroid hormone action ## Footnote It removes the hormone-receptor complex from DNA binding, terminating hormone action.
187
Which amino acid is absorbed from the intestine with the help of pyridoxal phosphate?
Amino acids
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What vitamin deficiency may result in Pellagra?
Deficiency in vitamin B6 due to inadequate conversion of tryptophan into vitamin B3 (niacin) ## Footnote Pellagra is characterized by dermatitis, diarrhea, and dementia.
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What neurological issue can arise in young infants due to vitamin B6 deficiency?
Convulsions due to deficient formation of GABA ## Footnote GABA is an inhibitory neurotransmitter in the brain.
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What type of anemia is associated with vitamin B6 deficiency?
Microcytic and hypochromic anemia due to deficient formation of heme and hemoglobin ## Footnote Microcytic anemia is characterized by smaller-than-normal red blood cells.
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What disturbance in metabolism is caused by a deficiency of vitamin B6?
Disturbance in amino acids metabolism leading to growth retardation and possible mental retardation ## Footnote Amino acid metabolism is crucial for protein synthesis and overall growth.
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How can vitamin B6 deficiency contribute to cancer risk?
Defective action of vitamin B6 on steroid DNA binding associated with breast, uterus, and prostate cancers ## Footnote This highlights the role of vitamins in regulating genetic expression.
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What condition is caused by the inability to convert Methionine to cysteine?
Homocystinuria ## Footnote This genetic disorder can lead to various health issues including cardiovascular problems.
194
What can result from hypervitaminosis of B6?
Neurological damage from intake of more than 200 mg/day ## Footnote Hypervitaminosis refers to the toxic effects of excessive vitamin intake.
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What is the daily requirement of vitamin B6?
2 mg/day ## Footnote Adequate intake is necessary to prevent deficiency-related health issues.
196
What are the primary sources of Pantothenic acid?
* Animal tissue (meat, liver, kidney) * Legumes ## Footnote Pantothenic acid is essential for various metabolic functions.
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What is the structure of Pantothenic acid?
Formed of pantoic acid connected to ß-alanine ## Footnote This structure is crucial for its function as a coenzyme.
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What is the main function of Coenzyme A?
Acts in the transfer of acyl groups (e.g., acetyl CoA, succinyl CoA, malonyl CoA) ## Footnote Coenzyme A is vital for metabolic pathways including the Krebs cycle.
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What is Acetyl CoA important for?
Metabolism of carbohydrates, lipids, and proteins ## Footnote Acetyl CoA serves as a key metabolic intermediate.
200
What is Succinyl CoA used for?
Used in heme synthesis and other metabolic reactions ## Footnote Heme is a component of hemoglobin, essential for oxygen transport.
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What is Malonyl CoA primarily used for?
Fatty acid synthesis ## Footnote Malonyl CoA is a crucial intermediate in lipid metabolism.
202
What is acyl carrier protein (ACP)?
A component of fatty acid synthase enzyme required for fatty acid synthesis. ## Footnote ACP is formed of pantothenic acid connected to phosphate and protein on one side and thioethylamine on the other side.
203
What are the daily requirements for pantothenic acid?
5 - 10 mg / day. ## Footnote Deficiency of pantothenic acid causes no effect in humans.
204
What are the main sources of biotin?
* Intestinal bacteria * Egg yolk * Animal tissues * Tomatoes * Yeast ## Footnote Intestinal bacteria synthesize most of the human requirements of biotin.
205
What is the structure of biotin?
Consists of a thiophen ring connected to urea with valeric acid as a side chain. ## Footnote Biotin acts as a CO2 carrier.
206
What is the function of biotin in enzyme activity?
Attaches to carboxylase enzymes to form biocytin, facilitating carboxylation reactions. ## Footnote This is catalyzed by holocarboxylase synthetase enzyme.
207
What is one example of a carboxylation reaction facilitated by biotin?
* Carboxylation of acetyl CoA to malonyl CoA * Carboxylation of pyruvate to oxaloacetate * Carboxylation of propionyl CoA to succinyl CoA ## Footnote These reactions are important in fatty acid synthesis and gluconeogenesis.
208
True or False: Deficiency of biotin occurs frequently in humans.
False. ## Footnote Biotin is widely distributed in food and synthesized by intestinal bacteria.
209
What can lead to biotin deficiency?
Ingestion of avidin, a glycoprotein present in uncooked egg white. ## Footnote Avidin tightly binds biotin and prevents its absorption from the intestine.
210
What role does biotin play in the regulation of the cell cycle?
Biotin has a role in regulating the cell cycle. ## Footnote This is one of the functions of biotin beyond its role as a cofactor.
211
What is the role of holocarboxylase synthetase enzyme in children?
It is responsible for the attachment of biotin to carboxylase enzyme. ## Footnote Deficiency of this enzyme leads to biotin deficiency manifestations.
212
List some manifestations of biotin deficiency.
* Muscle pain * Dermatitis * Glossitis * Loss of appetite * Nausea ## Footnote These symptoms indicate the importance of biotin in metabolic processes.
213
How do biotin requirements change during late pregnancy and lactation?
They increase. ## Footnote This is due to the higher metabolic demands during these periods.
214
Why is choline sometimes not regarded as a vitamin?
* Needed in a relatively big amount * Can be formed in the body from serine * Enters in structure of tissues ## Footnote These points highlight choline's unique characteristics compared to traditional vitamins.
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What are some physiological functions of choline?
* Formation of lecithin * Formation of sphingomyelin * Prevents fatty liver (lipotropic action) * Formation of acetylcholine * Oxidation produces betaine, which is a methyl donor ## Footnote These functions illustrate choline's importance in various biochemical pathways.
216
What is the structure of inositol?
It is a sugar alcohol derived from glucose. ## Footnote Inositol plays a crucial role in cell signaling and lipid metabolism.
217
List the physiological functions of inositol.
* Part of the structure of phosphatidyl inositol * Acts as a lipotropic factor * Inositol triphosphate (IP) acts as a second hormone messenger ## Footnote These functions are vital for cellular processes and hormone action.
218
What is phytic acid, and how does it affect calcium absorption?
It combines with calcium ions to form calcium phytate, which is insoluble in water, decreasing calcium absorption. ## Footnote This interaction can impact dietary calcium bioavailability.
219
What is the structure of lipoic acid?
It is 6-8 dithio-octanoic acid (8C). ## Footnote Lipoic acid is involved in energy metabolism.
220
What is a key physiological function of lipoic acid?
Acts as a coenzyme in oxidative decarboxylation of α-keto acids, e.g., pyruvic acid. ## Footnote This function is essential for energy production in cells.

Biochemistry (7 decks)

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