What are vitamins classified as in terms of their role in nutrition?
إجابة
(A)
Essential nutrients
2
Which of the following best describes Vitamin A (retinal) from a chemical perspective?
إجابة
(B)
A compound containing a cyclohexenyl ring
3
What enzyme is responsible for breaking down β-Carotene, a Vitamin A precursor?
إجابة
(A)
An enzyme involved in dioxygenation
4
In the intestinal lining, what cofactor is required by retinaldehyde reductase to convert retinal to retinol?
إجابة
(A)
A form of NADPH
5
Which of the following foods is a significant source of preformed Vitamin A?
إجابة
(A)
Dairy products, fats, and organ meats
6
The conversion between retinol and retinal necessitates the presence of a dehydrogenase or reductase, which, in turn, requires which of the following cofactors?
إجابة
(A)
NAD or NADP
7
What is a characteristic of fat-soluble vitamins?
إجابة
(D)
All of the above
8
What is the standard used to define one international unit of Vitamin A?
إجابة
(A)
The activity of 0.3 µg of Vitamin A alcohol
9
At what temperature does Lumirhodopsin remain stable?
إجابة
(D)
Below -50°C
10
In the bloodstream, how is retinol transported?
إجابة
(A)
Bound to a specific binding protein
11
What is the typical blood serum level of vitamin A, measured in mg per 100 ml?
إجابة
(B)
15-60
12
Which of the following is a symptom associated with a lack of vitamin A?
إجابة
(B)
Night blindness
13
A deficiency in Vitamin A can lead to which condition?
إجابة
(A)
Xeropthalmia
14
What is a key role that vitamin A plays in the body?
إجابة
(D)
To maintain the integrity of epithelial tissue
15
Which visual pigment contains retinal as a key component?
إجابة
(B)
Rhodopsin
16
In what process does retinoic acid take part?
إجابة
(C)
Glycoprotein
17
What form of retinal results when rhodopsin is exposed to light?
إجابة
(A)
All trans-retinal
18
The Carr-Price reaction is utilized for identifying which vitamin?
إجابة
(A)
Vitamin A
19
The following structure represents which of the following substances?
إجابة
(A)
Cholecalciferol
20
Under what condition is the absorption of Vitamin D enhanced?
إجابة
(A)
Acid pH of intestine
21
Which of the following is the most active form of Vitamin D in the body?
إجابة
(B)
1,25-Dihydroxycholecalciferol
22
What is the typical range for 25-hydroxycholecalciferol levels in a blood test, measured in ng/ml?
إجابة
(D)
8-55
23
What is the normal range for 1,25-dihydroxycholecalciferol in the blood, expressed in pg/ml?
إجابة
(A)
26-65
24
What is the typical concentration of 24,25-dihydroxycholecalciferol in the blood, measured in ng/ml?
إجابة
(C)
1-5
25
Which of the following is NOT a good source of Vitamin D?
إجابة
(C)
Milk
26
Which of the listed options contains the highest concentration of Vitamin D?
إجابة
(A)
Fish liver oils
27
A lack of Vitamin D can lead to which of these conditions?
إجابة
(A)
Rickets and osteomalacia
28
The biological activity of one international unit (I.U) of vitamin D is equivalent to how much cholecalciferol?
إجابة
(A)
0.025 µg of cholecalciferol
29
What type of light causes the breakdown of the ẞ-ring of 7-dehydrocholesterol, leading to the production of cholecalciferol?
إجابة
(C)
Ultraviolet irridation with sunlight
30
Which organs are involved in the synthesis of calcitriol?
إجابة
(A)
Both liver and kidney
31
Which substance contains a negligible amount of Vitamin E?
إجابة
(D)
Fish liver oil
32
What factor negatively impacts the effectiveness of tocopherols?
إجابة
(A)
Commercial cooking
33
Increased intake of which dietary component elevates the need for vitamin E?
إجابة
(C)
Polyunsaturated fat
34
Which mineral's demand is lowered by vitamin E?
إجابة
(C)
Selenium
35
Which of the following is considered a key natural antioxidant?
إجابة
(B)
Vitamin E
36
What process do tocopherols inhibit?
إجابة
(A)
Vitamin A oxidation
37
Creatinuria is linked to a shortage of which vitamin?
إجابة
(C)
E
38
Which scenario does NOT lead to a true or apparent lack of vitamin K?
إجابة
(B)
Total lack of red meat in the diet
39
Where is vitamin K primarily sourced from?
إجابة
(A)
Green leafy plants
40
What is a primary function of Vitamin A?
إجابة
(D)
All of these
41
From which source was Vitamin K initially extracted?
إجابة
(D)
Putrid fish meal
42
Which vitamin is produced by bacteria in the intestines?
إجابة
(D)
K
43
Vitamin K aids in modifying blood clotting factors by serving as a helper molecule for which enzyme?
إجابة
(A)
Carboxylase
44
Vitamin K assists in which process?
إجابة
(A)
Gamma carboxylation of glutamic acid residue
45
An excess of Vitamin K in newborns might lead to which condition?
إجابة
(B)
Jaundice
46
Dicoumarol counteracts the effects of which vitamin?
إجابة
(C)
Menadione
47
For those consuming large amounts of vitamin C, what is the typical serum ascorbic acid level?
إجابة
(A)
1-1.4 µg/100 ml
48
Which vitamin is most likely to be lacking in someone following a diet exclusively consisting of meat?
إجابة
(C)
Vitamin C
49
Where is the highest concentration of ascorbic acid found in the human body?
إجابة
(B)
Adrenal cortex
50
Which vitamin is essential for creating hydroxyproline (in collagen)?
