MDS PREP
Which of the following amino acids is a
precursor for epinephrine?
1. Valine
2. Leucine
3. Tyrosine
4. Cysteine
Biochemistry
Answer: 3
Epinephrine, also known as adrenaline, is a hormone and neurotransmitter that
is synthesized in the body from the amino acid tyrosine. Tyrosine is a
non-essential amino acid, which means that it can be synthesized in the body
from phenylalanine, another essential amino acid. The synthesis of epinephrine
occurs in two main steps:
1. Hydroxylation of tyrosine: Tyrosine is converted into dihydroxyphenylalanine
(DOPA) by the enzyme tyrosine hydroxylase. This is the rate-limiting step in the
synthesis of epinephrine.
2. Decarboxylation and further hydroxylation: DOPA is then decarboxylated to
form dopamine, which is further hydroxylated to produce norepinephrine.
Norepinephrine is the immediate precursor of epinephrine.
3. Formation of epinephrine: Norepinephrine is methylated by the enzyme
phenylethanolamine N-methyltransferase (PNMT) and converted into epinephrine.
The other amino acids listed are not directly involved in the synthesis of
epinephrine:
1. Valine and Leucine are branched-chain amino acids that are primarily involved
in the metabolism of muscles and energy production.
2. Cysteine is a sulfur-containing amino acid that is important for the
synthesis of proteins with disulfide bridges and is a precursor for other
molecules like glutathione and taurine, but not directly involved in the
synthesis of epinephrine.
Which of the following dental tissues is most likely to be effected by Vit-A
deficiency
1. enamel
2. dentin
3. cementum
4. pulp
Biochemistry Answer: 1
Enamel most likely effected by deficiency of vitamin A
Anemia is frequently associated with a deficiency of
1. vitamins A and D.
2. vitamins C and D.
3. vitamins E and K.
4. vitamin B12 and folic acid.
Biochemistry
Answer: 4
Anemia is a condition characterized by a decrease in the number of red blood
cells or a reduction in their oxygen-carrying capacity. Vitamin B12 and folic
acid are essential for the production of red blood cells. Deficiencies in these
vitamins can lead to megaloblastic anemia, where the bone marrow produces
abnormally large and immature red blood cells.
Symptoms from a riboflavin deficiency can be:
1. Cracks in the corner of the mouth (angular stomatitis)
2. Inflammation of the tongue (glossitis)
3. Eye and skin changes
4. All of the above
Biochemistry
Answer: 4
The eye change include an increase in blood vessels and inflammation of the conjunctivae, cornea is invaded by capillaries, producing opaque areas and even ulceration. Dermatitis characterized by a greasy and scaly reddened lesion develops on the skin around the nasolabial folds and may extend to a butterfly shape on the cheeks. There many also be lesions at the corners (canthi) of the eyes and lobes of the mouth.
Glycine is a:
1. Glycogenic amino acid, only
2. Ketogenic only
3. Glucogenic and ketogenic
4. Since It Is optically inactive therefore none of the above
Biochemistry
Answer: 1
Glycine is a Glycogenic amino acid, only
Which of the following is a common dietary saturated fatty acid?
1. Oleic acid
2. Stearic acid
3. Linolenic acid
4. Arachidonic acid
Biochemistry
Answer: 4
Saturated fatty acids are a type of fat that has a chemical structure with a
single bond between each carbon atom in the fatty acid chain and no double
bonds. These types of fats are typically solid at room temperature. Out of the
given options, stearic acid (C18:0) is the only saturated fatty acid. The others
are:
1. Oleic acid (C18:1) is a monounsaturated fatty acid, which means it has one
double bond. It is commonly found in olive oil, canola oil, and avocados.
2. Linolenic acid (C18:3) is a polyunsaturated fatty acid, specifically an
omega-3 fatty acid, with three double bonds. It is found in plant sources like
flaxseeds, chia seeds, and walnuts.
3. Arachidonic acid (C20:4) is also a polyunsaturated fatty acid, an omega-6
fatty acid with four double bonds. It is found in animal fats, such as meat, and
in smaller amounts in some plant oils like sunflower oil and peanut oil.
Stearic acid, on the other hand, is a common saturated fatty acid found in
various animal fats and certain vegetable oils like coconut oil, palm kernel
oil, and cocoa butter. It is known for its role in the structure of cell
membranes and as a precursor for the biosynthesis of cholesterol in the body.
While it is important to consume fatty acids for good health, excessive
consumption of saturated fatty acids has been associated with higher levels of
LDL (low-density lipoprotein) cholesterol, which is often referred to as "bad"
cholesterol, and an increased risk of heart disease. However, it is important to
maintain a balanced diet that includes both saturated and unsaturated fatty
acids in moderation.
Hyperuricemia in Lesch-Nyhan syndrome is due to a defect in which of the following pathways?
1) Purine biosynthesis
2) Pyrimidine biosynthesis
3) Purine salvage
4) Pyrimidine salvage
Biochemistry Answer: 3
Uric acid is a purine derivative, increased by purine salvage reactions that convert purines, purine ribonucleosides, and purine deoxyribonucleoside to mononucleotides (incorrect answer 4).
Such salvage reactions require much less energy than de novo synthesis (incorrect answers 1, 2). The liver is the major site of purine nucleotide biosynthesis and provides excess purines for other tissues that cannot synthesize purines.
A defect in hypoxanthine-guanine phosphoribosyl transferase, one of the enzymes of purine salvage, is responsible for purine overproduction and subsequent hyperuricemia observed in Lesch-Nyhan syndrome.
All of the following statements are true for the acetylcholinesterase receptor
EXCEPT that it
1). opens an ion channel.
2). binds to succinylcholine.
3). undergoes irreversible conformational changes when exposed to carbamates
4). is inactivated in myasthenia gravis
Biochemistry
Answer: 2
Acetylcholinesterase receptor opens an ion channel, undergoes irreversible conformational changes when exposed to carbamates , it is inactivated in myasthenia gravis