Purines And Pyrimidimes

Question 1

What is involved in formation of d-TMP from d-UMP?
A. N5, N10 methylene tetrahydrofolate 
B. Forms imino folate
C.N5 formyl folate
D. Dihydrofolate

Answer 1

Answer- A. N5,N10 methylene tetrahydrofolate

d-UMP is convert to dTMP which uses N5, N10 methylene tetrahydrofolate as a source of methyl group. This is an unusual reaction in that THF contributes to 1 carbon unit & 2 hydrogen atoms from pteridine ring which causes oxidation of THF to DHF.
Disorders of folate & vitamin B12 metabolism cause deficiency of TMP

Question 2

End product of purine metabolism in non-primate animal?
A. Uric acid
B. Ammonia
C. Urea
D. Allantoin

Answer 2

Answer- D. Allantoin

End product of catabolism of purine (adenosine & guanosine) nucleotides in mammals other than higher primates- Allantoin ( uricase converts uricase acid to allantoin )

Where as end product of catabolism of purine (adenosine & guanosine) nucleotides in humans- uric acid (lack of uricase)

Question 3

Inositic acid is the biological precursor of
A. Uracil & Thymine
B. Purines & thymine 
C. Adenylic acid & guanylic acid
D. Orotic acid Adam uridylic acid

Answer 3

Answer - C. Adenylic acid & guanylic acid

Question 4

Gout is a disorder of
A. Purine metabolism 
B. Pyrimidine metabolism
C. Oxalate metabolism
D. Protein metabolism

Answer 4

Answer- A. Purine metabolism

Gout is a metabolic disorder of purine catabolism.
It is characterized by high levels of uric acid in the blood.
Uric acid is the end product of purine catabolism.

Pyrimidine nucleotides unlike purine rings can be opened and degraded to highly water soluble structures like beta- alanine, beta- amino isobutyrate, NH3 & CO2

Question 5

False regarding gout is
A. Due to increased metabolism of pyrimidines
B. Due to increased metabolism of purines
C. Uric acid levels may not be elevated
D. Has a predilection for the great toe.

Answer 5

Answer - A. Due to increased metabolism of pyrimidines

Question 6

What is not true about gout
A. Abrupt increase in serum urate levels Is more common a cause for acute gout than an abrupt fall in urate levels
B. Patient maybe asymptomatic with high serum Uric acid for years
C. Development of arthritis correlates with level of serum Uric acid
D. Uric acid crystals at best seen by polarizing light microscope.

Answer 6

Answer - A. Abrupt increase in serum urate levels Is more common a cause for acute gout than an abrupt fall in urate levels

Question 7

Specific test for gout is 
A. Raised serum Uric acid level
B. Raised Uric acid in synovial fluid of joint
C. Raised urea level
D. Raised urease enzyme level

Answer 7

Answer- B. Raised Uric acid in synovial fluid of joint is a specific test for gout.

Question 8

A ten year child with aggressive behavior and poor concentration is brought with presenting complaints of joint pain and reduced urinary output.
Mother gives history of self-mutilitative behavior stating that he tends to mutilate his fingers. Which of the following enzymes is likely to be deficient in this child.
A. Adenosine deaminase
B. HGPRTase
C. APRTase
D. Acid maltase

Answer 8

Answer - B. HGPRTase

Lesch-Nyhan syndrome is an X-linked, recessive disorder associated with complete deficiency of hypoxanthine guanine phosphoribosyl transferase, therefore has inability to salvage hypoxanthine or guanine from which excessive Uric acid is produced.

C/F includes

1. Poor concentration
2. Mental retardation
3. Extremely hostile male children
4. Compulsive aggressive behavior
5. Self destructing tendencies- self mutilism by biting off their fingers, toes and lips.

Question 9

A 12 year old child presents with mental retardation and history of self mutilism. Which of the following tests will help in determining the diagnosis
A. Serum lead levels
B. Serum alkaline phosphatase levels
C. Serum lactate dehydrogenase levels
D. Serum Uric acid levels.

Answer 9

Answer- D. Serum Uric acid levels are increased in Lesch-Nyhan syndrome.