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MCQs PART



mcqs in ch 22 done by majhool

Which of the following compounds donate nitrogen atom to purine and pyrimidine :
- glycine.
- N10 - Formyltetrahydrofolate. 
- Aspartic acid. 
- Glutamic acid.
- Aspargine.


Uric acid is the end product of purine degredation (T) be carful not allantoin

Adenosin & cytosine are ribonucleoside (F) cytidine not cytosine

purine & pyrimidine are attathed to C 1 of pentose (T) t

PRPP synthase is ACTIVATED BY Pi ( T)t

IMP & UMP are the parent compound of both purine , pyrimidine respectively (F) omp not UMP

the end product of de novo purine synthesis is deoxyribonucleotide (F)
end product is ribonucleotide

IMP base is hypoxanthine (T) ( note that inosine is the same name of hypoxhanthine ribose)

synthesis of purine require N10 methylene THF (F) (N10 FormylTHF)

IMP synthesis require 2 ATP (F) (4ATP)

work on bacteria only ( not interfere with human cell function ) (T)t

trimethoprim is PAPA analog (F) ( folate analog)

methotrexate inhibit purine syntheis in baceria (F) ( in human )

Möycophenolic acid is potent competitive inhibitor of IMP dehydrogenase. F ( un competitive)

Adenylate kinase is irreversible reaction (F) it is reversible

Böoth NMP- & NDP- kinases are reversible enzymes. T

hypoxanthine-guanine phosphribosyltransferase(HPRT) use Hmp pathway
as a asource of ribose 5 phosphate (f) ( use PRPP as a source )

(HPRT) catalyse irreversible reaction (T)

de novo synthesis of purines requires much more energy compared to that of their 
salvage réactions.( T )

lesch-Nyhan syndrome is due to APRT dificiency (F) ( complete HPRT dificiency )

the lack of HPRT lead to : ( åÇã ÇÝåãåÇ ÌíÏÇ )
- increase PRPP - decrease IMP & GMP (MCQ)(NOT AMP)

Lack of HPRT lead to derease production of uric acid (F) increase

ribonucleotide reductase has two P group (T)t

ribonucleotide reductase is one subunit (F) ( multi sub unit ).

ribonucleotide reductase convert TDP (F)

thyredoxin reductase need NADH (F) NADPH

NADPH is the immediate donors for the hydrogen atoms needed for reduction.(F) (sulf hydryl group is the donar )

ribonucleotide reductase is activated by dATP (F) inhibited

an amino group is removed from adenosine to produce inosine ( adenosine deaminase ) (T)t

ADENOSINE DEAMINASE (ADA)DEFICIENCY : ( MCQ)(MCQ) * ( æÖÚÊå ÈÇáßÇãá áÃåãíÊå ) åÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇ ÇÇÇÇÇã

- in cytosol of all cells especially lymphocyte .
- autosomal recessive disorder .
- accumulation of adenosine .
- so accumulation of ribonucleotide & deoxyribonuleotide . 
- large dATP in red cell which inhibit ribonucleotide reductase , so inhibit DNA synthesis . (MCQ)
- In severe form , it causes severe combined immunodeficiency 
Disease ( SCID ), involving lack of both T , B cells . (MCQ)
-children die before two years of age .
- Treatment :
-bone marrow replacement or enzyme replacement .
- is the first genetic disease treated by gene therapy .
Aspartate donate C in both purine & pyrimidine ( F ) 

* carbamoyl phosphate synthase 11 : ( ßá ÇáÇÌÇÈÇÊ ÕÍíÍÉ æÊÐßÑ Çäå irreversible )
a) in cytosol .
b) source of N: amide group of glutamine
c) activator : ATP & PRPP .
d) inhibitor : UTP .
e) no need for biotin .

Pyrimidine ring is closed by dihydroorotate dehydrogenase (F) ( by dyhydroratase

( CPS 11 , aspartate transcarbamoylase , dihydrooratase )are all domain of the same polypeptide chain (T)

Dihydrooratate dehydrogenase use NADH & is the only enzyme in mitochondria (T)t

orotate is the first pyrimidine ring (T)

( both purine & pyrimidine synthesis require glutamine & PRPP (T)åÇã ÌÏÇ

- UMP synthase : (MCQ) ( very important ) ãÚáæãÉ åÇãÉ áíÓÊ ÓÄÇá
- a single polypeptide contain both :
1) orotate phosphoribosyl transferase
2) orotidylate decarboxylase

OROTIC ACIDURIA :is due to UMP dificiency & treated by uridine diet (T)t

Which of the following statements about nucleotide metabolism is incorrect?
a) sulfonamides competitively inhibit purine synthesis in human. ( answer )(bacteria)
b) IMP and OMP are parent purine and pyrimidine nucleotides, respectively.
c) the synthesis of AMP requires GTP.
d) AMP inhibits de novo purine synthesis.
e) folic acid analogs are competitive inhibitors of dihydrofolate reductase.


5-flurouracil ( thymine analogs) which convert to 5- FdUMP is inhibitor of thymidylate kinase (F) (thymidylate synthase )

*Salvage of Pyrimidine : ( ãÚáæãÉ åÇãÉ ÑßÒ ÚáíåÇ ÇáÏßÊæÑ )
- salvage pyrimidine bases ( FEW ) ( MCQ)
- salvage pyrimidine nucleoside ( more ) (MCQ )


Acyclovir : a substrate for thimidine kinase ( not synthase be careful) 

purine rings are not cleaved in human cell (T)t.
- pyrimidine rings are cleaved & opened TO HIGHLY SOLUBLE (T)t


Done by:
majhool 
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1 – Which of the following contribute N to both purine and pyrimidine:
a) glutamic acid.
b) glycine.
c) aspartic acid.
d) arginine.
e) ammonia.
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