Biochemistry

Question 1

What enzyme does Leflunomide inhibit?

Answer 1

Inhibits dihydroorotate dehydrogenase in pyrimidine synthesis

Question 2

What enzyme does methrotrexate (MTX), Trimetrhoprim (TMP), and Pyrimethamine inhibit

Answer 2

They inhibit dihydrofolate reductase (decreases deoxythymidine monophosphoate) in pyrimidine synthesis

• MTX in humans.
• TMP in bacteria
• Pyrimethamine in protozoa.

Question 3

What does 5-fluorouracil (5-FU) and its product capecitabine form and what enzyme does that formation inhibit?

Answer 3

They form 5-F-dUMP which inhibits thymidylate synthase (which decreases dTMP) in pyrimidine syntesis

Question 4

What does 6-mercaptopurine (6-MP) and its prodrug azathioprine inhibit?

Answer 4

They inhibit de novo purine synthesis

Question 5

What enzyme does mycophenolate and ribavirin inhibit?

Answer 5

They inhibit inosine monophosphate dehydrogenase in purine synthesis

Question 6

What enzyme does Hydroxyurea inhibit?

Answer 6

It inhibits ribonucleotide reductase in purine and pyrimidine synthesis

Question 7

In what phase does histone and DNA syntesis occur?

Answer 7

Their synthesis occurs during S phase

Question 8

What is the structural component of a nucleoside?

Answer 8

a nitrogenouse base + (deoxy)ribose (sugar)

Question 9

What is a nucleotide?

Answer 9

A compound consisting of a nucleoside linked to a phosphate group. They form the basis structural unit of nucleic acids such as DNA.

Question 10

Name the purines

Answer 10

Adenine & Guanine

- They consist of 2 rings

Question 11

Name the pyrimidines

Answer 11

Thymine (has a methyl group), Cytosine, Uracil

- They consist of 1 ring

Question 12

What is stronger a G-C bond or a A-T bond and why?

Answer 12

A G-C bond is stronger because it has three Hydrogen bonds unlike A-T bonds that only has 2 hydrogen bonds

Question 13

What are the Amino Acids needed for Purine synthesis?

Answer 13

Glycine
Aspartate
Glutamine

Question 14

What enzyme is required for adenosine and deoxyadenosine degradation and what happens when there is a deficiency in that enzyme?

Answer 14

• Adenosine deaminase (ADA) is required for their degradation.
• In ADA deficiency dexyadenosine triphosphate levels increase which causes lymphotoxicity.
• ADA deficiency is on of the major causes of autosomal recessive severe combined immunodeficiency disease (SCID)

Question 15

What does hypoxanthine-guanine phosphoribosyltransferase (HGPRT) do?

Answer 15

It converts hypoxanthine to inosine monophospate (IMP) and guanine to guanosine monophosphate (GMP)

Question 16

What happens when hypoxanthine-guanine phosphoribosyltransferase (HGPRT) is absent?

Answer 16

• There is a defective purine salvage which results in excess uric acid production and de novo purine synthesis.
• It results in Lesch-Nyhan syndrome which is X-linked recessive.

Question 17

What are the common clinical findings in Lesch-Nyhan Syndrome

Answer 17

• HRPRT*
• Hyperuricemia (orange “sand” [sodium urate crystals] in diaper)
• Gout
• Pissed off (agression, self mutilation)
• Retardation (intelectual disability)
• DisTonia

Question 18

What is the treatment for Lesch-Nyhan Syndrome

Answer 18

Allopurinol or febuxostat (2nd line)

Question 19

What enzyme does Allopurinol and febuxostat inhibit?

Answer 19

They inhibit xanthine oxidase

Question 20

What are the genetic code features?

Answer 20

• Unambiguous: each codon specifies only 1 amino acid
• Degenerate / redundante: most amino acids are coded by multiple codons (exeptions: methionine (AUG) and tryptophan (UGG) encoded by only 1 codon.
• Commaless, nonoverlapping: Read from a fixed starting point as a continuous sequence of bases (exeptions: some viruses)
• Universal: Genetic code is conserved throughout evolution (exception in humans: mitochondria)