BIOCHEM

Question 1

Where does the amino acid attach to tRNA?

Answer 1

CCA - Can Carry Amino acids

• CCA-OH at 3’ end
• Covalently bound
• Aminoacyl-tRNA synthetase uses ATP to attach the correct amino acid
• Anticodon of tRNA reads the codon on mRNA at the opposite end (top end of clover)

Question 2

Antibiotics that are inhibitors of prokaryotic protein synthesis at the 50S ribosome:

Answer 2

“Buy AT 30, CCELL at 50”

• Aminoglycosides (Gentamicin, Tobramycin)
• Tetracycline
• Chloramphenicol
• Clindamycin
• Erythromycin (a macrolide)
• Lincomycin
• Linezolid (23S RNA)
• Streptogramins
• Macrolides (Azithromycin, Clarithromycin) (23S RNA)

Question 3

$$$ In what metaboli creactions is folic acid (B9) involved?

Answer 3

• Synthesis of urines (A,G) and thymine (T) -> these nitrogenous bases are important for DNA and RNA synthesis
• Converted to tetrahydrofolate (THF), a conenzyme for 1-carbon transfer/methylation reactions

Question 4

What is the biologically active form of folic acid?

What is the intracellular storage form of folic acid (folate)

Answer 4

Tetrahydrofolate

N-methyl folate

Question 5

What are the characteristics of oflic acid deficiency?

Answer 5

• Neural tube defect
• Growth failure
• Megaloblastic anemia

Question 6

What is megaloblastic anemia

Deficiency in which 2 vitamins cause megaloblastic anemia?

How do you determine which one it is caused by?

Answer 6

A type of macrocytic (large RBC) anemia characterized by an elevated number of megaloblasts in the marrow

Folate and B12

Decreased serum level of either

Question 7

How much folate should a sexually-active woman of childbearing age take in order to prevent neural tube defects?

What results from excess of folate? Why?

Answer 7

0.4 mg of folic acid a day (4 grams if at high-risk for neural tube defects)

B12 deficiency results because this vitamin is used in making tetrahydrofolate?

Question 8

What is vitamin B12?

Answer 8

• Cobalamin
• Cofactor for homocysteine methyltransferase (transfers CH3 groups as methylcobalamin) and methylmalonyl-CoA mutase

Question 9

What metabolic reactions is vitamin B12 involved?

Answer 9

• Homocysteine and methyl-THF -> methionine and THF (required for SAM to function)
• Methylmalonyl CoA (coenzyme A) -> succinyl CoA

Question 10

What is teh biologically active form of B6 (pyridoxine)

What is the metabolic function of B6?

What drug can lead to a deficiency of B6 as well as B3?

Answer 10

• Pyridoxal phosphate
• Pyridoxal phosphate is a coenzyme for numerous enzymes including those of amino acid metabolism (transaminations and deaminations)

Question 11

What drug can lead to a deficiency of B6 as well as B3?

What are the clinical findings of a B6 deficiency?

Answer 11

• Isoniazid (for TB)
• Same as riboflavin deficiency + Convulsions (creates GABA), hyperirritability, and peripheral neuropathy