Drugs and Mechanisms of Action

Question 1

Sulfa Drugs (Sulfonamides)

Answer 1

Inhibit bacterial folate synthesis from PABA

Question 2

Trimethoprim

Answer 2

Inhibit bacterial dihydrofolate reductase

Question 3

Methotrexate

Answer 3

Inhibits eukaryotic dihydrofolate reductase (used as an anticancer agent)

Question 4

Hydroxyurea

Answer 4

Inhibits ribonucleotide reductase (this enzyme converts ribonucleotides to deoxyribonucleotides)

Question 5

Mycophenolic acid

Answer 5

Inhibit GMP synthesis from IMP (Purine nucleotide biosynthesis)

Question 6

5-Fluorouracil

Answer 6

Inhibit thymidylate synthase (converts dUMP to dTMP and requires tetrahydrofolate)

Question 7

Allopurinol

Answer 7

Inhibits xanthine oxidase (this enzyme converts hypoxanthine to xanthine and xanthine to uric acid)

Question 8

NSAID and aspirin

Answer 8

Inhibit cyclooxygenase and used as anti-inflammatory drug.

Question 9

Repeated infections, reduced T and B cell immunity. Accumulation of dATP results in inhibition of proliferation of T and B lymphocytes due to inhibitory effect of dATP on Ribonucleotide reductase

Answer 9

Severe combined immunodeficiency (autosomal recessive)

Question 10

Enzyme deficiency that leads to SCID

Answer 10

Adenosine deaminase (ADA), enzyme in the catabolism of purine nucleotides. It converts adenosine to inosine.

Question 11

Repeated infections and T-cell immunodeficiency

Answer 11

Purine nucleoside phosphorylase deficiency
Enzyme deficiency: Purine nucleoside phosphorylase (as described in the name), enzyme in purine nucleotide degradation.

Question 12

Clinical Features include: Self mutilation, hyperuricemia, mental retardation

Answer 12

Lesch-Nyhan syndrome (X-linked recessive)

Question 13

Enzyme deficiency that causes Lesch-Nyhan syndrome

Answer 13

HGPRT deficiency (Enzyme involved in the salvage of purine bases hypoxanthine and guanine)

Question 14

Clinical diagnosis for the following signs and symptoms: Megaloblastic anemia (due to reduced pyrimidine biosynthesis) growth retardation

Answer 14

Orotic aciduria

Question 15

Function of PRPP Synthetase

Answer 15

Synthesis of PRPP for purine and pyrimidine nucleotide synthesis

Question 16

Function of phosphoribosyl amidotransferase

Answer 16

Regulated/committed enzyme of purine nucleotide synthesis; Activators: PRPP; Inhibitors: ATP and GTP

Question 17

Function of Xanthine oxidase

Answer 17

Enzyme of purine degradation; forms uric acid from xanthine; Also forms xanthine from hypoxanthine; Inhibitor: Allopurinol (Febuxstat)

Question 18

Function of HGPRT

Answer 18

Enzyme of purine salvage pathway; deficiency causes Lesch Nyhan syndrome

Question 19

CPS-II

Answer 19

Regulated enzyme of pyrimidine biosynthesis (Inhibited by UTP; Activated by PRPP); cytosolic enzyme

Question 20

UMP synthase (OPRT and OMP decarboxylase)

Answer 20

Enzyme of pyrimidine biosynthesis; deficiency of the enzyme results in Orotic aciduria

Question 21

Ribonucleotide reductase

Answer 21

Converts ribonucleotides to deoxyribonucleotides; Inhibitor: Hydroxyuria

Question 22

Thymidylate synthase

Answer 22

Forms dTMP from dUMP for DNA synthesis:
Inhibitors: 5-Flurouracil, methotrexate (dihydrofolate reductase inhibitor)

Question 23

Clopidogrel

Answer 23

Antiplatelet drug: reduces chance of blood clot formation

Question 24

A patient is suspected to have a genetic cause associated with his symptoms. A test is given which detects a deletion of 500,000 base pairs of DNA from his chromosome 7. What
test was used to detect this?
1. FISH
2. cDNA array
3. G-banding
4. PCR RFLP

Answer 24

cDNA array

Question 25

Silent mutations

Answer 25

Have no effect on the amino acid produced by a codon because of redundancy in the genetic code

Question 26

Missense mutations

Answer 26

still code for an amino acid, but not the correct amino acid

Question 27

Nonsense mutations

Answer 27

Change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein

Question 28

Transcription factors 3 modes of action

Answer 28

1. Competition
2. Quenching
3. Blocking

Question 29

Competition of transcription factors:

Answer 29

The repressor binds enhancer sequence of the DNA and competes with enhancer proteins
-Reduces transcription by preventing enhancer protein binding

Question 30

Quenching of transcription factors:

Answer 30

The repressor binds to the activator protein and blocks its ability to bind the DNA site
-Repressor soaks up the activator protein
-Activator protein is not able to bind to the DNA

Question 31

Blocking of transcription factors

Answer 31

The repressor binds to the activator protein’s activating domain and prevents it from interacting with general transcription factors

Question 32

Epigenetics

Answer 32

A change in the expression of a gene that changes the phenotype without permanently changing the gene itself (DNA sequence) but instead involves changes in chromatin structure

Question 33

miRNA Drosha role

Answer 33

Processes long primary-miRNAs to pre-miRNA hairpin structures

Question 34

miRNA Dicer

Answer 34

Further processes them to single stranded RNA and initiates the formation of the RNA-induced silencing complex (RISC)

Question 35

Regulation by miRNA

Answer 35

1. Inhibition of translation on the ribosome
2. Degradation of the target mRNA

Question 36

Euchromatin (E)

Answer 36

Less condensed, more transcriptionally active

Question 37

Heterochromatin (H)

Answer 37

Condensed chromatin, less transcriptionally active

Question 38

Telomere

Answer 38

-At the ends of chromosomes
-Repeated sequences that allow the ends of the chromosomes to be replicated

Question 39

Centromere

Answer 39

-Centric heterochromatin
-Persists throughout interphase
-Constricted region that holds sister chromatids together
-Also the site of kinetochore formation

Question 40

Replication origin

Answer 40

-Location where DNA replication begins

Question 41

Ribosomes types

Answer 41

1. Membrane bound ribosomes
2. Free ribosomes
   Function: Sites of protein synthesis (translation)

Question 42

COP-1 coated vesicles

Answer 42

-Retrograde transport
-CGN back to rER

Question 43

COP-II coated vesicles

Answer 43

-Anterograde transport
-Carry newly synthesized proteins from rER to CGN