Biochemistry

Question 1

What are the stop codon(s)?

Answer 1

UAA, UAG, UGA

Question 2

What are the start codon(s)?

Answer 2

AUG

Question 3

What are the purines?

Answer 3

Adenine and Guanine - they have 2 rings

Question 4

What are the pyrimidines

Answer 4

Cytosine, uracil, and thymine - they have 1 ring

Question 5

Which A.A. are necessary for purine synthesis

Answer 5

GAG - glycine, aspartate and glutamine

Question 6

Which drugs impair pyrimidine synthesis?
Leflunomide
Methotrexate, trimethoprim, pyrimethamine
5-fluorouracil
6-mercaptopurine, azothioprine
Mycophenolate, ribovarin
Hydroxyurea

Answer 6

Leflunomide –> pyrimidine (dihydroorotate dehydrogenase)
Methotrexate, trimethoprim, pyrimethamine –> pyrimidine (dihydrofolate reductase)
5-fluorouracil –> pyrimidine (thymidylate synthase)
6-mercaptopurine (prodrug is azothioprine) –> purine
Mycophenolate, ribovarin –> purine (inhibit inosine monophosphate dehydrogenase)
Hydroxyurea –> both (inhibits ribonucleotide reductase)

Question 7

Which drugs (3) affect the purine salvage pathway?

Answer 7

Allopurinol and febuxostat inhibit xanthine oxidase
Low-dose aspirin inhibits excretion of uric acid to urine
Probenecid increases excretion of uric acid to urine

Question 8

What is the defect in Lesch-Nyhan Syndrome?

What are the features of Lesch-Nyhan Syndrome?

Answer 8

HGPRT (hypoxanthine guanine phosphoribosyltransferase) deficiency, enzyyme of the purine salvage pathway, resulting in excess uric acid production and de novo purine synthesis. X-linked recessive disorder.

Features: HGPRT
Hyperuricemia, gout, pissed off (aggression and self-maiming), retardation, and tone (dystonia)
Orange “sand” (sodium urate crystals) in diaper
Treatment: allopurinol or febuxostat

Question 9

Adenosine deaminase deficiency results in

Answer 9

autosomal recessive form of SCID
ADA is an enzyme in purine salvage and its absence leads to a build up of metabolites (dATP) that are toxic to lymphocytes

Question 10

Which A.A. are encoded my only 1 codon?

Answer 10

AUG - methionine

UGG - tryptophan

Question 11

Fluoroquinolones target which bacterial function?

Answer 11

Fluoroquinolones inhibit prokaryotic topoisomerase II (DNA gyrase) and topoisomerase IV, enzymes of DNA replication that create single or double strand breaks in DNA helix to remove supercoils

Question 12

What is the mutation in Sickle Cell Disease?

Answer 12

Missense mutation - substitution of glutamic acid with valine

Question 13

What is the mutation in Duchenne muscular dystrophy and Tay-Sachs disease?

Answer 13

Frameshift mutation

Question 14

Lynch syndrome is a defect in ____________

Answer 14

Mismatch repair

Lynch syndrome = hereditary nonpolyposis colorectal cancer

Question 15

In eukaryotes, what are the functions of RNA polymerase I, II, and III?

Answer 15

RNA Polymerase I –> rRNA
RNA Polymerase II –> mRNA
RNA Polymerase III –> tRNA

Question 16

Rifampin inhibits

Answer 16

DNA-dependent RNA polymerase in prokaryotes

Question 17

Anti-Smith antibodies are seen in

Answer 17

SLE (highly specific) and mixed connective tissue disease (MCTD)
Anti-Smith antibodies are anti-spliceosomal snRNP antibodies

Question 18

A child has coarse facial features, clouded corneas, restricted joint movement, and high plasma levels of lysosomal enzymes. This is most likely due to a defect in __________________

Answer 18

The child has I-cell disease (AKA inclusion cell or mucolipidosis type II) which is often fatal in childhood and is caused by a defect in N-acetylglucosaminyl-1-phsophotransferase. Golgi is unable to phosphorylate mannose residues on glycoproteins and they are secreted extra-cellularly rather than trafficked to lysosomes.

Question 19

What is the defect in Zellweger syndrome and Refsum disease?

What are their features?

Answer 19

Both are peroxisome disorders (commonly lead to neurological disease due to deficits in plasmalogen synthesis - important phospholipid in myelin)

Zellweger syndrome: hypotonia, seizures, hepatomegaly, and early death

Refsum disease: scaly skin, ataxia, cataracts/nightblindness, shortening of 4th toe, epiphyseal dysplasia)

Question 20

Vimentin stains for

Answer 20

Mesenchymal tissue and related tumours (e.g. sarcoma, endometrial, renal cell, meningioma)

Question 21

Desmin stains for

Answer 21

Muscle and related tumours (sarcoma)

Question 22

Cytokeratin stains for

Answer 22

Epithelial cells and related tumours (squamous cell)

Question 23

GFAP stains for

Answer 23

Neuroglia (E.g. astrocytes, Schwann cells, oligodendrocytes) and related tumours (astrocytoma, glioblastoma)

Question 24

Neurofilaments stain for

Answer 24

Neurons and related tumours (neuroblastoma)

Question 25

Which drugs act on microtubules

Answer 25

MGCVP - microtubules get constructed very poorly
Mebendazole (anti-helminthic)
Griseofulvin (anti-fungal)
Colchicine (anti-gout)
Vincristine/vinblastine (anti-cancer)
Paclitaxel (anticancer)

Question 26

What is the defect in Kartagener syndrome?

What are the features?

Answer 26

Kartagener Syndrome AKA primary ciliary dyskinesia

Cause: defect in dynein arm causing immotile cilia

Features: male and female infertility, increased risk of ectopic pregnancy, situs inversus, bronchiectasis, recurrent sinusitis, chronic ear infections, and conductive hearing loss

Question 27

What is the target of digoxin?

Answer 27

Na-K-ATPase

Prevents Na from exiting the cell thereby inhibiting Na/Ca exchange. Higher [Ca++]i increases heart contractility

Question 28

Which structures contain
Collagen I
Collagen II
Collagen III
Collagen IV

Answer 28

BST CRB
Collagen I
- Bone, Skin, Tendons, dentin, fascia, cornea
Collagen II
- Cartilage
Collagen III
- Reticulin, skin, blood vessels, uterus, fetal tissue
Collagen IV
- Basement membrane, basal lamina, lens

Question 29

Alport syndrome is due to

Answer 29

Defective col IV

Goodpasture’s Syndrome = antibody against col IV