Biochemistry

Question 1

Type 1 collagen

Answer 1

Most common

1. Bone
2. Skin
3. Tendon
4. Cornea
5. dentin
6. fascia
7. late wond repair

• Deficient in osteogenesis imperfecta type 1 (blue sclera)

Question 2

Type 2 collagen

Answer 2

Cartilage, vitreous body, nucleus pulposus

• Type II = car-two-lage

Question 3

Type 3 cartilage

Answer 3

​Reticulin

1. blood vessels
2. skin
3. uterus
4. fetal tissue
5. granulation tissue

• deficient in vasuclar type of Ehler’s-Danlos syndrome

Question 4

Type 4 collagen

Answer 4

1. Basement membrane
2. basal lamina
3. lens

• Defective in Alport syndrome
• targeted by autoantibodies in Goodpature’s syndrome

“Type 4 under the floor”

Question 5

I-Cell Disease:

• Pathophysiology:
• Signs/Symptoms:

Answer 5

Failure of the Golgi (often fatal in childhood)

• Pathophysiology:
  
  • defect in N-acetylglucosaminyl-1-phosphotransferase
  • failure of the Golgi to phosphorylate mannose residues on glycoproteins ⇒ proteins are delivered extracellularly rather than via lysosomes
• Signs/Symptoms:
  
  • coarse facial features
  • clouded corneas
  • restricted joint movements
  • high plasma levels of lysosomal enzymes

Question 6

What is a signal ribonucleotide (SRP)? What happens if they are absent/dysfunctional?

Answer 6

• traffics proteins from the ribosome to the RER
• Absent/dysfunctional ⇒ accumulation of proteins in the cytosol

Question 7

What amino acids are necessary for purine synthesis?

Answer 7

GAG

1. Glycine
2. Asparate
3. Glutamine

Question 8

1. DNA methylation
2. Histone methylation
3. Histone acetylation

Answer 8

1. DNA methylation ⇒ represses transcription
   
   • In prokaryotes only
   • “CpG Methylation Makes DNA Mute”
2. Histone methylation ⇒ reversibly represses DNA transcription
   
   • ​​”Histone Methylation Mostly Makes DNA Mute”
   • can activate in some cases depending on methylation site
3. Histone acetylation ⇒ allows transcription
   
   • Histone Acetylation makes DNA Active
   • relaxes DNA coiling

Question 9

Lesch-Nyan syndrome

• Pathophysiology
• Clinical signs/symptoms
• Treatment

Answer 9

• Pathophysiology
  
  • absent HGPRT → excess uric acid production and de novo purine synthesis
  • HGPRT → converts hypoxanthine to IMP and guanine to GMP
• Clinical signs/symptoms: HGPRT
  
  • Hyperuricemia
  • Gout
  • Pissed off (aggression, self-mutilation)
  • Retardation (intellectual disability)
  • DysTonia
• Treatment: allopurinol (1st line) or febuxostat (2nd line)

Question 10

DNA Replication

1. Orgin of replication
2. Replication fork
3. Helicase
4. Single-stranded binding protein
5. DNA topoisomerase
6. Primase
7. DNA polymerase III
8. DNA polymerase I
9. DNA ligase
10. Telomerase

Answer 10

1. Orgin of replication
   
   • sequence of base pairs in genome where replication begins
2. Replication fork
   
   • Y-shaped region where leading and lagging strands are synthesized
3. Helicase
   
   • unwinds DNA template
4. Single-stranded binding protein
   
   • prevents strands from reannealing
5. DNA topoisomerase
   
   • create a single or double-strand break to add or remove supercoils
   • Flouroquinolones - inhibit topoisomerases
6. Primase
   
   • makes RNA primer on which DNA polymerase III can intiate replication
7. DNA polymerase III
   
   • Prokaryotic only
   • 5’ ⇒ 3’ synthesis and proofreads with 3’ ⇒ 5’ exonuclease
8. DNA polymerase I
   
   • Prokaryotic only
   • Same as DNA poly III + RNA primer w/ 5’ ⇒ 3’ exonuclease
9. DNA ligase
   
   • Seals (joins Okazaki fragments)
10. Telomerase
    
    • Eukaryotes only
    • RNA-dependent DNA polymerase that adds DNA to 3’ ends of chromosomes to avoid loss of genetic material

Question 11

Describe how the lac operon repsonds to environmental change:

1. Low glucose ⇒
2. High lactose ⇒

Answer 11

Activated when glucose is low/absent and lactose is available:

1. Low glucose ⇒ ↑ adenylyl cyclase activity → ↑ generation of cAMP from ATP → activation of catabolite activator protein (CAP) → ↑ transcription
2. High lactose ⇒ unbinds repressor protein from repressor/operator site → ↑ transcription