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USMLE Step 1: Things I Cannot Remember > Biochemistry > Flashcards

Flashcards in Biochemistry Deck (12):
1

Type 1 collagen

 

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)

2

Type 2 collagen

Cartilage, vitreous body, nucleus pulposus

  • Type II = car-two-lage

3

Type 3 cartilage

​Reticulin

  1. blood vessels
  2. skin
  3. uterus
  4. fetal tissue
  5. granulation tissue
  • deficient in vasuclar type of Ehler's-Danlos syndrome

4

Type 4 collagen

  1. Basement membrane
  2. basal lamina
  3. lens
  • Defective in Alport syndrome
  • targeted by autoantibodies in Goodpature's syndrome

"Type 4 under the floor"

5

I-Cell Disease:

  • Pathophysiology:
  • Signs/Symptoms:

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

6

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

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

7

What amino acids are necessary for purine synthesis?

GAG

  1. Glycine
  2. Asparate
  3. Glutamine

8

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

  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

9

Lesch-Nyan syndrome

  • Pathophysiology
  • Clinical signs/symptoms
  • Treatment

  • 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)

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

  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

11

Describe how the lac operon repsonds to environmental change:

  1. Low glucose ⇒ 
  2. High lactose ⇒

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

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