Exam (elaborations)
USMLE STEP 1 CELLULAR BIOCHEMISTRY EXAM QUESTIONS AND ANSWERS
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USMLE STEP 1 CELLULAR BIOCHEMISTRY EXAM QUESTIONS AND ANSWERS...
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p53 - ANSWER Tumor suppressor gene that prevents cells from progressingfrom G1 to S phase
- In response to DNA damage, p53 will call in DNA repair enzymes
- If repair is not possible, p53 will call in BAX causing cell apoptosis
Rb - ANSWER Tumor suppressor gene that prevents cells from progressing
from G1 to S phase
- Normally unphosphorylated and binds to E2F
- When phosphorylated by Cyclin-CDK, it releases E2F allowing the
progression of the cell cycle
What phosphorylates Rb? - ANSWER CDK4/Cyclin D
E2F - ANSWER E2F is a transcription factor that binds to the E2F box
allowing transcription of S-phase genes
In order for a tumor to occur, how many copies must be mutated for a) p53 b)
Rb - ANSWER a) 2
b) 2
Mutations in Rb - ANSWER - Germline mutation = Bilateral retinoblastoma,
osteosarcoma
- Sporadic mutation = unilateral retinoblastoma
Mutation in p53 - ANSWER Leads to Li-Fraumeni Syndrome
Permanent tissues - ANSWER Always in G0 phase
- Cardiac myocytes, skeletal tissue, neurons, RBCs
Stable Tissues - ANSWER In G0 phase and enter G1 when stimulated
, - Hepatocytes and lymphocytes
Labile Tissues - ANSWER Never in G0 phase
- Divide rapidly and effected greatly by chemo
- Regenerate quickly from stem cells
- Bone marrow
- Skin
- Gut epithelium
- Hair follicles
- Germ cells
What Cyclin/CDK complex activates DNA replication? - ANSWER CDK
2/Cyclin A
What Cyclin/CDK complex activates DNA mitosis? - ANSWER
CDK1/Cyclin B
_____ and _____ are rich in SER - ANSWER liver hepatocytes and hormone-
producing cells of the adrenal cortex
_____ and ____ are rich in RER - ANSWER mucus secreting goblet cells and
plasma cells
Golgi Apparatus Modifications - ANSWER - Modifies N-oligosaccharides on
Asparagine
- Adds O-oligosaccharides on serine and threonine
- Adds mannose-6-P to proteins for trafficking to lysosomes
Inclusion Cell Disease (I-cell Disease) - ANSWER (inherited lysosomal
storage disease)
- Defect in N-acteylglucosaminyl-1-Phosphotransferase
- Failure of the golgi to phosphorylate mannose residues (ie. Mannose-6-P) on
Glycoproteins
- Proteins are secreted extracellularly rather than delivered to lysosomes
S/S: clouded corneas, restricted joint movement, coarse facial features,
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