Cellular Biochemistry USMLE Step 1 Exam Questions and Answers 100% Solved

Cellular Biochemistry USMLE Step 1

Exam Questions and Answers 100%

Solved


p53 - ✔✔Tumor suppressor gene that prevents cells from progressing from

G1 to S phase



- In response to DNA damage, p53 will call in DNA repair enzymes

- If repair not possible, p53 will call in BAX that causes cell apoptosis



Rb - ✔✔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

progression of cell cycle



What phosphorylates Rb? - ✔✔CDK4/Cyclin D
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, E2F - ✔✔E2F is a transcription factor that binds to the E2F box allowing

transcription of S-phase genes



In order for tumor to occur, how many copies must be mutated for a) p53 b)

Rb - ✔✔a) 2

b) 2



Mutations in Rb - ✔✔- Germline mutation = Bilateral retinoblastoma,

osteosarcoma



- Sporadic mutation = unilateral retinoblastoma



Mutation in p53 - ✔✔Leads to Li-Fraumeni Syndrome



Permanent tissues - ✔✔Always in G0 phase



- Cardiac myocytes, skeletal tissue, neurons, RBCs




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