USMLE PRACTICE QUESTION #52
TOPIC: Biochemistry/Collagen Synthesis
Today’s question will test your understanding of the fundamentals of collagen synthesis.
I’m Paul Ciurysek, MD, and this is The USMLE Times: An independent, subscriber-supported newsletter designed to help you survive medical school, pass your USMLE exams, and match into your dream residency program.
A group of medical students are trying to replicate the entire process of collagen synthesis in artificial human tissue. They must follow the precise steps in synthesizing normal collagen to achieve their desired outcome. Which of the following is the first step needed to achieve the desired outcome?
A. Glycosylation of pro-alpha-chain hydroxylysine residues
B. Cleavage of disulfide-rich terminal regions of procollagen
C. Translation of collagen alpha chains
D. Hydroxylation of specific proline residues
E. Hydroxylation of specific lysine residues
F. Exocytosis of procollagen into extracellular space
Detailed Breakdown of Answers + Correct Answer Below ⏬
ANSWER + QUESTION BREAKDOWN
The mental model used to answer this question comes from our detailed test-taking skills masterclass. Here’s how to think through this question:
Step 1. Determine what the question asks you to do: Identify the initial step in the process of collagen synthesis.
Step 2: Is this a first-, second-, or third-order question?
Answer: 1st order: Recognize the first step in collagen synthesis.
Step 3. Read the vignette to determine what’s being asked (it isn’t explicitly stated in the question’s last line).
Step 4. Consider what’s being asked and derive your answer.
Step 5. Look at the answer choices and select the option most closely resembling your thoughts from “Step 4” above.
GENERAL ANALYSIS
The question is straightforward and assesses your understanding of collagen synthesis. Collagen synthesis is crucial for the formation of connective tissues and involves multiple intracellular and extracellular steps.
ANSWER CHOICES:
ANSWER CHOICE A: Glycosylation of pro-alpha-chain hydroxylysine residues.
Glycosylation involves adding sugar molecules to hydroxylysine residues, which occurs after the initial synthesis and hydroxylation steps.
ANSWER CHOICE B: Cleavage of disulfide-rich terminal regions of procollagen
This step occurs extracellularly, where procollagen is cleaved to form tropocollagen.
ANSWER CHOICE C: Translation of collagen alpha chains
Translation is the process of ribosomes synthesizing proteins using mRNA as a template.
ANSWER CHOICE D: Hydroxylation of specific proline residues
Hydroxylation is a post-translational modification that occurs after translation.
ANSWER CHOICE E: Hydroxylation of specific lysine residues
Similar to proline hydroxylation, this is a post-translational modification.
ANSWER CHOICE F: Exocytosis of procollagen into extracellular space
Exocytosis is the process by which cells export materials, in this case, procollagen, into the extracellular matrix.
FINAL VERDICT…
The first step in collagen synthesis involves the translation of collagen alpha chains. This process occurs in the ribosomes, where mRNA is used as a template to synthesize the initial polypeptide chains, known as pre-procollagen. These chains undergo several post-translational modifications, including hydroxylation and glycosylation, before being assembled into a triple helix structure and eventually secreted into the extracellular matrix. Understanding the sequence of these steps is crucial for replicating collagen synthesis in artificial tissues.
CORRECT ANSWER: C) Translation of collagen alpha chains
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