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a single polypeptide chain 199 amino acids long. In the first experiment, the MRNA coding for prolactin is translated in a cell-free protein synthesizing system containing ribosomes, amino acids, TRNAS, aminoacyl-tRNA synthetases, ATP, GTP, and the appropriate initiation, elongation, and termination factors. Under these conditions, a polypeptide chain 227 amino acids long is synthesized. In a second experiment, the MRNA is translated in the same cell-free system to which you have added SRP. In this case, translation stops after a peptide about 70 amino acids long has been produced. In a third experiment, you use the same cell-free translation system to which you have added both SRP and endoplasmic reticulum vesicles, and you find that that the prolactin MRNA now produces a polypeptide that is 199 amino acids long. A) Explain these results.

a single polypeptide chain 199 amino acids long. In the first experiment, the MRNA coding for prolactin is translated in a cell-free protein synthesizing system containing ribosomes, amino acids, TRNAS, aminoacyl-tRNA synthetases, ATP, GTP, and the appropriate initiation, elongation, and termination factors. Under these conditions, a polypeptide chain 227 amino acids long is synthesized. In a second experiment, the MRNA is translated in the same cell-free system to which you have added SRP. In this case, translation stops after a peptide about 70 amino acids long has been produced. In a third experiment, you use the same cell-free translation system to which you have added both SRP and endoplasmic reticulum vesicles, and you find that that the prolactin MRNA now produces a polypeptide that is 199 amino acids long. A) Explain these results.

Human Anatomy & Physiology (11th Edition)
Human Anatomy & Physiology (11th Edition)
11th Edition
ISBN:9780134580999
Author:Elaine N. Marieb, Katja N. Hoehn
Publisher:Elaine N. Marieb, Katja N. Hoehn
Chapter1: The Human Body: An Orientation
Section: Chapter Questions
Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...
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**Experiments on the Synthesis of Pituitary Hormone Prolactin** **Overview:** This section describes a series of experiments conducted to study the synthesis of prolactin, a pituitary hormone composed of a single polypeptide chain of 199 amino acids. **Experiment 1:** The mRNA coding for prolactin is translated in a cell-free protein synthesizing system. This system includes ribosomes, amino acids, tRNAs, aminoacyl-tRNA synthetases, ATP, GTP, and the necessary initiation, elongation, and termination factors. Under these conditions, a polypeptide chain of 227 amino acids is synthesized. **Experiment 2:** The same mRNA is used in the same cell-free system, but with the addition of Signal Recognition Particle (SRP). In this scenario, translation halts after a peptide consisting of approximately 70 amino acids is produced. **Experiment 3:** The experiment uses the same cell-free translation system, now including both SRP and endoplasmic reticulum (ER) vesicles. Under these conditions, the prolactin mRNA successfully generates a polypeptide that is 199 amino acids long. **Question:** A) Explain these results. **Explanation of Results:** 1. **Experiment 1 Results (227 amino acids):** The mRNA is fully translated without any regulatory mechanisms influencing the process. This leads to the synthesis of a longer polypeptide than the native prolactin, suggesting that the cell-free system lacks a mechanism to halt the translation at the correct polypeptide length. 2. **Experiment 2 Results (70 amino acids):** The addition of SRP results in the translation stopping after roughly 70 amino acids. SRP is known to bind to the signal peptide sequences on emerging polypeptides and facilitate their transportation to the ER. The experiment illustrates that SRP can arrest translation as expected, but in the absence of the ER membrane, the process stalls after the initial stages. 3. **Experiment 3 Results (199 amino acids):** When both SRP and ER vesicles are included, the mRNA translates into a polypeptide of the correct length (199 amino acids). This demonstrates that SRP directs the nascent peptide to ER vesicles where translation resumes and completes correctly, resulting in the synthesis of the functional prolactin hormone. Adding ER vesicles provides the appropriate environment for SRP to dock
Transcribed Image Text:**Experiments on the Synthesis of Pituitary Hormone Prolactin** **Overview:** This section describes a series of experiments conducted to study the synthesis of prolactin, a pituitary hormone composed of a single polypeptide chain of 199 amino acids. **Experiment 1:** The mRNA coding for prolactin is translated in a cell-free protein synthesizing system. This system includes ribosomes, amino acids, tRNAs, aminoacyl-tRNA synthetases, ATP, GTP, and the necessary initiation, elongation, and termination factors. Under these conditions, a polypeptide chain of 227 amino acids is synthesized. **Experiment 2:** The same mRNA is used in the same cell-free system, but with the addition of Signal Recognition Particle (SRP). In this scenario, translation halts after a peptide consisting of approximately 70 amino acids is produced. **Experiment 3:** The experiment uses the same cell-free translation system, now including both SRP and endoplasmic reticulum (ER) vesicles. Under these conditions, the prolactin mRNA successfully generates a polypeptide that is 199 amino acids long. **Question:** A) Explain these results. **Explanation of Results:** 1. **Experiment 1 Results (227 amino acids):** The mRNA is fully translated without any regulatory mechanisms influencing the process. This leads to the synthesis of a longer polypeptide than the native prolactin, suggesting that the cell-free system lacks a mechanism to halt the translation at the correct polypeptide length. 2. **Experiment 2 Results (70 amino acids):** The addition of SRP results in the translation stopping after roughly 70 amino acids. SRP is known to bind to the signal peptide sequences on emerging polypeptides and facilitate their transportation to the ER. The experiment illustrates that SRP can arrest translation as expected, but in the absence of the ER membrane, the process stalls after the initial stages. 3. **Experiment 3 Results (199 amino acids):** When both SRP and ER vesicles are included, the mRNA translates into a polypeptide of the correct length (199 amino acids). This demonstrates that SRP directs the nascent peptide to ER vesicles where translation resumes and completes correctly, resulting in the synthesis of the functional prolactin hormone. Adding ER vesicles provides the appropriate environment for SRP to dock
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