Final answer:
The chromosome puff at region 3 represents a region of active gene transcription, correlating with the production and secretion of protein fraction 4. The puff's appearance and disappearance are temporary structural changes signaling active and halted transcription, respectively, and this process is explained by the Nobel Prize-winning Signal Hypothesis.
Step-by-step explanation:
The chromosome puff at region 3 refers to a region in the chromosome where the chromatin structure is relaxed to allow for active transcription of genes. This appears as a puff or swelling in the chromosome when observed under an electron microscope. The appearance and disappearance of this puff are associated with the transcription and subsequent translation of genes into proteins. Specifically, region 3 is actively transcribing genes responsible for the production of protein fraction 4. When the genes in region 3 are actively being transcribed, the chromosome puff appears. After the transcription phase is completed and the protein is subsequently secreted, the puff disappears, indicating a temporary structural change in the chromosome coinciding with gene expression.
The link between the chromosome puff and protein secretion is illustrated by the Signal Hypothesis, which suggests that secretory proteins have a signal peptide that directs them to the endoplasmic reticulum (ER) where the signal peptide is cleaved off as the protein enters the lumen. This hypothesis was put forward by Gunther Blobel, who was awarded a Nobel Prize for this work, and explains how proteins are synthesized and processed in eukaryotic cells before they are secreted.