Jesse is a 2-year-old boy who presents with difficulty in walking and poor control of movements. When the doctor examines Jesse, she notices that when his muscles contract, they are very slow to relax and remain contracted well after the movement has been performed. She sends a sample of his tissue for genetic analysis, and the lab reports a genetic defect that causes the pumps in the SR to operate much more slowly than normal. How does a defect in DNA lead to a malfunctioning protein? How does this finding explain Jesse's symptoms?

Verified step by step guidance

1. Understand the relationship between DNA and proteins: DNA contains the instructions for making proteins. A gene is a segment of DNA that codes for a specific protein. If there is a mutation or defect in the DNA sequence of a gene, it can lead to the production of a malfunctioning or improperly folded protein.
2. Explain the role of the sarcoplasmic reticulum (SR) and its pumps: The sarcoplasmic reticulum is an organelle in muscle cells that stores and releases calcium ions (Ca²⁺). Calcium ions are essential for muscle contraction and relaxation. The SR contains calcium pumps (specifically, SERCA pumps) that actively transport calcium back into the SR after a muscle contraction, allowing the muscle to relax.
3. Connect the genetic defect to the malfunctioning protein: If the DNA coding for the SERCA pump is defective, the resulting protein may not function properly. For example, the pump may work more slowly than normal, reducing its ability to efficiently transport calcium back into the SR.
4. Relate the malfunctioning protein to Jesse's symptoms: When the SERCA pump operates slowly, calcium remains in the cytoplasm of the muscle cell for a longer period. This prolonged presence of calcium keeps the muscle fibers in a contracted state, leading to delayed relaxation after contraction. This explains Jesse's difficulty in walking and poor control of movements, as his muscles are unable to relax quickly enough for smooth, coordinated motion.
5. Summarize the connection: Jesse's symptoms are caused by a genetic defect that leads to a malfunctioning SERCA pump. This defect disrupts the normal calcium cycling in his muscle cells, resulting in prolonged muscle contraction and difficulty in movement control.

Key Concepts

DNA and Protein Synthesis

DNA contains the genetic instructions for the development and functioning of living organisms. It is transcribed into messenger RNA (mRNA), which is then translated into proteins. Proteins are essential for various cellular functions, including muscle contraction. A defect in DNA can lead to the production of malfunctioning proteins, which can disrupt normal physiological processes.

Sarcoplasmic Reticulum (SR) Function

The sarcoplasmic reticulum (SR) is an organelle in muscle cells that stores and releases calcium ions, crucial for muscle contraction and relaxation. When a muscle contracts, calcium is released from the SR, allowing the muscle fibers to shorten. If the SR's calcium pumps operate slowly due to a genetic defect, calcium levels may not return to baseline quickly, leading to prolonged muscle contraction and difficulty in movement, as seen in Jesse.

Genetic Mutations and Their Effects

Genetic mutations are changes in the DNA sequence that can affect how proteins are made or function. These mutations can lead to the production of proteins that are either nonfunctional or less effective. In Jesse's case, the mutation affects the calcium pumps in the SR, resulting in impaired muscle relaxation and contributing to his symptoms of poor movement control and difficulty walking.