Final answer:
A defective protein is produced when a mutation affects the amino acid sequence coded by a gene, which can occur from missense, nonsense, insertion, or deletion mutations. These mutations can significantly alter protein function, as seen in conditions like sickle cell disease. The consequences of protein malfunction can range from mild to severe, depending on the protein's role.
Step-by-step explanation:
A defective protein can be produced by a cell when a mutation alters the amino acid sequence coded by the gene. This can happen due to different types of mutations such as missense, nonsense, insertion, or deletion mutations. Missense mutations cause a single amino acid change in a protein, which can affect the protein's function.
Insertion or deletion mutations can lead to a frame shift, changing the reading frame of the mRNA, which often results in non-functional proteins. Mutations in the DNA are permanent if not corrected and will continue to produce defective proteins, while mutations in mRNA will only affect the proteins made from that strand until the mRNA deteriorates.
For example, sickle cell disease is caused by a missense mutation where glutamic acid is replaced with valine in the hemoglobin protein, leading to impaired oxygen transportation. Other mutations might result in the production of a protein that does not function at all, which can be detrimental to the organism depending on the role of the protein.