The study of biochemical mutants in organisms such as Neurospora has demonstrated that some pathways are branched. The data shown in the following table illustrate the branched nature of the pathway resulting in the synthesis of thiamine: Growth Supplement _ Mutation Minimal Medium Pyrimidine Thiazole Thiamine thi-1 − − + + thi-2 − + − + thi-3 − − − + Why don't the data support a linear pathway? Can you postulate a pathway for the synthesis of thiamine in Neurospora?

Video transcript

Welcome back. Let's look at our next question. It says. Which of the following statements best describes how mutations and genes or chromosomes affect proteins. And let's look at our answer choices, noticing A choice D. Is both A. And B. So we may have more than one correct answer. Choice A says mutations can cause a gene to be nonfunctional by altering the code for generating the protein in the gene. Well, this is true. Um If the mutation causes the protein, some of some mutations cause the protein not to be expressed at all um and some might cause a protein to be expressed but um malfunctioning not able to carry out its function. And so these mutations can cause this gene to be nonfunctional, can produce a functional protein that can do its job. Choice B says mutations can also cause the protein to be over or under expressed or misfolded, which can lead to a variety of health problems. Well, this is also correct if there are mutations in the regulatory parts of the gene. Um you could cause an over or under expression of a protein um or to be misfolded. Since the folding three D. Structure of a protein depends on interactions chemical interactions between amino acids, Things like h hydrogen bonds, di sulfide bonds. And if you change mutate one of those amino acids that's involved in those bonds, it can change the folding enough so that the protein cannot do its job. So we see that we have both A and B. Being correct. So we can go ahead and pick choice D. Both A and B. But to be thoroughly, just look at choice. See here, Choice C. Says. Examples of diseases caused by mutations and proteins include sickle cell anemia, AIDS and Huntington's disease. Well, sickle cell anemia and Huntington's disease are both caused by mutations that affect proteins. In the case of sickle cell, A mutation in this gene, a single base pair change causes a change to the structure of hemoglobin, causing a change in the shape of the red blood cells in Huntington's disease. Um A gene mutation causes a mutation in a gene for a protein called Huntington's. So sickle cell anemia and Hunting disease are caused by mutations and proteins. Um but AIDS is not AIDS is caused by infection by the HIV virus. So that makes choice C. Not correct. So once again, which of the following statements best describes how mutations in genes or chromosomes affect proteins. And the answer is Choice D. Both A and B. See you in the next video