6.4 Getting the Edge in Skill 4 Questions
6.4 Getting the Edge in Skill 4 Questions
6.4 Getting the Edge in Skill 4 Questions
Skill 4 requires an understanding of how research data are evaluated. The best way to identify your strengths and weaknesses in this area is actually to read academic papers. However, just reading academic papers is not enough. You have to go through each calculation that has been performed and interpret each paper in light of your own statistical analysis. Think of yourself like a teacher grading a research paper. Read critically, and identify any flaws in the authors' analysis of data, including miscalculations. Finally, after reading each paper, summarize the value of the information. If you had a patient whose disease or treatment course could be affected by the information in the paper, do you believe that the information in the paper is reliable? Is it statistically significant? Did the discussion in the paper actually address the questions set forth at the beginning of the paper? As you read more papers, these questions will become easier to answer.
In addition to reading papers, it is essential that you answer a considerable number of practice questions in this area. Often, passages that are steeped in research also present a number of Skill 3 questions. Although we present these skills separately here, both are essential to understanding academic research papers. By seeking out practice passages and question sets that use both of these skills, these question types will become easier. You will then be able to maximize your score on Test Day.
When the AAMC released the specifications for the current version of the MCAT, it established the expected distribution as 10 percent Skill 4 questions for each science section.
Behavioral Sciences
Chapter 8 Behavioral Sciences
Chapter 8
Behavioral Sciences
A significant factor influencing a patient’s ability to heal from an injury or manage a chronic disease is that person’s psychiatric and socioeconomic status. When considering treatment options for a patient, a physician must take into account the patient’s ability to understand and adhere to a treatment plan. Patients with a psychiatric disorder or who are unable to afford their prescriptions are not likely to take medications as prescribed, unless the treatment regimen is simple and affordable. In an effort to emphasize the psychological and social aspects of medicine, the AAMC has added a section to the MCAT known as the Psychological, Social, and Biological Foundations of Behavior section. This section is approximately 65 percent psychology, 30 percent sociology, and 5 percent biology. In addition, another 5 percent of the psychology questions cover biologically relevant topics.
Biochemistry Practice Passage Explanations
9.3 Getting the Edge in Biochemistry
9.3 Getting the Edge in Biochemistry
Getting a high score on Test Day requires a very solid foundation in biochemistry because this subject area is heavily tested. However, it is important to develop a grasp of biochemistry in the context of the other sciences, especially biology, organic chemistry, and general chemistry. Many of the passages you encounter on Test Day require you to make connections between the other sciences and biochemistry. In addition, biochemical processes do not occur in isolation. Many of the passages and questions focus on how changes at the molecular level result in changes in the entire organism’s physiology.
On Test Day, biochemistry passages will feature a variety of figures, including graphs, charts, molecular structures, chemical equations, and visual representations of biochemical concepts. Be prepared to analyze a variety of different images because you will be repeatedly asked to do so on Test Day.
Biochemistry Practice Passage Explanations
Biochemistry Practice Passage Explanations
- (C)
The key to this question is a careful reading of the question stem and the passage. The question stem asks us which plate will have the highest and lowest percentages of partially translated proteins. Paragraph 2 tells us that telithromycin is more potent than erythromycin, so we might be led to predict that the order is plate 2 (telithromycin) > plate 1 (erythromycin) > plate 3 (control). That would lead us to (D), which is a trap. Paragraph 3 tells us that although telithromycin is more potent as an antibiotic, it is actually worse at inhibiting synthesis than erythromycin is! So the correct answer is actually plate 1 > plate 2 > plate 3, which matches (C).
- (D)
Paragraph 3 states that the mRNA sequence shown in Figure 2 makes a peptide macrolide resistant; it can escape the tunnel even if erythromycin or telithromycin is bound. If we want the greatest increase in inhibition, we need a significant change in the sequence of that peptide. To answer this question, we’ll need to use the genetic code in Figure 2 and look for a mutation that would lead to a different amino acid. By cycling through the choices, we find that the correct answer is (D): AAC codes for asparagine, whereas AGC codes for serine.
In (A), proximity to the start codon does not, by itself, increase the likelihood that a mutation would affect inhibition by macrolides. In (B), the third nucleotide in the codon is in the wobble position, which tends to be the most likely nucleotide to result in a silent mutation when altered. (C) might look promising: it changes the first nucleotide in the codon. A look at the genetic code, though, shows us that this is one of the few cases where such a mutation is actually silent; both CUG and UUG code for leucine.
- (D)
We’re looking for a change likely to happen in the presence of erythromycin. According to paragraph 4, erythromycin can cause the nascent peptide to fall out of the ribosome. However, because this happens without a stop codon, the nascent peptide is not released from the tRNA. So we would expect a buildup of peptidyl-tRNA, or peptides still bound to tRNA molecules. This matches (D).
In (A), because protein synthesis decreases, we would not expect the concentration of charged tRNAs to drop; if anything, they would increase. In (B), this would be true if erythromycin bound the two ribosomal subunits together, but nowhere does the passage imply this happens. In (C), paragraph 4 states that this kind of mutation results in the expression of proteins that would normally be stopped by erythromycin. However, it is unlikely that such a mutation would happen spontaneously in the first few minutes after erythromycin administration.
- (B)
The graph in the question stem represents the products of protein synthesis in normal E. coli cells. The graphs in the answer choices represent possible protein synthesis in E. coli after exposure to telithromycin. According to paragraph 3, the inhibition of synthesis is determined only by the nature of the N-terminal sequence of the peptide. Because we have no reason to believe that there is a specific correlation between N-terminal sequence and protein size, we would expect an overall decrease in protein synthesis at all molecular masses. This matches (B).
(A) would be correct if the inhibition was based solely on molecular size (in this case, inhibiting synthesis of proteins >150 kDa in mass). In (C), the total amount of protein produced is the same; according to paragraph 4, protein synthesis drops when macrolides are given. (D) shows partial inhibition, as the passage states, but only for proteins with high molecular weights; as with (A), we have no reason to believe the inhibition is limited to certain molecular weights.
- (B)
Where would we find radiolabeled methionine after five minutes? Every peptide chain begins with methionine; the only codon for Met also is the start codon. However, the majority of finished peptides do not have Met at their N-terminus. In most proteins, that initial Met, along with other N-terminal residues, are removed in post-translational processing. Among other things, that N-terminus sequence is often involved in signaling the destination of a protein (for example, whether it should end up in the cell membrane). There also is no mechanism for exchanging methionine in existing proteins, so the correct answer is (B).
In (A), most initial methionines are lost in post-translational processing. For (C), most proteins have internal methionines, but most of the initial methionines are removed. There is no mechanism in (D) for exchanging amino acids in existing proteins with new amino acids.