What is one common category of wrong answer in the MCAT CARS section?
An answer which is blatantly true and often common sense, which tempts the test-taker to select it, but is beyond the scope of the related passage and so is not the best answer. This section is difficult for science-minded pre-meds who are used to having a right and wrong answer to every question, because CARS requires you to pick the BEST answer.
Compare and contrast the innate and adaptive immunity.
Innate immunity is non-specific and includes structures like physical and chemical barriers like skin and tears. Adaptive immunity is highly-specific and depends on cells capable of responding to a specific antigen. The innate immune system uses cells such as Natural Killer (NK) cells, Macrophages, Neutrophils. The adaptive immune systems is comprised of cells like B cells and T cells. The innate immune system response is generally immediate or very fast. The adaptive immune response is slower, especially on the first exposure to an antigen, but faster with each successive exposure, and is also highly effective.
Describe post-transcriptional mRNA processing.
After transcription is complete inside the nucleus of a cell, the mRNA transcript goes through a series of processes before it can exit the nucleus and enter the cytoplasm. These processes alter the strand of mRNA. The process of splicing changes the transcript by removing portions called "introns" and leaving behind a continuous strand of "exons". The strand is also "capped" on the 5' side with a modified guanine, which acts as the aglet of a shoe lace and prevents the strand from being degraded in the cytoplasm. A string of adenine bases known as the "poly-A tail" is also added to the 3' end of the transcript in order to protect the important coding portion of the strand.