7 Tips for MCAT Biochemistry
Are you confused about the importance of MCAT biochemistry, or about the type of biochemistry content found in the MCAT exam? Anyone who has taken extensive biochemistry courses understands that there are countless numbers of enzymes, inhibitors, proteins, processes, etc. which are known and being discovered. However, MCAT biochemistry is only based on a typical 1-semester introductory university course and so the content is quite limited. Despite the limited scope, biochemistry represents 25% of the content from 2 different MCAT science sections! And so, among all MCAT sciences, only MCAT biology outranks MCAT biochemistry in importance (i.e. number of questions on the real exam).
Below are seven MCAT prep shortcuts that can be used to help remember some of this material and be more efficient when answering biochemistry questions in the MCAT exam.
There are 20 amino acids. Of them, 9 are essential, 6 are polar, 9 are non-polar, and 5 are charged. Mnemonics are a good way to keep these all straight.
||A Good Lawyer Aims High
||aspartate, glutamate, lysine, arginine, histidine
||SomeTimes Cats Try A Growl
||serine, threonine, cysteine, tyrosine, asparagine, glutamine
||Glycine, alanine, valine, leucine, isoleucine, methionine, proline
There are several types of blot tests, but there are three main blot tests with which you should be familiar. All three use a similar technique, but they differ in which type of molecule is detected and which probe is being used. The following acronym (SNOW DROP) tells you which technique is used to identify which type of molecule.
Calculating Isoelectric Points (pI)
Isoelectric points are calculated by taking the average of two pKa values. However, when given an amino acid with three pKa values, you need to know which two pKa values to use. Here is a shortcut to determine which pKa values to use, based on the fact that if you protonate the R-group there are two possible outcomes.
- If the atom that gets protonated is oxygen or sulfur, the protonated R-group is neutral. In this case, use the lower two pKa values to calculate pI.
- If the protonated R-group has a nitrogen, it’s going to get a positive charge. In this case, use the upper two pKa values.
Inhibitors and Kinetics
Competitive, uncompetitive, mixed and noncompetive inhibitors affect the kinetics of a reaction by changing the Km and Vmax. They each have a different effect on Km and Vmax, and it’s important to know which one does what. Below is a tool for remembering some of the interactions of inhibitors.
KoMpetitive Inhibition = KM Increases (Vmax is unchanged)
Non-KoMpetitive INhibition = NO KM Increase (but Vmax is decreased)
Uncompetitive Inhibition = BOTH Km and Vmax decrease
Nomenclature helps identify the action of different enzymes. You can determine the purpose of an enzyme by looking at its name, rather than by memorizing each enzyme or looking up its purpose. For example, succinate dehydrogenase; dehydrogenase indicates that it is an enzyme, catalyzes dehydrogenation, and is a type of redox reaction.
||Catalyze transfer of PO4 group between substrates
||Catalyze reduction of O2, redox reaction
||Introduce OH groups, redox reaction
||Use ATP to bring about the formation of C-N, C-O or C-S bonds to join molecules
||Remove carboxyl group from substrates non-hydrolytically
||Catalyzes dehydrogenation, redox reaction
||Catalyzes a reduction reaction
For biochemistry, understanding the ‘Big Picture’ is a great shortcut to utilize in your MCAT prep that will save time and prevent distraction from all the details that are going on in each metabolic process. The main idea in metabolism is that processes are all connected. For example, glucose feeds in to the glycolysis cycle, which is eventually converted to pyruvic acid to be used in the Citric Acid Cycle or to create lactic acid. There are numerous processes that make this happen, but in the end that is the ‘Big Picture’ and it is clear what processes will inhibit or promote other metabolic processes.
MCAT Biochemistry Tip Number 7!