MCAT Biology Question — Predominate Structures
- Apr 04, 2017
- MCAT Question of the Day
Click for Explanation
pH = pKa + log[COO–]/[COOH]
7.4 = 2.34 + log[COO–]/[COOH]
5.06 = log[COO–]/[COOH]
105.06 = [COO–]/[COOH]
[COO–] = 105.06[COOH]
Thus, the conjugate base COO= is the predominate form.
pH = pKa + log[NH2]/[NH3+]
7.4 = 9.60 + log[NH2]/[NH3+]
-2.2 = log[NH2]/[NH3+]
10-2.2 = [NH2]/[NH3+]
102.2[NH2] = [NH3+]
Thus, the acid NH3+ predominates.
Therefore, the structure in answer choice D is the most common form of glycine at a physiological pH.
Want more MCAT practice?
We’ve got options for every schedule and learning style!
From the best online MCAT course created by top instructors with 524+ MCAT scores to the most representative full-length practice exams and private tutoring, we can custom tailor your MCAT prep to your goals!
Not sure which option is right for you? Schedule a free MCAT consultation with an MCAT expert using the form below. No obligation, just expert advice.
Search the Blog
Free ConsultationSchedule Now
MCAT Blog How to Review MCAT Full-Lengths
Free MCAT Practice AccountNeed great MCAT practice?
Get the most representative MCAT practice possible when you sign up for our free MCAT Account, which includes a half-length diagnostic exam and one of our full-length MCAT practice exams.Learn More