RNA for the MCAT: Everything You Need to Know
/Learn key MCAT concepts about RNA, plus practice questions and answers
(Note: This guide is part of our MCAT Biochemistry series.)
Table of Contents
Part 1: Introduction to RNA
Part 2: Structure of RNA
a) Similarities to DNA
b) Differences with DNA
Part 3: Functions of RNA
a) mRNA
b) tRNA
c) rRNA
d) snRNA
Part 4: High-yield terms
Part 5: Passage-based questions and answers
Part 6: Standalone questions and answers
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Part 1: Introduction to RNA
What is RNA?
RNA, or ribonucleic acid, is one of the two types of nucleic acids. You may know the other as DNA, or deoxyribonucleic acid. DNA is important because it stores, selectively expresses, and transmits the genetic information our cells need to function. Although RNA serves a different purpose in the cell, it’s just as important as DNA!
RNA plays a vital role in proper genetic expression, helping create proteins that can enact changes in the cell. Outside of genetic expression, RNA can have catalytic functions throughout the cell, similar to enzymes. In fact, the abundance of non-coding RNA with catalytic function and RNA’s similarity to DNA supports the “RNA world,” suggesting that before DNA, RNA was the basis of life. Given how powerful RNA can be, understanding the different functions of RNA is necessary on the MCAT.
When studying RNA, it’s easy to confuse RNA and DNA because of their similarities. Both nucleic acids use similar coding languages and are involved in genetic expression. RNA also has a host of other functions outside of its involvement with the genetic code. As you read through this guide, organizing the differences between RNA and DNA as well as the different types of RNAs and their functions in a table can be useful. We’ve included an example later in this guide. Feel free to build upon it as you learn more about RNA!
Let’s get started!
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Part 2: Structure of RNA
a) Similarities to DNA
Since RNA and DNA share similar structures, we can start by comparing the two structures. Core to both RNA and DNA is their nucleic acid structure. This means that both molecules are composed of nucleotides and are chained together by a sugar phosphate backbone. This nucleic acid structure is shown below.
Figure: Nucleic acid structure of DNA (left) and RNA (right).
Nucleotides are the basic building blocks of nucleic acids. Combinations of nucleotides store the genetic information in RNA and DNA, and replication of these combinations makes inheritance possible. Each nucleotide consists of three different groups bound together: a phosphate group, a pentose sugar, and a nitrogenous base. The nitrogenous base on each nucleotide is slightly different, giving each nucleotide a unique identity. In DNA, the four nucleotides are known as adenosine monophosphate (adenine), guanosine monophosphate (guanine), cytidine monophosphate (cytosine), and deoxythymidine monophosphate (thymine).
RNA uses three of the same nucleotides: adenine, guanine, and cytosine. Instead of deoxythymidine monophosphate, RNA uses uridine monophosphate (uracil). We’ve highlighted the overlap and differences in nucleotide use between DNA and RNA in the Venn diagram below.
Figure: Nucleotides used in DNA and RNA.
b) Differences with DNA
When comparing the structures of RNA and DNA, it is important to note some key differences. One of the most striking differences is the double-stranded versus single-stranded status of the nucleic acids. DNA is double-stranded while RNA is single-stranded.
Figure: Organic structure of DNA (left) and RNA (right).
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