Molly Kiefer

MCAT Review Topic: Molecular Genetics

MCAT Molecular Genetics -magoosh
In its biology and biochemistry questions, MCAT will test you heavily on molecular genetics, so it’s a good idea to start brushing up on the basics as soon as you can.

Check out our video lesson on MCAT molecular genetics (including a transcript, for those who need it), and keep reading for a quick molecular genetics review.

MCAT Molecular Genetics Review

Molecular genetics is the field of biology that studies the structure and function of genes on the molecular level. DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are the building blocks of molecular genetics, so we’ll start our review there:

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  • DNA is the main component of chromosomes and the carrier of all genetic information.
  • RNA is a nucleic acid present in all living cells. RNA carries instructions from DNA on how to control the processes involved in protein synthesis.

DNA can be converted into RNA through a process called transcription. From there, RNA may then be converted into proteins.

DNA can also make more of itself in a process called replication.

DNA and RNA are both composed mainly of a five-carbon sugar, called pentose sugar (pent for five!) In the case of DNA, the pentose sugar is deoxyribose, while in RNA it’s simply ribose.

MCAT Molecular Genetics

The other two components of DNA (and RNA) are a nitrogenous base and a phosphate group.

The bases can either be pyrimidine or purine. Pyrimidine bases are cytosine (C), uracil (U), or thymine (T). Purine bases are adenine (A) and guanine (G). Our favorite trick for remembering which bases are which is through the mnemonics: “CUT the pie” (“pie” for pyrimidine) and “pure as gold” (Ag is the atomic symbol for gold).

When G and C bind, they form a three hydrogen bond. A can bind with T (in DNA) or U (in RNA), forming a two hydrogen bond.

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MCAT Molecular Genetics -magoosh

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  • Molly Kiefer

    Molly is one of Magoosh’s Content Creators. She designs Magoosh’s graphic assets, manages our YouTube channels and podcasts, and contributes to the Magoosh High School Blog.

    Since 2014, Molly has tutored high school and college students preparing for the SAT, GRE, and LSAT. She began her tutoring journey while in undergrad, helping her fellow students master math, computer programming, Spanish, English, and Philosophy.

    Molly graduated from Lewis & Clark College with a B.A. in Philosophy, and she continues to study ethics to this day. An artist at heart, Molly loves blogging, making art, taking long walks and serving as personal agent to her cat, who is more popular on Instagram than she is.


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