How to Understand DNA Structure

Three Parts:Understanding the Basic ComponentsBuilding a DNA StrandMemorizing the Important Features

Deoxyribonucleic acid or DNA is the genetic blueprint of the cell. It encodes all of the information for a cell to reproduce, make proteins, and function properly. Although it may seem that we have always known that DNA formed a double helix, just a few decades ago, this structure was not known. DNA has a very complex structure that took many years to decipher. Today, we know exactly how DNA looks and how it works.[1]

Part 1
Understanding the Basic Components

  1. Image titled Understand DNA Structure Step 1
    Draw a deoxyribose sugar. A deoxyribose sugar forms part of the sugar-phosphate backbone of DNA. The other important group is the phosphate group which will be discussed in the next step. Deoxyribose forms a ring structure with five carbons and an oxygen. Other hydrogen and hydroxide groups complete the sugar.[2]
    • Deoxyribose is called a pentose sugar because the ring structure is in the shape of a pentagon.
    • The carbons of the sugar are numbered from 1’ (one prime) to 5’ (five prime), starting with the first carbon on the right side of the ring and moving clockwise.
    • Deoxyribose is similar to the ribose sugar group, but it has one less oxygen, hence “deoxy” in the name.
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    Attach a phosphate group. A phosphate groups has one hydrogen, one phosphate, and four oxygens. The phosphate group attaches to the 5’ carbon of deoxyribose to make up one block of “sugar-phosphate” that makes up the backbone. This backbone of DNA repeats with every phosphate group attaching to the 5’ end of deoxyribose and forming phosphodiester bonds with the 3’ end of the next deoxyribose molecule.[3]
    • Just as we generally read from left to right, DNA is always read from 3’ to 5’.[4]
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    Define nitrogenous bases. There are four nitrogenous bases that encode all genetic information in DNA: adenine (A), cytosine (C), guanine (G), and thymine (T). The nitrogenous bases are ring structures formed of carbons, hydrogens, nitrogens, and oxygens. Adenine and guanine are large with a double ring structure while cytosine and thymine are smaller being made up of a single ring.[5]
    • Cytosine and thymine are known as pyrimidines and have a hexagonal ring structure.
    • Adenine and guanine are known as purines and have one hexagonal ring attached to one pentagonal ring.
    • Bases with one ring can only pair with bases with two rings; hence, A always pairs with T and G always pairs with C.
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    Attach a nitrogenous base to form a nucleotide. The nitrogenous base always attaches to the 1’ carbon of the deoxyribose molecule. The complete molecule of sugar, phosphate, and nitrogenous base is called a nucleotide. Many nucleotides combine together to form a strand of DNA.[6]
    • Remember, there are two complementary strands that make-up DNA.

Part 2
Building a DNA Strand

  1. Image titled Understand DNA Structure Step 5
    Understand base-pairing. Each nucleotide of DNA contains a single nitrogenous base: either a purine (two-rings) or a pyrimidine (one ring). A purine must always pair with a pyrimidine to form the correct structure of DNA. Adenine always pairs with thymine while cytosine always pairs with guanine. This is referred to as complementary base-pairing.[7]
    • Each base pair is held together by a weak force called a hydrogen bond. These weak hydrogen bonds allow the strands to be easily broken apart when they need to be copied during cellular replication.
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    Put everything together to build a DNA strand. The DNA winds like a spiral staircase into a double helix. The sugar-phosphate backbone is always the outside or “handrails” of the staircase. The nitrogenous bases are on the inside of the structure and can be considered the actual “stairs”.
    • The 3’ end always has a sugar group while the 5’ end is always a phosphate.[8]
    • You can draw a simplified version of a DNA strand by drawing two backbone strands that wind around each other and then drawing lines to represent the nitrogenous bases between the backbone lines.
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    Practice base-pairing with some examples. Every single strand of DNA has a complementary strand that pairs with it. Practicing writing out the complementary strands will help you understand DNA better. Remember, every DNA strand is read from 3’ to 5’ and its complementary strand will be written in the opposite direction.
    • Write the complementary strand to: 3’- GACTCCCTGGAAAGTCCAT-5’.
    • The complementary strand is 5’-CTGAGGGACCTTTCAGGTA-3’.

Part 3
Memorizing the Important Features

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    Make flashcards. Flashcards are one of the best ways to memorize things and reinforce that knowledge.[9] Make cards for all of the base pairs to remember which ones pair together and whether they are purines or pyrimidines.
    • You can also make flashcards with pictures of the structures so you can easily recognize them when you see them on a test.
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    Practice drawing the structure. Another good way to learn and understand the DNA structure is to draw it multiple times.[10] Repetition is important to learning and remembering. If you practice drawing the structure a few times a week, it will soon become very easy to do.
    • Label all of the important features as you draw to keep those in your memory as well.
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    Use mnemonics to remember the base-pairs. Mnemonics are memory tricks to help you remember complex things in an easy way. There are a handful of mnemonics that you can use to remember which bases pair with each other. Choose the one that works the best for you, or make up your own.[11]
    • The “circle” letters C and G pair with each other, while the “stick” letters A and T pair together.
    • Remember the phrase, “I like to look AT George Clooney.”
    • To remember which bases are pyrimidines versus purines: “Think of pyramids in Turks and Caicos” (T and C are the pyrimidines) and “All gold is pure” (AG is the chemical symbol for gold, A and G are the purines).


  • Talk to someone in the class who understands the material.
  • Be sure to look at diagrams of DNA to truly understand its structure.

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Categories: Biology | Chemistry