Structure of Nucleic Acids


RNA

Differences Between DNA and RNA

Structurally, DNA and RNA are nearly identical. As mentioned earlier, however, there are three fundamental differences that account for the very different functions of the two molecules.

  1. RNA is a single-stranded nucleic acid.
  2. RNA has a ribose sugar instead of a deoxyribose sugar like DNA.
  3. RNA nucleotides have a uracil base instead of thymine.
Other than these differences, DNA and RNA are the same. Their phosphates, sugars, and bases show the same bonding patterns to form nucleotides and their nucleotides bind to form nucleic acids in the same way.

The Uracil Base

The uracil base replaces thymine in RNA. Thymine and uracil are structurally very similar. Uracil has fundamentally the same structure as thymine, with the deletion of a methyl group at the 5' position. Uracil will base pair with adenine in the same way as thymine pairs with adenine ().

Figure %: Adenine:Uracil Base Pair

The Ribose Sugar

The ribose sugar is structurally identical to the deoxyribose sugar, with the addition of a hydroxyl group at the 2' position ().

Figure %: Ribose Sugar

The Three-Dimensional Structure of RNA

Unlike DNA, RNA cannot adopt the B-form helix because the additional 2' hydroxyl interferes with the arrangement of the sugars in the phosphate backbone. Although RNA does not adopt the highly ordered B-form of helix, it can be found in the A-form and does base pair to form complex secondary and tertiary structures. The primary structure of a nucleic acid refers to its sequence of base pairs. In RNA, the secondary structures are the two- dimensional base-pair foldings in which local sequences have regions of self- complementarity, giving rise to base pairs and turns. Common secondary structural motifs include hairpins, bulges, and loops ().

Figure %: Common Secondary Structures of RNA

The main difference between the three-dimensional structures of DNA and RNA is that in RNA the three-dimensional structure is single-stranded. The base- pairing that occurs in RNA is all through regions of self-complementarity. This three-dimensional arrangement is called the tertiary structure of RNA and it can be very complex.

Take a Study Break

SparkLife

The adorable Emma Watson!

Check out her 20 best red carpet looks here!

SparkLife

100 types of CRUSHES

Which have you crushed on?

SparkLife

Hot, fresh, celebrity tweets!

What are your favorite celebs saying? Click to find out!

SparkLife

Hate Bieber?

Read THIS.

Geek out!

The MindHut

We Rank the Doctors

Did we get it right?

The MindHut

Monsters of the Ocean

You'll never swim again.

The MindHut

Toop 10 Underrated Geniuses

They got no love!

The MindHut

Fantasy Book Covers...

...Recreated by THIS guy!

The MindHut

14 Animals That Changed the World

Proving history is totes adorbs.

The Book

Cover image

Read What You Love, Anywhere You Like

Get Our FREE NOOK Reading Apps