Nucleic Acids: Informational Macromolecules
That Can Be Catalytic

•Nucleic acids are polymers that are specialized for storage and transmission of information.

•Two types of nucleic acid are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

•DNA encodes hereditary information and transfers information to RNA molecules.

•The information in RNA is decoded to specify the sequence of amino acids in proteins.  

Nucleic Acids: Components

•Nucleic acids are polymers of nucleotides.

•A nucleotide consists of a pentose sugar, a phosphate group, and a nitrogen-containing base.

•In DNA, the pentose sugar is deoxyribose; in RNA it is ribose.

Nucleic Acids: Informational Macromolecules
That Can Be Catalytic

•DNA typically is double-stranded.

•The two separate polymer chains are held together by hydrogen bonding between their nitrogenous bases.

•The base pairing is complementary: At each position where a purine is found on one strand, a pyrimidine is found on the other.

•Purines have a double-ring structure. Pyrimidines have one ring.

Nucleic Acids – Structure

•The linkages that hold the nucleotides in RNA and DNA are called phosphodiester linkages.

•These linkages are formed between carbon 3 of the sugar and a phosphate group that is associated with carbon 5 of the sugar.

•The backbone consists of alternating sugars and phosphates.

•In DNA, the two strands are antiparallel.

•The DNA strands form a double helix, a molecule with a right-hand twist.

Nucleic Acids: RNA

•Most RNA molecules consist of only a single polynucleotide chain.

•Instead of the base thymine, RNA uses the base uracil.

•Hydrogen bonding between ribonucleotides in RNA can result in complex three-dimensional shapes.

Nucleic Acids: DNA to RNA

•DNA is an information molecule. The information is stored in the order of the four different bases.

•This order is transferred to RNA molecules, which are used to direct the order of the amino acids in proteins.

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DNA Homologies

•Closely related living species have DNA base sequences that are more similar than distantly related species.

•The comparative study of base sequences has confirmed many of the traditional classifications of organisms.

•DNA comparisons confirm that our closest living relatives are chimpanzees: We share more than 98 percent of our DNA base sequences.

Information  and the Code

• All hereditary information is stored in genes, which are parts of giant DNA molecules
• Genes code for the amino acids of proteins
• DNA is the archival copy of the code- kept in nucleus where it is protected & repaired
• DNA is organized with special proteins into chromosomes
• For protein synthesis a working copy of the code is made from RNA
• Overall scheme: DNA -> RNA -> protein
• Another version: "One gene, one enzyme"

The Code is Based Upon the Structure of DNA

• DNA has a sugar-phosphate backbone- sugar is deoxyribose
• DNA also has 4 types of nucleotide base : A, C, G, T
• A = adenine; C = cytosine; G = guanine; T = thymine
• Molecule is a double helix: 2 complementary strands where A = T, C = G
• The term"complementary" refers to the fitting together of 2 molecules like hand and glove
• In DNA complementary bases make good hydrogen bonds with one another
• Click for a more detailed look at DNA base complementarity
• Strands of helix are held together by hydrogen bonds between the bases
• This allows DNA to unwind for duplication and transcription
• (S = sugar; P = phosphate; B = base):
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DNA Facts

• Distance between nucleotides - .34 nm

• Distance between major grooves - 3.4 nm

• Diameter of molecule 2 um

• Middle of molecule - 3 rings - 1 purine and 1 pyrimidine

• Backbone - sugar phosphate

• One end of the backbone is OH ( 3') - The other end is 5'( PO4)