[IB Biology: Chemistry of Life]

Ch. 14

NUCLEIC ACIDS

Function: Nucleic Acids carry hereditary (genetic) information for all cells

Types: DNA (Deoxyribonucleic Acid) Diagram #1, Diagram #2

RNA (Ribonucleic Acid)

Nucleotides are the monomers (subunits) of all nucleic acids.

Structure of [Nucleotides]

a) Phosphate group (PO4)

b) Five carbon sugar: deoxyribose- 1 less oxygen than ribose (RNA)

c) Nitrogen base

Purines: adenine, guanine (double rings)

Pyrimidines: thymine, cytosine (uracil-RNA only) (single rings)

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Diagram at right is a simplified model of a nucleotide.

Sugar structure

A prime (') notes where a carbon is located on the sugar

Phosphate attaches to the 5' carbon

Nitrogen bases attach to the 1' carbon

-OH attaches to 3' carbon ( as well as the phosphate of the next nucleotide.

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Nucleic Acid Chain Structure

Phosphate at 5', hydroxyl at 3' form chains

Dehydration synthesis links 3' to 5' ends (Hydroxyl 3' to phosphate 5') 5'xxxxx3' - 5'xxxxx3' - 5'xxxxx3' etc.

Double helix structure

Double helix describes the spiral, double-stranded shape of DNA.

Bases point inward

Large purine (2 rings) always paired with small pyrimidine (1 ring) for consistent width

Adenine - thymine for two bonds (A-T)

Guanine - cytosine form three bonds (C-G)

Antiparallel: DNA is antiparallel. Its two strands run in opposite directions.

[Replication]

Fraenkel - Conrat Experiment : tobacco mosaic virus ( TMV ) and rib grass virus ( HRV ) (Read pp. 282-83)

Retro viruses : ( retro = backwards ) RNA virus uses RNA to code DNA of host ( HIV causing AIDS )

Reverse transcriptase enzyme codes DNA from virus RNA, inserts it into host cell.