Biomacromolecules

Pt III: Nucleic Acids

Nucleic acids

• Linear polymers made up of monomers called nucleotides.

• They are of critical importance to the cell because of their roles in the storage, transmission and expression of genetic information.

• They are essentially information molecules.

Two types of nucleic acid

• There are two major types of nucleic acid:– Deoxyribonucleic acid (DNA)– Ribonucleic acid (RNA)

• They differ in their chemical components and the role they play in the cell.

What are nucleotides?

• Each nucleotide is made up of three components:– A deoxyribose

sugar– A phosphate group

with a negative charge

– A nitrogen base

• Nucleotides are the monomers that make up nucleic acids.

Condensation reaction:

• The phosphate and sugar groups link via the condensation reaction.

• A water molecule is produced as a by-product.

Nitrogen bases

• Two families of nitrogen bases: the purines and pyrimidines.

• Purines – two ring structure– adenine (A) & guanine (G)

• Pyrimidines – single ring structure– cytosine (C), thymine (T) and uracil (U)– Uracil only found in RNA, it replaces thymine

which is only found in DNA.

Purines and Pyrimidines

MEMORY AID: PURLAGPURines are Larger,

Adenine and Guanine

Pairing between nitrogen bases• Bases contain many nitrogen

atoms and an oxygen functional group that are capable of forming hydrogen bonds between bases.

• Purines and pyrimidines have a complementary relationship – a purine always pairs with a pyrimidine.– A forms two hydrogen bonds with T

(or U)– G forms three hydrogen bonds with

C• This base pairing is a fundamental

property of nucleic acids and provides the mechanism for the coding of genetic information.

Ribonucleic Acid (RNA)

• Contains uracil instead of thymine.

Ribonucleic Acid (RNA)

• Multiple forms – all produced in the nucleus from a DNA template.– Messenger RNA (mRNA)– Transfer RNA (tRNA)– Ribosomal RNA (rRNA)

Deoxyribonucleic acid (DNA)

• Double stranded polynucleotides

• Two strands with complementary nitrogen base sequences pair to form a double helical structure.

• Base pairs are held together by hydrogen bonding.

• For base pairing to occur, the two strands run in opposite directions. We say the strands are antiparallel.

Memory Aids for DNA

• Atoms in DNA - PONCH– Phosphorous , Oxygen,

Nitrogen, Carbon, Hydrogen

• Nucleotide - t is for three parts– Base, sugar and phosphate.

• Difference between purines and pyrimidines – PURLAG– PURines are Larger, Adenine

and Guanine

• To remember pyrimidines – CUT– Smaller – have only one ring

so they have been CUT– Cytosine, uracil, thymine