NUCLEIC ACIDS CAPE BIOLOGY UNIT I MRS HAUGHTON
NUCLEIC ACIDS CAPE BIOLOGY UNIT I MRS. HAUGHTON
NUCLEIC ACIDS • Like proteins, nucleic acids are informational macromolecules. • The main function of nucleotides is the formation of DNA and RNA. • They are made up of individual units called nucleotides. • Individual nucleotides have three parts: – Phosphoric acid (H 3 PO 4) – Pentose sugar: two types occur – Organic base
PHOSPHORIC ACID • This has the same structure in all nucleotides.
PENTOSE SUGAR • Two types occur: – Ribose (C 5 H 10 O 5) – Deoxyribose (C 5 H 10 O 4)
ORGANIC BASE • There are five different bases which are divided into two groups: – Purines – Pyrimidines
PURINES • These are double rings comprising a six-sided and five-sided ring. • Two examples are found in nucleic acids and are the organic bases: – Adenine (found in DNA and RNA) – Guanine (found in DNA and RNA)
• General structure of a purine • Adenine • Guanine
PYRIMIDINES • These are single rings each with six sides. • Three examples are found in nucleic acids and are the organic bases: – Cytosine (found in DNA and RNA) – Thymine (found in DNA only) – Uracil (found in RNA only)
GENERAL PYRIMIDINE STRUCTURE
COMPLETED NUCLEOTIDE • The three components are combined by condensation reactions to give the following general nucleotide structures
DI- AND POLYNUCLEOTIDES • By a similar condensation reaction between the sugar and phosphate groups of two nucleotides, a dinucleotide is formed. • Continued condensation reactions result in the formation of polynucleotides.
TYPICAL DINUCLEOTIDE
POLYNUCLEOTIDE
RIBONUCLEIC ACID • RNA is a single stranded polymer of nucleotides. • The pentose sugar is RIBOSE. • The organic bases are adenine (A), guanine (G), cytosine (C) and uracil (U).
RNA MOLECULE
DEOXYRIBONUCLEIC ACID • DNA is a double stranded polymer of nucleotides. • The pentose sugar is DEOXYRIBOSE. • The organic bases are adenine (A), guanine (G), cytosine (C), and thymine (T). • Very long and may contain many millions of nucleotides.
• The two strands are coiled around one another in what is termed as a double helix. • To maintain this, purines will bond to pyrimidines by hydrogen bonds thus keeping the two strands together in precise conformation. • Adenine always bonds with thymine. • Guanine always bonds with cytosine.
DNA MOLECULE
HYDROGEN BONDS IN DNA • There are two Hydrogen bonds between Adenine and Thymine. • There are three Hydrogen bonds between Cytosine and Guanine.
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