2.3 – DNA Structure
2.3.1 – Outline DNA nucleotide structure in terms of sugar (deoxyribose), base and phosphate
Nucleotides are formed from a pentose sugar, phosphate, and a base.
- Phosphate links neighboring sugars together (PO43-)
- The sugar is either ribose for RNA or deoxyribose for DNA, which has one less oxygen
- Four types of bases, which comprise the coded genetic message
- Nitrogen-based ring structures
- Cytosine (C), Guanine (G), Adenine (A), Thymine (T)
- Nucleotides form sequences, which are instructions for the organism
- Changes to nucleotides cause mutations
2.3.2 – State the names of the four bases in DNA
Purines – Two Ringed Bases
- Adenine (A)
- Guanine (G)
Pyrimidines – Single Ringed Bases
- Cytosine (C)
- Thymine (T)
- Uracil replaces Thymine in RNA (U)
2.3.3 – Outline how DNA nucleotides are linked together by covalent bonds into a single strand
- DNA composed of two polynucleotide chains
- Nucleotides are covalently bonded
- Bond is a phosphodiester
- Two covalent bonds between the OH- and acidic phosphate group
- Nucleotides bond at the 3l (three prime) end of the molecule
- To form the polynucleotide, the nucleotides condense together one at a time, giving water in the reaction
2.3.4 – Explain how a DNA double helix is formed using complementary base pairing and hydrogen bonds
Complementary means matching
- A double helix is made up of two anti parallel polynucleotide chains
- Bases pair and are bonded with hydrogen bonds
- Adenine and thymine are the same distance apart as guanine and cytosine
2.3.5 – Draw and label a simple diagram of the molecular structure of DNA
- DNA is made up of two anti-parallel polynucleotide chains
- They form the double helix (“spiral” structure)
- The DNA has a sugar-phosphate backbone
- Bonded with complementary base pairs
- Adenine to Thymine
- Cytosine to Guanine
