3.3 – DNA Structure
3.3.1 - Outline DNA nucleotide structure in terms of sugar (deoxyribose), base and phosphate Nucleotides are formed from a pentose sugar, phosphate and a base. o
Phosphate links neighbouring sugars together (PO43-)
o
The sugar is either ribose for RNA or deoxyribose for DNA, which has one less oxygen
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Four types of bases, which comprise the coded genetic message
Nitrogen-based ring structures
Cytosine (C), Guanine (G), Adenine (A), Thymine (T)
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Nucleotides form sequences, which are instructions for the organism
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Changes to nucleotides cause mutations
3.3.2 - 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)
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3.3.3 - 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
3.3.4 - 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
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3.3.5 - 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
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