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EDEXCEL IAL BIOLOGY A-LEVEL 2.8-2.14 - NUCLEOTIDES AND NUCLEIC ACIDS
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EDEXCEL IAL BIOLOGY A-LEVEL 2.8-2.14 - NUCLEOTIDES AND NUCLEIC ACIDS
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EDEXCEL IAL BIOLOGY A-LEVEL 2.8-2.14 -NUCLEOTIDES AND NUCLEIC ACIDS
Draw the structure of a nucleotide
A pentose (5 carbon) sugar (either ribose or deoxyribose), a phosphate group and a
nitrogenous base (either adenine, guanine, cytosine, thymine or uracil)
Name the pentose sugars in DNA & RNA
DNA: deoxyribose RNA: ribose
Describe how polynucleotide strands form
Condensation reactions between nucleotides form strong phosphodiester bonds (sugar-
phosphate backbone)
Describe the structure of DNA.
Double helix of 2 deoxyribose polynucleotide strands (so there are 2 sugar-phosphate
backbones)
H-bonds between complementary base pairs on opposite strands (AT & GC)
Describe the structure of RNA.
Single stranded. Made up of ribose mononucleotides, linked through condensation
reactions. Possible bases are A,C, G and U. C pairs with G, A pairs with U
, Name the complementary base pairs in DNA.
2 H-bonds between adenine (A) + thymine (T)
3 H-bonds between guanine (G) + cytosine (C)
Name the complementary base pairs in RNA.
2 H-bonds between adenine (A) + uracil (U)
3 H-bonds between guanine (G) + cytosine (C)
Why is DNA replication described as semiconservative?
Strands from original DNA molecule act as templates
New DNA molecule contains one old strand and one new strand
Summarise the process of DNA replication
1. Double helix unwinds and the hydrogen bonds break, catalysed by DNA helicase
2. Complementary base pairing occurs between the template strand and free
nucleotides
3. The nucleotides are joined by phosphodiester bonds, catalysed by DNA polymerase
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