9700 · 6.1
Structure of nucleic acids and replication of DNA flashcards
Revision flashcards for Cambridge 9700 Structure of nucleic acids and replication of DNA (syllabus 6.1). Flip, recall, then mark a real past-paper question.
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What are the three components of a DNA nucleotide?
A deoxyribose sugar, a phosphate group, and a nitrogenous base (Adenine, Thymine, Cytosine, or Guanine).
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What type of bond joins adjacent nucleotides in a polynucleotide strand?
A phosphodiester bond, which is a strong covalent bond.
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Which nitrogenous bases are purines and what is their structure?
Adenine (A) and Guanine (G). They have a double-ring structure.
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State the complementary base pairing rule in DNA, including the number of bonds.
Adenine (A) pairs with Thymine (T) via two hydrogen bonds. Guanine (G) pairs with Cytosine (C) via three hydrogen bonds.
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What is the role of the enzyme DNA helicase in replication?
It unwinds the DNA double helix by breaking the hydrogen bonds between complementary base pairs, separating the two strands.
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What is the primary role of the enzyme DNA polymerase?
It synthesises the new DNA strand by adding complementary nucleotides and catalysing the formation of phosphodiester bonds. It moves along the template in a 3' to 5' direction.
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Explain the meaning of 'semi-conservative' replication.
Each new DNA molecule produced consists of one original (parental) strand and one newly synthesised strand.
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State two structural differences between DNA and RNA.
1. DNA contains deoxyribose sugar, while RNA contains ribose sugar. 2. DNA uses the base Thymine (T), while RNA uses Uracil (U). (Also: DNA is usually double-stranded, RNA is single-stranded).