CELS191 Moldule 2 Flashcards
Two types of nucleic acid
DNA and RNA
DNA Structure
A double-stranded helical molecule with particular features
Chargaff’s Rules
[A] = [T] and [G] = [C]
DNA components
phosphates, deoxyribose (a sugar), and the four nitrogenous bases, adenine, guanine, cytosine, and thymine
Nucleotide monomers are joined together
with
phosphodiester bonds to form a polynucleotide = nucleic acid
Formation of the Phosphodiester Bond
The hydroxyl group (OH) on the 3rd carbon of one nucleotide reacts with the phosphate group attached to the 5th carbon on another nucleotide
DNA (and RNA) strands are SYNTHESISED in
the
5´–> 3´
direction
The two DNA strands are
antiparallel,
5´ 3´
3´ 5´
The Watson-Crick model of DNA structure
The sugar-phosphate backbone is on the
outside. The bases are on the inside. Stabilised by hydrogen bonds
Semi-conservative model of replication in DNA
Each DNA strand of the double helix is used as a
template strand for the synthesis of two new strands.
Leading strand
Continuously synthesised in its 5’ → 3’ direction
Lagging strand:
Discontinuously synthesised in its 5’ → 3’ direction as Okazaki fragments
Primase
Enzyme (a type of RNA polymerase) that
makes an RNA primer = starting point for
DNA polymerisation
DNA Polymerase III
It needs an OH group onto which the phosphate group of the incoming nucleotide can be attached.
An enzyme that synthesises a new DNA strand by adding nucleotides complementary to the parental template strands
DNA Polymerase I
Two activities: Removes RNA primers (RNase H) and fills the gap with DNA nucleotides
(DNA polymerase)
