CELS L10 Flashcards
DNA Structure
Double helical
molecule
dna molecule structure
The DNA molecule is a double-stranded helical structure, composed of
two linear DNA strands that are in anti-parallel orientation to each other
How many polynucleotide chains make up a DNA molecule and how
are these organised in relation to each other?
Double Helix Structure:
The two chains are twisted around each other to form a double helix, which looks like a twisted ladder.
Antiparallel Arrangement:
The two strands run in opposite directions — one goes from 5′ to 3′, and the other goes from 3′ to 5′.
(Think of two roads running side-by-side but in opposite directions.)
Base Pairing:
The strands are held together by hydrogen bonds between complementary nitrogenous bases:
Adenine (A) pairs with Thymine (T)
Cytosine (C) pairs with Guanine (G)
Sugar-Phosphate Backbone:
Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups.
In which ‘direction’ does a DNA chain grow when being synthesised?
A DNA chain grows in the 5′ to 3′ direction during synthesis.
What does this mean?
New nucleotides are added to the 3′ end of the growing strand.
DNA polymerase (the enzyme that builds the new strand) can only add nucleotides to the 3′ hydroxyl (-OH) group of the sugar in the existing chain.
Simple way to remember:
Think of the strand like a train track:
The engine (DNA polymerase) lays new track from the 5′ end toward the 3′ end.
It can’t go backward—only forward toward the 3′ end.
How is the DNA helix stabilised?
Which nucleotide component(s) are located on the inside of the DNA
helix and which are located on the outside of the DNA helix?
