Structure and Replication of DNA Flashcards
DNA
It is the molecule of inheritance and it stored genetic information in its sequence of bases. The sequence determines the organisms genotype and the structure of its proteins.
Structure of DNA
A molecule of DNA consists of two strands each composed of repeating units called nucleotides. Each Nucleotide consists of a molecule of deoxyribose sugar joined to a phosphate group and an organic base.
Sugar-phosphate backbone
A strong chemical bond forms between the phosphate group of one nucleotide and the carbon 3 of the deoxyribose on another nucleotide.
Base-Pairing
Two of these strands of nucleotide become joined together by weak hydrogen bonds forming between their bases
Adenine (A) joins to Thymine (T)
Guanine (G) joins to Cytosine (C)
Antiparallel strands
A DNA strands 3 end on deoxyribose is distinct from the 5 end at a phosphate group. The chain is only able to grow by adding nucleotides to its 3 end. The DNA strand on the left has its 3 growing end at the bottom of the diagram and its 5 end at the top.
The arrangement of two strands with their sugar phosphate backbones running in opposite directions is described as antiparallel
Double Helix
In order for the base pairs to align with eachother the two strands in a DNA molecule take the form of a twisted coil called a double helix.
Replication of DNA
- DNA parental molecule composed of two complementary strands.
- Separation of two strands
- Each parental strand acts as a template
- Pool of individual nucleotides
- Alignment of individual nucleotides with nucleotides on templates
- Formation if sugar phosphate backbones in new strands
- Each DNA molecule composed of one new parental and one new strand
- Two DNA molecules genetically identical to original parental molecule
Enzyme control of DNA replication
The DNA molecule unwinds and weak hydrogen bonds between base pairs break, allowing the two strands to separate. These template strands become stabilised and expose their bases at a Y-shaped replication fork
