2.6 DNA & RNA Structure Flashcards
The structure of DNA allows efficient storage of genetic information.
What are nucleotides?
Recurring monomeric units that compose nucleic acids (genetic material of the cell).
Each nucleotide consists of 5-carbon pentose sugar, phosphate group, nitrogenous base.
What is DNA?
deoxyribonucleic acid
more stable double stranded form; stores the genetic blueprint for cells
Pentose sugar: Deoxyribose.
Base composition: Adenine (A), Guanine (G), Cytosine (C), Thymine (T)
Number of strands: double stranded – forms a double helix
What is RNA?
ribonucleic acid
more versatile single stranded form; transfers the genetic information for decoding
Pentose sugar: Ribose.
Base composition: Adenine (A), Guanine (G), Cytosine (C), Uracil (U)
Number of strands: single stranded.
How are nucleotide monomers linked into a single strand?
VIA a condensation reaction.
The phosphate group of one nucleotide attaches to the sugar of another nucleotide (at the 3’– hydroxyl (-OH) group) -> this results in a phosphodiester bond forming between the two nucleotides (and water is produced as a by-product). Successive condensation reactions result in the formation of long polynucleotide strands.
Hydrogen bonds holds complementary nitrogenous base pairs together - what are the bases, and how many H-bonds are required?
Adenine + Thymine (2 H-bonds)
Guanine + Cytosine (3 H-bonds)
Why are the DNA strands described as being antiparallel?
The strands must be funning in opposite directions for the bases to be facing each other.
Thus, the atoms organise themselves into the most stable configuration as the chain lengthens. This atomic arrangement results in the double helix (~10-15 bases per twist).
1953, James Watson and Francis Crick propose the structural organisation of the DNA molecule.
DNA models (3)
Trial and error demonstrated that:
DNA strands are antiparallel to form a double helix
DNA strands pair via complementary bases
Outer edges of bases remain exposed to allow access to replicative and transcriptional proteins
Rosalind Franklin controversy
The final construction of a correct DNA molecule owed heavily to the X-ray crystallography data generated by Franklin. This data confirmed the arrangement of the DNA strands into a helical structure, however was shared without Franklin’s knowledge or permission and contributed profoundly to the final design.
Hence, Franklin is now recognised as a key contributor to the elucidation of DNA structure
