DNA as the Genetic Material Flashcards
What are the components of DNA and RNA nucleotides?
Ribose Sugar, Phosphate and Base
What was the Chargaff Discovery?
There is significant DNA variation between species, thus DNA could be the genetic material.
(He looked at the number of bases in species DNA and found similar numbers of A-T and G-C)
What are Chargaff’s Rules?
A=T and G=C
The composition of DNA varies between species
What is the structure of DNA?
A double stranded helical molecule with particular features
What discoveries did Photo 51 (showing x-ray diffraction pattern of DNA from top view) lead to?
- DNA is a helical structure
- Bases perpendicular to the length of the DNA molecule
- Double stranded
Photo 51 also showed that the diameter of DNA is constant. What discovery did this lead to?
The confirmation that A=T and G=C (because a purine + a pyrimidine will equal a constant diameter and these pairs also reflect the numbers found by Chargaff)
How do we count carbons?
Start at oxygen and count clockwise from there.
What does 3 prime and 5 prime mean in terms of nucleotides?
3 prime is the third carbon and it has an OH group attached to it.
5 prime is the fifth carbon and it has the phosphate group attached to it.
How are polynucleotides formed?
Nucleotide monomers join together with phosphodiester bonds to form a polynucleotide = nucleic acid (deoxyribonucleic acid for DNA)
What is the formation of the phosphodiester bond?
The hydroxyl group on the 3rd carbon of one nucleotide reacts with the phosphate group attached to the 5th carbon on another molecule.
What direction are DNA (and RNA) strands synthesised in?
The 5 prime —-> 3 prime direction
What does the two strands of DNA being antiparallel mean?
They are synthesised in the 5 to 3 prime direction but for two strands to join together and make a double helix one has to flip. This is referred to as antiparallel orientation.
What are the key points of DNA structure?
Sugar-phosphate backbone, nucleotides are pointing in towards the helix (bases are in the middle), dotted lines are hydrogen bonds.
A bonds with T (two H bonds btw them), G bonds with C (3 H bonds between them), the hydrogen bonds stabilise the molecule. Two polynucleotide strands are oriented in opposite directions.
What type of replication does DNA do?
Semi-conservative replication.
This means that each strand of DNA from the double helix is used as a template strand for the synthesis of two new strands
