DNA and RNA Flashcards
What is the role of DNA?
Stores genetic information
What is the role of RNA?
Transfers genetic info from DNA to ribosomes
What are ribosomes made out of?
RNA and proteins
What monomer are DNA and RNA made from?
Nucleotides
Give the structure of a DNA nucleotide:
Phosphate group, deoxyribose, nitrogen-containing bases (adenine, thymine, cytosine and guanine)
Give the structure of an RNA molecule:
Phosphate group, ribose, nitrogen-containing bases (adenine, uracil, cytosine, guanine)
What reaction between 2 nucleotides forms what bond?
A condensation reaction between 2 nucleotides forms a phosphodiester bond
Describe the structure of DNA:
A double helix with two polynucleotide chains held by hydrogen bonds between specific complementary base pairs.
Is RNA longer or shorter than DNA?
Shorter
Why did scientists doubt that DNA held genetic code?
Because of it’s relatively simple composition.
Which scientists discovered the structure of DNA?
Watson and Crick
Name 4 differences between DNA and RNA:
- RNA is single-stranded whereas DNA is double-stranded.
- An RNA nucleotide contains a ribose sugar whereas a DNA nucleotide contains a deoxyribose sugar.
- DNA contains thymine but RNA contains Uracil.
- RNA is relatively short whereas DNA is long.
Why does DNA replicate?
So that each new cell has the full amount of DNA.
Why is it called semi-conservative replication?
Because half of the strands in each new DNA molecule are from the original DNA molecule.
This means there’s genetic continuity between generations of cells.
How is DNA replicated?
- DNA Helicase breaks hydrogen bonds between the complementary base pairs on the two DNA strands. Helix unwinds into 2 strands.
- Strands act as template strands. Free-floating nucleotides are attracted to exposed complementary bases.
- Condensation reactions join nucleotides together catalysed by DNA polymerase. Hydrogen bonds form between complementary base pairs.
During DNA replication, which end is DNA polymerase complementary to?
3’ (3 prime) so can only add nucleotides to the new strand from the 3’ end.
Which direction is the new strand made in?
5’ to 3’ direction
Why does DNA polymerase on one template strand work in the opposite way to another on the opposite strand?
Because the strands in the double helix are antiparallel
What evidence is there for semi-conservative replication?
Meselson and Stahl’s experiment:
- 2 samples of bacteria grown - one in light nitrogen and one in heavy nitrogen.
- Sample of DNA spun in centrifuge. Heavy nitrogen DNA settled lower because it’s heavier.
- Bacteria from heavy put in light. Another sample in centrifuge.
- If conservative, heavy DNA would still be together.
- If semi-conservative, settle between.
- Bacteria settled in middle.
