DNA, RNA and Protein Synthesis Flashcards
What is the function of deoxyribonucleic acid?
Store genetic information.
What is the function of ribonucleic acid?
Transfer genetic information from the DNA to the ribosomes.
Structure and function of a nucleotide.
Pentose sugar, nitrogen base and a phosphate group. They are the monomers of DNA and RNA.
What is the pentose sugar in DNA and the pentose sugar in RNA?
DNA - deoxyribose
RNA - ribose
What base replaces thymine in RNA?
Uracil.
How is the sugar-phosphate backbone formed?
Nucleotides join via condensation reaction between phosphate groups of one nucleotide and the sugar of another forming a phosphodiester bond, creating a polynucleotide.
What holds the two polynucleotide strands together?
Hydrogen bonds between complementary base pairings.
How many bonds form between the bases?
Two between A and T, three between G and C.
Describe the structure of DNA.
To antiparallel polynucleotides, twisted to form a double helix.
Structure of RNA.
Short, single polynucleotide strand.
Why does DNA replication occur?
So that daughter cells have the full amount of DNA.
What is semi conservative replication?
Replication where half of the strands in the new DNA molecule are from the original molecule - genetic continuity.
What does DNA helicase do in DNA replication?
Breaks hydrogen bonds between the bases on the two polynucleotide strands allowing the helix to unwind.
What happens in DNA replication after the helix unwinds?
The original strands act as template for free nucleotides that are attracted to their exposed complementary bases.
What does DNA polymerase do in DNA replication?
Catalyses the condensation reaction that join the free nucleotides to the original strand using hydrogen bonds.
Active site of DNA polymerase is coulee tart to the 3’ end of the new DNA strand and so can only add nucleotides to this new, what does this mean for the new strand?
The new strand is created in a 5’ to 3’ direction and the DNA polymerase moves down it in a 3’ to 5’ direction.
What did Meselson and Stahl show?
DNA is replicated semi-conservatively.
Describe Meselson and Stahl’s experiment.
- Two samples of bacteria grown, one in light nitrogen containing broth, one in heavy nitrogen containing broth
- Sample of DNA taken from each and spun in a centrifuge, pellet of heavy settled lower down than the pellet of light
- Bacteria grown in heavy nitrogen broth was then put in light nitrogen broth and left for one round of replication, a DNA sample was taken and spun in the centrifuge
- DNA settled in the middle showing that the DNA was a combination of heavy and light nitrogen - semi conservative
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