Nucleic Acids: Structure of DNA and RNA + DNA Replication Flashcards
What is the role of DNA?
It holds genetic information which are the instructions needed to make proteins.
What is the structure of the nucleotides in DNA?
What is the structure of DNA?
- DNA comprises two polynucleotide chains joined by hydrogen bonds between complementary base pairs and wrapped into a double helix.
- The polynucleotide chains are nucleotides joined together by phosphodiester bonds between the pentose sugar of one nucleotide and the phosphodiester group of another.
- The nucleotides contain a deoxyribose sugar, a phosphate group and a nitrogenous base.
- The bases present are adenine, thymine, cytosine and guanine.
What is the purpose of RNA?
Responsible for carrying genetic information from the DNA in the nucleus to the ribosomes. This can then be used to make proteins in the ribosomes.
What is the structure of the nucleotides in RNA?
What is the structure of an RNA molecule?
A single-stranded molecule made up of just one polynucleotide chain where the nucleotides are joined together by phosphodiester bonds.
What are the differences between RNA and DNA?
- DNA is double-stranded and RNA is only made up of one strand.
- RNA is much shorter compared to DNA.
- The nucleotides in DNA contain a deoxyribose sugar and the ones in RNA contain a ribose sugar.
- DNA contains thymine bases, unlike RNA. Instead, RNA has uracil bases.
What is the purpose of DNA replication?
To make an identical copy of the DNA so that after cell division, the daughter cells have the full set of genetic information.
Describe what happens during DNA replication.
- DNA helicase breaks the hydrogen bonds between the complementary bases of the DNA chains. This causes the DNA to unwind.
- Each strand is used as a template to make a new strand.
- Free nucleotides attach to their complementary bases due to complementary base pairing.
- DNA polymerase joins the nucleotides together by forming phosphodiester bonds between them.
- The hydrogen bonds reform between the new and old strands causing the DNA to rewind.
Why is the process of DNA replication considered semi-conservative?
- Each new DNA molecule contains one new strand and one old strand of DNA.
- Each strand of the parent DNA is used as a template to make a new strand.
Describe the Meselson-Stahl experiment.
- Bacteria were placed into plates containing an isotope of nitrogen, N15. They then took in that nitrogen to make their DNA.
- All the DNA made from this isotope is considered heavy.
- The bacteria were then placed into plates containing a lighter isotope of nitrogen, N14, so this nitrogen could be incorporated into the bacterial DNA.
- The DNA was removed and centrifuged.
- The DNA was put back on the plate for another round of replication.
- The distribution of light and heavy distribution was examined.
- The heavier bands sink to the bottom of the tube, the intermediate bands stay in the middle, and the lighter bands stay on top.
How does the Meselson-Stahl experiment prove that DNA replication is semi-conservative?
- If replication was conservative for the first and second generation of DNA you would have a light and heavy band. In the second generation, the light band would be slightly bigger than the heavy band.
- However, for the first generation, there was an intermediate band showing that each strand of the old DNA acted as a template for a new strand, and the new DNA was made of one old, heavy strand and one new, light strand. The second generation showed that one heavy strand of DNA and one light strand were used as templates for new strands. This created two DNA molecules that had both a light and heavy strand and two that had just light strands.
How is DNA packaged into chromosomes?
DNA is wrapped around proteins called histories. After this, the DNA folds even further to form chromatin, which is used to make chromosomes.
What are homologous chromosomes?
They are chromosomes that are the same size and contain the same genes.
How is DNA in eukaryotic cells different from the DNA in prokaryotic cells?
- The DNA in eukaryotic cells is much longer compared to the DNA in prokaryotic cells.
- The DNA in eukaryotic cells is associated with proteins, and the DNA in prokaryotic cells is not.
- The DNA of eukaryotic cells is linear and the DNA of prokaryotic cells is circular.
- The DNA of eukaryotic cells contain intros, and the DNA of prokaryotic cells does not.
Why does the DNA polymerase work in opposite direction during DNA replication?
- The active sites of the DNA have a specific shape.
- This means they are only complementary to the 3’ end of the DNA chain and they can only work in the 3’ to 5’ direction
- The two strands are antiparallel, so when the DNA polymerase molecules add new nucleotides to the chain, they will do so in the opposite direction to each other.
