2.6 (DNA Unit) Flashcards
State the two types of nucleic acid.
DNA
RNA
Explain how nucleotides can connect to form a nucleic acid polymer.
Nucleotides connect by creating covalent bonds between the sugar of one nucleotide and the phosphate group of another nucleotide in a condensation reaction.
State the names of the nitrogenous bases found in DNA and RNA.
DNA: cytosine, guanine, adenine, thymine
RNA: cytosine, guanine, adenine, uracil
Identify nitrogenous bases as either a pyrimidine or purine.
- Pyrimidine (single ring nitrogenous bases)
- cytosine
- thymine
- uracil
- Purine (double ring nitrogenous bases)
- guanine
- adenine
State the complementary base pairing rules.
- a purine complementary base pairs to a pyrimidine
- in DNA and RNA, guanine bonds with cytosine
- in RNA, adenine bonds with uracil
Compare the structure of DNA and RNA.
- RNA
- ribose
- single stranded
- A, G, C, U
- DNA
- deoxyribose
- double stranded
- A, G, C, T
Define antiparallel in relation to DNA structure.
- Adjacent molecules are oriented parallel to each other but oriented in opposite directions
- in DNA, one strand runs 5’ to 3’ and the complementary strand runs 3’ to 5’
Outline the formation of a DNA double helix by hydrogen bonding between nitrogenous bases.
Complementary DNA nucleotides form hydrogen bond between the nitrogenous bases, forming two strands (“double”) that wind around each other (“helix”)
Identify the four bases of DNA based on the numbers of rings (purines or pyrimidines) and the number of hydrogen bonds it can form.
- Pyrimidines have one ring. If it can form 2-H bonds it is thymine and if it can form 3 H-bonds it is thymine and if it can form 3 H-bonds it is cytosine. Uracil forms 2 hydrogen bonds
- Purines have two rings. If it can form 2 H-bonds it is adenine and if it can form 3-H bonds it is guanine
Outline the role of Chargaff, Watson, Crick, Franklin and Wilkins in the discovery of DNA structure.
- Chargaff: Charfaff determined that there are equal numbers of A and T bases and G and C in a DNA sample
- Watson: Watson figured out how the nitrogenous base pairs could fit within a DNA double helix while maintaining a constant helix diameter
- Crick: Crick suggested that the DNA backbone was anti-parallel
- Franklin: Franklin took clear, detailed X-ray diffraction photos that provided clues to DNA structure
- Wilkins: Wilkins used a method of X-ray diffraction to investigate the structure of DNA
Explain how Watson and Crick used model building to determine the structure of DNA.
Watson and Crick used model building to narrow down the possibilities for DNA structure and to eventually create an accurate representation of DNA that fit within the experimental evidence collected by Franklin and others.
State the experimental question being tested in the Hershey and Chase experiment.
Is the genetic material passed from one generation to the next composed of proteins or nucleic acids?
Explain the procedure of the Hershey and Chase experiment.
- Bacteria were infected with genetic material while proteins were labeled with radioactive sulfur, so separated particles within the bacteria were then distinguished according to their relationship with the radioactive phosphorus.
OR
(used viruses since they have both protein + nucleic acid) - Protein
1. radioactive sulfur atom labeled on protein coat (pour mixture into blender)
2. Centrifuge + test for radioactivity
3. Radioactive proteins NOT found in the cells - Nucleic Acid
1. Tagged a radioactive phosphorus in DNA
2. Centrifuge and test for radioactivity
3. Radioactive DNA in both bacteria
Explain how the results of the Hershey and Chase experiment supported the notion of nucleic acids as the genetic material.
Radioactive DNA ended up in bacteria, demonstrating that phage DNA codes for the formation of next generations phages. Phage proteins were only used to deliver DNA to the bacterial cell.
Outline the process of X-ray diffraction.
- X-ray beam shined on sample of DNA
- Atoms of DNA molecule scatter X-rays (diffract them)
- Diffraction pattern captured on photographic plate
