DNA (lesson nine)

Question 1

phenotypic characteristics

Answer 1

genes, carried on chromosomes in the form of DNA, are inherited and are responsible for our phenotypic characteristic

Question 2

Discovery of DNA

Answer 2

• In 1869, Friedrich Miescher isolated a compound found in the nucleus of cell
• He named this compound nuclein
• After this was isolated, many scientists did studies and experiments to determine if this was the hereditary material
• The chemical compound of nuclein was discovered in the 1920s, but it took decades still to determine it was responsible for heredity

Question 3

what happened in the 1930s?

Answer 3

• In the 1930s, Joachim Hammerling verified that genetic material was contained in the nucleus
• It was noted that in a single-celled algae called Acetabularia, the cell would only regrow if the nucleus was still present
• From this, he determined that the nucleus must contain the genetic material

Question 4

what happened in 1952?

Answer 4

• Hammerling’s hypothesis was not proven until 1952 by Alfred Hershey and Martha Chase
• They did so by showing that viruses only need to inject their DNA into a cell to take over their organelle to produce more virus
• This proved that DNA was the hereditary material

Question 5

what happened in 1920s?

Answer 5

• in the 1920s, Phoebus Levene discovered DNA had 3 main components
• A pentose sugar (5 carbon cyclical sugar)
• A phosphate group with a negative charge
• A nitrogenous base
• These components together are called a nucleotide

Question 6

Chemical Composition of DNA

Answer 6

there are only 4 possible nitrogenous bases that make up the nucleotides of DNA
- Adenine (A)
- Guanine (G)
- Thymine (T)
- Cytosine (C)

Question 7

how many pairs of nucleotides do you have?

Answer 7

You have about 3 billion pairs of nucleotides

Question 8

what happened in 1940?

Answer 8

• In 1940, Erwin Chargaff discovered a key relationship about the nitrogenous bases
• The amount of Adenine = The amount of Thymine
• The amount of Guanine = The amount of Cytosine
• This was a crucial clue that helped determine the structure of DNA

Question 9

what happened in 1951?

Answer 9

• In 1951, Rosalind Franklin studied DNA using X-ray crystallography
• While working with Maurice Wilkins, she discovered that the DNA molecules must have a helix, or corkscrew, shape

Question 10

what happened in 1953?

Answer 10

• In 1953, James Watson and Francis Crick met with Wilkins and saw the x-ray diffractions taken by Wilkins and Franklin
• From this image (image from slides) as well as other chemical information they knew about DNA, they built a model
• From this, they determined DNA had the double helix shape

Question 11

The Structure of DNA

Answer 11

• This model successfully accounted for the fact that
• DNA is made of a pentose sugar, a phosphate group and nitrogenous bases (Levene, 1920s)
• The proportion of A to T and C to G is equal (Chargaff, 1940)
• DNA has the shape of a helix (Franklin and Wilkins, 1951)