Lecture 2 - Review

Question 1

1) What often caused severe pneumonia found in many people with Spanish Flu?

Answer 1

It was caused by an H1N1 virus with genes of avian origin.

Question 2

2) Why could pneumonia with Spanish Flu not be cured?

Answer 2

Without previous exposure to the virus, the body’s immune system would not have been able to produce an efficient response. Just as importantly, however, the virus itself had not yet fully adapted to life in a human body. Contrary to expectations, it is not normally within a flu virus’s interests to kill the host.

There were no medications effective against the Spanish flu or antibiotics to treat the infections
that people got as complications of the flu. There were also no machines to provide mechanical ventilation and no intensive care units.

Question 3

3) What did Griffith find was the major difference between the R and the S strains of
pneumococcus pneumonia?

Answer 3

The difference was due to the presence of mucous coat in S strain bacteria, whereas the R
strain bacteria lacked them.

Experiment: Griffith injected both S and R strains into mice. The one which was infected with the S strain developed pneumonia and died while that infected with the R strain stayed alive.

Question 4

4) How did Avery, McCloud and McCarty prove that DNA is the genetic material?

Answer 4

Avery and McCarty observed that proteases - enzymes that degrade proteins - did not destroy
the transforming principle. Neither did lipases - enzymes that digest lipids. They found that the
transforming substance was rich in nucleic acids, but Ribonuclease, which digests RNA, did not inactivate the substance.

Question 5

5) What are the components of DNA?

Answer 5

DNA is made of chemical building blocks called nucleotides.

These building blocks are made of three parts: a phosphate group, a sugar group and one of
four types of nitrogen bases (Adenine, Thymine Cytosine, Guanine).

To form a strand of DNA, nucleotides are linked into chains, with the phosphate and sugar
groups alternating.

Question 6

6) What evidence did Watson and Crick use to discover the structure of DNA?

Answer 6

James Watson and Francis Crick described the structure of DNA, on April 25th, 1953, partly
due to information on the structure of an X ray crystal of DNA “Photo 51” taken by Rosalind
Franklin in Maurice Wilkins lab at Kings College, England

Question 7

7) What was Rosalind Franklin’s contribution the structure?

Answer 7

The discovery of the structure of DNA in 1953 was made possible by Dr. Rosalind Franklin’s Xray diffraction work at King’s.

Her creation of the famous Photo 51 demonstrated the double-helix structure of
deoxyribonucleic acid: the molecule containing the genetic instructions for the development of
all living organisms.

Question 8

8) How is DNA assembled?

Answer 8

DNA is assembled using deoxyribonucleotide triphosphates (dNTPs) including dATP,
dCTP, dGTP and dTTP.

o When the deoxyribonucleotide triphosphate is inserted at the 3’ end of the growing DNA
chain, the diphosphate is removed to give energy and only the deoxyribonucleotide
monophosphate remains in the DNA backbone.

Question 9

9) What are the dimensions of DNA?

Answer 9

The width of a single DNA molecule is approximately 20 Angstroms or 2 nm.

The length of one repeating nucleotide chain link (phosphate, sugar, base) is about 3.4
Angstroms.

Around 10.4 nucleotide units are required to complete one full twist of the DNA helix which is
34 Angstroms.

Question 10

10) How are the two strands of DNA arranged?

Answer 10

Double-stranded DNA consists of two polynucleotides that are arranged such that the
nitrogenous bases within one polynucleotide are attached to the nitrogenous bases within
another polynucleotide by way of special chemical bonds called hydrogen bonds.

Question 11

11) What is the difference in structure and function between DNA and RNA?

Answer 11

3 Structural differences in DNA and RNA are based on:
1) number of strands
2) the type of sugar,
3) and the type of bases used.

Functional Differences
DNA:
- Transmission of Genetic information and medium of long-term storage.

• The two chains run in opposite directions: a G in one chain pairs with a C in the opposite chain, and A pairs with T.
• The dotted lines between the bases represent
  the weak chemical bonds that hold the chains together.

RNA:
- There are many different types of RNA, but protein-coding genes are transcribed into messenger RNA or mRNA (aka to individual
recipes for each protein chain).

• mRNAs are shorter than DNA because they are only one gene length