Molecular structure of DNA and RNA - Identification of DNA as the genetic material

14 important questions on Molecular structure of DNA and RNA - Identification of DNA as the genetic material

Which 4 criteria must the genetic material meet and what does it mean?

1. Information: it must contain the information necessary to construct an organism;
2. Transmission: the genetic material must be passed from parents to offspring during reproduction;
3. Replication: it must be copied because the genetic material is passed during reproduction and division;
4. Variation: it must vary in ways that can account for the known phenotypic differences within each species.

What was known of the genetic material in the 1880s?

- It is a chemical substance;
- The chromosomes are the carriers of the genetic material.

What was not known of the genetic material in the 1880s?

The chromosomes contain DNA and proteins, and in the vicinity of chromosomes was found RNA. Researchers didn't know what exactly the genetic material is.
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Which 3 (groups of) researchers discovered something about the identity of the genetic material?

- Griffith;
- Avery, MacLeod and McCarty;
- Hershey and Chase.

Which 2 types of S. Pneumoniae did Griffith study?

- Bacteria that secrete a polysaccharide capsule, which have a smooth appearance;
- Bacteria that don't secrete a capsule, which have a rough appearance.

Which expected things did Griffith discover during his experiments with mice?

- The S bacteria killed the mouse, this type bacteria was found in the mouse's blood;
- The mouse survived when R bacteria were injected;
- The mouse survived when R, but heat-killed bacteria were injected.

What did Griffith conclude after his experiment?

Something from the dead type S bacteria was transformed to the live type R bacteria, in order to kill the mouse. However, he didn't know what this substance was.

What was the aim of the experiment of Avery, MacLeod and McCarty?

They wanted to discover the substance that was being transformed from the dead type S bacteria to the live type R bacteria during Griffith's experiment.

How was the experiment of Avery, MacLeod and MacCarty set up?

- They mixed extracts of DNA with type R bacteria, in order to see if DNA type R bacteria converts into type S.
- To make sure that it weren't some other substances that converted type R into type S, they added DNase (which digests DNA), RNase (digests RNA) and protease (digests proteins).

What were the results of the experiment of Avery, MacLeod and McCarty?

- When RNase or protease was added, type R still converted into type S;
- When DNase was added, no type R was converted into type S.

What did Avery, MacLeod and McCarty conclude after the experiment?

DNA had to be the genetic material (or: the transforming principle)

What sort of virus did Hershey and Chase use in their experiment?

They used the T2 phage, a virus that infects bacteria. It is composed of DNA and proteins. During infection, only the genetic material of the phage enters the bacteria cell.

How was the experiment of Hershey and Chase set up?

- To distinguish proteins from DNA, they used S-35 and P-32 to label phage proteins and DNA, respectively.
- They gave phages sufficient time to infect bacteria cells.

What were the results of the experiment of Hershey and Chase?

- Most of the P-32 had entered the bacteria cells,
- but most of the S-35 remained outside the cells.

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