The Molecular Basis of Inheritance

1) How was it proved that DNA (not protein) is the genetic material?

In 1952, Alfred Hershey and Martha Chase answered this question utilizing bacteriophages (viruses that infect bacteria). They used a radioactive isotope of phosphorous to tag the DNA in one culture of bacteriophages and radioactive sulfur to tag the protein in a second culture. The results showed that only DNA entered the bacteria infected by the virus. --> DNA must be the genetic material!

2) What is the basic structure of DNA?

1. double helix
2. nitrogenous bases - A, C, T, G
3. the strands are termed antiparallel

3) List some of the bacterial DNA replication proteins and their functions.

- helicase - unwinds parental double helix at replication forks

- topoisomerase - relieves "overwinding" strain ahead of replication forks by breaking, swiveling, and rejoining DNA strands

- primase - synthesizes an RNA primer at 5' end of the leading strand of each Okazaki fragment of lagging strand

- DNA ligase - joins 3' end of DNA that replaces primer to rest of leading strand and joins Okazaki fragments of lagging strand

Facts:

- DNA must be the genetic material

- DNA is a double helix, built up from 4 nitrogenous bases (A,T,C & G) with antiparallel strands

- A & T always pair as well as do C & G

- DNa polymerase can add nucleotides only to the 3' end of a molecule

- As DNa becomes more highly packaged, it becomes less accessible to transcription enzymes

Summary:

In 1950s, Harshey and Chase proved that DNA is the actual genetic material. The next big discussions in this area were based on the DNA structure. It is now known that DNA is a double helix, built up from 4 nitrogenous bases (A,T,C & G) with antiparallel strands.

Replication is the making of DNA from an existing DNA. The replication occurs in six major points:

1) it begins at origins of replication

2) replication bubble formation

3) DNA polymerases catalyze the elongation of the new DNA

4) DNA polymerase adds nucleotides to the growing chain (5' to 3')

5) continuous replication from 5' to 3' strands

6) Okazaki fragments (lagging strand) sealed together by DNA ligase

Extra:

DNA replication non-melodical song! :D