Chapter Sixteen: the molecular basis of inheritance

Q1: who found the model of double helix?

A1: James watson and francis crick

Q2: what did Griffth find in his work?

A2: Some sustance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic.

Q3:Is RNA also shaped helix?

A3: yes, because it needs hyrophobic nitrogenous bases in the molecule's interior.

Five Facts:

1. DNA ias the genetic material

2. Many protein work together inj DNA replication and repair

3. A chromosome consists of a DNA molecule packed together with proteins.

4. DNA replication copy gene from parental to offspring.

5. RNA is made based on DNA

Figure:

Structurally, DNA is usually found as a double helix, with two strands wrapped around one another. However, DNA can adopt other configurations and it can also exist in single-stranded forms.

Summary:

Experiments with bacteria and with phages provided the first strong evidence that the genetic material is DNA. Waston and Crick deduced that DNA is a double helix. Two antiparallel sugar-phosphate chains wind around the outside of the molecule; the nitrogenous bases project into the interior, where they hydrogen-bond in specific pairs, A with T, G with C. The Meselson-Stahl experiment showed that DNA replication is semiconservation: the parent molecule unwinds, and each strand then serves as a template for the synthesis of a new strand according to base-pairing rules.

DNA replication:1. helicase unwinds the parental double helix.

2. moelcules of single-strand binding protein stabilize the unwound tamplate strands

3. the leading strand is synhesized continously in the 5-3direction by DNA pol III

4. primase begins synthesis of the RNA primer for the fifth Okazaki fragment

5. DNA pol III is completing synthesis of the fouth fragment. When it reaches the RNA primer on the third fragment, it will dissociate, move to the replication fork, and add DNA nuclrotides to the 3 end of the fifth fragment primer.

6. DNA pol I remove primer with DNA.

7. DNA ligase bonds the 3 end of the second fragment to the 5 end of the first fragment.

In missmatch repair, enzymes correct errors that persist. The ends of eukaryotic chromosomal DNA get shorter with each round of replication. Telomerase catalyzes the lengthening of telomeres in germ cells. The bacterial chromosome is usually a circular DNA molecule with some associated protein. Eukaryotic chromatin making up a chromosome is composed mostly of DNA, histones, and other proteins.

Video:

http://www.youtube.com/watch?v=teV62zrm2P0