MOLECULAR BIOLOGY OF THE GENE CHAPTER 10

THE STRUCTURE OF THE GENETIC MATERIAL

1. EXPERIMENTS SHOWED DNA IS GENETIC MATERIAL

Virus- nonliving particle that is much smaller than a cell, that can infect living organisms S.E.M. of a T4 bacteriophage virus. (Reproduced by permission of Photo Researchers, Inc.)

Bacteriophage- a type of virus that infects bacteria.  Are made of a DNA or RNA core surrounded by a protein coat S.E.M. of bacteriophages attacking a bacterium

When bacteriophages goes inside a bacterium  The virus attaches to the cell surface  The virus then injects its DNA or RNA into the bacteria.  The genes of the virus make the bacterium produce more viruses  The result is the bacterium “pops” & is destroyed & hundreds of new viruses burst out.

PHAGE REPRODUCTIVE CYCLE

DISCUSS W/ PARTNER: Who remembers getting immunizations ? Why do people get immunizations? How do they work?

ETHICAL QUESTION: DISCUSS W/ PARTNER Some people believe autism is caused by preservatives in the vaccine. As a result some people have chosen not to immunize their children. What is your opinion?

Hershey & Chase Experiment: Radioactive Markers- used to track a substance inside an organism. Hershey & Chase were trying to figure out if genes were made of protein or DNA.  They wanted to figure out which part of the virus (the protein coat or DNA core) went inside the bacterium Martha Chase (1930- ) and Alfred Hershey ( ) Cold Spring Harbor Laboratory, 1953

Hershey & Chase used two radioactive markers to find out  Sulfur-35 ( 35 S) tracks or marks proteins  Phosporous-32 ( 32 P) tracks or marks DNA.

If 35 S was found in the bacteria, it would mean that the viruses’ protein had been injected into the bacteria.

If 32 P was found in the bacteria, then it was the DNA that had been injected.

Result: Nearly all the radioactivity in the bacteria was from phosphorus ( 32 P). Conclusion: The genetic material of the bacteriophage was DNA not protein.

2. DNA & RNA ARE POLYMERS OF NUCLEOTIDES

DNA & RNA  Are long molecules  Made of units (monomers) called nucleotides  The nucleotides have 3 parts: deoxyribose, a phosphate group, & a nitrogenous base (has nitrogen in it).

There are four kinds of nitrogenous bases in DNA: Adenine (A) Guanine (G) Cytosine (C) Thymine (T)

CHARGAFF’S RULES: A biochemist named Erwin Chargaff studied the amount of each base in DNA. He concluded the following:  The % of Guanine (G) is always equal to the % of Cytosine (C)  The % of Adenine (A) is always equal to the % of Thymine (T)  This is the same in all organisms

X-RAY EVIDENCE A scientist named Rosalind Franklin studied DNA X-ray diffraction; a technique she used to learn about the structure of DNA

THE DOUBLE HELIX 2 scientist named Watson & Crick studied the structure of DNA using 3-D models They used R. Franklin’s picture & built a 3-D model out of wire & cardboard A double helix in which 2 strands are wound around each other

They discovered that hydrogen bonds form b/w the nitrogen bases  This is what holds the 2 strands together (H bonds) Base Pairing- H bonds only form b/w adenine (A) & thymine (T); and cytosine (C) & guanine (G) Base Pairing explains Chargaff’s Rules