The structure and function of the genetic material will be explored in this chapter.
Historical researchers have shown that DNA is the genetic material.
There was an exciting period of scientific discovery in the middle of the twentieth century.
On the other hand, geneticists were analyzing the genetic material of living organisms.
The structure of DNA was described by biochemists in a frantic race.
The classic experiments performed during this era set the stage for an explosion in our knowledge of modern biology.
In this section, we will look at how DNA is able to fulfill these requirements.
He did an experiment with the bacterium.
He noticed that when thesebacteria are grown on culture plates, some of them, called S strainbacteria, produce shiny, smooth colonies and others, called R strainbacteria, produce colonies that have a rough appearance.
Under the microscope, S strainbacteria have a capsule that makes them smooth, but R strainbacteria do not.
In order to determine if the capsule alone was responsible for the virulence of the S strain, he injected mice with heat-killed S strainbacteria.
The mice did not die.
The strain kills mice.
Nonencapsulated R strain does not kill mice.
The heat-killed S strainbacteria do not kill mice.
If heat-killed S strain and R strain are injected into mice, they will die.
The mice were injected with a mixture of heat-killed S strain and live R strainbacteria.
The change in the R strainbacteria's phenotype was due to a change in their genetics.
The investigators began looking for the transforming substance to determine the chemical nature of the genetic material.
By the time the next group of investigators, led by Oswald Avery in the 1940s, began their work, it was known that the genes are on the chromosomes.
Many people thought that the genetic material of the chromosomes was due to the fact that there are up to 20 different amino acids in the proteins.
The basic building blocks of nucleic acids are only four types of nucleotides.
Some argued that the genetic material was not enough variability to be able to store information.
This means that the genetic material is DNA.
R strainbacteria are transformed into S strainbacteria so that they can produce a capsule and be virulent.
The addition of DNase prevents transformation from occurring.
The hypothesis that DNA is the genetic material is supported by this.
The substance's weight is large.
The possibility of genetic variability is suggested by this.
The addition of enzymes that degrade proteins has no effect on the substance.
This shows that there is no genetic material.
The genetic material and the transforming substance are shown in the experiments.
The evidence for the genetic material was overwhelming, even though some scientists remained skeptical.
They discovered that the radioactive tracers for DNA ended up in the bacterium, causing them to become transformed.
Hershey and Chase determined that the genetic material was the cause of the transformation.
The genetic material of the bacteriophage is found in the host cell, according to the experiments.
The genetic material of all living organisms was accepted by the early 1950s.
Understanding how the bases in DNA are composed is what we need to understand the structure of DNA.
The nucleotides have a nitrogen base and a 5-carbon sugar.
The sugar is called deoxyribose because it doesn't have an oxygen atom in the 2' position.
New chemical techniques were developed in the 1940s to analyze the base content of DNA.
In humans, the A and T percentages are about 31%, but in fruit flies they are about 27%.
The percentage of A always equals the percentage of T, and the percentage of G always equals the percentage of C. These relationships are called Chargaff's rules.
The sheer number of bases and the length of most DNA molecule are more than enough to provide for variability, even though only one of four bases is possible at each nucleotide position.
Each human chromosome typically contains about 140 million base pairs.
There is a lot of possible sequence of nucleotides.
4140,000,000 is the total number of possible nucleotides that can be present at each position.
The variability explains how each species has its own base percentages.
A researcher at King's College in London studied the structure of DNA using X-rays.
When X-rayed, an X-ray diffraction pattern results, the fibers are enough like a crystal.