Lecture 6 - DNA as Genetic Material - Part 1

A genetic condition where an individual lacks the ability to produce melanin, the pigment responsible for skin, hair, and eye color.

An inherited disorder where the body cannot properly break down homogentisic acid, a byproduct of the breakdown of tyrosine. This causes a buildup of homogentisic acid in the urine, which turns black upon exposure to air.

A scientific principle stating that a single gene controls the production of a specific enzyme. This enzyme plays a crucial role in a particular biochemical pathway.

A type of organism, like Neurospora crassa, that can grow rapidly on a simple minimal medium, containing only basic nutrients like salts and carbon sources.

A mutant organism that requires a specific additional nutrient, like an amino acid, to grow. It cannot synthesize this nutrient on its own.

A genetic study technique where researchers induce mutations in an organism and then observe the resulting changes in its growth and metabolic functions. This helps identify genes involved in specific biochemical pathways.

A type of cell containing only one set of chromosomes. Neurospora crassa is a haploid organism, making it a useful model system for genetic studies.

The process of combining genetic material from two different haploid individuals to produce a single diploid cell. This process is central to sexual reproduction and genetic diversity.

A situation where two different mutations in the same pathway can produce a functional product when combined, even though each mutation alone results in a non-functional pathway.

A type of cell that contains two or more genetically distinct nuclei. It forms when two different cells fuse together.

A group of genes that control all the steps in a specific metabolic pathway, such as arginine biosynthesis. Each gene is responsible for a single step in the pathway.

A change in the nucleotide sequence of a gene. Mutations can be harmful, beneficial, or neutral.

The process by which genetic information from one generation is passed on to the next.

The substance that carries genetic information and is responsible for the transmission of traits from parents to offspring.

A large biological molecule that comprises the genetic material of all living organisms. It is composed of nucleotides, which are made up of a sugar, a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, or thymine).

In 1928, Griffith discovered bacterial transformation, where bacteria change their form and function through the action of a transforming factor. He observed the transformation of rough (non-pathogenic) bacteria to smooth (pathogenic) bacteria.

The experiments involved two strains of Streptococcus pneumoniae: R cells (rough colonies) were non-pathogenic, while S cells (smooth colonies) were pathogenic and secreted a gelatinous capsule.

Griffith's experiments demonstrated that only living S cells caused disease. Heat-killed S cells did not cause disease. This laid the foundation for the discovery of the transforming factor.

Griffith's experiments showed that dead S cells could transform living R cells into living S cells. This transformation was attributed to a 'transforming factor' from the dead S cells.

Avery, MacLeod, and McCarty conducted experiments to identify the transforming factor. They treated heat-killed S cells with different enzymes: protease (destroys proteins), RNase (destroys RNA), and DNase (destroys DNA).

The experiments showed that DNase destroyed the transforming factor, while protease and RNase did not. This led to the conclusion that DNA is the transforming factor and the genetic material.

Hershey and Chase used bacteriophage T2 to study the role of protein and DNA in heredity. They labeled the phage proteins with radioactive sulfur (35S) and DNA with radioactive phosphorus (32P).

The results showed that the 32P-labelled DNA entered bacteria, while the 35S-labelled proteins did not. This proved that DNA, not protein, is the hereditary material.