Foundations of Genetic Material and the Central Dogma

Requirements for Genetic Material

Essential Properties of Genetic Material

For a molecule to be considered as genetic material, it must fulfill several key requirements. These properties ensure that the molecule can store, transmit, and express genetic information across generations.

• Replication: The genetic material must be able to make exact copies of itself to pass genetic information to the next generation.

• Storage of Information: It must be capable of storing all the information needed for the structure, function, and development of an organism.

• Expression of Information: The information stored must be accessible and usable to direct cellular processes, such as protein synthesis.

• Variation by Mutation: The genetic material must be able to change in a heritable way, providing the basis for evolution and diversity.

Key Term: Nucleotides are the building blocks of genetic material, and are linked together to form nucleic acids.

The Central Dogma of Molecular Biology

Flow of Genetic Information

The Central Dogma describes the directional flow of genetic information within a biological system:

• DNA makes RNA (transcription)

• RNA makes proteins (translation)

This process ensures that the genetic code stored in DNA is ultimately expressed as functional proteins, which carry out most cellular activities.

Types of RNA and Their Functions

Major Classes of RNA

• mRNA (messenger RNA): Carries genetic information from DNA to the ribosome, where proteins are synthesized.

• rRNA (ribosomal RNA): Structural and catalytic component of ribosomes, the site of protein synthesis.

• tRNA (transfer RNA): Brings amino acids to the ribosome during translation, matching them to the coded mRNA message.

Experimental Evidence for DNA as Genetic Material

Frederick Griffith's Experiment (1927)

Frederick Griffith conducted experiments with Streptococcus pneumoniae to investigate the nature of genetic material. He worked with two strains:

• Virulent (S strain): Causes pneumonia, has a polysaccharide capsule, and forms smooth colonies.

• Avirulent (R strain): Does not cause illness, lacks the capsule, and forms rough colonies.

Key findings from Griffith's experiment:

• When mice were injected with the avirulent strain and heat-killed virulent strain together, the mice died.

• This suggested that some "transforming principle" from the dead virulent bacteria converted the avirulent bacteria into a virulent form.

Significance: Griffith's work provided the first evidence that genetic information could be transferred between organisms, laying the foundation for the identification of DNA as the genetic material.

Additional info:

• Later experiments by Avery, MacLeod, and McCarty (1944) identified DNA as the "transforming principle" responsible for heredity.