Before lecture Questions:
Q: “A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses).” A: gene
Q: If one strand of a DNA molecule has the sequence of bases 5'-GATTACA-3', the other complementary strand would have the sequence 3'-CTAAGTG-5'
The two strands of the double helix are complementary, each the predictable counterpart of the other Adenine (A) always pairs with Thymine (T); and Guanine (G) always pairs with Cytosine (C)
Review of chapter 5 before lecture:
Nucleic acids store, transmit, and help express hereditary information
Understand the structure and function of nucleic acids
Examples:
Gene
“Central Dogma of Molecular Biology”
DNA v/s RNA
DNA sequence complementarity
From Chapter 5
Gene: discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses) “The Central Dogma of Molecular Biology”
Chapter 16 – The Molecular Basis of Inheritance
** Concept 16.1 – DNA is the genetic material
Objective: Understand how scientists figured out that DNA is the genetic material
Examples:
Bacterial transformation
Structural evidence
DNA replication: The process by which a DNA molecule is copied
** DNA is the genetic material
Transformation: (1) The conversion of a normal animal cell to a cancerous cell. (2) A change in genotype and phenotype due to the assimilation of external DNA by a cell.
Three experiments that suggest DNA is the genetic material:
1. 1931, suggests that there is genetic material in S cells and R cells experiment
(experiment suggest existence of genetic material that can transform bacteria)
Griffith studied two strains (varieties): bacteria of the S (smooth) strain can cause pneumonia in mice, they are pathogenic (disease-causing) b/c they have an outer capsule that protects them from an animal’s defense system bacteria of the R (rough) strain lack a capsule and are nonpathogenic (harmless)
Griffith injected mice with the two strains. He concluded that the living bacteria had been transformed into pathogenic S bacteria by an unknown, heritable substance from the dead S cells that allowed the R cells to make capsules.
Griffith’s work set the stage for Avery to identify the transforming substance, only when DNA was allowed to remain active did transformation occur, therefore he concluded the transforming agent was DNA
Additional evidence for DNA as genetic material came from studies of viruses that infect bacteria. (Bacteriophage (also called phages for short): A virus that infects bacteria) Virus: An infectious particle incapable of replicating outside of a cell, consisting of an RNA or DNA genome surrounded by a protein coat (capsid) and, for some viruses, a membranous envelope.
2. 1944, suggests DNA is genetic material 35S in protein, 32P in DNA
The transforming material is DNA
When proteins were labeled (batch 1), radioactivity remained outside the cells; but when DNA was labeled (batch 2), radioactivity was found inside the cells. Bacterial cells with radioactive phage DNA released new phages with come radioactive phosphorous.
* Conclusion: Phage DNA entered bacterial cells, but phage proteins did not. Hershey and Chase concluded that DNA, not protein, function as genetic material of phage T2.
Further evidence that DNA is the genetic material came from biochemist Erwin Chargaff. His findings became known as:
Chargaff’s rules: (1) the base composition varies between species, and (2) within a species, the number of A and T bases are equal and the number of G and C bases are equal.
3. 1953, structure of DNA was solved Watson & Crick
DNA replication: The process by which a DNA molecule is copied; also called DNA synthesis.
Double helix: The form of native DNA, referring to its two adjacent antiparallel polynucleotide strands wound around an
