BIO 311C Chapter Notes - Chapter 16: Nitrogenous Base, Purine, X-Ray Crystallography
Chapter 16: THE MOLECULAR BASIS OF INHERITANCE
● Of all nature’s molecules, nucleic acids are unique in their ability to direct their own
replication from monomers.
● Accurate replication of DNA and its transmission from one generation to the next provide
a basis for resemblance of offspring to their parents.
16.1
● The Search For the Genetic Material: Scientific Inquiry
○ The two chemical components of chromosomes--DNA and protein--emerged as
the leading candidates for the genetic material.
○ Until the 1940s, the case for proteins seemed stronger:
■ Biochemists had identified proteins as a class of macromolecules with
great heterogeneity and specificity of function, essential requirements for
the hereditary material.
■ Little was known about nucleic acids.
● The Search: Evidence That DNA Can Transform Bacteria
○ Frederick Griffith had two strains of a bacterium, one pathogenic
(disease-causing) and one nonpathogenic (harmless).
○ He was surprised to find that when he killed the pathogenic bacteria with heat
and then mixed the cells remains with living bacteria of the nonpathogenic strain,
some of the living cells became pathogenic.
■ Furthermore, this newly acquired trait of pathogenicity was inherited by all
the descendants of the transformed bacteria.
○ Griffith called the phenomenon transformation, now defined as a change in
genotype and phenotype due to the assimilation of external DNA by a cell.
■ The transforming substance was later identified as DNA.
● The Search: Evidence That Viral DNA Can Program Cells
○ Additional evidence that DNA was the genetic material came from studies of
viruses that infect bacteria.
○ These viruses are called bacteriophages (meaning “bacteria-eaters) or phages
for short.
○ Viruses are much simpler than cells. A virus is a little more than DNA (or
sometimes RNA) enclosed by a protective coat, which is often simply a protein.
■ To produce more viruses, a virus must infect a cell and take over the
cell’s metabolic machinery.
○ Phages have been widely used as tools by researchers in molecular genetics.
○ Hershey and Chase performed experiments showing that DNA is the genetic
material of a phage known as T2.
■ This phage infects E. coli
, a bacterium that normally lives in the intestines
of mammals.
■ They knew that the T2 phage could quickly turn an E. coli
cell into a
T2-producing factory and wanted to find out which viral
Document Summary
Of all nature"s molecules, nucleic acids are unique in their ability to direct their own. Accurate replication of dna and its transmission from one generation to the next provide replication from monomers. a basis for resemblance of offspring to their parents. The search for the genetic material: scientific inquiry. The two chemical components of chromosomes-- dna and protein --emerged as. Until the 1940s, the case for proteins seemed stronger: the leading candidates for the genetic material. Biochemists had identified proteins as a class of macromolecules with great heterogeneity and specificity of function, essential requirements for the hereditary material. The search: evidence that dna can transform bacteria. Frederick griffith had two strains of a bacterium, one pathogenic (disease-causing) and one nonpathogenic (harmless). He was surprised to find that when he killed the pathogenic bacteria with heat and then mixed the cells remains with living bacteria of the nonpathogenic strain, some of the living cells became pathogenic.
