Chapter 16: the Molecular Basis of Inheritance Flashcards
What are the two chemical components of chromosomes?
DNA and Protein
DNA replication allows genetic information to be inherited from a parent cell to daughter cells by_____________ and from generation to generation by _____________.
mitosis
starting with meiosis
Why did researchers originally think that protein was 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. Moreover, little was known about nucleic acids, whose physical and chemical properties seemed far too uniform to account for the multitude of specific inherited traits exhibited by every organism.
Define transformation.
Transformation is a change in genotype and phenotype due to the assimilation of external
DNA by a cell. When the external DNA is from a member of a different species, transformation results in horizontal gene transfer.
Distinguish between the virulent and nonvirulent strains of Streptococcus pneumoniae studied by Frederick Griffith
The S (smooth) strain can cause pneumonia in mice; it is pathogenic because the cells have an outer capsule that protects them from an animal’s immune system. Cells of the R (rough) strain lack a capsule and are nonpathogenic.
Summarize the experiment in which Griffith became aware that hereditary information could be transmitted between two organisms in an unusual manner.
Frederick Griffith studied two strains of the bacterium Streptococcus pneumoniae. To test
for the trait of pathogenicity, Griffith injected mice with the two strains independently, and
then injected a mixture of nonpathogenic R bacteria that had been incubated with
heat-killed pathogenic S bacteria.
Griffith concluded that the living R 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.
What was transferred from the heat killed S strain to the living R strain in Griffith’s experiment in 1928?
DNA - that controlled the production of the lethal protein in the S strain
What did Oswald Avery, McCarty, and MacLeod determine to be the transforming factor?
DNA
What is a bacteriophage?
How is it structured?
These viruses are called bacteriophages (meaning “bacteria-eaters”), or phages for short. Viruses are much simpler than cells. A virus is little more than DNA (or sometimes RNA) enclosed by a protective coat, which is often simply protein. To produce more viruses, a virus must infect a cell and take over the cell’s metabolic machinery.
Describe the means by which Hershey and Chase established that only the DNA of a phage
enters an E. coli cell. What conclusions did these scientists draw based on these observations?
Separate samples of the nonradioactive E. coli cells were allowed to be infected by the
protein-labeled and DNA-labeled batches of T2.
The researchers then tested the two samples shortly after the onset of infection to see which type of molecule—protein or DNA—had entered the bacterial cells and would therefore be capable of reprogramming them. Hershey and Chase found that the phage DNA entered the host cells but the phage protein did not. Hershey and Chase concluded that the DNA injected by the phage must be the molecule carrying the genetic information that makes the cells produce new viral DNA and proteins.
What are Chargaff’s rules?
Chargaff’s rules (base pairing rules) are:
1. The base composition varies between species.
2. Within a species, the number of adenines approximately equaled the number of thymines, and the number of guanines approximately equaled the number of cytosines
List the three components of a nucleotide.
Phosphate, sugar (deoxyribose or ribose), nitrogenous base
Who are the two men who built the first molecular model of DNA and shared the 1962
Nobel Prize for the discovery of its structure?
James Watson and Francis Crick
What was Rosalind Franklin’s role in the discovery of the double helix?
Rosalind Franklin, a very accomplished X-ray crystallographer, conducted critical experiments resulting in the photograph that allowed Watson and Crick to deduce the double-helical structure of DNA. She took the first X-ray defraction photo of DNA. Photo 51
Distinguish between the structure of pyrimidines and purines.
Purines—adenine (A) and guanine (G)—are characterized by a six-membered ring fused to a five-membered ring.
Pyrimidines—cytosine (C), thymine (T), and uracil (U)—are characterized by a
six-membered ring.
Fill in the blanks
Label the following image and understand each component
