Chapter 16 - The Molecular Basis of Inheritance Flashcards
Who are the two men credited for proposing the double helical model for DNA?
James Watson and Francis Crick
Who is the man that showed that genes exist as parts of chromosomes?
T.H. Morgan
What are the two chemical components of chromosomes?
DNA and protein
What is encoded in DNA and what does DNA direct?
Hereditary information; DNA directs the development of biochemical, anatomical, physiological, and (to some extent) behavioral traits
*DNA is reproduced in all cells of the body
Who is responsible for the initial discovery of the genetic role of DNA?
Frederick Griffith in 1928
- Griffith worked with two strains of bacteria, one pathogenic (disease-causing) and one nonpathogenic (harmless)
- When he mixed heat killed remains of the pathogenic strain with the living cells of the harmless strain, some living cells became pathogenic
- He called this phenomenon transformation
What is transformation?
A change in genotype and phenotype due to the assimilation of external DNA by a cell
What is a virus?
A virus is NA, and little more than DNA (or sometimes RNA) enclosed by a protective coat, which is often simply protein. To produces more viruses, a virus must infect a cell and take over the cell’s metabolic machinery
What are bacteriaphages?
Meaning “bacteria-eaters”; viruses that infect bacteria
*Phages for short
In 1944, who announced that the transforming substance was DNA?
Oswald Avery, Maclyn McCarty, Colin MacLeod
Who performed experiments showing that DNA is the genetic material of a phage?
1952; Alfred Hershey and Martha Chase
- 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
- The Hershey-Chase experiment was a landmark study because it provided powerful evidence that nucleic acids, rather than proteins, are the hereditary material, at least for certain viruses
*Radioactive sulfur in phage protein, radioactive phosphorus in phage DNA; conclusion - injected NA of the phage provided genetic information
What is DNA?
A polymer of nucleotides, each consisting of three components; a nitrogenous base, a pentose sugar called deoxyribose, and a phosphate group
The base can be adenine (A), thymine (T), guanine (G), or cytosine (C)
*The base composition varies from one species to another
Who reported that DNA composition varies from species to species?
Erwin Chargaff; 1950
What are Chargaff’s rules?
- The base composition of DNA varies between species
- For each species, the percentages of A and T bases are roughly equal and the percentages of G and C bases are roughly equal
Who used a technique called x-ray crystallography to study the molecule structure of DNA?
Maurice Wilkins and Rosalind Franklin
Franklin produced a picture of DNA using this technique, which indicated that;
- The helix makes one full turn every 3.4 nm along its length
- The bases are stacked just .34 nm apart
- There are ten layers of base pairs in each full turn of the helix
- The double helix alone is 2nm across
What is antiparallel?
The two sugar-phosphate backbones run in opposite directions
What are purines and pyrimidines? Which nitrogenous bases are which?
Purines - nitrogenous bases with two organic rings (adenine and guanine)
Pyrimidines - nitrogenous bases with one organic ring (cytosine and thymine)
What did Watson and Crick reason about the pairing of nitrogenous bases in DNA?
A purine and pyrimidine pair always results in a uniform diameter;
Adenine (A) can form two hydrogen bonds with thymine (T)
Guanine (G) can form three hydrogen bonds with cytosine (C)
- The base pairs are held together by hydrogen bonds
- The Watson-Crick model explains Chargaff’s rules: in any organism the amount of A = T and the amount of G = C
Who was awarded the nobel prize for their molecular model of DNA?
1953; Watson, Crick, and Maurice Williams
What happens when a cell copies a DNA molecule?
Each strand serves as a template for ordering nucleotides into a new, complementary strand; nucleotides line up along the template strand according to the base pairing rules and are linked to form the new strands
What is the semiconservative model of DNA replication that Watson and Crick predicted?
The two strands of the parental molecule separate, and each functions as a template for synthesis of a new, complementary strand
What are the other two completing models of DNA replication?
- Conservative model; the two parental strands reassociate after acting as templates for new strands, thus restoring the parental double helix
- Dispersive model; each strand of both daughter molecules contains a mixture of old and newly synthesized DNA
Whose experiments supported the semiconservative model?
Matthew Meselson and Franklin Stahl
They labeled the nucleotides of the old strands with a heavy isotope of nitrogen, while any new nucleotides were labeled with a lighter isotope