CHAPTER 2 Flashcards
(THE NATURE OF GENETIC MATERIALS)
_________, in 1869 where the study of chemistry of genes began.
Tubingen, Germany
_______ isolated nuclei from pus cells (white blood cells) in waste surgical bandages where he found that the nuclei contained a novel phosphorus-bearing substance that he named _______
Friedrich Miescher ; nuclein
_______ is mostly chromatin, which is a complex of DNA and chromosomal proteins.
Nuclein
19th century both DNA and RNA had been separated from the _______ that clings to them in the cell.
protein
Beginning 1930s, P. Levene, W. Jacobs, and others had demonstrated that:
______ is composed of ribose plus four nitrogen- containing bases.
____ contains deoxyribose plus four bases and each base is coupled with a sugar-phosphate to form nucleotide.
RNA ; DNA
(TRANSFORMATION IN BACTERIA)
_______ laid the foundation for the identification of DNA as the genetic material in 1928 with his experiments on transformation in the bacterium pneumococcus, now known as _________
Frederick Griffith ; Steptococcus pneumoniae.
CAPSULE - Spherical cell surrounded by a mucous coat.
SMOOTH - Characterized as smooth as the cells form large, glistenig colonies.
VIRULENT - Capable of causing lethal infections upon injection to mice.
WILD-TYPE ORGANISM
Lost the ability to form capsule.
Grows small, rough colonies.
AVIRULENT - no protective coat and is engulfed by the host’s white blood cells before it can proliferate enough to do any damage.
MUTANT STRAIN
KEY FINDING OF GRIFFITH’S WORK: heat-killed virulent colonies of S. pneumoniae could transform ________ to _________
avirulent cells to virulent ones
Neither the heat-killed virulent bacteria not the live avirulent ones by themselves could cause lethal infection but together, they’re ________.
deadly
The ______ trait passed from the dead cells to the live, _______ ones.
virulent ; avirulent
Transformation was not ______; the ability to make a capsule and therefore to kill host animals, once conferred on the avirulent bacteria, was passed to their descendants as a _________.
transient ; heritable trait
In other words, the ______ somehow gained the gene for virulence during transformation. This meant that the transforming substance in the heat- killed bacteria was probably the gene for ______ itself.
avirulent cells ; virulence
The missing piece of the puzzle was the _____________.
chemical nature of the transforming substance
(THE TRANSFORMING MATERIAL)
1944, _______, ____, and _____ supplied the missing piece in the study
Oswald Avery, Colin Mcleod and Maclyn Mccarty
They used a transformation test similar to Griffith’s and took pains to define the chemical nature of the transforming substance from virulent cells with the ff. steps:
(1) They removed the _____ from the extract with organic solvents and found that the extract still transformed.
protein
They used a transformation test similar to Griffith’s and took pains to define the chemical nature of the transforming substance from virulent cells with the ff. steps:
(2) They subjected it to digestion with various enzymes:
_______ and _______ which destroy protein but had no effect on transformation hence ruled out protein as the transforming material.
_______ which degrades RNA but alsp had no effect hence ruled out protein as the transforming material.
_____ which breaks down DNA, destroyed the transforming ability of the virulent cell extract with the result, they suggested that the transforming substance was DNA
Trypsin and Chymotrypsin ; Ribonuclease ; DNAse
Direct __________ supported the hypothesis that the purified transforming substance was DNA.
physical-chemical analysis
The analytical tools Avery and his colleagues used were the following:
Ultracentrifugation
Electrophoresis
Ultraviolet Absorption Spectrophotometry
Elementary Chemical Analysis
_________ where they spun the transforming substance in a very high-speed centrifuge or ultracentrifuge to estimate the size where the material with transforming activity sedimented rapidly by moving rapidly toward the bottom of the centrifuge tube which therefore suggests a very high molecular weight which is a characteristic of DNA.
ULTRACENTRIFUGATION
________ where they placed the transforming substance in an electric field to see how rapidly it moved and the transforming activity had a relatively high mobility which is also a characteristic of DNA because of its high charge-to-mass ratio.
ELECTROPHORESIS
______________ where they placed a solution of the transforming substance in a spectrophotometer to see what kind of ultraviolet (UV) light it absorbed most strongly. Its absorption spectrum matched that of DNA. That is, the light it absorbed most strongly had a wavelength of about 260 nm, in contrast to protein, which absorbs maximally at 280 nm.
ULTRAVIOLET ABSORPTION SPECTROPHOTOMETRY
__________ which yielded an average nitrogen-to- phosphorus ratio of 1.67, about what one would expect for DNA, which is rich in both elements, but vastly lower than the value expected for protein, which is rich in nitrogen but poor in phosphorus. Even a slight protein contamination would have raised the nitrogen-to-phosphorus ratio.
ELEMENTARY CHEMICAL ANALYSIS
(FURTHER CONFIRMATION)
With the mistaken notion from early chemical analyses that DNA was a _________ sequence such as ACTG-ACTG- ACTG and so on persaded many geneticists that it could not be the genetic material.
monotonous repeat of four nucleotide
_______ shown that bases were not really found in equal proportions in DNA.
1950, Erwin Chargaff
____________ of DNA varied from one species to another the same with genes, which vary from one species to another.
Base composition
_______ had refined and extended Avery’s findings where he puriefied the transforming substance to the point where it contained only 0.02% protein and showed that it could still change the genetic characteristics of bacterial cells hence he implies that such highly purified DNA could transfer genetic traits other than R and S.
Rollin Hotchkiss
______________ performed another experiment that added weight of evidence to the claim that genes were made of DNA. Their experiment involved a bacteriophage which is a bacterial virus called T2 which infects the bacterium Escherichia coli.
1952, A.D Hershey and Martha Chase
The term bacteriophage is usually shortened to _________
phage
During infection, the phage genes enter the ________ and direct the synthesis of new _________.
host cell ; phage particles
The phage is composed of ______ and ______ only.
protein and DNA
(Do the genes reside in the protein or in the DNA?)
On infection, most of the DNA entered the bacterium, along with only a little protein. The bulk of the protein stayed on the outside. Because DNA was the major component that got into the host cells, it likely contained the genes. Of course, this conclusion was not unequivocal; the small amount of protein that entered along with the DNA could conceivably have carried the genes. But taken together with the work that had gone before, this study helped convince geneticists that ______ and not _____ is the genetic material.
DNA, and not protein,
The Hershey–Chase experiment depended on radioactive labels on the DNA and protein—a different label for each.
The labels used were ______ for DNA and _________ for protein.
DNA is rich in _______ but phage protein has none, and that protein contains ______ but DNA does not.
phosphorus-32 (32 P) ; sulfur-35 (35 S)
phosphorus ; sulfur
Hershey and Chase allowed the ______- to attach by their tails to bacteria and inject their genes into their hosts. Then they removed the empty phage coats by mixing vigorously in a blender. Because they knew that the genes must go into the cell.
labeled phages
(What went in, the 32 P-labeled DNA or the 35 S- labeled protein?)
it was the DNA. In general, then, genes are made of DNA.
(THE CHEMICAL NATURE OF POLYNUCLEOTIDES)
Mid-1940s, biochemists knew the fundamental structures of _____ and ______
DNA and RNA.
Component parts of DNA:
the constituents was _______, _______ and ______.
Four bases found was _____, _____, _____ and _____
Nitrogenous Bases, Phosphoric Acid, and Deoxyribose
adenine (A), cytosine (C), guanine (G) and thymine (T).
Component parts of RNA:
the constituents was ______, ________ and _______
Four bases found was ______, ______, _______, and ________
Bases, Phosphoric Acid and Ribose.
adenine (A), cytosine (C), guanine (G) and Uracil (U).
(BASE STRUCTURE)
adenine and guanine are related to the parent molecule, __________ while the other bases are ________
purines (double ring) ; pyrimidines (single ring).
(STRUCTURE OF SUGARS)
They differ only ______
one place.
______ contains hydroxyl (OH) group in the 2 position.
Ribose
_________ lacks the oxygen and has hydrogen (H), represented by vertical line.
Deoxyribose
When the bases and sugars in RNA and DNA are joined together into units they are called __________
nucleosides
The names of the nucleosides derive from the corresponding bases:
(BASE)
Adenine
Guanine
Cytosine
Uracil
Thymine