Chapter 11 Flashcards
how did griffiths experiments indicate the presence of a transforming factor in bacteria
In Griffiths’s experiments, harmless and heat-treated harmful bacteria (which would also have no effect on the mouse’s health if solely injected). The predicted outcome of this experiment would thus be a healthy mouse, however, the mouse died, this suggested the presence of a transforming factor in the heat-treated deadly bacteria that converted the harmless bacteria into a deadly strain as the harmless bacteria itself could not transform into anything harmless without exterior influence.
what did averys experiments add to the knowledge gained from griffiths experiments
Griffiths’s experiments suggested the existence of a transforming factor within bacteria, a substance that could cause heritable changes in other strains of bacteria. These substances were thought of to be either protein or DNA at the time and to prove the degree of involvement of one over the other in this matter, Avery subjected a mixture of both strains of bacteria (harmless and harmful yet heat treated) to protein destroying enzymes, and it was observed that the colonies of harmless strains were still transformed. Next, they treated the mixture with DNa-destroying enzymes, here, no transformation took place This solidified Griffiths’s transforming factor as DNA.
describe the experimental design that allowed hershey and chase to distinguish between the two options for genetic material
Knowing that viruses were composed of DNA and proteins, and how they reproduce by infecting cells that will in turn pass on their genetic material, Hershey and Case used radioactive isotope to label the phages’ proteins and DNA, sulfur and phosphorous respectively to ascertain whether phages injected DNA or proteins to infect living bacterial cells. These separately labelled phages were allowed to infect separate cultures of cells and blended them to shake any loose parts of the phages that remained outside the bacterial cells. When protein coats were labelled, most of the radioactive activity was observed to be present outside of the cells, conversely, when DNA was labelled, most of the radioactive captivity was observed within the cells. Given as how phages inject cells with their genetic material to direct the cell’s machinery, it could be concluded that DNA was the hereditary material.
virus
a apckage of nucelic acid wrapped in a protein coat. unlike living things virsues are not made of cells. also, a virus can only reproduce by infecting a living cell with its genetic material. this genetic material then directs the cells machinery to make more viruses
bacteriophage
a virus that infects bacteria
DNA
-deoxyribonucleic acid.
-the heritable genetic information is stored in a molecule called DNA.
-DNA is a kind of nucleic acid a polymer built from monomers called nucleotides.
-sugar is deoxyribose
-double stranded
RNA
-rubonucleic acid
-sugar is ribose
-single stranded
ribose
C₅H₁₀O₅
5 carbons
forms deoxyribose when forming DNA, loses 1 Oxygen ato
nucleotides info
the building block of monomers of nucleic acid polymers. only four types of nucleotides make DNA.
-a ring shaped sugar called deoxyribose
-a phosphate group (a phosphorus atom surrounded by four oxygen atoms)
-a nitrogenous base (a single or double ring of carbon and nitrogen atoms with functional groups)
all nitrogenous bases
larger double ringed/purines: adenine, guanine
single ringed/ pyrimidines: thymine, cytosine
structure of dna strands
Nucleotides are joined to one another by covalent bonds that connect the sugar of one nucleotide to the phosphate group of the next. This repeating pattern of sugar-phosphate-sugar-phosphate is called a sugar-phosphate “backbone.” The nitrogenous bases are lined up along this backbone
Just as amino acid monomers combine and form a polypeptide, the nucleotides of a nucleic acid polymer can combine in many different sequences.
Since nucleotide chains also vary in length, from only a few hundred nucleotides to millions of nucleotides, the number of possible nucleotide sequences is essentially unlimited.
discovering the structure of dna strands
Using the clues provided by Franklin’s work, Watson and Crick created a new model in which two strands of nucleotides wound about each other. This formed a twisting shape called a double helix
Their model placed the sugar-phosphate backbones on the outside of the double helix and the nitrogenous bases on the inside. They hypothesized that the nitrogenous bases that aligned across the two strands formed hydrogen bonds. This new model successfully represented DNA’s structure.
Watson and Crick realized that the individual structures of the nitrogenous bases determine very specific pairings between the nucleotides of the two strands of the double helix. These pairings are due to the sizes of the bases and their abilities to form hydrogen bonds with each other.
complementary base pairs
The purine adenine pairs with the pyrimidine thymine, and the purine guanine pairs with the pyrimidine cytosine. In the biologist’s shorthand, A pairs with T, and G pairs with C. A is also said to be “complementary” to T, and G is complementary to C.
So, while the sequence of nucleotides along the length of one of the two DNA strands can vary in countless ways, the bases on the second strand of the double helix are determined by the sequence of the bases on the first strand. Each base must pair up with its complementary base. Base-pairing rules set the stage for understanding how the information in DNA is passed through generations.
how does DNA replicate by using a template
during dna copying the two strands of the double helix separate. each single strand acts as a negative for producing a new complementray strand. nucleotides line up one by one across the existing strand as predicted by the base pairing rules. enzymes called polymerase help spee dup the process of formation of ocvalent bonds to link the nucleotides together to form the two new dna strands called daughter strands.
what does dna polymerase do
an ezyme responsible for speeidng up the process of forming covalent bonds between the nucleotides of the new dna strand.
