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32 terms

Chapter 9

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What was levene's tetranucleotide structure hypothesis?
-the hypothesis proposed that DNA was made up of equal amounts of adenine, guanine, cytosine, and thymine
-tetranucleotides organized in a repeating manner--whether you have a large piece or a small piece its all the same
-static molecule
If correct, would this structure be consistent with a hypothesized role of DNA as the genetic informational molecule?
-no, it would not
-the reason being that levene proposed that DNA is a static molecule, with no variation in the nucleotide sequence
What are the three main components of a nucleic acid?
-phosphate group
-sugar
-base
What are the five nitrogenous bases?
-adenine
-thymine
-guanine
-cytosine
-uracil
What is the difference between a purine and a pyrimidine?
-purines have a double ring
-pyramidines have a single ring
Which nitrogenous bases are purines?
-adenine
-guanine
Which nitrogenous bases are pyrimadines?
-thymine
-cytosine
-uracil
In what way does RNA differ from DNA?
-the sugar used in RNA is oxyribose; the sugar used in DNA is deoxyribose
-the base uracil is found in RNA instead of thymine
What is a nucleoside?
-a nitrogenous base plus a sugar (with no phosphate group)
Why, in the early 1900s, did many scientists believe that proteins, rather than DNA, were the carriers of genetic information?
-because proteins are biochemically more complex than nucleic acids
-(there are 20 amino acids versus 4 nucleotides)
-the idea prevailed that nucleic acids were "too simple" to be the genetic material
Describe the four components of the Fred Griffith experiments
-living S type bacteria injected into a mouse, mouse dies, type S bacteria isolated from dead mouse
-living R type bacteria injected into a mouse, mouse lives, no living bacteria isolated from mouse
-heat-killed S type bacteria injected into a mouse, mouse lives, no living bacteria isolated from the mouse
-heat-killed S type bacteria + live type R bacteria injected into mouse, mouse dies, type S bacteria isolated from dead mouse
What were the critical and unexpected results of this experiment?
-when heat-killed S type bacteria + live type R bacteria were injected into a mouse, the mouse dies
-extracts from tissues of the dead mouse were found to contain living type S bacteria
What can account for these results?
-something from the dead type S bacteria was transforming the type R bacteria into type S
What then did Griffith "discover"?
-bacterial transformation
What is bacterial transformation?
-the ability of living cells to take up DNA released from dead cells
What question did Avery, MacLeod, and McCarty attempt to answer?
-What substance is being transferred from the dead type S bacteria to the live type R?
What did they do to attempt to find an answer?
-used biochemical purification procedures and specific digestive enzymes to assess DNA, RNA, and proteins as possible genetic material
What was the first step of the experiment?
-DNA, RNA, and protein was extracted from the S strain streptococcus pneumoniae cells
What was the next step?
-DNA, RNA, and protein extracts were mixed with Type R cells
What was the key discovery?
-only one of the extracts-DNA-was able to convert the type R bacteria into type S
What were the implications of this?
-DNA is responsible for transformation
-DNA therefore carries genetic information
What steps were taken to rule out possible contamination of DNA extract?
-type S DNA extract was combined with DNase, RNase, and protease (within 3 different tubes)
What were the results?
-transformation did not occur when type R cells were mixed with type S DNA extract that also contained DNase
What did these results indicate?
-that any remaining RNA or protein in the extract was not acting as the genetic material
-the degradation of the DNA in the extract by DNase prevented conversion of type R to type S
What is Chargaff's rule?
-the amount of A in DNA equals the amount of T, and the amount of G equals C
-total purines (A+G) equal total pyramidines (C+T)
What did the x-ray diffraction work of Franklin suggest?
-DNA has a helical structure
-DNA is composed of 2 or more strands
-DNA contains 10 bases per helical turn
What did Watson and Crick do?
-proposed the double-helix structure
What information did Watson and Crick use to develop the DNA double helix structure?/On hat lines of evidence was their structure based?
-chargaff's rules
-x-ray diffraction data
-3-D modeling
-knowledge of nucleotide components
What are the key structural features of DNA?
-DNA Is composed of 2 strands
-2 strands form a right-handed double-helix
-2 strands run anti-parallele to each other (in regards to their 5' to 3' directionality)
-Phosphate and sugars for DNA "backbone"
-Bases protrude inward
-Bases hydrogen bond according to AT-GC rule (which explains Chargaff's data)
-There are 10 nucleotides in each strand per complete 360 degree turn of the helix
-Linear distance of a complete turn is 3.4 nm
-Each base pair traverses 0.34 nm
-Major and minor grooves are present
What does the AT/GC rule imply?
-that we can predict the sequence in one strand if the sequence in the opposite strand is known
What is meant by complementary base pairing?
-A will always bind with T
-G will always bind with C
-allows us to predict the sequence in one DNA strand if the sequence in the opposite strand is known
-allows DNA template to be used for RNA transcription
-helps to determine the secondary structure of RNA
How does complementary base pairing help to determine the secondary structure of DNA?
-base pairing allows short segments of RNA to form double-stranded regions