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When using a type 2 topoisomerase, explain the function of the "g-segment" of DNA.
The g-segment is held in place at the DNA binding domain of the enzyme.
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What does the "g" stand for in "g-segment."
"G" stands for "gate," indicating that this is the point at which the DNA will be broken.
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When using a type 2 topoisomerase, explain the function of the "t-segment" of DNA.
The t-segment triggers the closing of the two ATP binding domains around it, trapping it in place.
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What does the "t" stand for in "t-segment."
"T" stands for "transport," indicating that it is the segment of DNA that will pass through the "gate."
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________ discovered that X-rays cause mutations.
Henry Muller.
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__________ discovered that heat extracts of virulent S. pneumoniae could make nonvirulent S. pneumoniae virulent.
Frederick Griffith.
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What gene determined virulence in S. pneumoniae?
A smooth cell wall - indicating the presence of a capsule.
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What is the process by which bacteria pick up extracellular DNA and incorporate it into their own?
Transformation.
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Who concluded that the "transforming factor" is DNA, not protein or RNA? How?
- Maclyn McCarty.
- It was destroyed by DNase, but not protease (trypsin) or RNase.
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Who used radioactive tracers to show that DNA is the genetic component of bacteriophages?
Alfred Hershey and Martha Chase.
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What were the tracers used by Hershey and Chase?
35S for proteins and 32P for nucleic acids.
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In DNA, what is Euchromatin?
"True," active genes that are expressed.
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In DNA, what is heterochromatin?
Genes at telomeres and centromeres - not expressed.
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True or False?
Bacterial chromosomes are more compact that Human chromosomes.
- True.
- Bacteria chromosomes = 1,000 genes / Mb
- Baker's yeast = 500 genes / Mb
- Drosophila = 80 genes / Mb
- Homo sapiens = 9.3 genes / Mb
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What is a particle containing a defined ratio of DNA and protein?
That is, two coils of DNA wrapped around a protein spool.
A nucleosome.
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What is a protein that binds DNA non-specifically and acts as the protein spool in a nucleosome?
A Histone.
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What is the term for "a series of protein containing structures on a string of DNA"?
Chromatin.
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How many subunits make up the core of a histone? They are primarily (Beta strands / alpha helices).
- Eight - an octamer.
- Alpha Helices.
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There are ______ types of subunits in the histone. There are _____ copies of each for ______ total subunits. Each subunit has _____ amino-terminal tail.
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True or False?
Any DNA sequence can be wrapped around a nucleosome?
- True.
- Histone-DNA spooling is non-specific. The interactions only exist between the protein sidechains and the phosphate backbone, not the base pairs.
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Histone # _____ is outside of core and binds linker DNA between nucleosomes.
Histone # 1.
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How many base pairs of DNA make two tight wraps around the octamer core?
140 base pairs.
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The wraps contribute (positive / negative) supercoils to the DNA.
- Negative.
- Human DNA exists in negative supercoils.
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The N-terminal tails of the subunits of a histone serve what function?
They determine how the chromatin packs together.
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Chromatin is ____ nm in diameter, and coils into a filament of _____ nm.
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Which diameter of chromatin is ideal for transcription processes?
10 nm.
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Starting from a strand of DNA, list the order (8 steps) in which the DNA packs into a chromosome ready for mitosis.
- 1.) DNA
- 2.) 10 nm chromatin
- 3.) 30 nm filament
- 4.) Filament loops
- 5.) Rosettes (of 6 loops)
- 6.) Coils (of 30 rosettes)
- 7.) 1 Chromatid (of about 10 coils)
- 8.) Sister chromatids
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True or False?
Histones are non-specific and therefore exist in only one state.
- False.
- Modifications to histone tails make slight changes to their function.
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A methylated arginine on a histone tail has what effect? An acetylated lysine?
- 1.) 30 nm filament formation, decreasing gene expression
- 2.) Breakdown of filament, allowing histone sliding and gene expression
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True or False?
Histone sliding along DNA hinders control proteins from reading DNA sequences.
- False.
- It allows DNA reading and transcription.
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