GN 311 - EXAM 3 |170 QUESTIONS AND ANSWERS
First to isolate DNA. - -Meischer
-Demonstrated the phenomenon of transformation, but did not identify the transforming
principle. - -Griffith
-Identified DNA as the transforming principle through the use of different enzyme
treatments on bacterial samples. - -Avery, McCarty, and MacLeod
-Identified DNA as the genetic material in bacteriophages by radio-labelling their DNA and
protein parts. - -Hershey and Chase
-Discovered the helical structure of DNA using X-ray crystallography. - -Franklin
-Determined that DNA for yeast consisted of an equal amount of purines and pyrimidines
(A = T, G = C). - -Chargaff
-Published the structure of DNA
- A pairs with T; G pairs with C
- 1 turn = 10 bp long
- Right-handed DNA (B-DNA) - -Watson and Crick
-Guanine - -
-Adenine - -
-Cytosine - -
-Thymine - -
-Uracil - -
-List the purine (double-ringed) bases. - -Adenine
Guanine
-List the pyrimidine (single-ringed) bases. - -Cytosine
Thymine
Uracil
-How many hydrogen bonds connect A and T together? - -2
-How many hydrogen bonds connect G and C together? - -3
-The 5' end of DNA has a... - -phosphate group
,-The 3' end of DNA has a... - -hydroxyl group
-The DNA backbone consists of... - -deoxyribose sugars and phosphate
-The RNA backbone consists of... - -ribose sugars and phosphate
-What carbon position differentiates DNA from RNA? What is at this position in DNA? In
RNA? - -2' carbon position; DNA has -H, RNA has -OH
-What kind of bonds link the sugar-phosphate backbone together? - -Phosphodiester
-What gives DNA its negative charge? - -The phosphate group
-What is the purpose of the 1' carbon position of sugars? - -Attachment of sugar to base
-What is the purpose of the 3' and 5' carbon positions of sugars? - -3' attaches with the 5'
end of the next nucleotide
-What is the main force in stabilizing the double helix? - -Hydrophobic interactions
produced and maximized by base stacking.
-The center (bases) of DNA is hydro... - -phobic (no charge)
-The backbone of DNA is hydro... - -phillic (negative charge)
-Why are major and minor grooves in DNA important? - -Help determine how proteins
interact with bases; a major groove allows more space for larger proteins to interact with
DNA.
-What is the most biologically-relevant form of DNA (i.e., which DNA form is the most
common)? What are two characteristics of this form? - -B-DNA
- Right-handed coil
- 10 bp per turn
-During gel electrophoresis, DNA fragments travel in what direction? Which fragments
travel further down? - -Negative to positive; smaller fragments travel further
(Migration distance is inversely proportional to DNA size)
-How is UV light used to measure the concentration of nucleic acids? - -The ring structures
of bases absorb UV light. The amount and state of DNA can be determined by the amount of
UV absorption at the A260 level.
, Denaturation separates double-stranded DNA into single-stranded DNA. This separation
produces the hyperchromic effect, which is when the denaturation of DNA exposes it to
more UV light, leading to greater UV absorption.
The more nucleic acids there are, and if DNA is single stranded, the greater the UV
absorption.
-Hyperchromic shift - -The increase in UV absorption of denatured DNA.
-Explain the relationship between melting curves and base composition. - -The melting
curve is the temperature at which 50% of the DNA is denatured and 50% of the DNA is still
intact.
A higher G-C content produces a higher melting curve due to the strong base-stacking
energies. As such, the melting curve shifts to the right.
-Chromatin - -The complex of DNA, chromosomal proteins and RNA within the nucleus.
-Heterochromatin - -- Darker staining parts of the chromosome
- Fewer genes
- Usually condensed
- Usually not involved in crossing over
- Replicates late in S phase
- Two types: constitutive vs. facultative
-Euchromatin - -- Lighter staining parts of the chromosome during interphase
- Where most actively transcribed genes lie
- Condenses and relaxes
-Constitutive heterochromatin
Give an example. - -Always heterochromatic
E.g., centromeres
-Facultative heterochromatin
Give an example. - -Can switch between heterochromatin and euchromatin
E.g., Barr bodies
-Explain how DNA is packaged. Why is packaging necessary? - -Naked DNA is very long
and therefore must be compacted to occupy a very small space within the cell.
Naked DNA is wound around about twice to form a nucleosome. These nucleosomes then
wind around themselves and subsequent compact forms continue to wind around
themselves until a chromosome is created.
-How wide is naked DNA? Nucleosomes? - -Naked DNA is 2 nm wide; nucleosomes are 11
nm wide.
First to isolate DNA. - -Meischer
-Demonstrated the phenomenon of transformation, but did not identify the transforming
principle. - -Griffith
-Identified DNA as the transforming principle through the use of different enzyme
treatments on bacterial samples. - -Avery, McCarty, and MacLeod
-Identified DNA as the genetic material in bacteriophages by radio-labelling their DNA and
protein parts. - -Hershey and Chase
-Discovered the helical structure of DNA using X-ray crystallography. - -Franklin
-Determined that DNA for yeast consisted of an equal amount of purines and pyrimidines
(A = T, G = C). - -Chargaff
-Published the structure of DNA
- A pairs with T; G pairs with C
- 1 turn = 10 bp long
- Right-handed DNA (B-DNA) - -Watson and Crick
-Guanine - -
-Adenine - -
-Cytosine - -
-Thymine - -
-Uracil - -
-List the purine (double-ringed) bases. - -Adenine
Guanine
-List the pyrimidine (single-ringed) bases. - -Cytosine
Thymine
Uracil
-How many hydrogen bonds connect A and T together? - -2
-How many hydrogen bonds connect G and C together? - -3
-The 5' end of DNA has a... - -phosphate group
,-The 3' end of DNA has a... - -hydroxyl group
-The DNA backbone consists of... - -deoxyribose sugars and phosphate
-The RNA backbone consists of... - -ribose sugars and phosphate
-What carbon position differentiates DNA from RNA? What is at this position in DNA? In
RNA? - -2' carbon position; DNA has -H, RNA has -OH
-What kind of bonds link the sugar-phosphate backbone together? - -Phosphodiester
-What gives DNA its negative charge? - -The phosphate group
-What is the purpose of the 1' carbon position of sugars? - -Attachment of sugar to base
-What is the purpose of the 3' and 5' carbon positions of sugars? - -3' attaches with the 5'
end of the next nucleotide
-What is the main force in stabilizing the double helix? - -Hydrophobic interactions
produced and maximized by base stacking.
-The center (bases) of DNA is hydro... - -phobic (no charge)
-The backbone of DNA is hydro... - -phillic (negative charge)
-Why are major and minor grooves in DNA important? - -Help determine how proteins
interact with bases; a major groove allows more space for larger proteins to interact with
DNA.
-What is the most biologically-relevant form of DNA (i.e., which DNA form is the most
common)? What are two characteristics of this form? - -B-DNA
- Right-handed coil
- 10 bp per turn
-During gel electrophoresis, DNA fragments travel in what direction? Which fragments
travel further down? - -Negative to positive; smaller fragments travel further
(Migration distance is inversely proportional to DNA size)
-How is UV light used to measure the concentration of nucleic acids? - -The ring structures
of bases absorb UV light. The amount and state of DNA can be determined by the amount of
UV absorption at the A260 level.
, Denaturation separates double-stranded DNA into single-stranded DNA. This separation
produces the hyperchromic effect, which is when the denaturation of DNA exposes it to
more UV light, leading to greater UV absorption.
The more nucleic acids there are, and if DNA is single stranded, the greater the UV
absorption.
-Hyperchromic shift - -The increase in UV absorption of denatured DNA.
-Explain the relationship between melting curves and base composition. - -The melting
curve is the temperature at which 50% of the DNA is denatured and 50% of the DNA is still
intact.
A higher G-C content produces a higher melting curve due to the strong base-stacking
energies. As such, the melting curve shifts to the right.
-Chromatin - -The complex of DNA, chromosomal proteins and RNA within the nucleus.
-Heterochromatin - -- Darker staining parts of the chromosome
- Fewer genes
- Usually condensed
- Usually not involved in crossing over
- Replicates late in S phase
- Two types: constitutive vs. facultative
-Euchromatin - -- Lighter staining parts of the chromosome during interphase
- Where most actively transcribed genes lie
- Condenses and relaxes
-Constitutive heterochromatin
Give an example. - -Always heterochromatic
E.g., centromeres
-Facultative heterochromatin
Give an example. - -Can switch between heterochromatin and euchromatin
E.g., Barr bodies
-Explain how DNA is packaged. Why is packaging necessary? - -Naked DNA is very long
and therefore must be compacted to occupy a very small space within the cell.
Naked DNA is wound around about twice to form a nucleosome. These nucleosomes then
wind around themselves and subsequent compact forms continue to wind around
themselves until a chromosome is created.
-How wide is naked DNA? Nucleosomes? - -Naked DNA is 2 nm wide; nucleosomes are 11
nm wide.
