DNA Structure Flashcards
What is Chargaff’s Rule?
- Chargaff’s rules state that DNA from any cell of any organisms should have a 1:1 ratio of pyrimidine and purine bases and, more specifically, that the amount of guanine should be equal to cytosine and the amount of adenine should be equal to thymine. This pattern is found in both strands of the DNA
What are the purine bases?
- Thymidine
- Guanosine
What are the Pyrimidine bases?
- Adenosine
- Cytidine
What structural features can be seen from Franklin and Wilkins DNA Photo?
- The base is perpendicular to the axis
- The Helical Structure of the DNA
What structural features of DNA were discovered by Watson and Crick
- The base is perpendicular to the axis
- The Helical Structure of the DNA
- Double stranded DNA: allows base pairing (A → T, G → C)
- Phosphate backbone on the outside
- Meets Chargaff’s rule
What type of chemical bonds are important in DNA structure?
- Covalent Bonds
- Hydrogen Bonds
- Hydrophobic “Bonds”
What are Hydrogen Bonds?
- A weak bond between an electronegative atom and a hydrogen atom (electropositive), that is, covalently linked to a second electronegative atom.
What are Covalent Bonds?
- Strong Bonds formed by the sharing of electrons between atoms
What are Hydrophobic “Bonds”?
- The association of non-polar groups with each other while present in aqueous solutions because of their insolubility in water.
Where in the DNA are Covalent Bonds found?
- In Bases and Sugars
- In phosphodiester linkages
https: //docs.google.com/document/d/1Nzo4FTzXCbwOZjpoc_J_4IF3gsOXPcoyC2BowELmx0U/edit?usp=sharing
What is the Hydrophobic Core?
The stacked base pairs in the DNA are bonded together and these bonds create a Hydrophobic core.
https://docs.google.com/document/d/1Nzo4FTzXCbwOZjpoc_J_4IF3gsOXPcoyC2BowELmx0U/edit?usp=sharing
How do Hydrophobic “Bonds” work?
- Water molecules are very polar
- Compounds that are similarly polar are very soluble in water (“Hydrophilic”)
- Compounds that are nonpolar (no charged groups) are very insoluble in water (“Hydrophobic)
Draw and label diagrams of the Hydrogen Bonds and Hydrophobic “Bonds”
https://docs.google.com/document/d/1Nzo4FTzXCbwOZjpoc_J_4IF3gsOXPcoyC2BowELmx0U/edit?usp=sharing
What is the overall polarity of DNA?
- DNA does not have an overall polarity because the two strands of the double helix have opposite polarity
Draw and label an example of how the two strands in DNA are of opposite polarity.
https://docs.google.com/document/d/1Nzo4FTzXCbwOZjpoc_J_4IF3gsOXPcoyC2BowELmx0U/edit?usp=sharing
Draw and label the Space-filling diagram of DNA.
https://docs.google.com/document/d/1Nzo4FTzXCbwOZjpoc_J_4IF3gsOXPcoyC2BowELmx0U/edit?usp=sharing
In the Space-filling diagram of DNA, what features are demonstrated?
Space-filling diagram of DNA shows:
- Stacked nature
- Two grooves; the major and minor groove.
- The difference between important for recognition by enzymes involved in gene regulation and histone binding
- Right-handed double helix (B-DNA)
What are the alternate forms of DNA?
- Right handed (A)
- Right handed (B)
- Left handed (Z)
What are the features of Right handed (A) DNA?
- It has 11 base pairs per turn and a Helix diameter of 2.3nm
What are the features of Right handed (B) DNA?
- It has 10 base pairs per turn and a Helix diameter of 1.9nm
What are the features of Left handed (Z) DNA?
- It has 12 base pairs per turn and a Helix diameter of 1.8nm
Draw a diagram of the Alternate forms of DNA
https://docs.google.com/document/d/1Nzo4FTzXCbwOZjpoc_J_4IF3gsOXPcoyC2BowELmx0U/edit?usp=sharing
What is DNA Supercoiling?
Supercoiling occurs when the molecule relieves the helical stress by twisting around itself.
- This supercoiling causes a DNA molecule to collapse into a tightly coiled structure - Overtwisting leads to
postive supercoiling, while undertwisting leads to negative supercoiling
When does Supercoiling occur?
Introduced into a DNA molecule when one or both strands are cleaved and when the complementary strands at one end are rotated or twisted around each other with the other end held fixed in space—and thus not allowed to spin
