Chapter 8 Nucleic Acids Flashcards
What are the 3 components to nucleotides and the two bonds associated with it?
purine/pyrimidine base, phsophate group, and pentose sugar
phosphoester bond & N-beta-glycosyl bond (N1 or N9)
What are some of the characterisitcs to nitrogenous bases?
ring structure, heterocyclic, hydrophobic, planar due to resonance, exist in 2 isomeric forms called tautomers, aubsorbs UV (260 nm)
Name the purines and pyrimidines
purines (large structure)- adenine, guanine
pyrimidine (small) - cytosine, thymine, uracil
What are some of the characteristics of pentose sugar
heterocyclic, closed 5 C ring; furanose, hydrophilic, non-planar.
explain the difference between minor and major grooves.
The minor periodicity of 3.4 Ao represents the distance between two adjacent base pairs while major periodicity of 34 Ao represents one complete turn of the helix with 10 bases.
In the watson-crick model of DNA, explain hydrophobicity and number of h-bonds between bases
Backbone hydrophilic, bases hydrophobic
G-C pairs have 3 hydrogen bonds
A-T pairs have 2 hydrogen bonds
How did Watson-Crick model show which bases paired up?
the space between pairs was 20 Ao, which requires a pyrimidine and purine. 2X pyrimidine too small, 2X purine too large
Explain some of the characteristics to Chargaff’s rules
Molar amount of adenine is equal to molar amount of thymine, while molar amount of guanine is equal to molar amount of cytosine. A = T; G = C ; A + G = T + C
DNA from different tissues of the same species have the same base composition
DNA base composition does not change with age, nutritional state, or change altered environment
What are some of the forces that stabilizes vs. destabilizes DNA double helix, explain how they work/function.
hydrophobic interactions - stabilize
- hydrophobic inside and hydrophilic outside
stacking interactions – stabilize
- relatively weak but additive van der Waals forces; > 5Ao
hydrogen bonding – stabilize
- relatively weak but additive and facilitates stacking
electrostatic interactions - destabilize
- contributed primarily by the (negative) phosphates - affect intrastrand and interstrand interactions - repulsion can be neutralized with positive charges (e. g., positively charged Na+ ions or proteins)
What is the differences between A, B, an Z form DNA.
A (short): right handed, diameter 26 Ao, 11 base pairs per turn, 2.6 Ao helix rise per base pair.
B (normal): right handed, diameter 20 Ao, 10.5 base pairs per turn, 3.4 Ao helix rise per base pair.
Z (elongated): left handed, diameter 18 Ao, 12 base pairs per turn, 3.7 Ao helix rise per base pair.
What is the chemical compound that can be found in Z-like duplex, what about A?
Z-like = 5-methylcytosine
A-like = multiple G’s, RNA-DNA hybrids and ds RNA
What are the 4 unusual DNA structures?
palindrome: sequence is mirror repeated on opposite side of helix
Mirror repeat: sequence is repeated out from center, mirror like, on same side of sequence
Cruciform: two palindrome forming a hump on either side, looks like a T.
Hairpin: hump on just one side of sequence
What is the base pair found in a triple helix?
Hoogsteen base pairing
What is a guanosine tetraplex
base paring that exist at the end of telomeres where guanine base pairs with itself.
What is monocistronic?
single gene is on an RNA sequence
