Chapter 14: 14.1 Nucleic Acid Structure Flashcards
Define:
Nucleotides
Monomers that constitute nucleic acids
What do nucleotides consist of?
- A sugar
- Phosphate groups
- A nitrogenous base (Adenine, Thymine, Cytosine, Uracil, or Guanine)
How are the bonds in the DNA double-helix formed?
A dehydration reaction between the -OH group on the 3’ carbon of one nucleotide and the phosphate on the 5’ carbon of an adjacent nucleotide to form a covalent bond
What are the covalent bonds formed for by the dehydration reactions between nucleotides called?
Phosphodiester bonds
What is the directionality of DNA strands?
5’ to 3’ directionality
* 5’ end refers to the carbon attached to the phosphate group
* 3’ end refers to the carbon attached to the -OH group
DNA consists of two strands of nucleotides twisted around each other to form…
A double helix
The DNA helix has the bases pointed inwards, meaning it has a…
Sugar-phosphate backbone
How are two DNA strands arranged?
Arranged in antiparallel conformation
* One strand is in the 5’ to 3’ direction
* Other is in the 3’ to 5’ direction
What pairings do bases form in a DNA double helix?
Purine-pyrimidine pairs
The bases that form the purine-pyrimidine pairs are said to be ————- to each other
Complementary
State:
Purine-pyrimidine pairings and bond numbers
- A pairs with T, forms 2 hydrogen bonds
- C pairs with G, forms 3 hydrogen bonds
Why are the DNA bases paired up in such a way?
It is the only combination that gives the correct geometry
Adenine and guanine are…
Purines (two-ringed structure)
Cytosine and thymine are…
Pyrimidines (single-ring structures)
Besides hydrogen bonding between base pairs, what other intermolecular forces act in DNA strands?
Base stacking interactions
* Occurs between bases on the same strand
* Driven by the hydrophobic effect
