Chapter 13.2.1 (Exam 3) DNA Structure Flashcards
DNA Has a Structure That Suits Its Function
Describe the chemical composition of DNA.
DNA is a polymer of nucleotides
What are the 3 components of a nucleotide?
Nitrogenous base
Pentose sugar
Phosphate groups
How do nucleotides differ?
Nucleotides differed only in the bases:
Purines: Adenine (A) and Guanine (G)
Pyrimidines: Cytosine (C), Thymine (T), and Uracil (U)
What is Chargaff’s rule? The formula?
In DNA, the amount of purines is always equal to the amount of pyrimidines
A + G = C + T
But the relative abundances of A + T versus G + C varies among species
What evidence for DNA’s structure was found using X-ray diffraction by Rosalind Franklin?
Double-stranded helix with 10 nucleotides in each full turn
The sugar-phosphate backbone of each strand must be on the outside
Which DNA structure model satisfied both Chargaff’s rule and the X-ray diffraction data?
The model paired purines on one strand with pyrimidines on the other, resulting in uniform width
The bases are on the inside of each strand
The sugar-phosphate groups are on the outside of each strand
The chains run in opposite directions—antiparallel
What are the key features of DNA structure?
It is a double-stranded, right-handed helix
It is antiparallel
The strands are held together by complementary base pairing (H-bonds)
The outer edges of the bases are exposed in major and minor grooves
What are the forces that keep DNA strands toghether?
Hydrogen bonds between complementary base pairs hold the two strands of the DNA helix together
van der Waals forces occur between adjacent bases on the same strand
How is the direction of DNA strands determined?
Direction is determined by sugar—phosphate bonds
Phosphate groups connect the 3′ C of one sugar with the 5′ C of the next
What are antiparallel strands?
One strand has a free 5′ phosphate group—the 5’ end
The other chain has a free 3′ hydroxyl group—the 3’ end
Why is the double-helix structure is essential to DNA function?
Stores a huge amount of genetic information
Susceptible to mutations
Precise replication
Genetic information is expressed as the phenotype
