Unit 3.2 (dna) Flashcards
What kind of bases have strong UV absorbance? At what frequency does this occur?
Purines all have strong UV absorbance (max ~260 nm)
What is a Nucleoside?
Nitrogenous Base + Sugar
Sugar = 2’-deoxy-D-ribose
Bond = B-N-glycosidic bond
What is a nucleotide?
Nucleoside + Phosphate
By default, phosphate group is on the 5’OH group (can also be on 3’ C)
What is cAMP? Why is it important?
Derived from ATP
cAMP is used in many biological process in intracellular signaling as an important 2nd messenger
What is Zidovudine?
Many antivirals are nucleoside/nucleotide analogs
Zidovudine is a nucleoside analog reverse transcriptase inhibitor used to treat HIV
What is Emtricitabine?
Another antiviral medication that is also used for the treatment of HIV infection for adults and children
What are minor bases?
RNA, particularly tRNA, contains minor bases
In DNA, these are usually methylated forms of the major bases (usually have roles in regulation or in protecting genetic information
What makes Inosine significant?
Inosine is commonly found in tRNAs essential for wobble base pairs
Describe the structure of the two classes of polynucleotides
Nucleotides joined by phosphodiester linkages
RNA = Ribonucleic acid (2’ OH) (Uracil)
DNA = Deoxyribonucleic acid (2’ H) (Thymine)
Describe the primary structure of DNA/RNA
Sequence of nucleotides
Read from the 5’ end to the 3’ end
What is the biggest difference between DNA and RNA? (RNA’s problem)
Stability!
RNA is susceptible to base catalyzed hydrolysis (due to presence of 2’ OH)
What are Chargaff’s rules?
Explains base ratios in DNA
#G = #C
#A = #T
Who solved 2° structure of DNA? What is the 2° structure?
Watson and Crick
The Double Helix
Whose data was important for Watson and Crick to determine the secondary structure of DNA? (they stole it)
Rosalind Franklin’s X-ray fiber diffraction data was crucial (also used Erwin Chargaff’s rules)
What simple principle is DNA replication based on?
Complementarity!
Describe the central dogma of molecular biology
Describe B DNA structure. What kind of helix does it have? Where are the bases relative to helix? Describe the major and minor grooves. Where are the phosphate backbones located? What is the pitch? How many bases per turn? What is the helix rise?
In what direction do the two chains run in a B DNA helix?
The two chains are antiparallel
Describe the difference between syn- and anti- conformations in nucleotide sugars in DNA/RNA
What handedness is A DNA? Describe its major and minor groove. What kind of molecules assume an A DNA structure?
Right handed
Major Groove: Narrow and Deep
Minor Groove: Wide and Shallow
RNA-RNA/RNA-DNA hybrids assume A-DNA structure
“Dried out DNA” (75% vs 92% humidity)
What is the naturally occurring form of DNA?
B DNA
What handedness is Z-DNA? Describe is major and minor grooves. Where does this form of DNA occur?
Left Handed
Major Groove: Flat
Minor Groove: Narrow and Deep
Occurs in alternating purine-pyrimidine tracts (favored in high salt conc.)
What are Telomeres? What are they rich in?
Ends of Linear Chromosomes (keep them from unravelling)
Guanidine-rich regions
Describe the general structure of RNA
Most (but not all) RNA is single-stranded
Has “wound back” double helical regions that assume A type helix
