DNA Structure Flashcards
What is Rett Syndrome?
A genetic disorder that causes defects in the methyl-CpG-binding protein 2 involved in chromatin conformation.
Neurodevelopment disorder that only affects females, lethal in males.
What is the central dogma?
Flow of information from DNA to RNA and eventually to proteins
What type of covalent bond joins deoxyribonucleotides?
3’,5’-phosphodiester bonds
What is the primary structure of DNA?
Covalent makeup and base pair sequence
What is the secondary structure of DNA?
Stable structure taken up by some or all of the nucleotides.
I.e. double helix
What is the tertiary structure of DNA?
Complex folding of eukaryotic chromatin and bacterial nucleoids to form large chromosomes.
What are some features of the DNA molecules?
- Joined by 3’,5’-phosphodiester bonds
- Each strand has a 5’ and 3’ end, and thus polarity
- the two strands are antiparallel
- the two strands are complementary
What are Chargaff’s Rules?
Adenosine=thymine and guanosine=cytidine
Purines=Pyrimidines
Species have different base compositions
What are four characteristics of the DNA double helix?
- Two strands coiled around the axis of symmetry.
- antiparallel
- Hydrophilic backbone on outside, hydrophobic bases on the inside.
- Major and minor grooves
What is Actinomycin D?
Anti cancer drug that intercalates between the planar bases
What is B-DNA?
Right-handed double helix.
Hydrophilic backbone on outside, bases on the inside.
10 bp/turn
Most common form of DNA in nature
What is Z-DNA?
Rare left-handed double helical form of DNA
Occurs in G-C rich sequences
May be related to gene regulation
What is A-DNA?
Right-handed helix produced by dehydrating the B form.
11 bp/turn and planes are tilted away from the perpendicular to the axis
Conformation found in DNA-RNA hybrids or RNA-RNA double-stranded regions
What is the importance of denaturing DNA molecules?
Allows access to encoded information.
What causes DNA denaturation?
Heat
-pH extremes
Urea
Other denaturing agents
What is the hyperchromic effect?
Absorbance to UV light goes up as DNA becomes denatured (more single-stranded)
What causes the Tm of a region of DNA to be higher or lower and why?
The amount of GC base pairs in the region, due to GC having 3 H-bonds instead of 2.
More GC = higher Tm
How is DNA packaged in viruses?
Genome surrounded by a protein coat
How is DNA packaged in bacteria?
A single circular chromosome housed in their nucleoid and smaller circular plasmids that often have no function, but can give antibiotic resistance.
How is DNA packaged in eukaryotes?
Packaged into chromatin
What is chromatin?
The complex of nucleic acids (DNA and RNA) and proteins (histones and nonhistones) comprising eukaryotic chromosomes
What is the difference between Euchromatin and heterochromatin?
Euchromatin - loosely packaged and transcriptionally active, beads on a string DNA
Heterochromatin - tightly packaged and transcriptionally inactive
What are histones?
DNA-binding proteins that contain large amounts of basic amino acids (positively charged) such as lysine and arginine which attract negatively charged DNA.
What are nucleosomes?
The structural unit for packaging chromatin consisting of a DNA strand around a histone core.
