DNA Structures

• 1 degree level of DNA


  nucleotides joined by phosphodiester bonds
• 2 degree level of DNA


  3D structure modeled by Watson and Crick
• 3 degree level of DNA

  complex packaging of DNA into double helix, formed by supercoiling
• Nucleotide consists of...


  phosphate group, sugar, and nitrogenous base
• RNA vs DNA nucleotide

  ribose instead of deoxyribose sugar, OH 2' instead of H, U instead of T
• Phosphate groups attach to 3' by phosphodiester bonds, bases bond by hydrogen bonds
• B-DNA: most common form, typical structure under normal conditions, right-handed manner
• A-DNA: less common, more compact, under specific conditions ex. dehydration
• Z-DNA: left-handed manner, zig-zag shape, under specific conditions ex. high salt concentrations
• Central Dogma of Molecular Biology


  the sequential flow of genetic info: DNA (replication) to RNA (transcription) to proteins (translation)
• Chromatin


  highly complex with several levels of organization, comprised of DNA, RNA, and proteins that result in the formation of chromosomes
• Histones


  help organize and stabilize DNA at nucleosomes
• Euchromatin


  less condensed, located at chromosome arms, unique DNA, contains most genes, replicated throughout S phase, crossing over is common, often transcribed
• Heterochromatin


  more condensed, found at centromeres and telomeres, repeated sequences, contains few genes, uncommon crossing over, low transcription rate
• Chromosomal puffs


  regions of relaxed chromatin that are actively going through transcription
• Artificial chromosomes require...

  telomeric sequences, centromeric sequences, one or more origins of replication
• Transposable Elements

  DNA sequences that have the ability to move from one location to another within a genome, comprise high % of genome (humans - 45%), DNA-only and retrotransposons
• Flanking Direct repeats


  DNA sequences that are identical, located adjacent to the insertion of a transposable element, acts as a marker of transposable elements