dna

• Nucleotides


  Monomers that make up nucleic acids (DNA and RNA)
• DNA


  • Carries hereditary information
  • Reproduces itself (replication)
  • Supplies information to make RNA and proteins
• Replication fork


  Point in DNA where replication begins
• DNA replication


  1. Opening up of DNA superstructure

  2. Relaxation of higher-order DNA structures

  3. Unwinding of double helix

  4. Primer/primase synthesis

  5. DNA polymerase activity

  6. Ligation of Okazaki fragments
• Polymerase chain reaction (PCR)


  Technique to amplify DNA by making millions of copies
• PCR process


  1. Primers hybridize to target DNA

  2. Polymerase extends primers

  3. Process repeated in cycles to exponentially increase copies
• Base excision repair (BER)


  DNA repair pathway that recognizes and removes damaged DNA bases
• BER pathway


  1. DNA glycosylase removes damaged base

  2. Endonuclease cleaves backbone

  3. Exonuclease removes damaged site

  4. DNA polymerase inserts correct nucleotide

  5. DNA ligase seals backbone
• Cells contain thousands of different proteins
• Hereditary information was thought to reside in genes within chromosomes
• DNA carries the hereditary information
• Each gene controls the manufacture of one protein
• RNA and DNA are polymers built from nucleotides
• Nucleotide is composed of a base, a monosaccharide, and a phosphate
• Nucleoside is a compound of D-ribose or 2-deoxy-D-ribose bonded to a purine or pyrimidine base
• Nucleotide is a nucleoside with a phosphoric acid esterified to the monosaccharide
• DNA primary structure is the sequence of nucleotides from 5' to 3' end
• DNA secondary structure is the double helix
• DNA is coiled around histones to form nucleosomes, which are further condensed into chromatin and chromosomes
• DNA and RNA differ in their bases, sugars, and number of strands
• Different types of RNA have different functions (snRNA, siRNA, tRNA, rRNA, mRNA, miRNA)
• Genes are segments of DNA that direct protein/RNA synthesis
• Exons are DNA sections that code for proteins/RNA, introns do not code
• Acetylation-deacetylation of histones helps open up DNA superstructure for replication
• Topoisomerases relax DNA supercoiling during replication
• Helicases unwind the DNA double helix at the replication fork
• Primers are short RNA oligonucleotides that initiate DNA synthesis by polymerases
• DNA polymerase catalyzes complementary base pairing and backbone synthesis
• Okazaki fragments are short DNA fragments synthesized on the lagging strand
• DNA ligase joins the Okazaki fragments and seals nicks
• PCR uses primers complementary to target DNA to exponentially amplify copies
• DNA repair pathways like BER detect and remove damaged DNA bases
• Central dogma


  Information contained in DNA molecules is expressed in the structure of proteins

  
• Gene expression


  The turning on or activation of a gene
• Transcription


  1. DNA double helix begins to unwind near the gene to be transcribed

  2. Only one strand of the DNA is transcribed

  3. Ribonucleotides assemble along the unwound DNA strand in a complementary sequence

  4. Enzymes called polymerases catalyze transcription

  
• RNA polymerases in eukaryotes


  • RNA polymerase I catalyzes the formation of most of the rRNA
  • RNA polymerase II catalyzes mRNA formation
  • RNA polymerase III catalyzes tRNA formation as well as one ribosomal subunit

  
• Eukaryotic gene


  • Structural gene that is transcribed into RNA, made of exons and introns
  • Regulatory gene that controls transcription, not transcribed but has control elements like the promoter

  
• Promoter


  Unique to each gene, contains an initiation signal and consensus sequences like the TATA box
• Transcription process


  1. Initiation: RNA polymerase interacts with promoter regions via transcription factors

  2. Elongation: RNA polymerase zips up complementary bases, in 5' to 3' direction

  3. Termination: Termination sequence at the end of each gene

  
• Post-transcription modification


  • Transcribed mRNA is capped at both ends, introns are spliced out
  • tRNA is trimmed, capped, and methylated
  • Functional rRNA undergoes post-transcription methylation