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DNA

DNA. The Nuclear genome consists of DNA in the nucleus of eukaryotic cells – this is what we typically think of as our Genome :. A Genome is the unique set of chromosomes (or DNA) in one cell of an organism.

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DNA

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  1. DNA

  2. The Nuclear genome consists of DNA in the nucleus of eukaryotic cells – this is what we typically think of as our Genome: • A Genome is the unique set of chromosomes (or DNA) in one cell of an organism. • Humans have 2 sets of chromosomes (one from each parent: we are diploid.) • Our genome consists of 3 x109 base pairs • ~25,000 genes (no one knows exactly yet).

  3. Plant Cell Animal Cell Nucleus Chloroplast Mitochondrion

  4. Chloroplasts (photosynthesis machinery in plants, algae) have their own DNA (called the • Plastid genome) • 7.5-25 x 103 base pairs • 100-1000 copies depending on whether the cell is actively dividing (more when dividing). • ~100 genes • Mitochondria have their own DNA (called the Mitochondrial genome) • ~1.7 x 104 base pairs • several copies • ~40 genes

  5. Nucleic Acids • DNA • RNA

  6. DNA • Deoxyribonucleic acid • double helix • “intelligent molecule” • made of nucleotides

  7. Nucleus CELL image from the National Human Genome Research Institute (NHGRI) Genetic Illustrations. One human cell Has ~1 meter of DNA DNA is partitioned into 46 separate linear molecules (chromosomes, 23 from each parent) All of it is crammed into the cell's nucleus (a few micrometers) Robert H. Austin, James P. Brody, Edward C. Cox, Thomas Duke and Wayne Volkmuth FEBRUARY 1997 PHYSICS TODAY

  8. 2 nm DNA 11 nm 30 nm Chromatin 300 nm 700 nm Chromosome 1400 nm Richarddawkins.net

  9. Nucleotide • Sugar (deoxyribose) • Phosphate • Nitrogenous Base • adenine (A) • thymine (T) • cytosine (C) • guanine (G)

  10. DNA is double-stranded • adenine is always across from thymine • cytosine is always across from guanine • bases are held across from each other by weak hydrogen bonds A T C G

  11. The Sugar in the “backbone” is RNA: ribose DNA: deoxyribose This OH group is replaced by H (hydrogen atom) in Deoxy-ribose

  12. 3’ 5’ 5’ 3’ DNA is anti-parallel: One strand is 5’to 3’ The strand across from it is 3’ to 5’

  13. How do We Know the Structure of DNA? Watson & Crick 1953

  14. Diffraction PatternsReciprocal Space http://www.matter.org.uk/diffraction/geometry/3D_reciprocal_lattices.htm Click here for a groovy interactive experience (Grab and drag one of the white dots) X-ray crystallography revisited

  15. DNA X-ray diffraction pattern X-ray crystallography revisited

  16. 34 Angstroms X-ray crystallography revisited

  17. 3.4 Angstroms X-ray crystallography revisited

  18. X-ray crystallography revisited

  19. X-ray crystallography revisited

  20. X-ray crystallography revisited

  21. X-ray Diffraction pattern → Molecular Structure 1953 Discovery → Nobel Prize

  22. Wavelength of diffracted light should match size of object for optimal resolution Why x-rays?

  23. A DNA molecule • not a rigid, static structure • (as x-ray diffraction pictures might suggest) • under constant thermal fluctuations • local twisting, stretching, bending, and unwinding of the double-strands. http://www.uic.edu/classes/phys/phys461/phys450/ANJUM04/ X-ray crystallography revisited

  24. B Z A • The most common DNA structure in solution is B-DNA. • DNA has several helical conformations A-DNA, Z-DNA, S-DNA • Under conditions of • applied force • low hydration • ...

  25. B-DNA Long and thin Most common in solution Right-handed helix 27.3 A diameter 3.4 A rise/base pair ~ 10 bases/turn A-DNA Short and broad Low hydration Right handed helix 25.5A diameter 2.3A rise/base pair ~11 bases/ turn Z-DNA Longer and thinner Left-handed helix 18.4 A diameter 3.8 A rise/base pair ~12 bases/ turn

  26. DNA Replication • 2 strands of DNA “unzip” - separate • primers are placed on each strand • DNA polymerase (an enzyme) builds new strands of DNA, using the original strands as templates

  27. RNA • Ribonucleic acid • single stranded • also made of nucleotides

  28. RNA nucleotides • Sugar (ribose) • Phosphate • nitrogenous base • adenine • cytosine • guanine • uracil

  29. Types of RNA • mRNA: messenger RNA, carries the DNA code out of the nucleus to the ribosome • tRNA: transfer RNA, carries amino acids to the ribosome • rRNA: ribosomal RNA, part of the ribosome

  30. Transcription (making RNA) • DNA unzips • one strand of DNA acts as a template • RNA polymerase reads the DNA bases • RNA nucleotides are placed across from the complimentary DNA bases • RNA separates from DNA • DNA zips back up

  31. The “code” of DNA is the order of the bases • The code is universal among organisms • DNA from one organism can be read in the cells of another organism

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