1 / 21

Lecture 2 Properties of DNA

Lecture 2 Properties of DNA. Reference: Chapter 28: Biochemistry by Voet and Voet. Lecture 2: Outline. C-value paradox Gene size, genome size Topology of DNA Denaturation and renaturation of DNA. gene sizes. Largest known mammalian gene is DMD gene 2.5 Mbp (0.1% of the genome)

burian
Download Presentation

Lecture 2 Properties of DNA

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 2 Properties of DNA Reference: Chapter 28: Biochemistry by Voet and Voet

  2. Lecture 2: Outline C-value paradox Gene size, genome size Topology of DNA Denaturation and renaturation of DNA

  3. gene sizes Largest known mammalian gene is DMD gene 2.5 Mbp (0.1% of the genome) Causes Duchenne’s muscular dystrophy (DMD) characterized by rapid progression of muscle degeneration which occurs early in life. ‘scoliosis’

  4. DMD gene maps to chromosome Xp21 DMD affects mainly males Mutations in DMD gene lead to non functional dystrophin protein DMD

  5. genome sizes organism Number of base pairs(kb) viruses Lambda bacteriophage ( λ)48.6 bacteria Eschericia coli 4,640 eukaryotes Yeast 13,500 Drosophila 165,000 Human 3.3 x 106

  6. Does size matter? C-value paradox Boa constrictor Genome size: 2.1 Gbp Homo sapiens sapiens Genome size: 3.2 Gbp mountain grasshopper Podisma pedestris Genome size: 18 Gbp protozoan Amoeba dubia Genome size: 670Gbp C value: DNA content of a haploid cell

  7. Comparative genome sizes C-value paradox Why is there a discrepancy between genome size and genetic complexity?

  8. Due to the presence of repetitive (junk?) DNA Repetitive DNA families constitute nearly one-half of genome (~45%) Protein domains contribute to organism complexity

  9. Topology of DNA DNA supercoiling: coiling of a coil Important feature in all chromosomes Allows packing / unpacking of DNA Supercoiled DNA moves faster than relaxed DNA

  10. Supercoiling topology No supercoiling (left) to tightly supercoiled (right) • negatively supercoiled (right handed) • Results from under or unwinding • Important in DNA packing/unpacking e.g during replication/transcription • positively supercoiled (left handed) • Results from overwinding • Also packs DNA but difficult to unwind Analogy = phone cord

  11. Supercoiling takes 2 forms toroidal (DNA around histones) or interwound (bacterial chromosomes)

  12. Supercoiled DNA needs to be unwound /wound when necessary Unwound during transcription/replication Wound before cell division Supercoils can be relaxed by • Single strand nicks (topoisomerase I) • Double strand breaks (toposiomerase II)

  13. Topoisomerase I • Cause temporary single strand breaks in DNA • Allows free rotation of helix • Acts by breaking phosphodiester linkage via tyrosine active site

  14. Topoisomerase II (DNA gyrase) • ATP hydrolysis mediated double strand break • Inhibitors are effective antibiotics and cancer chemotherapy agents

  15. Why does a plasmid (circular DNA) that has never been cut give more than one band on a gel? Full length linear Relaxed circle supercoiled EBr

  16. Denaturation and renaturation of DNA Applications in polymerase chain reaction (PCR) http://www.dnai.org/b/index.html

  17. Denaturation of DNA Also called melting Occurs abruptly at certain temperatures Tm – temp at which half the helical structure is lost

  18. DNA melting curve

  19. Tm varies according to the GC content High GC content - high Tm GC rich regions tend to be gene rich

  20. Renaturation of DNA Also called annealing Occurs ~ 25oC below Tm Property used in PCR and hybridisation techniques

More Related