MCB 150 Lecture 37 Notes

Announcements

• The deadline for checking the accuracy of grades entered into the ATLAS web gradebook is Wednesday, May 7.
• The deadline for requesting a Conflict Final is also May 7.
• Regular student hours are available today, Friday, and next Wednesday, with additional times on May 9 & 12.
• The Final Exam is scheduled for Monday, May 12, from 7:00-10:00 PM in the same lecture hall.

Viral DNA Integration and Replication

• HIV uses integrase to splice viral DNA into the host DNA.
• The process begins with the release of the viral RNA genome and proteins into the host cell.
• Reverse transcriptase copies viral RNA into DNA.
• Integrase and viral DNA then enter the nucleus.
• Host machinery replicates the viral RNA.
• Receptor-binding glycoproteins facilitate specific binding and fusion of viral and host membranes.
• Translation of viral RNA results in a polyprotein.
• Protease cleaves the polyprotein into individual proteins.
• Viral assembly occurs at the membrane, followed by budding.

Genome Comparisons

• Human Skin Cell:
  • Approximately 6,000,000,000 base pairs (bp) of DNA
  • Contains around 20,000 genes
  • Produces about 100,000 proteins
  • Has a length of about 30 μm
• Pyrococcus woesei:
  • Approximately 1,900,000 bp of DNA
  • Contains around 2,000 genes
  • Produces about 2,000 proteins
  • Has a length of about 1 μm
• Carsonella ruddii:
  • Approximately 160,000 bp of DNA
  • Contains around 182 genes
  • Produces about 182 proteins
  • Has a length of 10-30 μm
• Pandoravirus salinus:
  • Approximately 2,500,000 bp of DNA
  • Contains around 2,500 genes
  • Produces about 2,500 proteins
  • Has a length of about 1 μm

Mobile Genetic Elements: Plasmids

• Plasmids are extrachromosomal molecules of circular, double-stranded DNA.
• They carry from a few to a few dozen genes.
• Plasmids are found in many prokaryotes, some yeast, plants, and protozoans.
• They are nonessential in wild-type conditions.

Useful Properties Plasmids Confer to Host

• Plasmids can carry genes that enable bacteria to live in inhospitable environments:
  • Soils contaminated with toxic metals like mercury and lead.
  • Industrial chemicals and petroleum by-products (oil slicks).
  • Pesticides & herbicides.
  • Competition with other bacteria (bacteriocins).
• Plasmids can carry resistance factors that destroy/modify antibiotics.
• Plasmids can carry genes for transferring plasmid via conjugation.

Plasmid Replication and Copy Number

• Plasmids have their own origin of replication.
  • Replication is not synchronized with the replication of the host chromosome but depends on host machinery.
• Plasmids can be present in multiple copies in a cell.
  • The number of copies can vary.
  • Naturally occurring plasmids: copy number is 1 or 2 to 10.
  • Engineered plasmids can have up to 500 copies per cell, making them invaluable tools for molecular biology.