Bacteriophages have tails Animal viruses have an envelope around the capsid

1. Viruses are not cells because they can’t reproduce on their own. A virus needs a host cell to replicate. Viruses are made up of a genome (single or double stranded DNA or RNA) enclosed in a protein coat (capsid). • Bacteriophages have tails • Animal viruses have an envelope around the capsid

2. Viruses come in many shapes. Each type of virus infects a specific type of cell.

3. Viruses have no enzymes or ribosomes so they can’t replicate DNA or make proteins. They must infect host cells, and take over their machinery in order to make new viruses. Viral coats exist to protect the genome and to transport it to a host cell. The viral genome is injected into a host cell where it can replicated, transcribed and translated. New viruses are then assembled and released from the host cell.

5. The lytic cycle of the bacteriophage leads to immediate death of the host and about 200 viruses being released.

6. In the lysogenic cycle, the bacteriophage hides in the bacterial DNA as a prophage for many generations.

7. Animal viruses may have an envelope outside of the capsidto help the virus enter the host cell. Envelope proteins are made on bound ribosomeson the ER of the host cell.

8. Retroviruses like HIV have a single-stranded RNA genome. They have an enzyme called reverse transcriptase that makes a DNA copy of RNA. This DNA can then be incorporated into the host cell’s DNA as a PROVIRUS.

9. Attachment and entry • Reverse transcriptase makes DNA from the RNA template • 3. DNA is incorporated into chromosomal DNA = provirus • 4. viral mRNA and proteins are made • 5. new viruses are assembled and released Steps of HIV Infection

10. How do viruses make us sick? • damage or kill cells by causing lysosomes to release hydrolytic enzymes • are toxic or cause infected cells to produce toxins • attack cells that cannot divide • activate the immune system, causing fever, aches, and inflammation

11. Viruses probably evolved after 1stcells from fragments of cellular nucleic acids • Genetic material of viruses is similar to their hosts • Some viral genes are similar to cellular genes • viruses are similar to plasmids and transposons(mobile genetic elements)

12. Prions—misfoldedproteins that convert normal proteins into the “evil,”misfoldedstate cause scrapie, mad cow disease, and Creutzfeld-JakobDisease (CJD) Prions can increase in number without actually being able to replicate.

13. Bacteria have 1 circular chromosome made of double stranded DNA It has fewer associated proteins than a eukaryotic chromosome. Many bacteria contain plasmids—small circular, double-stranded DNA that contains extrachromosomal genes

14. Binary fission produces genetically identical clones. DNA replication occurs before division.

15. There are 3 major sources of genetic variation in bacteria • Transformation • Bacterial cell incorporates DNA from surroundings • This DNA can be integrated into bacterial chromosome by crossing over • Progeny will carry a new combination of genes

16. 2. Transduction • Gene transfer from one bacterium to another by a bacteriophage • Random pieces of host genome are packaged with the virus • When phage infects a new cell, it now gets the DNA from the former host

17. 3. Conjugation • Direct transfer of genes between two cells that are temporarily joined • The ability to transfer DNA is conferred by the F plasmid • DNA “donor” cells (F+) extend sex piliout to “recipient” (F-) cells, forming a bridge to transfer DNA

18. Chromosomal genes can be transferred during conjugation when the F plasmid integrates into the bacterial chromosome. This makes it an Hfr (high frequencey of recombination) cell. Only some parts of the chromosome are transferred before the bridge disintegrates, and then crossing over can occur.

19. Transposable Elements: DNA sequences that can “jump” from one chromosome to another. Simple insertion sequence just has transposase Transposon has another gene as well

20. Regulation of gene expression is slower than simply inactivating an enzyme, but it’s more economical for the cell

21. Structural gene—codes for a polypeptide • Operon—cluster of adjacent structural genes with related functions • Has one promoter region so expression of genes is coordinated and regulated together • Transcription makes one long mRNA that gets translated into several polypeptides • Operator—part of DNA in the promoter that controls access of RNA polymerase (accessible unless repressed) • Repressor—binds to operator to block RNA polymerase access to operator

22. Repressible operon—ON until turned off • Example: trpoperon • 5 genes coding for enzymes involved in tryptophan synthesis • ON until too much tryptophan is made

23. The trpoperon repressor is inactive when produced. Tryptophan acts as a corepressor to activate the repressor, bind to the operator, and turn off production of tryptophan.

24. Inducible operon—OFF until turned on • Example: lacoperon • 3 genes coding for enzymes involved in breakdown of lactose • OFF until lactose is present

25. The lactose repressor is active when produced. When lactose is present, it’s converted to allolactose, an isomer. Allolactose binds to the repressor, inactivating it, to allow RNA polymerase access to turn on transcription, resulting in lactose breakdown.

26. cAMP is present when cell respiration slows downfrom lack of glucose. Bacteria only break down lactose for energy when glucose isn’t present. CAP (catabolite activator protein)activates lac operononly when glucose isn’t around.