1. Regulation of Gene Expression
Prokaryotes
Eukaryotes
Virus

2. Gene Expression Functions of the three parts of an operon
Role of repressor genes in operons
Impact of DNA methylation and histone acetylation on gene expression
The role of oncogenes, proto-oncogenes and tumor suppressor genes in cancer

3. Operons
In bacteria, genes are often clustered into units called operons
Three parts
Promoter: RNA polymerase binding site; begins transcription
Operator: controls access of RNA polymerase to genes
Genes of the operon: entire stretch of DNA required

4. Operons Regulatory Gene
Produce repressor proteins that may bind to the operator site
Blocks the RNA polymerase and the operon is off
Repressible Operon
Normally on but can be inhibited
Anabolic –builds molecules
Inducible Operon
Normally off but can be activated
Catabolic – breaks down food molecules (energy)

5. Viral structure Virus: “poison” (Latin) Size
infectious particles consisting of a nucleic acid in a protein coat
Size
Smaller than ribosomes
Tiniest are about 20nm in diameter

6. Viral structure Capsid Viral envelope
Protein shell that surrounds the genetic material
Viral envelope
Some viruses have these glycoprotein coats that surround the capsid and aid in infecting their hosts

7. Viral structure Genome DNA or RNA Double or single stranded
Bacteriophages (phages)
Viruses that infect bacterial cells
It is believed there are approximately 1031phage particles on the planet with approximately 1025 infections per second.
Bacteriophage are located anywhere you can isolate bacteria and are generally abundant in soil and water.

8. Common Structural Features
Capsid (Head): Comprised of one or more proteins forming a protective covering around the nucleic acids. Can vary in shape and size.
Genomic Material: Nucleic acids (DNA or RNA, but not both) contained with the capsid encoding essential viral proteins. May also encode additional genes obtained during viral passage.
Tail (optional): Hollow protein tube used to transfer nucleic acids from phage capsid to bacterium during infection. Can be long or short.
Base plate and fibers (optional): Involved in attachment of phage to bacteria prior to infection.

9. Viral reproduction: Viruses reproduce only in host cells
Viruses have a very limited host range
Human cold virus infects only the cells of the upper respiratory tract of Homo sapiens
Has to do with receptor molecules on the cell membrane

10. Viral reproduction: Lytic Cycle
Viral reproduction occurs only in host cells.
Two variations
Lytic
Lysogenic
The lytic cycle
Attachment
Injection
Hydrolyzation
Assembly
Release (lysis)
Results in death of host cell by rupturing the cell, releasing multiple copies of the virus
Called a virulent virus

11. Viral reproduction: Lytic Cycle

12. Viral reproduction: Lysogenic Cycle
Genetic material of virus becomes incorporated into the host cell DNA
It is replicated along with the host cell’s DNA
Called prophage DNA
Called a Temperate virus
phage capable of using the lytic and lysogenic cycles
May give rise to lytic cycle under certain conditions
Example is Herpes virus or cold sores

13. Viral reproduction: Lysogenic Cycle (Temperate)

14. RNA viruses: Retroviruses
Use the enzyme reverse transcriptase to transcribe DNA from an RNA template (RNADNA)
The new DNA then permanently integrates into the host DNA
Host transcribes the DNA back to RNA and may be used to synthesize viral proteins or may be released in infect more cells
Example: HIV

15. Viroids and prions Viroids Prions
tiny, naked circular RNA that infect plants
do not code for proteins, but use cause errors in regulatory systems that control plant growth
Prions
infectious proteins that cause misfolding of normal proteins in various animal species
Example mad cow disease

16. Bacterial genetics
Nucleoid: region in bacterium densely packed with DNA (no membrane)
Plasmids: small circles of DNA
Reproduction: binary fission (asexual)

17. Bacterial DNA-transfer processes
Transformation: genotype alteration by the uptake of naked, foreign DNA from the environment (Griffith expt.)
Transduction: phages that carry bacterial genes from 1 host cell to another •generalized~ random transfer of host cell chromosome •specialized~ incorporation of prophage DNA into host chromosome
Conjugation: direct transfer of genetic material; cytoplasmic bridges; pili; sexual

18. Bacterial Plasmids
Small, circular, self-replicating DNA separate from the bacterial chromosome
F (fertility) Plasmid: codes for the production of sex pili (F+ or F-)
R (resistance) Plasmid: codes for antibiotic drug resistance
Transposons: transposable genetic element; piece of DNA that can move from location to another in a cell’s genome (chromosome to plasmid, plasmid to plasmid, etc.); “jumping genes”