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ProkaryotesEukaryotesVirus
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
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
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)
Virus: “poison” (Latin) infectious particles
consisting of a nucleic acid in a protein coat
Size Smaller than
ribosomes Tiniest are about
20nm in diameter
Capsid 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
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.
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.
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
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
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
Use the enzyme reverse transcriptase to transcribe DNA from an RNA template (RNADNA)
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
Viroids 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
Nucleoid: region in bacterium densely packed with DNA (no membrane)
Plasmids: small circles of DNA
Reproduction: binary fission (asexual)
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
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”