prokaryotes eukaryotes virus. functions of the three parts of an operon role of repressor genes in...

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”