Bacteria and Viruses

Bacteria and Viruses

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BACTERIA

Bacteria - small one celled organismsBacteria like a warm, dark, and moist environment

They are found almost everywhere:-water -air-soil -food-skin -inside the

body-on most objects

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Spiral:spirilla

rod-shaped: bacilli, bacillus

Round:cocci

3 Shapes of 3 Shapes of BacteriaBacteria

Bacteria are classified by shape into 3 groups:

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Bacillus anthracis - rod, vegetative stage prokaryote (bacterium)Image Number: 21185A

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Major Structures of a Bacteria Cell

•Capsule•Cell wall•Ribosomes•Nucleoid•Flagella•Pilli•Cytoplasm

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Capsule

Major Structures of a Bacteria Cell

keeps the cell from drying out and helps it stick to food or other cells

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Cell wall

Major Structures of a Bacteria Cell

Thick outer covering that maintains the overall shape of the bacterial cell

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Ribosomes

7 Major Structures of a Bacteria Cell

cell part where proteins are made

Ribosomes give the cytoplasm of bacteria a granular appearance in electron micrographs

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Nucleoid

7 Major Structures of a Bacteria Cell

a ring made up of DNA

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Flagella

7 Major Structures of a Bacteria Cell

a whip-like tail that some bacteria have for locomotion

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PilliMajor Structures of a Bacteria Cell

hollow hair-like structures made of protein

allows bacteria to attach to other cells.

Pilli-singular Pillus-plural

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Cytoplasm

Major Structures of a Bacteria Cell

clear jelly-like material that makes up most of the cell

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•Binary Fission- the process of one organism dividing into two organisms•Fission is a type of asexual reproduction

Reproduction of Reproduction of BacteriaBacteria

How?...The one main (circular) chromosome makes a copy of itselfThen it divides into two

•Asexual reproduction- reproduction of a living thing from only one parent

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BINARY FISSION

Bacteria dividing Completed

Reproduction of Reproduction of BacteriaBacteria

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Bacterial Cell & Nucleiod DNA Ring

DNA replication

Cell wall synthesis

Cell separation

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•The time of reproduction depends on how desirable the conditions are

•Bacteria can rapidly reproduce themselves in warm, dark, and moist conditions

•Some can reproduce every 20 minutes

(one bacteria could be an ancestor to one million bacteria in six hours)

Reproduction of Reproduction of BacteriaBacteria

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Bacteria Survival Endospore- •a thick celled structure that forms inside the cell•they are the major cause of food poisoning•they can withstand boiling, freezing, and extremely dry conditions•it encloses all the nuclear materials and some cytoplasm

•allows the bacteria to survive for many years

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Bacillus subtilisEndospore-the black section in the middle

highly resistant structurescan withstand radiation, UV light, and boiling at 120oC for 15 minutes.

Bacteria Survival

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Bacteria Survival – Food sources

parasites – bacteria that feed on living things

saprophytes – use dead materials for food (exclusively)

decomposers – get food from breaking down dead matter into simple chemicals

important- because they send minerals and other materials back into the soil so other organisms can use them

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Harmful Bacteria

Communicable Disease – Disease passed from one organism to another

This can happen in several ways:•Air•Touching clothing, food, silverware, or toothbrush•Drinking water that contains bacteria

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Human tooth with accumulation of bacterial plaque (smooth areas) and calcified tartar (rough areas)

Harmful Bacteria

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Controlling Bacteria3 ways to control

bacteria:1) Canning- the process of sealing food in airtight cans or jars after killing bacteria

•endospores are killed during this process2) Pasteurization- process of heating

milk to kill harmful bacteria

3) Dehydration- removing water from food•Bacteria can’t grow when H2O is

removed •example: uncooked noodles & cold cereal

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Controlling BacteriaAntiseptic vs. DisinfectantsAntiseptic- chemicals that kill

bacteria on living things•means – “against infection”Examples: iodine, hydrogen peroxide, alcohol, soap, mouthwash

Disinfectants- stronger chemicals that destroy bacteria on objects or nonliving things

Welcome to the world of viruses

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General Structure of Viruses• Size range –

– most <0.2 μm; requires electron microscope

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General Structure of Viruses• Capsids

– All viruses have capsids - protein coats that enclose and protect their nucleic acid

– The capsid together with the nucleic acid are nucleocapsid

– Some viruses have an external covering called envelope; those lacking an envelope are naked

– Each capsid is constructed from identical subunits called capsomers made of protein

Structure of Virus

General Structure of Viruses• Two structural types:

–Helical - continuous helix of capsomers forming a cylindrical nucleocapsid

– Icosahedral - 20-sided with 12 corners– Vary in the number of capsomers– Each capsomer may be made of 1 or several proteins– Some are enveloped

Helical Nucleocapsids

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General Structure of Viruses• Viral envelope

– Mostly animal viruses– Acquired when the virus leaves the host cell– Exposed proteins on the outside of the envelope,

called spikes, essential for attachment of the virus to the host cell

General Structure of Viruses• Complex viruses: atypical viruses

– Poxviruses lack a typical capsid and are covered by a dense layer of lipoproteins

– Some bacteriophages have a polyhedral nucleocapsid along with a helical tail and attachment fibers

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Figure 6.9

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Nucleic Acids• Viral genome – either DNA or RNA but

never both• Carries genes necessary to invade host cell

and redirect cell’s activity to make new viruses

• Number of genes varies for each type of virus – few to hundreds

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Nucleic Acids• DNA viruses

– Usually double stranded (ds) but may be single stranded (ss)

– Circular or linear

• RNA viruses – Usually single stranded, may be double stranded,

may be segmented into separate RNA pieces

How Viruses Are Classified• Main criteria presently used are structure,

chemical composition, and genetic makeup• Currently recognized: 3 orders, 63 families, and

263 genera of viruses• Family name ends in -viridae, i.e.Herpesviridae• Genus name ends in -virus, Simplexvirus• Herpes simplex virus I (HSV-I)

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Mode of Viral MultiplicationGeneral phases in animal virus multiplication

cycle:1. Adsorption – binding of virus to specific

molecule on host cell2. Penetration – genome enters host cell3. Uncoating – the viral nucleic acid is released

from the capsid4. Synthesis – viral components are produced5. Assembly – new viral particles are constructed6. Release – assembled viruses are released by

budding (exocytosis) or cell lysis

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Adsorption and Host Range• Virus coincidentally collides with a susceptible

host cell and adsorbs specifically to receptor sites on the cell membrane

• Spectrum of cells a virus can infect – host range– Hepatitis B – human liver cells– Poliovirus – primate intestinal and nerve cells– Rabies – various cells of many mammals

Penetration/Uncoating• Flexible cell membrane is penetrated by the

whole virus or its nucleic acid by:– Endocytosis – entire virus is engulfed and

enclosed in a vacuole or vesicle– Fusion – envelope merges directly with

membrane resulting in nucleocapsid’s entry into cytoplasm

Replication and Protein Production• Varies depending on whether the virus is a

DNA or RNA virus• DNA viruses generally are replicated and

assembled in the nucleus• RNA viruses generally are replicated and

assembled in the cytoplasm

Release• Assembled viruses leave host cell in one of two

ways:– Budding – exocytosis; nucleocapsid binds to

membrane which pinches off and sheds the viruses gradually; cell is not immediately destroyed

– Lysis – nonenveloped and complex viruses released when cell dies and ruptures

• Number of viruses released is variable– 3,000-4,000 released by poxvirus– >100,000 released by poliovirus

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Damage to Host Cell

Cytopathic effects - virus-induced damage to cells

1. Changes in size and shape2. Cytoplasmic inclusion bodies3. Inclusion bodies4. Cells fuse to form multinucleated cells5. Cell lysis6. Alter DNA7. Transform cells into cancerous cells

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Figure 6.16

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