Bacteria and Viruses 1

2 BACTERIA Bacteria - small one celled organisms  Bacteria like a warm, dark, and moist environment They are found almost everywhere: -water-air -soil-food -skin-inside the body -on most objects

3 Spiral: spirilla rod-shaped: bacilli, bacillus Round: cocci 3 Shapes of Bacteria Bacteria are classified by shape into 3 groups:

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

5 Major Structures of a Bacteria Cell Capsule Cell wall Ribosomes Nucleoid Flagella Pilli Cytoplasm

6 Capsule Major Structures of a Bacteria Cell  keeps the cell from drying out and helps it stick to food or other cells

7 Cell wall Major Structures of a Bacteria Cell  Thick outer covering that maintains the overall shape of the bacterial cell

8 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

9 Nucleoid 7 Major Structures of a Bacteria Cell  a ring made up of DNA

10 Flagella 7 Major Structures of a Bacteria Cell  a whip-like tail that some bacteria have for locomotion

11 Pilli Major Structures of a Bacteria Cell  hollow hair-like structures made of protein  allows bacteria to attach to other cells.  Pilli-singular  Pillus-plural

12 Cytoplasm Major Structures of a Bacteria Cell  clear jelly-like material that makes up most of the cell

13 Binary Fission- the process of one organism dividing into two organisms Fission is a type of asexual reproduction Reproduction of Bacteria How?... The one main (circular) chromosome makes a copy of itself Then it divides into two Asexual reproduction- reproduction of a living thing from only one parent

14 BINARY FISSION Bacteria dividing Completed Reproduction of Bacteria

15 Bacterial Cell & Nucleiod DNA Ring DNA replication Cell wall synthesis Cell separation

16 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 Bacteria

17 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

18 Bacillus subtilis Endospore-the black section in the middle  highly resistant structures  can withstand radiation, UV light, and boiling at 120oC for 15 minutes. Bacteria Survival

19 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

20 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

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

22 Controlling Bacteria 3 ways to control bacteria: 1) Canning- the process of sealing food in airtight cans or jars after killing bacteria endospores are killed during this process 2) Pasteurization- process of heating milk to kill harmful bacteria 3) Dehydration- removing water from food Bacteria can’t grow when H 2 O is removed example: uncooked noodles & cold cereal

23 Controlling Bacteria Antiseptic vs. Disinfectants Antiseptic- 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 24

General Structure of Viruses Size range – – most <0.2 μm; requires electron microscope

27 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

34 Figure 6.9 9/1/09Mickey Dufilho

35 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 9/1/09Mickey Dufilho

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 Multiplication General phases in animal virus multiplication cycle: 1.Adsorption – binding of virus to specific molecule on host cell 2.Penetration – genome enters host cell 3.Uncoating – the viral nucleic acid is released from the capsid 4.Synthesis – viral components are produced 5.Assembly – new viral particles are constructed 6.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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48 Damage to Host Cell Cytopathic effects - virus-induced damage to cells 1.Changes in size and shape 2.Cytoplasmic inclusion bodies 3.Inclusion bodies 4.Cells fuse to form multinucleated cells 5.Cell lysis 6.Alter DNA 7.Transform cells into cancerous cells 9/1/09Mickey Dufilho

49 Figure /1/09Mickey Dufilho