Chapter 19Bacteria and Viruses

Remember homeostasis?

• Maintaining proper internal conditions

• pH, temp., water/salt balance, O2, CO2, etc.

Factors for Disease• 1. genetics- inheritance• 2. microorganisms

– pathogen: disease-causing agent

• 3. pollutants/poisons (ex: asbestos, lead)• 4. organ malfunction• 5. harmful lifestyles (tobacco, alcohol, lack of

nutrition or exercise)

19-1 Bacteria• Prokaryotes• Monera• Can be beneficial or disease-causing– Good: intestinal bacteria– Bad: strep throat, pneumonia

• Everywhere!

Identified by:• Shape- bacilli (rod), cocci (round), spirilla

(spiral)

• Cell walls- Gram +/- (peptidoglycan)• Movement- flagella, slime• Metabolic diversity- heterotrophs and

autotrophs (chemo- or photo-)

Bacteria Energy Production

• Respiration or fermentation (with or without O2)

• Obligate aerobes: needs O2 to live• Obligate anaerobes: cannot live with O2• Facultative anaerobes: can live with or

without O2

Bacteria Reproduction• Binary fission: (asexual) DNA is

replicated and the organism splits in half

• Conjugation: (sexual) genetic info is exchanged across a “bridge”

• Spore formation: haploid cell that can withstand hard conditions and form a new organisms when the time is right

Importance of Bacteria

• Decomposers- break things down• Nitrogen fixation- cycles N thru

atmosphere• Human uses: food, oil spills,

medicine, intestines

Treating Bacteria• Bacteria have homeostasis too! Change the

conditions to stop growth – Temp, salt, pH, etc.

• Sterilization (heat), disinfection (chemicals)• Antibiotics- kill bacteria or stop reproduction

19-2 Viruses• Categorized by what they infect:

– Plant, animal, bacteriophage

• Capsid- protein coat- signifies which host to infect (host must have a receptor)

• NOT alive- has genetic material but can’t repro on own

• Ex: flu virus, HIV

Virus Replication

• Lytic: enters host cell, copies itself continuously and bursts (lyses)

• Lysogenic: combines/replicates viral DNA with host DNA– Prophage: viral DNA embedded

within host DNA

Treating Viruses• Antibiotics WILL NOT work!• Prevention is key!• Vaccination: inject a weak form of a

virus in order to get the antibodies (immunity)

The Body’s Defense System• homeostasis= includes regulating

microbes• Lines of defense:• 1. physical barriers- block entry

(skin)• 2. inflammation- increased blood

flow• 3. immune system

Immune System• Recognizes the “bad guys”• Every bacteria/virus has antigens (proteins)• Immune system makes antibodies• Antibodies fight the antigens• Vaccines- shows antigens ahead of time-

allows body to create antibodies (immunity)

White Blood Cells (WBCs)

• Immune system MVP• 2 types:• 1. B cells: make antibodies

– Memory B cells

• 2. T cells:– Killer T cells: kill infected cells– Helper T cells*: help all other WBCs

When the immune system goes wrong…

• Allergic reactions- increase in system- produces histamines

• Autoimmune diseases- system attacks self• Immunodeficiency- decrease in system-

helper T cells destroyed (ex: AIDS)• inflammation- older people

Other Pathogens

• Protozoa- unicellular parasites• Algae/Dinoflagellates- produce toxins– ex: red tide

• Fungi- athletes foot, ringworm• Parasitic Worms- tapeworm

Viroids and Prions• Viroids: single stranded RNA

molecules enter infected cells• Prions: tiny protein particles enter

the brain and affect the nervous system- no DNA/RNA– Ex: mad cow disease