Viruses

Nonliving particles that carry genetic information

        Capable of replicating DNA only within host cell

Named after the disease they cause or the organ they infect

Bacteriophage- virus that infects bacteria

Adenovirus- infects the adnoid tissues

HIV- Human Immunodeficiency Virus

Structure of Virus

        Carry genetic material (DNA or RNA) and structural proteins

                that protect nucleic acids (capsid)

        May have envelope- around capsid, composed of lipids

        Inner core of DNA/RNA carries instructions to copy virus,

can only be done using host cell machinery

        Genomes are very small- very few genes

The only goal of a virus is to make more viruses-disease=side effect

Viruses are specific to the cells they infect

        Proteins in capsid recognize receptor proteins in host

plasma membrane- lock and key

        Binding and attachment allow the virus to enter the host

        Virus can then hijack host replication/transcription/

translation machinery to make more viruses

2 Life Cycles of Viruses

        Lytic- gets into host, makes more viruses, lyses host

        Lysogenic- gets into host, integrates into genome

(provirus) lays dormant or produces more viruses

in a manner that does not kill the host (exocytosis)

or goes dormant then gets activated

                Cold sores- herpes virus

                Chicken pox/shingles- varicella zoster

Retroviruses: HIV

        RNA virus

        In order to integrate into host genome, viral RNA must

be changed into DNA- reverse transcriptase

        Infects white blood cells- immune system

        Constant stream of virus production

        Eventually WBCs get killed off during lytic cycle

        Infected individual susceptible to infection

Viruses have been associated with cancer

        Viruses can convert normal cells into tumor cells

                retroviruses

                papilloma viruses

                Hepatitis B virus

Emerging Viruses

        Viruses that may have just developed, mutated or come in

contact with humans for the first time

        Because of lack of prior contact, tend to cause severe disease

Ebola

Marburg

Lassa- hemorrhagic diseases

SARS

        Severe Acute Respiratory Syndrome

        Causes pneumonia like symptoms

                Fever, headache, discomfort, cough, difficulty breathing

        Person to person contact    

        Corona virus

Bacteria

Archaebacteria- live in extreme conditions

Eubacteria- the bacteria you know about

                Heterotrophic or autotrophic

                Disease causing bacteria are heterotrophs

                Autotrophs can be chemosynthetic or photosynthetic

Structure of a bacterium

        1 circular chromosome

        Plasma membrane selective permeability

        Cell wall target of many antibiotics

        Plasmids- small circular pieces of DNA, carry ~ 3 genes

        Capsule- some bacteria- made of glycoproteins

                Bacteria with capsule more likely to cause disease

        Pili and flagella- locomotion and cellular interactions

Gram Positive Bacteria

        Very thick cell wall

Gram Negative Bacteria

        Thinner cell wall and have an outer membrane

Bacteria can be one of 3 shapes

        Coccus- spherical

        Rod

        Spiral

Reproduce by binary fission

        Cell copies itself by doubling material then divides in half

        Daughter is clone (genetically identical) of mother

Genetic recombination occurs by

        Conjugation- bacterial sex

        Mutation

        Transformation- bacteria takes up random DNA

                Vital for biotechnology

Bacteria can live in a variety of environments

        Aerobic

        Anaerobic

Have many adaptations to enhance survival

        Endospores- response to adverse conditions, dormant phase

        Toxins- bacterial proteins that are poisonous to host- can help

make food available to the bacteria, aid life cycle,

transmission

                Botulinum toxin

                Tetanus toxin

                Cholera toxin/ heat labile enterotoxin

Importance of bacteria

        Nitrogen fixation

        Decomposition

        Fermentation of foods (cheese, pickle, yogurt, sauerkraut)

        Disease

Plasmids

Small circular DNA

Can be replicated independent of chromosome

Can be transmitted from bacterium to bacterium