Viruses and BacteriaChapters 19 & 27

Bacteria Small Less organized Viruses Even smaller Simpler Lacking structure Metabolic

machinery

Tobacco mosaic virus

Viral structure Protein coat surrounds nucleic

acids Nucleic acid (DNA or RNA) Linear, circular, single or double

stranded

Viral structure RNA genome: Flu, measles, AIDS, SARS DNA genome: Herpes, small pox, mono, hepatitis

B

Helical Rodlike in appearance Isometric Spherical shaped

Viral structure

Virus

Virus

Bacteriophages

Bacteriophages

Viral structure Capsid: Protein sheath surrounds nucleic acid core Few different proteins-repeated Envelope: Surrounds the capsid Made of proteins, lipids, and glycoproteins Derived from host cell’s membrane

Virus host range All organisms are affected by viruses Host range: Cells suitable for a virus Viruses replicate in only a few types of

cells Examples: HIV affects certain WBC Hepatitis affects the liver Common cold virus infect lining of

upper respiratory tract

Virus host range Rabies virus has a broad host

range Infects several species Some viruses lay dormant for

years HIV or herpes Some do not cause any problems

Viral replication Not considered organisms Unable to reproduce

independently Lack ribosomes Enzymes for protein synthesis Obligate intracellular parasites

General viral replication Enter host cells Reproduce Viruses replicate Host’s genetic machinery Their genes are translated into

proteins

Transcriptionand manufactureof capsid proteins

Self-assembly of new virus particles and their exit from the cell

Entry anduncoating

Fig. 19-4VIRUS1

2

3

DNA

Capsid

4

Replication

HOST CELL

Viral DNA

mRNA

Capsidproteins

Viral DNA

Viral replication Phage replication 1. Lytic cycle 2. Lysogenic cycle

Viral replication Lytic cycle: Virus kills infected host cell when

replicating Virulent virus: Virus multiplies within the host Eventually rupturing the host

Bacteriophages

Virulent viruses

Lysogenic viruses Incorporate viral nucleic acid into

genome of the host cell Does not kill host Prophage: Viral nucleic acid is part of the

host genome

Lysogenic Virus Transformation: Genetic alteration of a cell’s

genome by introducing foreign DNA

Phage conversion: Foreign DNA is from the virus

Lysogenic Virus Prophage genes can make toxins Makes bacteria more serious Diphtheria, botulism and scarlet

fever

Scarlet fever

Animal Virus Replication Viruses cause illnesses in animals Classified according to genome RNA or DNA Many have envelopes

(glycoproteins)

Animal Virus Replication Bind to cell membrane at receptors Enter cell Viral RNA used as template Makes more viral RNA Combines with capsid Exits host (buds) Encased in envelope derived from host

Fig. 19-7

Capsid

RNA

Envelope (withglycoproteins)

Capsid and viral genomeenter the cell

HOST CELL

Viral genome (RNA)

Template

mRNA

ER

Glyco-proteins

Capsidproteins Copy of

genome (RNA)

New virus

Influenza

Varicella virus

Shingles

Epstein Barr virus

Polio virus

HIV

HIV Retrovirus (“backwards”) Transcribes an RNA template into

a DNA Reverse transcriptase Provirus New integrated viral DNA Does not leave host

Fig. 19-8aGlycoprotein

Reversetranscriptase HIV

RNA (twoidenticalstrands)

Capsid

Viral envelope

HOST CELL

Reversetranscriptase

Viral RNA

RNA-DNAhybrid

DNA

NUCLEUS

Provirus

ChromosomalDNA

RNA genomefor thenext viralgeneration

mRNA

New virus

HIV Human immunodeficiency virus 1981 T-4 cells (CD4 cells) Lymphocytes Unable to fight off other diseases Maybe asymptomatic for 10 years AIDS (acquired immunodeficiency

syndrome)

Fig. 19-8b

HIVMembrane ofwhite blood cell

HIV entering a cell

0.25 µm

New HIV leaving a cell

HIV Symptoms Fatigue Weight loss Lymphadenopathy (swollen lymph

glands) Neurological disease

HIV Opportunistic infections Candidiasis (yeast) Pneumocystis carinii pneumonia Kaposi sarcoma TB

HIV

HIV Transmission Blood Transfusion or shared needles Intercourse Mother to fetus

Hepatitis B Infection of the liver Jaundice Decreased liver function Contact through bodily fluids

Ebola virus

Ebola virus Hemorrhagic fever Africa Fever, joint pain Internal & external bleeding

SARS (severe acute respiratory syndrome)

SARS Respiratory infection Coronavirus 2003 China

Vaccines Inactive version of pathogen Causes immune system to form

antibodies Hepatitis MMR, Polio, Rotavirus Smallpox Diphtheria (Td)

Emerging virus Virus that starts in one organism Passes on to another Disease progresses SARS, Ebola and HIV West Nile

Emerging virus Mutations Increased transmission (global) Other animals Bats SARS Chickens Avain flu Epidemics Pandemics

Virus Viruses appear to cause certain human

cancers. Hepatitis B virus associated with liver cancer. Epstein-Barr virus Linked to several types of cancer in parts of

Africa, notably Burkitt’s lymphoma. Papilloma viruses are associated with cervical

cancers. HTLV-1 retrovirus causes a type of adult

leukemia.

Plant Viruses Horizontal transmittance Viruses enter damaged plants Vertical transmittance Inherits a virus from a parent Travel easily through the plant Brown spots Stunt growth

Viroids Small circular RNA molecules Replicate in host plants Stunt growth of plants

Prions

Infectious proteins Infect animals Neurological disease (encephalopathy) Mad cow disease

Prokaryotes

Prokaryotes Resemble first organisms on earth Most abundant (over 5000 kinds) Understanding prokaryotes help

understand disease, genetics and ecology

Bacteria structure Shapes Bacilli: rod shaped Cocci: spheres Spirochetes: spiral shaped Bacilli & cocci - form colonies Spirochetes swim alone

Prokaryote structure Cell wall Maintains shape Keeps cell from swelling &

rupturing Peptidoglycan: Polysaccharides with polypeptide

links

Gram staining helps classify bacteria

Gram + (purple color) Simpler Thick complex network of

Peptidoglycan Around the outside of the cell

Prokaryote structure

Prokaryote structure Gram – (red color) Peptidoglycan is a thin layer Sandwiched between two plasma

membrane layers Harder to treat with antibiotics

that affect cell wall synthesis

Cell wall

Gram stain

Gram stain

Prokaryote structure Internal structure Internal membranes Cellular respiration Plasmids Small independently replicating

circles of DNA

Plasmid

Flagella Made of proteins Anchored to cell wall Spin-pull bacteria through water

Prokaryote structure

Prokaryote structure Pili Hair like structure Located on some prokaryotes Help bacteria attach to structures

Prokaryote structure Ribosomes Only organelle Smaller than eukaryotes Tetracycline and chloramphenicol

are antibiotics Affect bacteria ribosomes Kills

Prokaryote structure Endospores Thick-walled structure Surrounds genome & a small part

of the cytoplasm Protects in harsh environments Develops new generations later

Variation Mutations Genetic recombination CDC

Variation Mutations Rapidly divide UV, radiation, chemicals enhance

mutations Change to respond to

environment Resistance to antibiotics

Variation Transformation Foreign DNA is added to the bacterial

DNA Transduction Phages carry genetic information from

cell to cell. Conjugation Genetic info is transferred between 2

bacteria that are joined

Staphylococcus aureus

Staphylococcus aureus

Streptococcus

Bacillus anthracis (Anthrax)

Lyme disease

Tuberculosis Mycobacterium tubericulosis Respiratory disease Increase in incidence due to AIDS Increased incidence of drug

resistance TB skin test (PPD)

Prokaryotes Benefits Chemical recycling Decomposers Fixation Photosynthesis fix CO2

Nitrogen fixation Reduce N2 (from atmosphere) to NH3

Prokaryotes Symbiotic relationships Plants give bacteria sugars Bacteria give plants usable nitrogen Cows-bacteria in gut Helps digest cellulose Humans-E. Coli in large intestine Produces vit B12 & K

Nutrition Photoautotrophs Sun for energy CO2 for carbon Chemoautotrophs Energy from ammonia, sulfur or

iron CO2 for carbon

Nutrition Photoheterotrophs Sun for energy Organic molecules for source of

carbon Chemoheterotrophs Obtain carbon & energy from

organic molecules Decomposers and most pathogens

Prokaryotes Oldest form of live (3.5 billion

years ago) 1 billion years before eukaryotes 1970-1980’s two groups Archaebacteria (Archaea) Bacteria

Prokaryotes Large diversity among themselves Based on many criteria such as

amino acid sequences Refer to book to see differences