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Chapter 24: Viruses
Objectives:• Summarize the discovery of viruses• Describe why viruses are not
considered living organisms• Describe the basic structure of viruses• Compare the lytic and lysogenic cycles
of virus replication• Summarize the origin of viruses
Virus Structure-vary in shape and size
All viruses contain two main parts:1) Nucleic Acid (Genome) – Either DNA or RNA2) Capsid – protein coat or lipid protein coat (many different shapes)
– Helical – Tobacco Mosaic Virus (TMV), Rabies, measles– Icosohedreon – Adenovirus, Herpes Simplex, Chicken Pox, Polio– Spherical – Influenza Virus
3) Envelope – bilipid membrane that surrounds the capsid (only some viruses)
– Formed from nuclear membrane or cell membrane as it leave the host cell
– Proteins in the envelope helps new viruses recognize host cell.Examples: Influenza, chicken pox (varicola), HIV
Function of Viruses
1) Cause Disease by infecting the host cell
2) Used in Genetic Research and biotechnology
Characteristics of Viruses
Virus are nonliving!– Are not made of cells– Do not have organelles or cytoplasm– Can’t carry out metabolic processes such as
metabolism and homeostasis– Do not grow through Cell Division– Can’t reproduce outside their host cell
(Need host cells structures to reproduce)
Wendell Stanley was the first scientist to crystallize a virus. This is evidence that viruses are not made of cells and are not alive.
Classification of VirusesA. Genetic Material:
1) RNA or DNA2) Single Stranded or Double Stranded3) Linear or Circular Genetic Information
B. Capsid:1)Shape2)Presence or absence of an envelopeExample: SARS – RNA, Single Stranded, Linear, lollipop-shaped capsid and enveloped (chart pg485)
Classification cont.
- Different viruses infect bacteria, plant and animal hosts
- due to receptor site forming to specific proteins on cell wall or membrane
Bacteriophages – viruses that infect bacteria
Obligate intracellular parasites(Viruses)
Viruses replicate only by using the host cellsenzymes and organelles to make moreviruses. Protein synthesis is controlled by the
viral genome and the host cell becomes a virus
makingfactory.
Protein Synthesis review1) Transcription: DNA -> mRNA2) Translation: mRNA -> proteins
Two methods:1) vDNA->mRNA –> make new viruses
(in cytoplasm)
2) DNA – Provirus – (Gets incorporated into Host Cell’s DNA) – Makes new viruses
Replication in DNA viruses
Replication in DNA Viruses
Method 1
1. Virus enters the host cells cytoplasm and takes control of the host cells protein synthesis pathway
2. Enzymes transcribe mRNA from the viral DNA
3.Host ribosomes translate Viral mRNA into viral proteins and enzymes replicate the viral DNA
4.New viral particles are assembled (Capsids and nucleic acids)
Replication in DNA Viruses
Method 21) Viral DNA is injected into the host
cell2) Viral DNA moves into the nucleus
and becomes incorporated into the host cells DNA as a provirus
3) Virus takes over the cell and makes newe viruses as a provirus
Replication in RNA viruses
RNA VirusesRNA 1) The vRNA serves right away as mRNA and
then is translated into proteins (New Viruses)2) Viral RNA is transcribed into mRNA and then is
translated into proteins and new viruses
Retro RNA VirusesContain Reverse Transcriptase which uses RNAas a template to create DNA, which is theninserted into the host cells DNA
Lytic Cycle vs. Lysogenic Cycle Reproduction of viruses
Lytic Cycle: Reproduction of Virulent Virus• Destroy the cell they infectStages:1) Adsorption2) Penetration3) Replication4) Maturation (Assembly)5) Release
Lysogenic Cycle: Reproduction of Temperate Virus• Lays dormant in the host cell before it destroys it• When triggered will go into the lytic cycle
Lytic Cycle – followed when virus is virulent (active)
1. ADSORPTION- virus particle attaches to a host cell.
2. ENTRYThe particle injects its genetic instructions (DNA or RNA) into the hostInjected genetic material ‘hi-jacks’ the cell’s machinery and recruits the host’s enzymes.
3. REPLICATION Enzymes make parts for the new virus particles
4. ASSEMBLY -new particles assemble the parts into new viruses
5. RELEASE -Cell explodes (lyses) releasing new viruses which search for a new host cell
Lysogenic Cycle - followed when virus is in latent or temperate state
The steps of the lysogenic cycle:1) Viral nucleic acid enters cell 2) Viral nucleic acid attaches to host cell nucleic acid, creating a prophage 3) Host cell enzyme copies viral nucleic acid4) Cell divides, and virus nucleic acid is in daughter cells 5) At any moment when the virus is "triggered", the viral nucleic acid detaches from the host cell's DNA and enters stage 2 of the lytic cycle.
Common symptoms that appear to "trigger" the viral DNA are hormones, high stress levels (adrenaline), and free energy within the infected cell.
Viral Diseases
• Vector – intermediate host that transfers a pathogen or parasite to another organism– Ex: humans, mosquitos, ticks, fleas.
• Human viral diseases - chickenpox, shingles, viral hepatitis, AIDS, etc…
• Protease inhibitors – drugs that block virus reproduction
• Oncogenes – viral genes that cause cancer by messing with cell division checkpoints
• Proto-oncogene – controls cell growth
Prevention and Treatment
Vaccine – weakened sample of virus or virus parts which triggers your body’s immune system
Attenuated virus – weakened virus that cannot cause disease
Inactivated virus – unable to replicate in host
Natural immunity - antibodies are specialized proteins formed in B cells of immune system
- antibodies block attachment sites of viruses
http://www.pbs.org/wgbh/nova/bioterror/vaccines.html
Disease causing particles even smaller than viruses
Viroids
– short single strand of RNA without a capsid
- interfere with cell processes and cause new viroids to be made
- are found only in plants
Prions
- glycoprotein particle
- able to reproduce in mammalian cells
- Prion diseases: mad cow disease; Creutzfeldt-Jakob disease & kuru (degenerative nerve diseases of the brain)
Genetic engineering
Genetic engineers use viruses to carry desirable genes from one cell to another
Improved agriculture – herbicide tolerant soybeans; rot resistant tomatoes; fast growing fish; meatier chickens
Correcting genetic disorders - experimental; only done in animal with success; not allowed in humans
Pest control – insert genes of plants that create chemical to resist insects into crop plants such as corn
Manufacturing of medicine - human insulin &clotting factors 8 & 9
http://www.pbs.org/wgbh/harvest/engineer/transgen.html
Bacteria Objectives
• Describe the common methods used to identify bacteria
• Identify 3 Archael groups, 5 bacterial groups
Characteristics of Domain Archaea
• Prokaryotic cells• Unicellular• Cell Walls do not contain peptidoglycan• Cell Membranes contain other types of
hydrocarbons in addition to fatty acids• rRNA shows they are more like Eukaryotes• Contain Introns in their DNA• Heterotrophs and Autotrophic Chemotrophs
III. Kingdom Archaebacteria – the most primitive organisms
(archae = ancient)
live in harsh conditions including
- acidic hot springs
- very salty water
- environments with no oxygen
- near undersea volcanic vents
- different from other bacteria
- cell wall composition (pseudomurien)
- Cell membrane
- rRNA
Phyla 1: Methanogens:
- obligate anaerobes (oxygen kills them)
- metabolizes hydrogen gas and CO2 to methane gas
- live in the bottom of swamps, sewage, and inside the digestive tracks of many animals
Helps
- grazing animals process cellulose
- termites process wood
- in industry to treat sewage, purify water.
Phyla 2: Thermoacidiphiles
- can live in extremely hot and acidic water or deep in the ocean near hydrothermal vents in the ocean floor
- Ex: hot springs of Yellowstone Natl Park, ice of Iceland
- chemotrophs = process sulfur compounds to produce energy
Phyla 3: Halophiles:
- live in extremely salty (saline) environments,
ex: Dead Sea
- use the salt to generate ATP.
IV. Kingdom Eubacteria (Eu = true) “Germs”
• Found almost every where on Earth
• Characteristics: – peptidoglycan in cell wall – may have outer covering of glycocalyx
(sticky sugars) that keeps cells from drying out
1) Composition of the cell wall – identified with Gram staining technique
Gram positive – stains purple – thick outer layer of peptidoglycan
Gram negative – stains pink/red – lipid layer covering thin layer of peptidoglycan
Characteristics used for classifying:
2. Method of getting energy
autotroph – chemotroph or phototroph
heterotroph - free living or parasite
saprophytes – break down other organisms into nutrients
3) Type of metabolism
obligate aerobe – must have oxygen; dies without it
obligate anaerobe – dies if exposed to oxygen; processes ATP by fermentation
facultative anaerobe – uses oxygen when it can but doesn’t need it
4) Shape of bacterial cells
round coccus (cocci)
rod shaped bacillus (bacilli)
spiral shaped spirillus
Domain Bacteria
• Shapes (cont’d)– Sphere-shaped
• Called cocci– In chains, called streptococci– In grapelike clusters called
staphylococci
5) How cells grow (prefixes are added to coccus)
a) staphylo – cells grow in clumps
b) strepto - cells grow in chains
c) diplo - cells grow in pairs
6) Motility – movement
a) flagellated – move with flagellum or flagella
b) slime layer allows gliding
c) spirochete - cork-screw rotation
Reproduction – 2 types
Asexual - most common
Binary fission – chromosome replicates cytoplasm, membrane and wall divide into two new cells
Sexual – exchanges genetic info giving variation
a) conjugation – two bacterial cells get side by side and hair-like “pili” connect to provide tube to pass info
b) transformation – living bacterial cell absorbs dead related bacterial DNA and incorporates it into genome
c) transduction – a virus transfers DNA from one bacterium to another
Endospores
- special dehydrated cells formed by some bacteria to survive bad living conditions
- ex: high temperatures, harsh chemicals, radiation, lack of moisture
- dormant as endospore
- when conditions improve cell is revived
- ex. Anthrax
Gram positive
- thick outer layer of peptidoglycan (stains purple)
- may be beneficial or cause disease
- may be used to make yogurt, pickles, and buttermilk
- or to make medicines using biotechnology
Ex. Strep throat ; staph infections; tuberculosis
Phyla groups:
Phyla groups:
Gram negative taxa
A) Proteobacteria
• may have symbiotic lifestyle
• ex. Nitrogen fixing bacteria inside legumes (peas, beans, alfalfa, and clover)
• In human and animal intestines, help break down foods (enteric bacteria)
• Some in soil or fresh water and process iron and other minerals as an energy source (chemotrophs)
C) Cyanobacteria
• Gram-negative • contain chlorophyll (but not
chloroplasts), perform a plant-like photosynthesis releasing oxygen as a by-product
• Ex. Filamentous bacteria (grow in stagnant water)
D) Spirochetes
- gram negative
- spiral shaped
E) Chlamydia (no peptidoglycan)
- gram negative
- round shape
- are parasites to animal cells
Bacteria and Disease
Toxins – poisons produced by some bacteria
1) endotoxin - created inside the bacterial cell and released as the cell dies; usually Gram negative
bacteria
2) exotoxin – secreted by living bacterial cell into surrounding environment (host); usually Gram-positive bacteria
3) enzymes – some bacteria secrete enzymes that break down the surrounding tissue and damage it
Pathogens – bacteria that cause disease
Antibiotics – chemicals that kill bacteria by interfering with cellular functions such as protein or cell wall synthesis
Gram positive bacteria that cause disease need different antibiotics than Gram negative bacteria
Broad spectrum antibiotics affect a wide variety of bacteria within the taxa
Antibiotic Resistance in Bacteria
• most of the population dies, some survive
• Survivors reproduce and are no longer affected by antibiotic
• Occurs when antibiotics are overused or used improperly
Vocabulary list for honors
Taxonomy binomial nomenclature phylogeny
Dichotomous key phylogenetic chart binary fission
Virus capsid antibiotics
Envelope lytic cycle endospore
Lysogenic cycle vaccine conjugation
Natural immunity morphology pathogen
Viroids prions tranformation
Methanogens thermoacidiphiles transduction
Halophiles obligate aerobes saprophyte
Obligate anaerobes facultative anaerobes endotoxin
Chemotrophs phototrophs exotoxin
V. Kingdom Protista
Basic Characteristics: eukaryotes; most are unicellular; most are heterotrophs
Habitats: aquatic habitats or moist soil
Characteristics used for classification
•how they obtain energy – heterotrophic; autotrophic; saprophytic
•number of cells – unicellular or multicellular
•Motility – ability to move and movement structures
Reproduction
Asexual (most common): Binary fission(unicellular)
Multiple fission (divide into more than 2 cells)
Sexual: Conjugation (genetic information is swapped and stored in a 2nd nucleus)
Protozoans – “animal-like” protists
Characteristics: unicellular; heterotrophs
Phlya Groups:
Sarcodinians – feed and move with pseudopods (streaming cytoplasm) freshwater- amoebas; marine – forminiferans and radiolarians
Ciliaphorans – feed and move using cilia (small whisker –like structures)
Ex. Paramecium, stentor
Zooflagellates (Sarcomastigophora)- move with one or more flagella
May be free-living or parasitic and cause disease
Ex. Trichonympha, trypanosoma, giardia
Sporazoans (Apicomplexa) – no motility structures
All animal parasites; spore-formers; have complex life cycles with two or more host organisms
Ex. Plasmodium
Algae – “plant-like” protists
Characteristics: unicellular or multicellular
All are phototrophs with chloroplasts and pigments
Unicellular phyla are grouped together under the heading phytoplankton
Phlya Groups:
Dinoflagellates (Dinoflagellata)
Unicellular with two unequal sized flagella; marine;some species exhibit bioluminescence (light producing) others produce toxins (Gonyaulax) that cause “red tide”
Euglenophytes (Euglenophyta) have two flagella no cell wall;cell membrane has flexible pellicle; all freshwater habitat; Ex. Euglena
Diatoms (Bacillariophyta) have 2 sided cell walls made of silica (glass) that fit into each other like a petri dish; may have circular, triangular (mostly marine)or rectangular (mostly freshwater) body shapes
Gold Algae (Chrysophyta) contain gold pigments(carotenoids) as well as chlorophyll; most unicellular but some species form colonies
Green algae (Chlorophyta)
contain chlorophyll a & b; have cell walls composed of cellulose;unicellular, colonial, and multicellular species; freshwater and marine habitats as well as moist land
Ex. Ulva (sea lettuce), volvox, spirogyra
Red algae ( Rhodophyta)
contain red pigment as well as chlorophyll; most species tropical marine; all multicellular; may live in deep water habitats because red pigment helps absorb red lower energy light ex. seaweeds
Slime Molds – “Fungi-like” protists
Characteristics: all saprophytes; live in moist soil or moist organic matter
plasmodial slime molds - 2 stage life cycle
feeding stage – (plasmodium) very large digesting mass of cytoplasm that creeps along the decaying material
reproducing stage (fruiting body) stalked structures that hold haploid spores which fuse when living conditions are good or stay dormant if living conditions are bad
Cellular slime molds – 2 stages
feeding – single haploid cells that creep along like an ameoba;
pseudoplasmodium – matting of individual cells in a colony to share nutrients during bad living conditions; they eventually form fruiting bodies that produce more haploid spores which become individual organisms
Water molds
Grow in filaments called hyphae which break down organic matter
Some are parasitic to animals like fish or plants like blight on potatoes
Genetic engineering
Genetic engineers use viruses to carry desirable genes from one cell to another
Examples: improved agriculture; correcting genetic disorders; pest control; manufacturing of medicine
http://www.pbs.org/inthebalance/terrorism/virus-or-bacteria.html
Fungi Kingdom
· Eukaryotes
· Heterotrophic:
- most saprophytes
- some parasites
· Most multicellular;
one is unicellular
· Most sessile
Structure:
• Cell walls made of chitin (tough, flexible carbohydrate)
Multicellular fungi are made up of hyphae
(small tubules filled with cytoplasm and nuclei)
Hyphae form an interconnected mass called the mycelium and cytoplasm of all cells flow between the hyphae
Hyphae may have walls called septa which still have holes for the cytoplasm to flow through
Hyphae produce enzymes that are secreted into the environment and then nutrients are reabsorbed through hyphae
Asexual Reproduction:
3 ways depending on structure
• Multi-cellular –regeneration; (single celled- mitosis & cell division)
Budding - new organism forms from small piece of mycelium
Asexual spore formation from fruiting bodies
Spores spread by wind,
water, animals (*most common)
Sexual reproduction – positive and negative hyphae fuse together to form spores
Sexual reproduction is possible in the common molds, club fungi, and sac fungi only
Classification:
Classified by structures used for reproduction
Group names are divisions not phyla (used to be
classified as plants):
Common molds (Zygomycota)
Club fungi (Basidiomycota)
Sac Fungi ( Ascomycota)
Imperfect fungi (deuteronomycota)
1. Common molds (Zygomycota)
No septa in hyphae
Asexual reproduction - most common
Sexual reproduction spores formed in sporangium
Examples: bread mold, fruit molds
Club fungi (Basidiomycota)
Reproduce sexually by producing spores in basidium
Located in gills under the cap
Examples: mushrooms, bracket fungi, shelf fungi,
Puffballs
2. Sac Fungi ( Ascomycota)
reproduce sexually by means of ascus
bulb like projections that form from the hyphae
examples: yeasts, truffles, morels, powdery mildews
Imperfect fungi (deuteronomycota)
no sexual reproduction; asexual only
examples: the fungus that cause ringworm, athete’s foot, nail infections
Impact:
environment - help to eat up or break down dead organisms
symbiosis
a) lichen live with cyanobacteria; fungus offers protection, cyanobacteria offer food
b)plant growth – fungus grows on root tips of some plants; plants get benefit of all ready broken down nutrients as well as extra support; fungus get nutrition from plant
human
help as food sources, medicines (penicillin), food processing, genetic engineering of proteins
disease
destroy plants and trees
property damage to wood structures
human infection