Viruses Unit 2

Viruses

• small size and genome

• acellular (nucleic acid and protein)

• DNA or RNA genome (either one, doesn’t have both)

• All obligate intracellular parasites. (needs a host to survive)

• 0.02-0.2um (20nm-200nm)

Genetics Virus

• dsDNA, ssDNA, dsRNA, or ssRNA genome

• Single chromosome or segmented (multiple)

• most contain linear chromosome(s) in capsid

Bacteria

• All dsDNA genome

• Most contain one circular chromosome

• May contain non-essential, extrachromosomal DNA= plasmids

Eukaryotic (Fungi, algae, protozoa, helminths) (host cells)

• All dsDNA genome

• All contain multiple linear chromosomes

• Chromosome number is characteristic for each species

Genome

• DNA or RNA

• ds or ss (double-stranded or single-stranded)

• single or segmented

Capsid Shape Viruses

• Icosahedral (Poliovirus, Herpes simplex)

• Helical (Rabie virus, tobacco mosaic virus)

• Complex (bacteriophage, varicella virus)

+/- envelope virus

• Nucleic acid + protein + (some) phospholipid bilayer envelope.

• A virus envelope is a lipid bilayer surrounding the viral capsid, derived from the host cell membrane, and studded with viral proteins that facilitate infection and immune evasion.

• REMEMBER: Cell membranes (also made of lipids) envelopes can help viruses enter cells called fusion.

Viral Replication

1. Attachment: viral receptors bind to host cell receptors

2. Entry (Penetration and uncoating): Endocytosis, naked and envelope viruses can use and Fusion, envelope viruses only.

3. Synthesis (DNA, RNA, Proteins): DNA replication, Transcription, and Translation (making protein)

4. Assembly: Structure of virus, capsid shape

5. Release: Cell Lysis (it explodes) or budding (only envelope viruses use budding to exit cell)

Varicella-Zoster Virus (VZV)

• Is a human herpesvirus that causes chickenpox upon initial infection and can reactivate later in life to cause shingles. (chickenpox/shingles)

• Lytic: Virus begins on skin

• Latent: Virus in nerve ganglia

Viral infection

• Occurs when a virus enters the body, hijacks healthy cells to replicate, and causes illness.

• Cytopathic Effects (CPE): Refers to the structural changes in host cells caused by viral infections, which can be critical for diagnosing viral diseases.

Binary Fission

1. A young cell

2. Chromosome is replicated, new and old chromosomes moved to different sides of cell.

3. proteins band forms in center of cell

4. septum formation begins

5. when septum is complete, cells are considered divided. Some species will separate completely as shown here, while others remain attached, forming chains or double, for example.

Bacterial growth Care

1. Lag phase: cells are preparing to divide; see little change in growth medium. Duration varies by organism and nutritional factors.

2. Log Phase: Exponential/logarithmic growth. Cells are the most metabolically active and divide at max rate. (growth>death)

3. Stationary Phase: Depletion of resources/increase in waste/ space gone. Growth slows, death increases. (growth=death)

4. Death Phase: Conditions for growth deteriorate (death>growth)

Psychrophiles

• -10 C to 10 C

• -20 C Household freezer

• 4 C household fridge

Mesophiles

• 10 C to 40 C

• 25 C Room temperature

• 37 C Human Body temperature

Thermophiles

• 40 C to 80 C

• 65 C Human Enzymes denatured

Extreme Thermophiles

• 80 C to 100 C

• 100 C Water Boils

Psychotropic Bacteria

• group of microorganisms that can grow at low temperature

• psychrotrophs (-5 C to 35 C)

if a protein starts to denature (unfolded) is due to:

1. Changes in pH

2. Changes in Salt concentration

3. Changes in temperature

4. Presence of reducing agents (disrupt s-s bond)

Plasmolysis

A biological process where the cytoplasm of a cell shrinks away from the cell wall due to the loss of water, often caused by osmosis. In a hypertonic solution, water moves out of the cell, leading to plasmolysis and cell death. This process is significant in understanding how microorganisms interact with their environment and how salt concentrations affect microbial growth.

Transmissible Spongiform Encephalopathies (TSEs)

group of rare brain diseases that cause the brain to become damaged and 'spongy,' and they are caused by abnormal proteins called prions.

Gene

A length of DNA chromosomes that provide information for a particular cell function. It contains the necessary code to make either a protein or an RNA molecule.

Cytopathic Effects (CPE)

• Refers to the structural changes in host cells caused by viral infections, which can be critical for diagnosing viral diseases

Human Prion Diseases

Creutzfeldt-Jakob Disease (CJD)

Creutzfeldt-Jakob Disease (CJD)

A rare degenerative brain disorder caused by abnormal proteins called prions, leading to rapid cognitive decline and ultimately death.

Animal Prion Diseases

Scrapie

Scrapie

a fatal, degenerative prion disease that affects the nervous system of sheep and goats, caused by abnormal misfolded proteins that induce neurodegeneration.

Obligate Aerobes

• Require oxygen (for metabolism) and are catalase positive

• Have enzymes to detoxify O2-

• Dense growth on top

Obligate Anaerobes

• Cannot tolerate oxygen and are catalase-negative

• O2 is lethal-no enzymes to detoxify

• Dense growth on bottom

Facultative Anaerobes

• Growth best with oxygen but can also grow anaerobically (growth without oxygen)

• Have enzymes to break down toxic O2-

• They are catalase positive

•  dense growth at the surface and turbidity throughout the rest of the tube.

Aerotolerant anaerobes

• Tolerate but do not use oxygen.

• They are catalase positive

• Do not use O2 in cell respiration

• Can partially break down toxic oxygen compounds

• growth equally spread out in the tube

Microaerophiles

• Use small amounts of oxygen

• they produce small amounts of catalase

• require small amounts of O2 but do not grow at atmospheric O2 levels.

• Some enzymes to break down toxic O2-

Acidophile

• growth pH 1-5

• Fungal growth on fruit

Alkaliphile

• Growth pH 9 or more

• Mountain water system

Halophile

• High Salt or Ion liking Organisms

• Bacterial growth in high salt lake

Transcription

DNA to mRNA

Translation

mRNA to protein

Silent Mutation

No effect on phenotype

Missense Mutation

Small or medium effect on phenotype (sickle cells)

Nonsense Mutation

Large effect on phenotype, stops the phenotype

Frameshift

Large effect on phenotype, changes all the phenotype adding a letter to it.

Insertion

Adds to the DNA sequence

Deletion

takes off something from the DNA sequence

Mutation rate

Probability of a particular mutation as a function of time

Mutagens

Physical or chemical agents that can cause mutations

Physical

Radiation (x-rays, UV light)

Chemical

Formaldehyde, ethylene oxide gas, nitrous acid, ethidium bromide, muster gas.

Environment

Drugs, cosmetics, food additives, pesticides, insdustrial compounds.

DNA polymerase proofreading

Can repair any mismatched bases

Photoreactivation by photolyase

DNA repair mechanism that utilizes visible light to restore DNA damage caused by ultraviolet (UV) radiation.

Nucleotide Excision Repair (NER)

It’s a way your cells fix damaged DNA by cutting out a bad section and replacing it.

Conjugation

Unidirectional transfer of DNA through direct cell to cell contact. (From donor to recipient)

Direct (a donor)

Transformation

Unidirectional transfer of extracellular DNA into cells.

Undirect (not a donor)

Transduction

Transfer of DNA from one bacterium (donor) to another (recipient) through bacteriophage “carrier”

Undirect (not a donor)

Sterilization

Complete removal or destruction of all microbial life (used on inanimate objects)

Disinfection

Removal or destruction of pathogens from non-living surfaces

Antisepsis

Removal or destruction of pathogens from living surfaces.

Microbiocidal

Agents that kill microbes

Micro biostatic

Agents that reduce microbe numbers or inhibit growth of microbes

Detergents

binds lipids → pull membranes apart → cidal

bar soap, hand soap, dish soap

soaps or detergents; amphipathic

Quats

denatures protein + disrupt membranes → cidal

benzalkonium chloride, cetylpyridinium chloride

quatemary ammonium compounds; amphipathic

Phenolics

phenol-derived compounds

household disinfectant

denature proteins + disrupt membranes → cidal

Halogens

reactive elements

chlorine, iodine, fluorine

denature proteins → cidal

Chlorine

dissolves in water, strong disinfectant

bleach, pool chlorine

denatures proteins → cidal

Iodine

Skin antiseptic

iodine solution, betadine

denatures protein → cidal

Fluorine

low concentration antimicrobial

fluoride in toothpaste

denature proteins → cidal

Alcohols

rapid- acting antiseptics

ethanol, isopropanol

denatures proteins + damage membranes → cidal

Aldehydes

strong disinfectants/sterilants

Glutaraldehyde (2%)

denature proteins + DNA → cidal

Hydrogen Peroxide

reactive oxygen compound

H2O2 (3% 35%)

Produces toxic oxygen radicals → damages cells → cidal

Ethylene Oxide

Gas sterilant for heat-sensitive items

sterilizing medical equipment

denatures protein + DNA → cidal

Heavy Metals

metal ions bind proteins

silver, nitrate, copper, zinc

denatures proteins → cidal