Viruses Characteristics of Viruses Viruses are NOT alive

Viruses

Characteristics of Viruses • • Viruses are NOT alive They do not have a cytoplasm or organelles Cannot carry out cellular functions They do not divide (reproduce) outside host cell

Viral Size and Structure • Viruses are super small! • The shape of a virus is the result of its genome and protein coat – capsid • Some viruses have a bilipid membrane called an envelope that surrounds the capsid

Classification of Viruses • Viruses can be classified by: – if the have RNA or DNA – If genome is single stranded or double stranded – The nature of their capsid – Presence or absence of envelope Example: SARS is a single-stranded, linear RNA and envelope virus with lollipop-shaped proteins that make the envelope look like a crown

Viral Replication • Viruses need a host cell! • They can spread from host to host through the air, water, food, or bodily fluids (yuck) • Viruses infect both prokaryotes AND eukaryotes

Viral Replication • Viruses need to recognize a proper host cell before they can infect it. • Viruses are obligate intercellular parasites – they replicate only by using host cell enzymes and organelles to make more viruses

Viral Replication Pathway “lock-and-key” fit between proteins and receptor molecules of host cells A viral infection begins when a virus enters the host cell. The viral genome takes over the metabolic machinery of the cell and makes new viruses

Replication in DNA Viruses • When DNA viruses enter a host cell, it makes m. RNA, which is the template for making proteins • Other DNA viruses insert their DNA into the host cell’s chromosome – This inserted viral DNA is known as a provirus – The host cell’s enzymes then transcribe the provirus into m. RNA and create viral proteins

Replication in RNA Viruses • The genome of some RNA viruses enter host cells and acts as m. RNA • They are then translated into new viral proteins! Yikes! • Retroviruses contain the enzyme reverse transcriptase in addition to RNA

Retroviruses • Reverse transcriptase uses RNA as a template to make DNA which then inserts into the host cell’s genome. • Reverse transcriptase reverses the normal process of making proteins https: //www. youtube. com/watch? v=73 Qarmy. H Htw

Replication in Viruses That Infect Prokaryotes • Bacteriophages (phages) are viruses that infect bacteria

The Lytic Cycle • During the lytic cycle, a virus invades a host cell, produces new viruses, and ruptures (lyses) the host cell – Lysis is the process of phage particles bursting from the bacteria cell and destroying it! • Viruses that reproduce only by the lytic cycle are virulent. – Virulent viruses destroy the cell that they infect

The Lytic Cycle

The Lysogenic Cycle • Allows viruses to hid in their host cell for days, months, or years! • These viruses are called temperate viruses Phage DNA that is integrated into a specific site of the host cell’s chromosome is called a prophage

The Lysogenic Cycle

Viruses: Tools for Biotechnology • They are important research tools! We can replace large pieces of DNA of a phage with DNA of a particular interest!

The Origin of Viruses • Most scientists believe viruses evolved from early cells – One hypothesis is that the first viruses were probably naked pieces of nucleic acid that could travel from cell to cell – The viruses entered cells through damaged cell membranes – Over time genes evolved that coded for protective protein coats as well as signaling for specific cells

The Origin of Viruses • Evolution by Natural Selection! • Think of some examples!

Vectors of Viral Disease • Because viruses are lifeless particles, their spread depends on other agents. • A vector is an intermediate host that transfers a pathogen or a parasite to another organism Examples of vectors for viruses: animals, mosquitoes, ticks, fleas, YOU!

Vectors of Viral Disease • The West Nile virus, (causes fever, headache, coma, paralysis, and even death) infects mainly birds. • If a mosquito bites a bird infected with West Nile virus, then bites a human, the virus can spread!

• • • Examples of Viruses in Humans flu Chickenpox Measules Polio Viral hepatitis Cold Yellow fever West Nile And much more

Viruses and Cancer • Cancer is the result of: Uncontrolled Cell Growth • Some viruses contain viral oncogenes, genes that cause caner by blocking the normal controls on cell reproduction

Viruses and Cancer • Other viruses cause cancer because the viral DNA inserts itself into a host’s chromosome near a proto-oncogene, which usually controls cell growth. • The proto-oncogene is converted to an oncogene. https: //www. youtube. com/watch? v=Cn 502 md 6 la. E https: //www. youtube. com/watch? v=a. C-jn. Y 2 t 1 Wc

Emerging Viral Diseases • Emerging diseases are illnesses caused by new or reappearing infectious agents that typically exist in animal populations –often in isolated habitats- and can infect humans who interact with these animals Example: Recent Ebola outbreak blamed on a bat infecting a human

Chickenpox and Shingles pg. 489 Tamar

Benny VIRAL HEPATITIS PG. 489

Acquired Immune Deficiency Syndrome (AIDS) Pg. 490 Hadar

Short Essay • Vaccinations • Vector Control and Drug Therapy • Emerging Viral Diseases