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UNC-Chapel Hill BIOC 108 - 7.1

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7.1 – Infectious Disease:What is infectious disease? Caused by pathogenic microbes or microorganisms and other infectious agens  They must:o Colonize the host (wound, insect bite)o Reach an appropriate niche (lungs, kidney)o Avoid host defenses (evolve rapidly)o Replicate (may need host machinery)o Exit infected host o Spread to an uninfected host Causes of Infectious Disease:  Viroids, viruses, prions (proteins), bacteria, fungi, nematodes, arthropods, macroparasitesTransmission of Infectious Diseases: Person-to-person contact Bites from insects/animals Ingesting contaminated food/water Exposed to organisms in the environment  Signs and symptoms vary but often include fever and fatigue  Prevent efforts include vaccination, thorough hand washing Bacteria: large group of unicellular microorganisms that have cell walls but lack organelles and organized nucleus, most are harmless or even beneficial o Escherichia colio Hemophilus influenzao Mycobacterium tuberculosis o Vibrio cholera Fungi: spore-producing organisms that feed on organic matter, can be unicellular or multicellular eukaryotes o Candida albicans – yeast infection o Microsporum – ringworm, athletes footPrions: proteinaceous infectious agents that can fold into multiple structures, at least one of the structures is transmissible to other prions, in mammals prion diseases affect the brain or other neural tissues o Normal protein = prP o Disease causing form of prion protein = PrP 5Co CJD, a prion disease, very difficult to diagnose, linked to ingestion of beef tainted with BSEViruses: an infective agent that consist of a nucleic acid molecule coat, replicates only inside the living cells of other organisms, can infect all types of life forms from bacteria, to plants, to animals ***most abundant type of biological entity  They are not free-living organisms, they can replicate themselves Bacteria vs. Viruses: Viruses are small, they cannot be seen on a light microscopes and pass through sterilizing filters that trap bacteria Viral genomes are small (most bacteria have a few 1000) Viruses contain a single type of nucleic acid, RNA or DNA, the rest of their body is protein or glycoprotein Viruses don’t have their own lipids, glycolipids, sugars, polysaccharides and metabolites like ATP and amino acidsWhat does a virus look like? All viruses consist of a protein shell called the CAPSID which contains the viral nucleic acid Capsids are arranged based on 2 fundamental plans = the helix and the icosahedron Viruses have burst kinetics of growth:o Bacterial growth is exponentialo Viral growth is nearly instantaneous, a BURSTWhy do viruses make us sick?  Huge expansion of viral particles can cause host cell to rupture = cytolytic effect Rhinovirus = common cold, symptoms caused by the body’s immune response to lysis  They rely on the host cell gene expression and replication machinery to get to where tey want to go  But they need lots of viral proteins Viruses modify host cell transcription and translation machinery so they preferentially make viral proteins instead of normal proteins a cell needs to function  Antibiotics are antibacterial drugs7.2 – Clinically Significant Viruses Infectious viruses originate in many sources Viruses are fairly specific as to the type of tissue that they can infect, requiring a specific membrane protein which allows themto attach to and enter those cells Many mosquito-borne viruses can be transmitted sexually by infected people who are often unaware in the early stages, can also be spread through blood Many viruses have only a single stranded RNA as their genome, which makes them more compact (smaller)… these always include their own polymerase to replicate or translate this RNA New viruses such as Zika and Dengue are almost unkown in the US, but the mosquito vector is becoming more common in the southern states due to global warming For most viruses, vaccination is our only effective treatmentsViral Origins: viral type vs. animal reservoir (zoonotic disease: transferred from animal to human) Influenza – birds, pigs Rabies – bats, dogs, foxes Ebola – bats, monkeys, pigs HIV 1 and 2 – chimpanzees, monkeys West Nile – birds Zika – monkeysRoute:- Skin contact – HPV- Respirartory – cold viruses, influenza- Fecal/oral – polio, hepatitis A, Ebola- Milk – HIV, Ebola- Transplacental – rubella, HIV, Zika- Sexually – HSV 1 & 2, HPV, hepatitis B, Zika- Insect vector – yellow fever, dengue fever, Zika- Animal bite – rabies- Infected body fluid – Ebola- Blood – HIV, hepatitis BWhat about inside the virus?o Viral genomes can either be double stranded or single stranded DNA or RNAo Only ONE strand of the virus contains the genetic information2 DNA Strands:  DNA sense strand is a concept used to compare the polarity of nucleicacid The 2 complementary strands are differentiated as sense and antisense  Only 1 strands is translated into an mRNA to make proteins needed byvirus to complete its replication  RNA polymerase will read the DNA template to make RNA (which is complementary to anti-sense strand) mRNA has same sequence as sense strand1 DNA Strand: positive strand RNA can serve directly as an mRNA molecule for translation of viral proteins positive strand of RNA can go straight to the ribosome, which translates RNA to make protein  negative strand: the virus has to bring its own RNA-dependent RNA polymerases, the host cell doesn’t have any that can copy RNA (the template is RNA, so new strand is RNA)Classes of Viruses: Dna single or double stranded RNA viruses: positive strand can be translated into protein, positive strand (polio), negative (rabies)  Reverse transcription occurs with positive strand RNA with HIV-1, virus brings its own polymerases to make double stranded DNA How do viruses infect us? – depends on the type of virus1. Enveloped Viruses: acquire a lipid bilayer from the host cell during budding, protein is encaseda. Poxvirus, herpesvirus, warts virus 2. Nonenveloped Viruses: no lipid bilayer because they exit host cells by lysis (protein on outside) a. Influenza virus, rotavirus, mumps, HIV, corona virus Both enveloped and non enveloped viruses must bind a host cell surface protein to gain entry!- There will be a glycoprotein or glycolipid on the surface of the cell, where a virus will bind to - These are only


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