SC NATS 1670 Lecture Notes on Virology (Part 1)

part BASIC CONCEPTS IN HUMAN 2 VIROLOGY - when viruses can sense that the immune system is there, the virus is going to reduce the amount of this lmp still to the level that it is enough to make the cells to be replicated but not to be recognized by the immune system In 20th century, a virologist sa...

part BASIC CONCEPTS IN HUMAN 2 VIROLOGY - when viruses can sense that the immune system is there, the virus is going to reduce the amount of this lmp still to the level that it is enough to make the cells to be replicated but not to be recognized by the immune system In 20th century, a virologist said that the virus is a piece of bad news wrapped in a protein (most cases this is not correct) All livings things survive in a sea of viruses We are exposed to millions viruses viruses are infecting all living things First 8% of our genome is made of viruses that were captured in the genome and they are there all the time hepatitis b virus infected about 350 million people worldwide in a chronic way HIV infected people 40 million people worldwide THE 1918 SPANICH FLU PANDEMIC 50-100 million deaths worldwide Viruses are part of our ecology Viruses like the varcella zoster virus, we need them to infect us early as possible 1519 A.D SMALLPOX WAS TRANSFERRED FROM EUROPE TO THE AMERICAS smallpox reached Europe from East from China in 710 A.D was transferred to the America by Hernando Cortes Hernando Cortes invaded Mexico and conquered millions of Aztecs - less than 600 men helped - horses - weapons aztecs were defense less when the Ebola started to raise its head and to be active last year - obesity, tobacco, and alcohol = killed million of people in the U.S only VIRUSES ARE THE MOST COMMIN CAUSE OF ACUTE INFECTIONS IN HUMAN in adults, the total virus infections in the world exceeded several billions cases each year rabies, Ebola, smallpox have high mortality rates Polio, rubella are some viruses that can lead to long term disability WHAT IS A VIRUS? tiniest simplest form of life on earth Goal is to reproduce Diseases causes by viruses are protect a force in the history of man as war and natural disasters Influenza 15th century Italians called it that because they believed it was caused by the influence of stars and plants There are hundreds of different cold viruses in your lifetime, at least 50 of them will catch you A virus is an organism with TWO PHASES: 1. OUTSIDE OF THE CELL: THE VIRUS PARTICLE (VIRION) 2. THE VIRUS INSIDE THE INFECTED CELL G Inside the infected cell, the virus can be replicated to make protein, can enter the nucleus, genome proteins will leave the infected cells f C (chemical Stage) Ibiological stage) Virus becomes a virus particle no activity, no metabolism Virus is pieces of genetic material that are arranged together more of the chemical stage viruses are not cellular organism Obligate intracellular parasites - must have a cell that will accept them and allow the virus to replicate in the cell, some cell may be killed - virus must enter a host cell to replicate - they cannot perform metabolism on their own outside of the cell - virus particles are complexes of nucleic acids and proteins (this stage they are not considered life forms) VIRUSES sur vive because they they make huge number of mutants The selection remove the non-fittest - if they are too passive, their host defence loses control of their growth, become eliminated some viruses depend on the host to survive natural evolution of viruses operates on their spreading capacity, not on their ability to cause a disease Viruses cannot replicate six feet below the ground, the death of the infected host compromises the survival of the infecting virus VIRUS-HOST EQUILIBRIUM the natural evolution of a microbe operates on its spreading capacity, not on its ability to cause a disease polio - - influenza In ↳ the good 1918 following years equilibrium - VS. Ebola ↳ not virus too good equilibrium natural selection favours less or non-virulent microbes A well adapted microbes ideally grow in its host without causing a significant damage many severe viral diseases represents failure of the virus to adapt to its host which is an accident for both POLIO the first written record of a virus infection = hieroglyph from Memphis 3700BC, Memphis Ancient Egypt priest Uma showed typical clinical signs of paralytic poliomyelitis ↳ kid confirmed most infected people are totally asymptomatic, can spread the virus by fecal overall transmission 9% of people with symptoms will have mild like flu symptoms 1% comes with polio myelitis, only a few will be killed and will not have to infect other people ↳ Why they have a strong 7 Still equilibrium around until 1957 seasonal flu virus killing people but not the same level as 1918 Came back in 1976 Influenza virus of 1919 learned how to have better equilibrium Ebola virus outbreaks are limited to Africa Ebola virus acute disease, death up to 90% of infected people shortly after infection Most severe problems happened in 2014 infecting different regions Ramesses V’s preser ved mummy shows that he died of small pox in 1143 B.C - example of an aggressive virus Virus particles are NOT CELLULAR ORGANISM all cellular life has the following characteristics in common: - DNA AND RNA, dna must be expressed all the time - making proteins, must have genetic material to make ribosomes - converting chemicals to energy - reproduce by division - cell membrane, regulation scanned by electrons, viruses were revealed to be spheres and spindles and geometric shapes - THE YEAR 1892 - DMITRI IWANOWSKI - showed that extracts from diseased tobacco plants can transmit displease to other plants by infectious agent smaller than a bacteria opened the gate that something can be replicated = birth of the field called VIROLOGY - highly diverse in overall morphology and in the nature of their genetic material DIVERSITY OF VIRUSES different method of replication Different structure and size Host range viruses need to replicate to make proteins simply to stay around not stable in their environment in most cases, cannot sur vive on its own Replicating only in its host cell Virus sole purpose is to make many copies and infect other host cells Variation in Replication Cycle I LYSOGENIC GROWTH CYCLE. In lysogenic growth cycle, viruses are incorporated into the host’s chromosomes and are transmitted to the host’s daughter cells 8% of our genome is made of viruses HIV is integrated in the genome of the cell, when making new cell the viral genome will be in the new cell When bacterial cells are infected with their virus lysogenically Creamy bacterium diphtheria is infected lysogentically with a better phase bacteriophage that can enter the genome of the diphtheria and the toxin that this bacteria is making is actually made by the bacteriophage genome.LYTIC REPLICATION CYCLE 2 viral particles are made and released from the cell ↳ ↳ EXAMPLE OF LYSOGENIC TO LYTIC SWITCH IS HIV HIV INFECTS US LYSOGENITICALLY AND THE VIRUS CAN STAY IN MEMORY CELLS through virus particles HIV IS INFECTING US FOR LIFE BECAUSE THE INFECTION IS LYSOGENIC AND THE MEMORY CELLS ARE THERE TO STAY, AND SECONDLY, VIRUSES IN THE BLOOD WHICH ARE COMING FROM ACTIVATED MEMORY CELLS GENERAL STEPS IN LYTIC VIRAL REPLICATION entry into a host cell Replication of the viral genome The production of viral proteins The assembly of a new generation of virus particles Exit from the infected cell Viral genome viruses can use rna or dna Can use segmented or non segmented - segmented means their genome is made out of may chromosomes - ex: rotavirus have 12 segments so they are non segmented single stranded or double stranded Linear or circular in positive sense RNA viruses, (+) ssRNA, the genome contains the same sequences as the mRNA required to produce viral proteins In negative sense RNA viruses, (-) ssRNA, the base sequence in the genome are complementary to those in viral mRNAS male ters encell e instead of making one enzyme, it will make a long sequence of all the enzyme onto the same polypeptide Certain protase is needed to separate the enzymes to make them activated or structural/processed proteins RNA dependent and RNA polymerase are made in the cell that just got infected by translating the genome of the virus directly to make -rna and all +rna Then will all make a lot of proteins - virus genome need to make a copy of itself before it is available for translation -ssRNA enters the cell and make rna dependent polymerase in the previously infected cell, comes with rna polymerase because it cannot make it in the cell The first step cannot be translation but it must be copying the rna genome into a +ssrna during the translation of the positive rna to the negative rna, proteins will be separated to start with , - coro from crown - RNA & ↑ N < E ! - ↳ liver