Introduction to Viruses Flashcards
How many viruses are there compared to other microorganisms on Earth?
There are more viruses than any other microorganism on this Earth.
How old are viruses estimated to be?
Viruses are at least 4 billion years old.
Are all viruses harmful?
Not all viruses are bad.
What type of DNA do humans have more of compared to eukaryotic DNA?
Humans are made of more viral DNA than eukaryotic DNA.
Define a virus.
Genetic element that can multiply only in a living host cell.
What characterizes a virus in terms of its living status?
Not living, can’t reproduce independently.
What is an obligate intracellular parasite?
A parasite that needs a host cell for energy, metabolic intermediates, and protein synthesis.
What is a virion?
Virus particle, extracellular form of a virus, exist outside host and facilitates transmission from one host cell to another
Virion
-Replication/reproduction occurs only upon infection (entry to host cell)
-Contain nucleic acid : DNA or RNA
-No cytoplasmic membrane or organelles
What types of nucleic acids can viruses contain?
DNA or RNA.
What is the structure of a virion?
Capsid surrounding nucleic acid; some have a phospholipid envelope.
What is the nucleocapsid?
Capsid + nucleic acid.
What is an envelope in the context of viruses?
Phospholipid bilayer from host cell membrane + viral protein.
envelop of virus
-phospholipid bilayer from host cell membrane + viral protein
-many posses glycoproteins (spikes) : recognize, bind receptors of host cell
-outermost layer provides protection and recognition site for host cell
2 types of viruses based on envelop
Naked virus: nucleocapsid
Enveloped virus: nucleocapsid + envelope (phospholipid) + may have spikes (glycoprotein)
What happens to the capsid during the intracellular state of a virus?
Capsid is removed; virus exists as nucleic acid.
Who showed that tobacco mosaic disease was transmissible from disease plant to healthy plant?
Chemist Adolf Mayer in 1886.
What significant discovery did Dimitri Iwanowski make?
He found that an infectious agent smaller than bacteria passed through a porcelain filter.
He filter the sap of diseased plant through porcelain filter that designed to retain bacteria.
What did Wendell Stanley do?
Isolation, characterization, and crystallization of TMV.
Who said some viruses can lead to cancer
Sarah Stewart
What hypotheses exist about the origins of viruses?
- Viruses arose prior to or from cells ~4 billion years ago
- Viruses require host cell→ evolved after cells appeared
- Viruses existed in a precellular era (RNA-World), free living
Viruses have mechanism to quickly move genes, they enrich gene diversity of hosts by facilitating gene transfer (How)
1.horizontal gene trensfer (prokaryotic cells)
2.earliest viruses co-existed with host cells: a lot of gene transformation → Later evolved killing host cells
3.viruses as part of the RNA world played a role in RNA to DNA transition?
-Some RNA viruses evolved DNA genomes to protect their genomes from cellular ribonucleases
-DNA is more stable than RNA
-Use of the host cell machinery to replicate
virus comprise ~ % of the nucleic-acid-containing particles, but due to its small size, viruses only comprise ~ % ef the biomass on Earth.
94%
5%
What is the size range of most viruses?
require electron microscopy
20–1000 nm in length
20–300 nm, with giant viruses about 500 nm in diameter
What is a giant virus, and when was the first one discovered?
The first giant virus, Mimivirus, was discovered in 2003, first seen in its amoebae host
Giant virus
-first one discovered in 2003, named Mimivirus, first seen in its amoebae host
-large capsid of ~ 400 nm with protein filaments extending ~ 100 nm from the suface
-large genome encode ~1000 genes (DNA genome)
-Nucleocytoplasmic Lange DNA viruses (NLDV): replicate in both the host’s cell nucleus and cytoplasm
-only infect eukaryotic unicellular hosts
ex. amoebas, algae, and other protists
-their genomes are large and very diverse.
What is a virophage?
Small DNA viruses that replicate only in cells co-infected with a giant virus.
What is an example of a virophage?
Sputnik, which replicates only in Mimivirus infected amoeba cells.
Fill in the blank: Viruses control bacterial populations and influence the evolution and diversity of their host organisms, known as _______.
Bacteriophages (phages).
What impact does climate change have on viruses?
Increases the risk of new infectious diseases.
Hypothesis of giant virus
1.they may have been small viruses, but they steal genes from their host
2.they originated from bacteria, archaea and even other viruses. acquired genes by lateral transfer from bacteria or viruses with an intra-amoebal life style
What have played a significant role in evolution of eukaryotes through gene exchange
Giant viruses
Giant viruses have their own viral parasites: Virophages
-virophages: small DNA viruses that replicate only in cells co-infected with a giant viruses
-they use the viral replication factory established by the giant virus
-parasitic relationship with the co-infecting giant virus
Ex.Sputnik: first virophage discovered, replicates only in Mimivirus infected amoeba cells, decrease the Mimivirus replication by ~70%
-virophages may improve survival of the host
ex. by preventing cell lysis by the giant virus
Most viruses are not pathogenic, many co-exist with us, many play a crucial role in many ecosystems.
What help control bacterial populations and influence the evolution and diversity of their host organisms
Bacteriophages
Bacteriophages (phages)
viruses that infect and kill bacteria
possible alternations for antibiotics
phage therapy to combat bacterial infection in human
Viruses can infect nearly all organisms
