List and explain the shared characteristics of viruses
1- Viruses are very SMALL (10-400 nm)(smaller than cells)
2- Viruses can’t grow so they have a FIXED SIZE
3- Viruses all have GENETIC MATERIAL (DNA or RNA)
4- All viruses have a CAPSID protein layer
5- All viruses have NO CYTOPLASM to undergo the metabolic reactions for reproduction
6- Viruses have zero to a few ENZYMES
7-Not living
Explain what characteristics make viruses diverse.
Viruses are highly variable because they can:
- have an envelope from the host cell membrane
- specific shapes
- RNA or DNA which can be single or double- stranded
- have varied shapes and structure (helical, polyhedral, spherical, or irregular)
- obligatory intracellular parasites which means they need a host
- No homeostasis
Differentiate between Bateriophage Lambda, HIV, and Coronavirus
HIV and Coronavirus are spherical and enveloped whereas Bacteriophage Lambda has an irregular shape and is naked (no envelope). Lambda Phage has a tail sheath, tail fibers with protein receptors, a capsid capsule with DNA, and a base plate whereas Coronavirus has protein spikes and HIV has glycoprotein spikes (protein receptors). Bacteriophage Lambda has DNA inside the capsid whereas both Coronavirus and HIV have singlestranded RNA (HIV has two strands but coronavirus one). Also, HIV infects white blood cells, Bacteriophage lambda bacteria E. coli, The final difference is that HIV is considered a retrovirus because of the presence of reverse transcriptase, a molecule that produces DNA from RNA.
Describe the steps of the Lytic Life Cycle
First occurs attachment where the protein receptors of the virus attach to the protein receptors of the cell. Then, is the penetration stage as the virus injects its genetic code into the cell. The DNA is then replicated and then used for the biosynthesis/protein synthesis of the necessary components for the virions. Then follows the maturation/assembly stage where the components form into a virus. Finally, the release stage occurs as enzymes from the virial DNA break the membrane causing lysis and the spread of the virulent virus in the path to harm and override another cell.
Describe the stages of the lysogenic life cylce.
The lysogenic cycle is the viral life cycle that doesn’t necessarily end in the release of virulent virions. With bacteriophage lambda, it begins when the tail fibers attach to the bacteria’s protein receptors. Then, the proteins on the tail sheath contract and the virus injects its genome into the cell. The phage DNA then circulates and enters the lysogenic cycle. Here the phage DNA joins the bacteria genome during recombination creating prophage. The prophage is replicated normally with the genome as the cells undergo mitosis or meiosis. Occasionally, the prophage may excise from the bacterial chromosome and commence the lytic cycle.
Define covergent evolution
Organisms that have different origins but end up in similar conditions due to environmental factors which bias fitness. The bias towards fitness then leads to similar adaptations as a result, and thus similarties between previously dissimilar viruses.
List the three viral evolutionary theories
1- Virus First hypothesis
2- Regressive/degeneracy hypothesis
3- Escape/vagrancy hypothesis
Descrbie the degeneracy/regressive hypothesis
Viruses originated from parasitical cells which used bigger cells for resources. As time passed, the parasitical cells shed unnecessary structures effectively becoming viruses.
Outline the evidence that covergent evolution occured to viruses
- Viruses are obligatory intracellular parasites
- Protein outer boundary, the apsid, no cytoplasm
- Have genetic material which is shared by all things and Earth’s organisms
Define outbreak
An increase in the occurrence of a disease in a specific area or location and at a specific time.
Define epidemic
A widespread occurrance of an infenctious disease in a community in a specific period of time
Define pandemic
A widespread occurance of a disease spread over a country or the world at a specific time.
Distinguish between geneticshift and genetic drift
Antogenic drift produces small incremental changes in the viral genome whereas antigenic shift is faster as it is recombination of genetic materail of two or more different viral strains that infect the same cell. Antigenic drift produces slow variation in the surface proteins of the virus whereas antigenic shift causes fast. Antigenic shift results in viruses that can’t be detected by the immune system but antigenic shift results in a totally new cell capablke of creating pandemics. HIV undergoes rapid antigenic drift whereas the influenza virus has the ability to undergo antigenic shift.
Explain what type of antigenicshift/drift influenza undergoes
The influenza virus undergoes antigenic shift as its genetic material recombines with other viral genes to form new viruses
Explain what type of antigenicshift/drift HIV undergoes
HIV undergoes antigenic drift because it has small changes in its DNA and thus outer protein structure due to mutations.
Describe the consequences of fast evolution in viruses
Quick viral evolution complicates treatment because mutations often render the virus irrecognizable to the immune system. When the immune system is unable to spot the virus, vaccines become inefficient since they rely on the immune system’s responses.
Explain why viruses have high adaptation rates
Viruses have short generation time, high mutation rates, and undergo high amounts of natural selection. (mention adaptations and big populations)