Unit 12: disease and infection
Virus
Features
Viruses are small. Furthermore, they are the tiniest of all microbes. This is because viruses are made up
of DNA/RNA surrounded by a protein (capsid) rather than actual cells. To protect its nucleic acid genome
from the harsh environment, each virus has a protein capsid. A capsid's primary function is to protect,
transport, and deliver the complete set of DNA in an organism. Because viruses are not made of cells,
they lack many characteristics of living things. They cannot, for example, grow, generate energy,
generate waste, or regulate their own temperature. For these reasons, viruses are classified as non-
living structures. Additionally, viruses cannot keep themselves in a stable state so are also regarded as
non-cellular. Because viruses lack the cytoplasm and enzymes required for reproduction, they can only
reproduce within a host cell. They also lack ribosomes and thus cannot produce proteins on their own.
Viruses lack the specialised machinery required to generate energy, grow, reproduce, or maintain
homeostasis on their own. This is why they infiltrate host cells and use those specialised organelles to
replicate and create new viral particles.
Disease
Viruses can cause many diseases such as covid 19, aids, Ebola, influenza, herpes, and measles.
Respiratory droplets are released when a person with covid coughs, sneezes, breathes, sings, or talks,
allowing the virus to spread. One may breathe in these droplets, or they may end up in their mouth,
nose, or eyes.
Life cycle
A virus must navigate several challenges before it can penetrate the host cells. For intruders, cellular
membranes act as barriers. All animal viruses must initially break through the plasma membrane as their
primary defence. For some viruses that copy their DNA in the nucleus, the nuclear membrane serves as
the second defence. Entry, genome replication, and exit are the three steps that make up the virus life
cycle. Entry is the initial phase. When a virus particle enters a host cell, it binds to the cell surface by
attachment, penetrates to the cytoplasm through penetration, and sheds its capsid through uncoating.
Following uncoating, the bare viral genome is used for viral genome replication and gene expression.
Once all the viral proteins and genomes have accumulated, a progeny virion particle is formed, which is
subsequently discharged extracellularly. The exit consists of virion assembly and release from the cell.
Viruses can't multiply on their own; instead, they rely on the protein synthesis pathways of their host
cell to do it. This usually happens when a virus inserts its genetic material into host cells, co-opts the
, proteins to generate viral replicates, and multiplies until the cell explodes from the large number of new
viral particles.
Action in a human
A virus enters the body (often by the nose, mouth, or eyes) and bonds to a host cell before inserting its
genetic material. The host cell's mechanisms can then be used by the virus to produce the components
it needs to multiply. These components combine to create fresh viruses, which eventually emerge from
the host cell and propagate to further cells within the same host or in a different host. When a virus
enters a living cell, the cell's machinery is reprogrammed to produce viral proteins and genetic material
that allows the virus to replicate. Enveloped viruses rob cells of their lipid coating. Then, fresh virus
particles spread to other cells, transforming them into more viral factories. Viral replication leads to
fever, chills and body aches.
K12.nc.us. (2020). [online] Available at:
https://www.cabarrus.k12.nc.us/cms/lib/NC01910456/Centricity/Domain/7913/virus.pptx.
Kidshealth.org. (2019). Germs: Bacteria, Viruses, Fungi, and Protozoa (for Parents) - KidsHealth. [online]
Available at: https://kidshealth.org/en/parents/germs.html.
Microbiology Society (2020). Viruses | What is microbiology? [online] Microbiologysociety.org. Available
at: https://microbiologysociety.org/why-microbiology-matters/what-is-microbiology/viruses.html.
Khan Academy. (n.d.). Are viruses dead or alive? (article) | Cells. [online] Available at:
https://www.khanacademy.org/test-prep/mcat/cells/viruses/a/are-viruses-dead-or-
alive#:~:text=Viruses%20are%20not%20made%20out%20of%20cells%2C%20they%20can.
https://byjus.com/question-answer/why-can-t-viruses-reproduce-outside-the-host-organism/
Mayo Clinic (2017). Germs: Protect against bacteria, viruses and infection. [online] Mayo Clinic. Available
at: https://www.mayoclinic.org/diseases-conditions/infectious-diseases/in-depth/germs/art-20045289.
Mayo Clinic. (n.d.). Germs: Protect against bacteria, viruses and infections. [online] Available at:
https://www.mayoclinic.org/diseases-conditions/infectious-diseases/in-depth/germs/art-20045289.
[Accessed 9 Nov. 2022].
Caltech Science Exchange. (n.d.).
How Do Viruses Infect Our Cells? [online] Available at:
https://scienceexchange.caltech.edu/topics/covid-19-coronavirus-sars-cov-2/virus-infection.
Bacteria
Virus
Features
Viruses are small. Furthermore, they are the tiniest of all microbes. This is because viruses are made up
of DNA/RNA surrounded by a protein (capsid) rather than actual cells. To protect its nucleic acid genome
from the harsh environment, each virus has a protein capsid. A capsid's primary function is to protect,
transport, and deliver the complete set of DNA in an organism. Because viruses are not made of cells,
they lack many characteristics of living things. They cannot, for example, grow, generate energy,
generate waste, or regulate their own temperature. For these reasons, viruses are classified as non-
living structures. Additionally, viruses cannot keep themselves in a stable state so are also regarded as
non-cellular. Because viruses lack the cytoplasm and enzymes required for reproduction, they can only
reproduce within a host cell. They also lack ribosomes and thus cannot produce proteins on their own.
Viruses lack the specialised machinery required to generate energy, grow, reproduce, or maintain
homeostasis on their own. This is why they infiltrate host cells and use those specialised organelles to
replicate and create new viral particles.
Disease
Viruses can cause many diseases such as covid 19, aids, Ebola, influenza, herpes, and measles.
Respiratory droplets are released when a person with covid coughs, sneezes, breathes, sings, or talks,
allowing the virus to spread. One may breathe in these droplets, or they may end up in their mouth,
nose, or eyes.
Life cycle
A virus must navigate several challenges before it can penetrate the host cells. For intruders, cellular
membranes act as barriers. All animal viruses must initially break through the plasma membrane as their
primary defence. For some viruses that copy their DNA in the nucleus, the nuclear membrane serves as
the second defence. Entry, genome replication, and exit are the three steps that make up the virus life
cycle. Entry is the initial phase. When a virus particle enters a host cell, it binds to the cell surface by
attachment, penetrates to the cytoplasm through penetration, and sheds its capsid through uncoating.
Following uncoating, the bare viral genome is used for viral genome replication and gene expression.
Once all the viral proteins and genomes have accumulated, a progeny virion particle is formed, which is
subsequently discharged extracellularly. The exit consists of virion assembly and release from the cell.
Viruses can't multiply on their own; instead, they rely on the protein synthesis pathways of their host
cell to do it. This usually happens when a virus inserts its genetic material into host cells, co-opts the
, proteins to generate viral replicates, and multiplies until the cell explodes from the large number of new
viral particles.
Action in a human
A virus enters the body (often by the nose, mouth, or eyes) and bonds to a host cell before inserting its
genetic material. The host cell's mechanisms can then be used by the virus to produce the components
it needs to multiply. These components combine to create fresh viruses, which eventually emerge from
the host cell and propagate to further cells within the same host or in a different host. When a virus
enters a living cell, the cell's machinery is reprogrammed to produce viral proteins and genetic material
that allows the virus to replicate. Enveloped viruses rob cells of their lipid coating. Then, fresh virus
particles spread to other cells, transforming them into more viral factories. Viral replication leads to
fever, chills and body aches.
K12.nc.us. (2020). [online] Available at:
https://www.cabarrus.k12.nc.us/cms/lib/NC01910456/Centricity/Domain/7913/virus.pptx.
Kidshealth.org. (2019). Germs: Bacteria, Viruses, Fungi, and Protozoa (for Parents) - KidsHealth. [online]
Available at: https://kidshealth.org/en/parents/germs.html.
Microbiology Society (2020). Viruses | What is microbiology? [online] Microbiologysociety.org. Available
at: https://microbiologysociety.org/why-microbiology-matters/what-is-microbiology/viruses.html.
Khan Academy. (n.d.). Are viruses dead or alive? (article) | Cells. [online] Available at:
https://www.khanacademy.org/test-prep/mcat/cells/viruses/a/are-viruses-dead-or-
alive#:~:text=Viruses%20are%20not%20made%20out%20of%20cells%2C%20they%20can.
https://byjus.com/question-answer/why-can-t-viruses-reproduce-outside-the-host-organism/
Mayo Clinic (2017). Germs: Protect against bacteria, viruses and infection. [online] Mayo Clinic. Available
at: https://www.mayoclinic.org/diseases-conditions/infectious-diseases/in-depth/germs/art-20045289.
Mayo Clinic. (n.d.). Germs: Protect against bacteria, viruses and infections. [online] Available at:
https://www.mayoclinic.org/diseases-conditions/infectious-diseases/in-depth/germs/art-20045289.
[Accessed 9 Nov. 2022].
Caltech Science Exchange. (n.d.).
How Do Viruses Infect Our Cells? [online] Available at:
https://scienceexchange.caltech.edu/topics/covid-19-coronavirus-sars-cov-2/virus-infection.
Bacteria
