Episode 27 recaps the connection between the coronavirus and the content on the AP Bio exam.
Episode 27 recaps the connection between the coronavirus and the content on the AP Bio exam. Viruses are nonliving agents (1:05) with a hijacking infection strategy. Coronaviruses are named for their club-like proteins sticking out from the surface (2:45). The viral RNA genome is translated by host cell ribosomes (4:20). Biotechnology, like PCR, is used to test for viral presence in test swabs (5:20). Viral genomes are able to evolve over time, with high mutation rates (5:55).
The Question of the Day asks (7:12) “What do we call the branch of medicine that studies the distribution and control of disease?”
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Hi and welcome to the APsolute Recap: Biology Edition. Today’s episode will recap AP Bio & the Coronavirus
Lets Zoom out:
One of the great things about studying science is the ability to understand the natural world. But as Uncle Ben once said to Peter Parker, “With great power comes great responsibility.” There is a lot of information swirling around right now. As critical scientific thinkers, it is our responsibility to follow facts and not fear. This episode will focus on the biology of the coronavirus, and how it connects to the content you’ve learned in preparation for the AP Exam.
Lets Zoom in:
Beginning with - what is a virus? And how does it differ from a cell? Viruses are infections nonliving agents that cannot reproduce by itself. In fact, its lack of ability to reproduce independently is one of the main reasons why viruses are not classified as living things. The general viral infection strategy is to 1. attach to a host cell 2. Sneak its genetic material into the host through injection or full entry 3. Hijack the host’s molecular machinery so that it produces and assembles more viruses and 4. Bud out of the cell, sometimes causing lysis in the process.
Viruses come in all shapes and sizes and consist of a nucleic acid core, an outer protein coat, and sometimes an outer envelope made of host proteins and phospholipids. I know! These are the same organic molecules that cells are made of - but viruses don’t have organelles nor do they use energy - so, still considered nonliving. That bottle of lysol you are spraying on every doorknob or purell you are using on your hands. It doesn’t kill viruses, it just disassembles them - making them ineffective. Scientists have never been the most creative with naming. Most molecules, cells, species and other discoveries are either named after what it looks like, what it does, or after the scientist themselves. So take the Coronavirus or COVID 19. There are many types of coronaviruses, seven of which infect people. A few cause the common cold and others have more severe effects like MERS, SARS, or our current pandemic SARS-COV-2. Named coronaviruses after the crown of club-like proteins extending from the spherical surface and known as COVID19 since this is the Coronavirus Disease 2019.
If you look at COVID19 under a microscope, it would essentially be a spikey ball. Coronaviruses are enveloped single stranded RNA viruses. Recall that RNA is made of nucleotides, containing a ribose sugar, phosphate group and nitrogenous bases A, U, C or G. The single strand is held together through covalent bonds between phosphate and ribose of adjacent nucleotides. It will also have a 5’ cap and 3’ poly-A-tail, just like mRNA, to protect the strand from enzymatic degradation in the cytoplasm. Enveloped viruses are surrounded by a phospholipid bilayer which was taken from the host cell during budding. It's a great strategy, as far as viral success goes. When the virus leaves the host cell, it is automatically coated in and disguised by the hosts own chemical tags. This makes it easier for the virus to enter additional host cells, without being marked as a foregin invader. The viral proteins are ligands (we learned about ligands in the cell communication unit). The ligand binds with host receptors and enters the host through receptor mediated endocytosis.
The coronavirus enters the body through the nose, mouth or eyes, attaching to cells in the airway, specifically to the ACE2 protein receptor on epithelial cells. The virus infects the cell through fusing its lipid envelope, and once inside - releases its RNA. Since the viral genome is already in RNA form, there is no need for transcription. The infected cells' ribosomes translate the RNA into proteins which keep the immune system from attacking and help assemble new copies of the virus. The genetic code is universal! The host cell ribosome has no indication it is translating the wrong instructions. The proteins produced follow the same endoplasmic reticulum and golgi apparatus route in the endomembrane system pathway. Each infected cell can release millions of copies of the virus before it wears out. These new viruses might then infect nearby cells or end up in droplets that escape the lungs through coughing or sneezing.
Advances in biotechnology have improved the speed, accuracy, and effectiveness of tracking disease outbreaks. Phylogenetic software is used to create cladograms. This allows researchers to see relatedness between viral strains and correlate probable spread patterns and treatment options. Additionally, PCR or polymerase chain reaction is used to test for the presence of the virus from small samples taken from people thought to have the infection. The PCR test looks for the presence of viral genes in a nose or throat swab, a sign of an active infection. This is different from a blood test, which would be testing for antibodies, a sign that you previously had a viral infection. Antibodies are produced by the immune system in defence. These Y shaped proteins surround and attach to the viral surface proteins. This blocks the virus from interacting with another host cell (like placing handcuffs on a suspect).
Why humans? And why now? Although viruses are non-living, they are still capable of evolving through natural selection. COVID-19 is the chemical cousin to several other viruses, and shares a recent common ancestor with bat coronaviruses. RNA viruses have high mutation rates, through base substitution, insertion, deletion or antigenic drift. Mutations are the reason why we currently need an updated annual flu vaccine. But remember, a virus can only penetrate a host cell with a specific matching receptor. The viral proteins are folded into tertiary and quaternary structures that are specific to the host receptor. As to why now? That is less clear. Evolution doesn’t have goals or dated deadlines, but simply responds to environmental change. And so, just as COVID evolved to infect humans, it may also evolve away from human hosts.
To Recap.
The coronavirus is made of RNA, a protein coat, and phospholipid envelope. Practice social distancing - because this keeps you from coming into contact with respiratory droplets from other people - which is how the virus travels. Wash your hands - the soap dissolves the phospholipid envelope of the virus and the virus falls apart. Be a good science filter - know the facts, keep calm, and study on. Please visit the CDC and WHO for current information.
Today’s Question of the day is about diseases.
Question: What do we call the branch of medicine that studies the distribution and control of disease?