 Hello and welcome to Physiology Open. Does coronavirus effect only lungs? Why people infected with coronavirus may have GI symptoms like DiDi also? These are the questions which we will try to answer in this video on mechanism of action of coronavirus. This diagram is showing the structure of coronavirus. It is an enveloped single-stranded positive strand RNA virus with a helical protein code. The lipoprotein envelope of the virus has three important proteins. S protein that is a spike protein, M that is membrane protein and E that is envelope protein. Like any other virus, coronavirus also needs a host cell to multiply. So that means it should interact with the host cell and gain entry into the cell so that it could use the machinery of the cell for its own multiplication. So how does coronavirus gain entry into the human host cell? There is an enzyme present on the membrane of the epithelial cells of alveoli in lungs known as angiotensin converting enzyme 2. It is similar to angiotensin converting enzyme that is ACE enzyme which converts angiotensin 1 to angiotensin 2. However this ACE2 further degrades this angiotensin 2 and produces other form that is angiotensin 1 to 7. The action of this form of angiotensin are completely opposite to that of angiotensin 2. So basically it has a very important function in renin angiotensin system since it prevents over function of angiotensin 2 by counteracting its function. Anyway the spike protein of the coronavirus binds to this ACE2 enzyme present on alveolar epithelial cells. Now once it binds another protease enzyme named as TMPR SS2 present nearby cleaves a part of this S protein of coronavirus and kind of activates it. Because of this cleavage the envelope now fuses with the alveolar cell membrane and the virion is taken up inside the cell by a process known as endocytosis. Then the envelope fuses with the membrane of the endozome which has been taken up releasing the RNA into the cytoplasm of the host cell. The virus then uses host ribosomes and enzymes for translating RNA to proteins and also for replication of its RNA. Then the newly synthesized RNA and proteins assemble in Golgi apparatus taking a part of membrane also and they release from the cell. So basically the virus multiplies in the cell, leaves it and then infects other cells. During this process the virus actually evades our immune system and because of which our immune system gets kind of confused and there is over activation of immune system which leads to pathogenesis of the disease. Anyways pathogenesis is a subject of another video. So wherever this ACE2 enzyme is present coronavirus can gain entry into these cells. So that is responsible for tissue tropism of coronavirus that is the specific organs which the coronavirus will be able to affect. So now that's responsible for respiratory symptoms which occur in patients infected with coronavirus because this ACE2 is present on alveolar epithelial cells. But this ACE2 enzyme is also expressed in other tissues. These are small intestinal epithelial cells which is responsible for GI symptoms in some patients. It has been found that in some patients there are positive stool samples of coronavirus. Then it is also present in cardiac tissue. Yes there are patients with cardiac symptoms also that is palpitations and chest tightness also on liver and that's why it is being speculated that why some patients may die of liver failure due to coronavirus. Also one interesting fact is that this novel coronavirus that is SARS-CoV-2 has 10 to 20 times more affinity to ACE2 enzyme present on humans than the spike from the SARS virus which caused the epidemic of 2002. That is why this is the reason that why SARS-CoV-2 is able to spread more easily from person to person than the earlier coronaviruses. Okay thanks for watching the video. If you liked it do not forget to subscribe to the channel Physiology Open. Thank you.