In our airways, the air we breathe comes into contact with a mixture of different 在人类呼吸道，空气会经过并接触到
types of healthy respiratory cells. 不同类型的呼吸道健康细胞。
Some respiratory cells have hair-like structures that move the mucus along. 有些呼吸道细胞有纤毛结构，用于推动粘液。
SARS-CoV-2 coronavirus targets these hairy cells. SARS-CoV-2病毒针对这些纤毛细胞。
The virus itself is deceptively simple. 这种病毒看上去非常简单。
It consists of only a few parts, but together these parts 只包含几个部分，但是这些部分合在一起
create a highly effective virus. 构成了非常高效的病毒。
It has an outer membrane with three types of proteins on it, spike 病毒外层是一层膜结构，上面镶嵌了三种蛋白质： 刺突蛋白，
envelope and membrane proteins. 包膜蛋白和膜蛋白。
Inside the virus, an assembly of nucleocapsid proteins hold 在内部，一系列核壳蛋白将遗传物质
together its genetic material. 包裹其中。
A single strand of viral RNA. 遗传物质是单链病毒RNA。
The spike protein is responsible for making contact with the host 刺突蛋白负责跟宿主细胞进行接触，
cell and starting the infection. 开启感染过程。
It has a coat of sugars that hides it from the body's immune system. 刺突蛋白附有糖基结构，使宿主免疫系统难以识别。
Many of the variants of SARS-CoV-2 are characterized by mutations on SARS-CoV-2有很多结构变化，特征就是发生在刺突蛋白
this spike protein, seen here in red. 上的变异，在这里显示为红色。
These mutations can influence its function, some making 这些变异能够影响刺突蛋白的功能，有些
the virus more infectious. 变异能够增强病毒的传染性。
Many mutations are unique to each variant, but some, like D614G, are found 有些可变结构在不同的毒株中各不相同，但另外一些结构，比如 这里的D614G，
in each of the variants of concern. 则在受关注毒株中反复出现。
When the virus closes in on a host cell, its spike proteins open up and 当病毒接近宿主细胞时，表面的刺突蛋白会打开
bind to a receptor on the host cell. 跟宿主细胞上的受体结合在一起。
The outer part of the spike protein is then cut off by a 而后刺突蛋白的外部结构被
protein on the host cell membrane. 宿主细胞膜上的蛋白结构切去。
This frees the inner core of the spike protein, which is cut open. 这使得刺突蛋白的内部结构暴露出来，
The spike protein then unfurls and anchors into the host cell, 其内部可以展开，并钩上宿主细胞，
pulling the virus closer until the cell membrane and the viral 然后将病毒跟宿主细胞膜拉近，
membrane fuse, allowing the viral genome to enter the host cell 直到病毒包膜跟宿主细胞膜融合，病毒的 基因组得以进入宿主细胞。
Inside the cell a ribosome meets the viral RNA and starts 在细胞内部，某个核糖体碰上病毒RNA，开始
to translate its genetic code. 翻译病毒的基因代码。
The result is a long protein chain containing 得到一个包含无结构蛋白（nsps）的长链
non-structural proteins or nsps.
Initially, these nsps are all attached to one another, but some of 一开始，这些无结构蛋白连接在一起，但是有些
the nps are able to cut the chain. 无结构蛋白能够将长链切开，
The result of this cutting is the release of another nsp, which is able to grab onto 使得另一种非结构蛋白被释放出来，这中非结构蛋白能够
a ribosome and occupy it in such a way that the ribosome can only read viral RNA 附着并占据核糖体，使得他们只能读取病毒RNA
and not the host cells own RNA. 而不再读取宿主细胞自己的RNA。
This means that the virus takes over the cell's protein production 这样病毒就控制了细胞的蛋白质生产机制
machinery, turning the host cell into a virus building factory. 将宿主细胞变成了病毒加工厂。
Meanwhile, the long protein chain is cut into individual nsps. 与此同时，长链蛋白继续被切分成单个非结构蛋白（nsps），
Eventually, the production of nsps stops due to the presence 直到核糖体读取到
of a knot in the viral RNA. 病毒RNA中的一个纽结结构。
This prevents the remaining RNA, which codes for the machinery involved 纽结结构使得后续的RNA——可以生成
in duplicating the viral genome from passing through the ribosome. 复制病毒基因组所必需的蛋白质器件——无法被核糖体读取。
A protein production can either stop here, or the knot in the 蛋白质合成可以停在这里，也可以在纽结结构打开
viral RNA can slip, allowing the remaining viral RNA to be read. 之后继续，使后续病毒RNA也可以被读取。
Because of the knot, the translation of the viral RNA often stops prematurely. 由于纽结的存在，病毒RNA的翻译经常提前结束。
This is an ingenious way for the virus to control how many proteins are being made. 这是病毒控制蛋白质合成的机制。
More of the membrane modifying nsps from before the knot and fewer of the RNA 纽结之前的RNA产生更多的膜修饰nsps越多，
processing nsps from after the knot. 纽结之后的RNA产生的，用来处理RNA的nsps就越少。
The nsps that are embedded into the membrane cause it to curve. 这些nsps镶嵌于细胞膜上，改变了细胞膜的平坦状态，
This disrupts the flat shape of the. 导致细胞膜卷曲，
And creates a structure called a double membrane vesicle or DMV. 从而产生一种叫做DMV的膜结构。
These DMVs create a safe, enclosed environment for the DMV为病毒基因组的复制提供了
viral genome to be copied. 安全的封闭空间。
Inside the DMV several nsps combine to form the machinery 在DMV内部，一些非机构蛋白（nsps）结合在一起，
to create new viral RNA. 形成可以产生新的病毒RNA的结构。
Firstly, a complimentary strand is made to act as a reference. 首先，会产生一条跟病毒RNA互补的RNA链条
This reference then becomes the template for a new strand identical 作为参考模版，根据这个模版，可以
to the original viral genome. 生成跟原病毒RNA一样的RNA基因组。
In addition to the full length viral genome, a set of shorter 除了全长的病毒基因组之外，还会生成一些
RNA strands is also created. RNA片段。
These shorter strands are called subgenomic RNA and will be processed 这些片段称为次基因组RNA，他们会被
by the host cell to create the proteins that go into the new viral particle. 宿主细胞加工，合成病毒颗粒所需要的蛋白质，
The subgenomic RNA exits the DMV through an nsp pore. 这些次基因组RNA通过nsp形成的孔结构离开DMV，
After exiting, it makes its way back to a ribosome and is translated 到达核糖体，被翻译成新的SARS-CoV-2病毒
to make the main proteins that will constitute the new SARS-CoV-2 所需要的蛋白质：
viral particle, a spike envelope membrane and nucleocapsid proteins. 刺突蛋白，包膜蛋白和核壳蛋白。
The newly created nucleocapsid protein sits right by the DMV 新生成的核壳蛋白停留在DMV孔洞旁边
pore, ready to grab onto the viral genome RNA as it exits the DMV. 等新的病毒RNA出来的时候就粘附上去。
The nucleocapsid protein then begins packaging the RNA into what will become 然后核壳蛋白开始自组装，把病毒RNA打包成
the contents of the new viral particles. 新的病毒颗粒的内容物。
After the spike envelope and membrane proteins have been made, they go 刺突蛋白、包膜蛋白和膜蛋白生成之后，
to a different part of the cell. 他们会到达细胞的另外位置，
There the membrane proteins are able to catch the nucleocapsid 在这里膜蛋白会吸附核壳蛋白和病毒基因组
proteins and viral genome.
This makes the membrane bend inwards and a new viral particle eventually buds. 使得这部分膜结构向内卷曲，在内部产生完整的病毒颗粒。
When the membrane compartment containing the viral particle fuses with the outer 这种包含病毒颗粒的膜结构跟细胞膜结合，
cell membrane, the viral particles are then released from the cell, but 就会将病毒颗粒释放出细胞，
that's only the first wave of SARS-CoV-2 particles that will be expelled. 这还只是释放出的第一波SARS-CoV-2病毒颗粒，
Eventually the host cell produces so many viral particles that it dies and 最终，宿主细胞会产生非常多的病毒颗粒而后死掉，
releases a whole wave of new virus particles into the surrounding tissue, 将新的病毒颗粒释放到周围的组织中，
ready to spread and infect nearby cells. 感染附近的细胞。
This completes the life cycle of a single SARS-CoV-2 coronavirus. 这就是一个SARS-CoV-2冠状病毒的完整生存周期。