Virus structure and Classification

                                                       where we talk about the viruses how to

kill viruses how to culture viruses what

are the properties of viruses and how

viruses replicate wh

at are the different

type of infectious viruse

s for us for

human for other animals so viruses are

micro organisms and they're as small as

100 nanometers that means that they are

kind of thousands folds smaller than a

bacteria which is in order of micrometer

now bacteria can be visualized with

normal microscope like lab microscopes

and all but with sophisticated

fluorescent microscopes or for

sophisticated high-resolution light

microscope we cannot see our virus

because our light microscope resolution

is somewhere around 200 nanometer

theoretical range be below 200 nanometer

it cannot delineate between two

different features so our resolution is

poor in order to visualize viruses we

either need electron microscope or we

need super resolution microscope

obviously there are other biochemical

and molecular way of detecting virus but

just to visualize them we need either

super resolution or electron microscope

so they are that small so let's talk

about few quick features about the

viruses so they are inanimate objects

that don't have a cellular organization

and when they are outside of the host

they are pretty much inanimate they

don't have a life but they come to life

when they get inside the host pretty

much like the zombies so viruses are

obligate intracellular parasite

therefore right now despite of no

cellular organization one might expect

that their mode of replication or their

mode of reproduction would be relatively

easier just like budding kind of stuff

which east used to use right

unfortunately it's way more complicated

than we can imagine and they have

sophisticated mechanism that they use

for replication I

several videos on viral replication both

for RNA and DNA viruses so do click on

the link at the in screen to visit that

now they are unaffected by the

antibiotics because they are not

bacteria so why they would be affected

on antibiotics and because bacterial

membrane property or the way antibiotics

work is very different for viruses so

this is an overall structure of a virus

and let's just go through its key

features one by one so first of all they

have a coat it's like a jacket so the

jacket of the virus is known of envelope

mostly they're made up of lipids which

are derived from the host cell membrane

now if you go inside the envelope there

would be a proteinaceous coat this

protein Isha's cork is known as capsid

which is encasing the viral genome so

that means if you remove the capsid what

you would end up getting is the viral

genome which might be DNA or might be

RNA and virus are the only one type of

organism in this whole world who use DNA

and RNA I mean they can potentially use

DNA or RNA as the genetic material all

of the organism use DNA as their genetic

blueprint they don't encode the

information in RNA but virus does and

that has a very interesting implication

in terms of evolution people think that

these viruses are the prevalent

organisms from the RNA world now they

have different type of cap seeds and cap

seeds have different shapes and sizes

these cap seeds can be classified based

on their symmetry like here in tobacco

modest mosaic virus we see this kind of

helical organization of the cap seeds

with the advancement of structural

biology and now we classify that as a

helical capsid symmetry now there are

other capsid symmetry types such as it

was a head roll like adenoviruses have

this kind of symmetry we'd come to what

is eco Sahara land all of these things

very few viruses have very complex kind

of capsid symmetry and we're not going

to talk that much about these complex

symmetry in this video but let's talk

about icosahedron which is a polyhedra

having 12 vertices and twin deficits so

simply these icosahedron symmetric and

we also present him the capsid that

means it simply has 20 faces now the

shape of these unified the the monomers

of these eyes icosahedral cap so mirrors

are these ICA's hydral cap seeds might

be varying in shape for example this

case the facet is triangular in shape

and in the lower example it is hexagonal

in shape so depending upon what type of

shape they take it might defect it might

it might be different right so and it

has important biological implication

which would we would understand in this

whole video series when we try to

understand their virulence their

mechanism of action and all of these

things now an important terminology we

need to understand when we are talking

about biology is belper Mars Palpa Mars

are glycoproteins spike proteins which

are present on the viral capsid or may

be in the viral envelope of a virus okay

so that means simply these proteins

which are spikes or envelope proteins

these are actually performers okay they

are known as purple Mars now envelope

gives virus its biological property or

biological attribute it also determines

its virulence how it would enter the

cell make it more dangerous so this

envelope is very important but the good

thing about envelope is it is a lipid so

it would be susceptible to the action of

detergent so will come about come to

what are the detergent and disinfectants

could be used to kill virus essentially

so we are going to talk about that in

this whole video series now let's talk

about the classification of the viruses

so viruses are classified based on their

genetic materials based on their

symmetry and all of these things and

presence of envelope and all of these

things so we understand the basis of

classification while we read read the

their features now there are DNA viruses

which could be either enveloped or non

enveloped the non-enveloped viruses are

known as the naked viruses now the

envelope viruses might have dsDNA dsDNA

as their genetic material they could

also have

single-stranded DNA as their genetic

material now

this case I am giving example of both in

case of non-enveloped viruses you could

also have single strand or double

double-stranded DNA for the move

stranded DNA viruses which are enveloped

key examples that we always get to hear

from people are harpies bad nap box etc

whereas in case of the double-stranded

DNA they are Popova adeno and parvo

virus parvo is the single-stranded DNA

viruses which are naked so this is a

very important concept or very important

classification that we just need to keep

in the back of our head now RNA viruses

also have RNA as their genetic material

so they could have either

double-stranded RNA or a single-stranded

RNA now the single-stranded RNA the key

example of the double stranded RNA virus

is a real virus now the single-stranded

double single-stranded RNA viruses are

divided or the sub classified into two

groups positive sense RNA and negative

sense RNA don't understand these terms

what are positive sense RNA water- sense

RNA it would be ultra clear when we talk

about the mode of replication of the RNA

viruses and the link would be given in

the in screen so please watch this video

till the end okay so the positive sense

RNA virus there examples are toca virus

flava very edgy corona' very G rare

ability etc whereas the naked viruses

which don't have the envelope they are

pecan already family so we just talked

about the family name I'm not talking

about any specific virus name and the

enveloped virus are generally Brunner

viridi / AMEX so ortho makes a very dear

ab divinity etc so this video pretty

much give you an overview of the virus

features their cellular feature I mean

we cannot talk about cellular features

when we are talking about viruses

because they are not sell but molecular

features of the viruses and also it

talks about the genetic material that

the virus has and we classified the

viruses as DNA and RNA viruses based on

the genetic material and based on their

envelope presence of envelope or their

symmetry and all of these things