Virology lecture 1 | Virus structure and classification

Summary

This 20th lecture in the microbiology series delves into the intricate world of viruses and prions, exploring their elusive nature and the challenges in their discovery since 1884. The video explains the unique structure and function of viruses, distinguishing them from living cells due to their dependence on host cells for replication. It covers the diversity in viral shapes and sizes, the protective role of the capsid, and the significance of the viral envelope in host interaction. The lecture also touches on the specificity of viruses to certain host tissues, known as tissue tropism, and their varying host ranges, offering a comprehensive introduction to these fascinating entities.

Takeaways

• 🌟 The script introduces the topic of viruses and prions, highlighting the start of a new lecture series focusing on their structure and function.
• 🔍 The history of virus discovery is discussed, emphasizing that viruses were not identified until 1884 due to their small size, which is beyond the resolution of light microscopes.
• 🌱 The script explains that viruses are non-cellular particles with a definite size, shape, and chemical composition, and they are not considered true living organisms because they require a host cell to replicate.
• 🧬 It outlines that viruses contain either DNA or RNA as their genetic material, and they lack the machinery for protein synthesis, relying on the host cell for replication.
• 🌐 The diversity of viruses is highlighted, with nearly 1,500 known types and an estimated 400,000 more, emphasizing the vast number of viruses yet to be discovered.
• 🔬 The importance of electron microscopy in studying viruses is mentioned, as it allows for detailed visualization and understanding of their structure.
• 💉 The script discusses the obligatory intracellular nature of viruses, their filterability, and the fact that they can contain proteins and have tissue specificity.
• 🌀 It describes the various shapes of viruses, including round, rod-shaped, and complex structures, and how these shapes can be icosahedral, helical, or more irregular geometrical forms.
• 🛡️ The functions of the viral capsid and envelope are explained, with the capsid protecting the nucleic acid and the envelope facilitating host-cell fusion and tissue specificity.
• 🧬 The core of the virus, which contains the nucleic acid, is detailed, noting that the viral genome can be either DNA or RNA but not both, and that the number of genes varies among different viruses.
• 🏠 The concept of host range and tissue tropism is introduced, explaining that viruses have specific hosts and tissues they can infect, such as hepatitis B's specificity to liver cells.

Q & A

What is the main topic of the 20th lecture in the microbiology series?

The main topic of the 20th lecture is the structure and function of viruses.

What is the significance of the year 1884 in the study of viruses?

In 1884, it was postulated that rabies was caused by an agent smaller than bacteria, marking the beginning of the search for viruses.

What are the two different sets of lectures planned for viruses?

The two sets of lectures planned are one on the structures and properties of viruses, and another on human viruses, common infections, and diseases they cause.

Why are viruses considered non-cellular particles?

Viruses are considered non-cellular because they lack the ability to carry out metabolic processes on their own and require a host cell to replicate.

How do viruses differ from true living organisms?

Viruses differ from true living organisms because they do not exhibit all the characteristics of life outside of a host, such as metabolism and growth.

What is the role of the capsid in a virus?

The capsid is a protein coat that encloses and protects the viral nucleic acid, forming the nucleocapsid.

What is the difference between enveloped and naked viruses?

Enveloped viruses have an additional lipid membrane surrounding the capsid, while naked viruses do not have this extra layer.

What are the two main types of viral capsid structures?

The two main types of viral capsid structures are helical and icosahedral.

What is the function of viral spikes in enveloped viruses?

Viral spikes help the virus to specifically bind to their target tissue and facilitate entry into the host cell.

What is the significance of the viral genome being either DNA or RNA but not both?

The viral genome being either DNA or RNA signifies the virus's simplicity and specialization in carrying the necessary genes to invade the host cell and redirect its activity for viral replication.

What is tissue tropism, and how does it relate to viruses?

Tissue tropism refers to the specificity of a virus to infect certain types of tissues or cells, such as hepatitis B being specific to liver cells.

Outlines

00:00

🌐 Introduction to Virology and Virus Structure

This paragraph introduces the topic of the video series on microbiology, specifically focusing on viruses and prions. The lecturer outlines the aim of the lecture series to discuss the structure, function, and diseases caused by viruses. It highlights the historical discovery of viruses, their elusive nature due to their small size, and the development of the field of virology from the late 19th century to the 1950s. The paragraph emphasizes the unique nature of viruses as non-cellular entities that require a host cell to replicate and their dual role in both biological and computer sciences.

05:03

🔬 Exploring Virus Characteristics and Diversity

The second paragraph delves into the characteristics of viruses, including their obligate intracellular parasitism, filterability, genetic makeup of DNA or RNA, and the presence of a protein coat known as a capsid. It discusses the various shapes and sizes of viruses, such as round, rod-shaped, and helical forms, and the distinction between enveloped and naked viruses. The paragraph also touches on tissue specificity and host attachment sites, illustrating the diversity of viruses with examples like hepatitis B and tobacco mosaic virus, and the use of electron microscopy to visualize these microscopic entities.

10:03

🧬 Dissecting the Components of Viral Structure

This paragraph breaks down the structure of viruses into their coverings and central core. It explains the role of the capsid in protecting the genetic material and the potential presence of an envelope in some viruses. The paragraph describes the two main types of capsid structures: helical and icosahedral, and the significance of spikes in virus-host interactions. It also discusses the composition of the viral core, which may contain DNA or RNA and occasionally enzymes, and how viruses differ from living cells due to their lack of protein-synthesizing machinery.

15:05

🛡️ The Protective Role of Capsid and Envelope

The fourth paragraph focuses on the functions of the capsid and envelope in a virus. It explains how the capsid safeguards the viral nucleic acid from external damage and how the envelope facilitates fusion with host cells, contributing to tissue specificity and ease of infection. The paragraph also describes the maturation process of the envelope and the role of spikes in binding to target tissues. Additionally, it touches on complex viruses like bacteriophages and poxviruses, which have unique structural components beyond the typical capsid and envelope.

20:09

🧬 Viral Genome and Host Specificity

The final paragraph discusses the core component of a virus—the nucleic acid, which can be either DNA or RNA. It explains that viruses carry the necessary genes to invade host cells and redirect cellular activities to produce new viruses. The paragraph also covers the differences between DNA and RNA viruses, including the concepts of positive and negative sense RNA. Furthermore, it addresses the host range and specificity of viruses, highlighting tissue tropism as a key factor in determining which cells a virus can infect, using hepatitis B as an example of a virus with a narrow host range.

Keywords

💡Virus

A virus is an infectious agent that can only replicate inside the living cells of an organism. In the video, the term 'virus' is central to the theme, as the script discusses the structure, function, and history of viruses. The video emphasizes that viruses are obligate intracellular parasites, meaning they require a host cell to replicate, and they can cause various diseases in humans, animals, and plants.

💡Prions

Prions are infectious agents composed of protein in a misfolded form that can induce other proteins to misfold similarly. The script briefly mentions prions alongside viruses, indicating that they will be discussed in separate lectures, suggesting that prions are another type of infectious agent that differs from viruses in composition and mechanism of infection.

💡Viral Structure

The viral structure refers to the physical makeup of a virus, including its protein coat, or capsid, and its genetic material, which can be either DNA or RNA. The script delves into the details of viral structure, explaining the importance of the capsid in protecting the virus's genetic material and the various shapes viruses can have, such as icosahedral, helical, and complex forms.

💡Nucleic Acid

Nucleic acids are the genetic material of viruses, which can be either DNA or RNA. The script explains that the viral core contains nucleic acid, which carries the genetic information necessary for the virus to replicate. The type of nucleic acid (DNA or RNA) and whether it is single-stranded or double-stranded are crucial to understanding how a virus functions and replicates.

💡Capsid

The capsid is the protein coat that surrounds and protects the nucleic acid of a virus. The script describes the capsid as a critical component of the virus structure, forming the nucleocapsid, which is essential for protecting the virus's genetic material from external damage and facilitating cell entry.

💡Envelope

An envelope is an external membrane that surrounds some viruses, providing an additional layer of protection and aiding in the process of viral entry into host cells. The script explains that enveloped viruses have an extra layer derived from the host cell membrane, which can contain proteins or spikes that help the virus to bind to and enter target cells.

💡Tissue Tropism

Tissue tropism refers to the specificity of a virus to infect certain types of cells or tissues. The script uses the example of hepatitis B to illustrate tissue tropism, explaining that this virus specifically targets liver cells, demonstrating the concept of host range and specificity in viral infections.

💡Icosahedral

Icosahedral is a term describing a geometric shape that viruses can have, characterized by 20 equilateral triangular faces. The script mentions icosahedral as one of the shapes of virus capsids, such as in the case of poliovirus and herpes simplex virus, indicating a regular, symmetrical structure.

💡Helical

Helical refers to a virus structure that resembles a spiral or coil, typically formed by the genetic material and protein subunits arranged in a helical pattern. The script uses tobacco mosaic virus as an example of a helical virus, highlighting this as one of the common shapes of viral capsids.

💡Bacteriophage

A bacteriophage, or phage, is a virus that specifically infects bacteria. The script mentions bacteriophages in the context of different types of viruses, indicating that while some viruses infect animals or plants, bacteriophages target bacterial cells, illustrating the diversity of viral hosts.

💡Viral Genome

The viral genome is the complete set of genetic information of a virus, which can be either DNA or RNA. The script discusses the viral genome as being essential for the virus to invade a host cell and redirect the cell's activities to produce new virus particles, emphasizing the simplicity and efficiency of viral genetic material.

Highlights

Introduction to the 20th lecture in the Microbiology series focusing on the structure and function of viruses.

The elusive nature of viruses and their discovery in 1884, highlighting their small size not visible under light microscope.

The differentiation between viruses and prions, and the plan for two sets of lectures on their structures, infections, and diseases.

Historical context of virus discovery, including the postulation of rabies being caused by an agent smaller than bacteria.

The identification of tobacco mosaic virus in the 1890s as an important milestone in virus research.

The multidisciplinary nature of virology by the 1950s, with the discovery of various types of viruses.

Characteristics of viruses as non-cellular particles with definite size, shape, and chemical composition.

The dual nature of viruses as non-living entities outside a host cell and behaving like living organisms within a host.

The importance of viruses in various fields, including human welfare and computer technology, as agents of infection or 'malware'.

The diversity of known and estimated viruses, with only 1,500 identified out of an estimated 400,000 types.

The use of electron microscopy in visualizing viruses and gathering information on their components.

General characteristics of viruses, including their obligatory intracellular nature and filterability.

The composition of viruses containing DNA or RNA and the presence of a protein coat known as a capsid.

The various shapes of viruses, such as round, rod-shaped, and helical, and their significance in identification.

The concept of tissue specificity in viruses, with examples like Hepatitis B infecting liver tissue.

The structure of viruses, including the nucleocapsid and the distinction between enveloped and naked viruses.

The role of viral envelopes in facilitating fusion with host cells and their contribution to tissue specificity.

The core of a virus, consisting of nucleic acid, and the absence of cellular machinery for protein synthesis.

The types of viral genomes, which can be either DNA or RNA, and the distinction between positive and negative sense RNA.

The concept of host range and specificity in viruses, with examples of tissue tropism and narrow host ranges.

Transcripts

welcome friends welcome to another video

tutorial from tsoumas Valley G and here

we are at the 20th lecture of

microbiology lecture series and from now

we're starting with Viral la G lecture

so this is the first lecture of Y roller

G and we're going to talk about the

virus structure and function in little

bit details so if you want to know about

the virus this video is just for you

stay tuned and watch it okay now in this

lecture we want to talk about viruses

and prions

okay so virus like organisms we want to

talk about along with viruses so there

will be two different set of lectures

for viruses one is this one regarding

the structures and properties of virus

and how the infect how they multiply and

there will be another lecture on human

viruses and some very common infections

and diseases caused by the human viruses

and it's cure okay so let us begin with

this first lecture on viruses and prions

the very first thing that I want to

share is the search of the virus elusive

virus and the search began not very

earlier its until 1884 not until that

time we discovered virus because Eve

iris is so small that we cannot know the

presence of virus with the help of even

light microscope light microscope is not

enough to give us the details about the

virus so when the light microscopy was

was invented many organisms which we

cannot see with naked eye is visible

like bacteria protozoa but not the

viruses until 1884 where we passed two

postulated that the rabies was caused by

something which is much smaller than

bacteria and which has a different way

of approaching and infecting organisms

and hosts at 1884 so again we pass to

started that thinking and then 1890s

even offski and base Ehrlich show

the disease in tobacco was caused by a

virus and it lists um this virus this is

tobacco mosaic virus another disease

which is very common in tobacco is

actually caused by virus which is funded

by different industries and the works

start to begin in 1890s you can imagine

it's not that far away so the research

gradually begins from the time period

and by the time at 1950s viral OG was a

multi fair like you know it's a what I

can say multi-phase discipline ok so

where we have you know we have

discovered a lot of different type of

viruses non-cellular particles with a

definite size shape and chemical

composition we know that they have

proteins in it they have some other

chemical components in it but they are

not a true living organism because they

are not behaving the same all the time

that means once we provide them with a

living cell they behave like a living

organism once we take away that cell

they are not behaving like a living

organism so the the property and the

nature of viruses depends on the

presence of another living cell which is

known as the host so whenever you find

the host the virus is living without the

host while the viruses are nonliving

material that's we cannot even put virus

in that free domain concept where this

is totally separate the foundations of

biology if you think about you know this

is a fascinating field and you probably

have heard of this term viruses and

every single lame and even heard this

term virus because whenever something

critical is thought about something

which is a very dangerous which can make

you sick and fell asleep all slick

example is virus in it because this term

is used not only in disease for a human

welfare as well as you know in computer

technology in this field the computer

virus so whenever say something can

destroy things or

bad for your health for your health of

your PC that's the virus nonliving

agents that infect all life-forms

example Farge versus animal virus animal

why this is goin attack animal cells

while Farge is attack bacteria that's

why we call them bacteriophage vial

cultivation differs from bacterial

cultivation near about 1,500 known

viruses are there and estimates to be

near about 4 lakh type of virus result

there among them we only identify and

know 1500 type and the more we develop

the electron micrograph e electron

microscopy sorry it allows us to

visualize viruses with much up close and

we gather much more information

regarding the different body component

of a virus like in case of bacterial

fast this is a picture of a typical

bacteria faj which has a head a collar

and the helical see the tail pin spikes

and all so what are the general

characteristics of a virus if you look

at this this pictures given here all

these three pictures are electron

micrographs of different size and shape

viruses these are round shape virus this

is also rod shaped virus this is like a

very rope lie coiled virus so viruses

are obligatory intracellular parasites

intracellular means they love to be

present inside the cell and they take up

nutrients from the host and they can

virtually make the host very sick and

can kill it they are filterable the

virus is Latin for the word poison they

contain DNA or RNA they contain a

protein code ok and the code is known as

cap seed made up of cap so mirrors ok

they are of various shapes this cap

seeds are of various shape some are

enclosed by an envelop some are without

the envelop those one without the

envelop are known as naked virus those

with the envelop known as enveloped

virus some viruses have spikes which are

mostly made up with proteins and most

viruses are

tissue specific so they have this tissue

specificity that means

certain virus will infect a certain type

of tissue for example hepatitis B

infects the liver tissue host arranged

it determined by the specific host

attachment sites and the cellular

factors that a virus has okay now

viruses are of different shapes and

sizes you can see this picture and that

can help you understand how much

diversify this virus is are and you can

see this equal I seems pretty big of a

cell in contrast with the size of the

viruses where you can see this is the

red blood cell 10,000 nanometer in

diameter ecoli near about 3,000 to 1000

nanometer in this case of a rectangular

rod shaped structure while the virus if

you think about most of them are very

very small you can see even the smallest

one bacteria phages near 424 nanometer

so the e.coli three thousand five

thousand and in contrast vector 524

nanometer only other than than

poliovirus 30 nanometer adenovirus 90

nanometer you can see it contains much

more spikes like that there are square

viruses or like rectangular viruses like

vaccine yeah 300 by 200 by 100 I can see

whenever we show you the different size

and shapes of virus you can see it's all

kind of geometrical shapes that are

available they are polyhedrons so they

have different planes and multiple

planes are present and we can see

different kind of structures you can see

videos like this kind of rod like

structure tobacco mosaic virus another

rod shape structure very long 250

nanometer by very thin 18 nanometer thin

you can see back to a Fajr T 4 that is

225 nanometer and bacteriophage m13 you

can see 800 into 10 nanometer only

Ravi's virus 170 to 70 nanometer so

they're of different type of shapes and

sizes and you can see ebola virus is a

pretty big 970 nanometer near about

equalise thousand nanometer range but

it's totally different of a structure so

and you

there's a huge place of a viruses and

virus community that we don't know about

we only know very fraction of that of

their virus community so maybe many

other variety of viruses are available

viruses as I said are polyhedron so why

polyhedrons because of the different

planes they have they can be either this

round shape measles virus

harpus simplex virus which is enveloped

in this case as you can see and there

are you know these are the shapes

poliovirus parvo virus okay polyhedral

shapes that are that are present always

okay so either icosahedral and different

kind of so these are icosahedral viruses

as you can see herpes simplex virus

poliovirus parvo virus now polio virus

and parvo virus are icosahedral viruses

without the capsule but so they are Nick

they are naked viruses and herpes

simplex is enveloped viruses helical

virus as you can see tobacco mosaic

virus rabies virus measles virus are

helical and there are complex virus

which does not have any fixed

geometrical structure they have multiple

structures linked for example back

shofars hades icosahedron and there is

this the rest of the region of the body

as you can see apart from this region

small linker is a collar and the rest of

the contractile body portion is of like

a tobacco mosaic virus helical pattern

so they are composed of multiple

geometrical shapes now the viral

structure can be divided into two

different type you know the covering and

the central core okay so the covering

can be of two different type capsid must

be present in a virus that is the

protein coat inside of which the genetic

material is present now there may or may

not be enveloped okay if envelop is

present enveloped virus if envelope is

absent then naked virus central core can

consist of DNA or RNA that is nucleic

acid molecule or they may also contain

along with that they also contain

enzymes not found in all viruses but in

very few cases they

enzymes present but most of the time

they only have DNA or RNA in the core

okay so viruses we are no resemblance to

since they don't have any protein

synthesizing machinery at all that's why

they are totally different

compared to any living cell they don't

have that their idea of protein

synthesis so they are not involved in

the physiological properties of a cell

they don't follow those rules so how

they survive and how they replicate how

they make their more copies they can

only make more copies when they attack

their host once they are attached with

their host they hijack the protein

synthesis machinery of their host and

then they utilizes the hosts enzymes for

the protein synthesis okay general

structure so we know the the basic

composition of a viral structure now if

you think about every single component

like capsids all viruses have cap seeds

as I told you earlier protein code that

enclose all the and protect the nucleic

acid of the virus and the capsid

together with the nucleic acid is known

as nucleo capsid and as you can see in

both this pictures this is the nucleic

acid you can see either it can be DNA or

RNA it doesn't matter but this is the

capsid this desire cos'è Hedren

structure is the cap seen both occasion

but in some occasion maybe this

icosahedron is the last layer there is

no other envelope so it is naked virus

so nuclear naked nucleo capsid virus and

some other occasion envelope the virus

where we have the cap seed and it is

covered by the envelope and they envelop

may or may not carry spikes okay for few

viruses the envelope protrude some

spikes out and some other viruses there

are no spike instead of the spike there

is the very other protein components

that are present in the envelope okay

but generally this spike help them to

interact with their host cell surface

and and adherence and start to get in

guard and inserted into the host cell

Anini each capsid is made of identical

protein subunits known as caps so

meanors okay so the cap summers are the

protein subunits which are linked with

one another stitched to one another to

form the icosahedron structure now there

are 2 structural capsid types available

helical and icosahedron two different

capsid types that are present now the

helical and icosahedral the difference

between the two if you look at here that

the helical are tobacco mosaic virus one

example and icosahedral is the one that

we studied here okay

folio virus that we that we discussed

earlier poliovirus herpes simplex virus

parvo virus those one icosahedral

contains 20 side with 12 corners so it's

a complex geometrical shape where

helical structure is just made up with

protein subunits they are present in

stack of one another like a helical coil

inside of which the genetic material is

present okay

and there are complex a virus like

bacterial phase which contains the

capsid that is a protein seed the

protein head and tail and there's a

spike and the attachment plate all these

things are present and inside the capsid

head the genetic material is present now

if you think about the viral envelop we

have talked about the cap seed you know

capsid is a must for a virus because it

is the primary protective envelope

primary protective structure for a virus

but in some viruses there are enveloped

external membrane that is present

outside so most of the animal viruses

have this envelope surrounding the

capsid layer itself so ackward when the

virus leaves the host cell generally

this capsid is formed due to the

modified version of the same membrane of

the host itself so let's assume that

this is the host cell and if this is

let's say the virus and the virus is

taking a part of the vesicle out

and once they bulge out from the host a

portion of the cell membrane from the

host cell is captured and that becomes

the envelop and that envelope as we know

the host cell surface contains many

receptors and other protein molecules so

that's why that that envelope of the

virus contains many of those cell

surface protein structures known as the

spikes okay so made of how many

identical put protein subunits it

protects the genetic material may be

involved in cell entry as well as say

Lexy because you know once they have

this envelope now next time when this

virus is going to attack another host

the fusion becomes lot easier because

now the host cell surface is a cell

membrane made up with phospholipid

membrane now this envelope is also made

up with similar phospholipid component

so they can interact quite well and the

fusion can be facilitated even faster

okay now this is another thing envelop

as I said that located outside of the

capsid and as I said it is a coil during

the viral maturation so you think about

this picture you can see that this is

the genetic material inside capsid

preventing the genetic material okay

composed of many protein subunit known

as cap Samir's and the envelope outside

may or may not contain spike but they

are mostly made during the maturation

that means while the virus is going out

the virus is coming out of the host okay

and it is fascinating facilitating this

virus to attack another healthy host

okay and the spikes help this virus to

specifically bind to their target tissue

and infect it

now what are the functions of capsid

envelope

I just penchant about it the capsid

protects the nucleic acid material from

an external damage okay and the envelop

helps the virus to fuse with another

healthy host and also it has some role

in tissue specificity if the envelope

contains spike now the complex viruses

complex virus is like bacteriophage

or poxviruses why we call them complex

virus particularly if you look at

bacteria fat this is vector alpha why we

call it complex because these virus they

don't have any particular geometrical

shape they have icosahedral head they

have a very thin collar and they have a

helical sheath and they also have a base

plate tail fibers are attached to it so

it's it's very complex with multiple

components okay

let's we call them complex virus because

they have multiple components all

together while pox virus lacks the

typical capsid and are covered by a

dense layer of lipoprotein only think

about it instead of having those complex

proteins of Venus known as the caps

amoenus they are only covered by dense

layer of aleppo proteins so there is a

lipoprotein layer only for pox virus

now it's all about we've talked about

that envelope and cap seed but what

about the core the core part of a virus

which definitely is required without

this part the virus is not virus itself

is the nucleic acid the makeup and then

the makeup of the nature of virus itself

viral genome can be either DNA or RNA

but can never be both it can be either

DNA or RNA unlike animals and plants I

know we have DNA RNA both genetic

material is the DNA but RNA is also

found to carry the message but in virus

they have either DNA or RNA not the both

they carries genes necessary to invade

the host cell and then simply they

redirect cells activity to make new

viruses so the virus's job is not to do

everything on its own that's why virus

is very simple and very lightweight and

very small because they don't need to

carry proteins inside the cell

they have protein coat outside but they

don't need to carry enzymes because what

they will do

once the infect and attack a host they

will hijack the host machinery of

protein synthesis and they will produce

the necessary proteins they need to get

multiplied and to get spread number of

genes varies for each type of virus few

to hundreds okay now if we compare

between two different type of virus DNA

viruses usually double-stranded but

maybe single-stranded now the DNA can be

either circular or linear we will talk

about the example letter RNA viruses

obviously are single-stranded may be

double-stranded may be segmented into

separated RNA pieces single stranded RNA

geebo genome ready for immediate

translation are positive sense RNA they

are known as positive sense

the single son Darren is immediately

ready for the translation process and

single-stranded RNA that must be

converted into a proper form unknown as

negative since RNA because you know when

we studied the transcription we've

talked about the same strand of the RNA

antisense strand of the RNA right coding

strand non-coding strand but in this

case this idea is little different in

case of virus and viral infection virus

is carrying RNA if that RNA is

completely ready to be translated we

call it a positively sense or positive

sense RNA but if the RNA needs to be

converted that means you know if that

RNA acts as a template to make another

RNA and that another RNA is translated

into proteins then the earlier RNA is

known as negative sense that means

positive sense RNA can only be converted

into proteins negative sense RNA needs

to be converted into positive sense RNA

first and then convert it into proteins

another very important thing is host

range and specificity you can see this

picture animation in the left hand side

here host range and specificity is

another very important property of virus

virus has its specific host or range it

can be narrow or it can be broad

generally virus host range is narrower

than a bacterial host range because they

can only attack a particular type of

host this is known as tissue tropism

like you know in case of plants we know

gravitropism phototropism so similarly

for virus is we have tissue drop ISM

that means a virus one particular virus

hepatitis B infects liver

so it is specific to infant liver cells

so even if you try and check whether

this virus infect other part of the cell

you you try it with a cell line if you

provide liver cell then only will see

the virus to be thriving okay

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