a

Centrosome and Centrioles

in our discussion on the cytoskeleton of

eukaryotic cells we briefly mention a

structure known as the central zone but

what exactly is the central cell and

what are its functions these are the

questions that we're going to address in

this lecture so the centrosome is our

microtubule organizing Center of

eukaryotic cells also known as MTO C now

one centrosome is found per eukaryotic

cells and only animal eukaryotic cells

have our centrosomes plant cells and

fungi do not have centrosomes they have

other structures that are responsible

for building microtubules building and

organizing microtubules now every single

one of our centrosome in any given

eukaryotic animal cell consists of a

pair of two centrioles that are oriented

at a 90-degree angle with respect to one

another and these two centrioles are

basically embedded in hundreds of

proteins so let's suppose this is our

eukaryotic animal cell so this is our

nucleus and right next to our nucleus we

have the centrosome so we have hundreds

of proteins in this space we have a

condensed mass of proteins and inside

that proteins we have two centrioles

that are oriented at a ninety degree

angle with respect to one another and we

also have these microtubules that

permeate throughout the entire cell now

what exactly is the function of our

central zone the central zone basically

functions in our cell cycle it helps the

cell divide so during our inter phase of

the cell cycle we replicate our central

zone and during our prophase the

centrosome basically migrates to both

ends and then they create or extend

those microtubules that grab our

chromosomes and separate those

chromosomes

during cell division now the centrosome

is also involved in organizing and

creating and extending the microtubules

that constitute our cytoskeleton

remember as the cytoskeleton is

basically the scaffolding of our cell it

gives the cell structure and it gives

the cell its shape and there are three

different types of fibers and one of

these fibers are our microtubule fibers

so within a centrosome we have our

centrioles what exactly is a centriole

so the center of the centrosome contains

a pair of centrioles that are a

cylindrical array of nine triplet

microtubules that are connected to one

another by special protein connecting

fibers now this pattern is commonly

known as the nine to three microtubule

pattern and we see that the centrioles

are simply specialized structures

specialized microtubule structures now

what exactly is the structure of our

central what exactly does it look like

well it looks something like this

we have the top to bottom view of our

central and the side view of the

centrioles so we have 1 2 3 4 5 6 7 8 9

triplets each one of these consists of

not three of these individual

microtubules and each one of these

triplets is connected by our connective

protein fiber now if we take this

centriole and we flip it this way we

rotate it sideways we get the following

side view so we have the nine triplets

that are connected by these purple

regions our fibers so now that we know

what the centrosome is and what the

centriole is what exactly is the

function of our central that are found

within our central zone so we have three

very important functions so function

number one is basically what we

mentioned earlier the centrioles which

are found in

is centrosome are involved in cell

division in separating our chromosomes

during our cell cycle so centrioles are

involved in the formation of mitotic

spindle fibers during cell division

however recent evidence shows that if we

actually destroy our centrioles our cell

cycle still takes place mitosis still

takes place so basically we can imagine

that centrioles make our separation of

chromosomes very efficient however they

are not exactly necessary for mitosis to

actually take place now what exactly is

the second function of the centriole

well basically the centriole is our

region that extends and creates those

microtubules and microtubules compose

our our cytoskeleton now the

cytoskeleton is basically responsible

for arranging and organizing the

organelles found inside our cell so we

see that the placement of the centrioles

within the cell determines the position

and location of the nucleus as well as

the other organelles inside our body and

that's exactly why the centrosome that

contains Essentials is found right next

to our nucleus in fact inside neuron

cells the location of our central zone

basically determines into which

direction the axon will grow on any

given neuron cell so this makes sense

because the microtubules are the largest

and the thickest components the thickest

fibers of our cytoskeleton cytoskeleton

is composed of three different types of

fibers we have microfilaments

intermediate filaments and our

microtubules and finally the third

function of the centriole so the

centrioles are responsible for forming

the flagella and the cilia that

cells have so one of the centrioles

remember we have two centrioles one

central is called the daughter central

the other central is called the mother

centriole so it's the mother centriole

that can develop into the basal body and

the basal body is basically the

structure in the cell that is

responsible for forming cilia as well as

flagella and cilia and flagella are two

types of specialized structures that

basically allow the cell to move they

mobilize the cell so we see that all

those centrioles are not exactly

necessary for the survivor of the

individual cell the centrioles and

centrosomes are necessary for the

survival of the organism as a whole for

example if we examine a specific type of

cell that needs flagella our sperm cells

if specific if our sperm cells do not

have centrioles or centrosomes they

cannot form our basal body and they

cannot form the flagella and a sperm

cell without a flagella will not be able

to reach the target cell and that means

our organism will essentially die off it

will not survive although maybe

individually the cells will in fact

survive