p katin cells cells and more cells

8/18/2019 P Katin Cells Cells and More Cells

1/35


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3/35

t


4/35

e l o IT

. . . . . .

, R.. . .. p b1; . 1m . 1

od

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of S

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S N

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5/35


6/35

Do you have a mir r

or

at home? Go

and

take a good

look at you rself. h

er

e is your nose, you r

ea

rs, yo ur eyes

and your mouth. the mirro r is large or if you have

al ready crawled up o n a chai r, then you can see yo ur

shoulde rs, you r arms a nd your stomach. Where d id all

those diffe rent

par

ts of you co me from?

h

ey simply

grew. Re memb

er

, yo u w

er

e sma ller on you r last birthday

th an yo u a re now. And you r arms were sma ller, and

your legs, and

your

ears, and eve n you r nose. And two

years ago on you r birthday you w

er

e even smalle r. Y

ou

probably don t remember wha t yo u looked like

thr

ee

yea rs ago.

I bel ieve me and if you don t, ask your

moth

er

, or fa the r or grandmot

her

befo

re

th at you were

very small.

And before that? Befor e that you were very tiny,

smaller han he smallest dot on a p iece of pa per. And

yo u

ca

n t give tha t dot legs or a rms or a nose. Not because

th e pe nc il is too thi ck, but beca use you did n ot hav e th em

th en. And you didn t have

ea

rs, or eyes, or a stomach. .

Yo u

wer

e a

ce

ll. One t iny, litt le cell.

you want

10

know what a cell is and where it came

from, read fur ther.


7/35


8/35

Le t s go to th e zoo. First we

wil

visit the lion.

The

re

h

e

i

s

.

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e

t

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.

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.

Not on ly the lion s nose is m ade of c ells, b

u

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o

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.

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t

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.

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w

o

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d

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how ma ny ce

s his nose h as?

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o

u

a

r

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a

l

s

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a

d

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f

t

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n

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u

s

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.

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u

t

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li

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t

l

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l

a

t

e

r

.

•

•

M

_

•


9/35


10/35

·

l

@ _

HOW

BIG ARE CELLS?

Very ve ry sma ll So small that you can only see them

with a microscope A cell

s

a million times sma ller th an

you

are

If

we

co

uld take

ce

lls and put them in a line on

your

rul

er

there would be

abou

t a th ousand of them

between the sma llest divisions on the ruler which is one

millimeter

The

cell is to a gra in of sand what the grain

of sand

s

a wheel on a car Even a tiny dot on a piece

of

pa

p

er

is a lot bigg

er

than the ord ina ry cell

See

how small

cells

are

?

•


11/35


12/35

J

WHAT COLOR ARE CELLS

When you go to bed tonight, look at yo urself carefu

ll

y.

You will p

robab

ly nd at least a few da rk spots, or birth-

ma rks, on your skin. They are

dark

because the cells in

them a re full

of

black o r da rk brown matt

er

And you have fed ce lls.

Th

ey

l

oat in your blood. In

each d

rop of

blood there are several million of these ce lls.

If

y

would take them

out

of that drop as is d

one

when

analysing yo ur blood , then the red color would leave the

blood along with those cells. Blood is red because

it

con-

tains red ce

lls

But most cells are colorless and transparent That is

why

ce

lls are colored with a special dye so we can see

them under the microscope. Then they become blue, red,

green and even luminous if they are dipped in special

luminous dye.


13/35


14/35

v

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A

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sa uce rs . T hey a

re

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b

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:

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h

a

p

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s

.


15/35


16/35

WHAT ARE CELLS MADE OF?

Basically cells are made of protein. And they have fat , lik

in soup broth. It even floa ts in the cell like fat in a soup bow

you let sit for too long.

he

outside of cells al

so

have a laye

of t l

Besides protein and fa t,

there

is a lso sugar. In some cell

ther

e is more, in othe rs less. Beets ha ve so much that they ar

even called suga r beets. Sugar which you sprinkle on you

cereal

is

made fr om the cells of these beers.

Cells c

onta

in other substances but th

ere

is

so little of them

thai we

will

not talk about them. Except

for

one.

A person needs all the parts of his body: his

ar

ms, and legs

and stomach. But the most im

po

rtant p

art

is his head and th

brain inside

it.

You see,

it

directs

the

arms, and legs, and even

the stomach. Your bra in remembers wha t h

ap

pen ed yeste rda

and thinks about what to do tomorrow. Wel there is somethin

a litt le like that

in

the cell.

h

is substance looks like thin threads

hin and long. And the

name

of it is long. t is

pro

bably th

longest and most complicated word you have ever heard. t i

de ox

y

ribo nu

-cleic acid.

h

ere

is no t much of it in your cells. Much less than protein

fat and sugar. But it is the most

imponant

substance in you

cells, and we will ta lk about it later. And so we don t have 1

write (

here

we go ) deoxyribonucleic acid

ever

y time,

we

wil

shorten it. We

will

take the rst letter

0 ,

and the letter N from

the middle, and then the lett

er

A instead

of

the word acid . So

from Ihat long word we have only three lette rs DNA. hat i

what eve

ryo

ne calls th is substance. BUI don t forget tha t th i

is only a shonened fo rm of th e real name: deoxyribonuclei

acid.


17/35


18/35

HOW ARE CELLS MADE

Cells

ar

e very ve

ry

complicated. So

co

mplicated that no one

knows eve ryt hing

about

how they

ar

e made. Scien tists

ar

e still

trying 10 fi nd out more. For th is there are complicated instru

ments and huge microscopes.

The

y are so big that special build

ings have

be

constructed for them. II is fun ny

thai

in

or

d

er

to see a cell hun

dre

ds of times smaller tha n a gra in of sand we

need a microscope as big as a house But with these microscopes

scientists ha ve been able to

learn

someth ing

abo

ut how a cell is

made.

Let us begin with the outside.

Al

l cells are sur rounded by

a thin covering made of protein and fat. This covering is called

a membrane or a plasma membrane to be more exact. It is so

th in that you can barely see it even with the most powerful

microscope.

if

you look very carefully you will notice that the

line

ac tually two.

The

membrane

ma

de of

two layers -

the

outer and the inner

Though it is very diffic ult to gel a good lo

ok

at the ce ll mem

brane it is still very important . I will te ll you why.

Your mother and fa ther feed you. Sometimes they give you

a delicious pie

and

at ether rimes not so delicious cereal. But

you need eat both because they are good fo r you. T hey

wou ld not give you food that was bad f

or

you.

This is what

rotein

Q cell

or plasma

mem r ne

I

at

s like

•

-


19/35


20/35

·

•

Cells

have

decide

for

themselves what is good for them

and

wha t is harmful. Ma ny different substances float

around

them. But what is

amazi

ng is that only good things get into the

cell. It is the membrane which sees 10 this.

t

allows useful sub-

stances to pass freely

bU

I it

doe

s not lei ha

rmf

ul substances in.

This

means it can

distinguish one substance from another. So

far we know very little of how

it

does this.

But that

is

n all the ce ll membrane can do

When cells touch one anot

her

, thei r membran es slick together.

If they did not do this we wou ld fa ll apart into millions of separate

cells. But a cell on ly sticks to a ce

ll

which is the same kind and

does not stick 10 a cell which is different. Th is m

ean

s the

membr ne c n distinguish one ce

ll

rom nother

So, the outside of a ceU

is

its memb

rane

. And what

is in-

side? Everything that is insi

de

the m

emb

rane

is called eyre-

plasm. t is the maj

or pan of

the cell. And there

is

a reason.

Cytoplasm is like a large factory. T he protein

and

sugar and fat

which cells are made of are all produced in the cytoplasm.

J ust like in a real fac tory, the f nish

ed

products are sent

to different places on order. Some remain in the cytoplasm,

ot hers

ar

e sent f

ur

ther, to the m

embran

e,

and

sti

ll

others

ar

e

sen t out

of

the ce ll like, f

or

examp

le, the sa liva in your

mout

h .

And the substances in a cell a re not the only ones to move in

different directions. T he cell itself does.


21/35


22/35

•

Do

you

remember when you cut

you

r fi nger not lo

n

ago

ry

to fi nd the cut. hereis alm ost no sign

of

it. Because cells

moved towards the wou nd fro m a

ll

sides a nd filled

it

up. Your

cut

healed. But ce lls do no t ha ve a r ms a nd legs. In o rder to mo ve they

ha ve to stretch o ne side a nd pull up the o ther like a wo rm . For

this the ce ll has muscles like yo u and I do only they a re ve ry

hin

h

ese are also located in the cytoplas m.

An d

nall y we ha ve co me

to

the most impo rta nt

pan he

nucleus is in th e cytoplas m

and

it contains

the

thi ng the cells need

most. Yo u haven fo r

got

te n a lready ha ve you?

hat

s rig ht

ONA. Something so imp

ortant

must be gua r

de

d. hatis wh y the

nucleus is surro unded by its o wn membr

an

e ca lled a nu cl

ear

membr

an

e or a nuclea r envelope. J ust like

the

cell is. T he

nucleus is much sma lle r than the cell so the l

on

g threads of DNA

a re wrap ped in tigh t bra ids so they ca n a ll 1. hese

ar

e called

chromosomes.

Eac h of you r ce lls has 46 of them. And ea ch of mine does too.

T he cells of

normal people contai n 46 chromosomes. Read th e

next chapter 10 fin d out why we need ch romoso mes.

Nucleus

ow a cell is made

ell orplasma

memb

r n

yt p

asm

Nucleus


23/35

ucle r

membr ne

ucleus


24/35

®

WHY DO WE NEED CHROMOSOMES?

A

mouse

d

oe

s not look like a n el

ephant

a nd a beetle

does not lo

ok

like a co w. No one would mix you up with

the boy next door o r co nfuse him with his broth

er if

they

are not

twin s.

Why is that ? You might say that a mou se is small

and

a n elephant is big

and

has a

tr

unk.

Th

e

oy

ne x t door is

sn ub-nosed a nd has frec kles a nd doe s not loo k a nythi ng

like you . .

And ag ain I ask

why

y doesn t a m

ou

se look like

an elepha nt? Why does the boy next doo r ha ve a snub

nose and freck les

and

yo u don t?

y

don t people look

like one a nothe r? ndwhy don ta nimals?

T h s a depends on chr omosomes. A mouse s chromo

so mes are not like th ose of an elephant and yours

are

not

like those of

the

boy next door. Everything that makes one

living

cr

eature different from another is contained in the

chromosomes. And how th e

ce

lls co me togeth

er

to make

a nose in stead of a stomach . And what color some

one s eyes should be. And th e color of his hair. And

th e sha pe of h is

ea

rs. And th e length of h

s

n

ng

er

s.

All of this infor ma tion is co ntai

ne

d in the chro mo

so mes. .

The

language of chromosomes is

not

simple . And the

re cordings do not loo k anythin g like ou r writing. By the


25/35


26/35

way people did not a lways wri te with letters he Chinese

nd

J apanese still use specia l symbols instead of letters

ca lled hieroglyphics And several nationalities in ancien t

times used knots

on

a rope for recording infor

m -

tion

T he c

hro

mosomes look like those kno t recordings

But instead of knots specia l substa nces r e faste ned to the

threads of DNA here a re only fou r of them: adenine

guanine cytosine a nd thymine T hey a re shortened to the

fi

rst letters of

e ch

word: A G C nd T

hey

re like

the letters of the cell alphabet Words re made from these

Only in ou r language words a re

of

diff

er

en t lengths

here re short ones like ca t and long ones like rh inoce-

ros But in the language of chromosomes all the words

have only three letters here is CAG TAG AGA CCC

and m

or

e

oge

the r they f

orm

l

on

g orders showing what

how nd when the cell should do something

he language of chromosomes is very precise

nd

even in the longest recordings there are usually no

mist

k

es

•

]

i


27/35


28/35

You a lrea dy know tha t you grew from one single ce ll B how did

that happen? T he ce ll is so

tiny

and look at how big and tall you have

ecome

I will

te ll

you how it happened

h

e cell bega n to divide

irst

into

two and the n the two into four Each of them divided in half again and

th is

went

on and on II is impossible 10

count

how many cells a re in your

body now Pr

obab

ly many millions

And you are still growing Every second the cells in your body con-

tinue to divide and

there are

m

or

e and m

or

e

of

them In your arms and

in

your

le

gs

an

d in your ea rs And each of

those

ce lls has a membrane

citoplasm and a nucleus And in the nucleus the re are 46 chromosomes

And the chromosomes in the new ce lls are exactly like those in th e very

f rst one This is because the cell makes anothe r nucleus membra -

ne cytoplasm and complete set of chromosomes before it divides

So when it does divkle everyth ing is evenly split between

th e

WO

ce lls

h

is way there are ident ical chromosomes in

all

the ce lls and that

means Ihe orders which

are

written on them are also identical

B there is a r iddle The orders are identical but the cells are differ-

ent Some are round ot hers are oval some are black

others

are red

Maybe not everythi ng is written in the ch romosomes? Scie ntists th ink

everything is But some ce lls obey one orde r while othe r ce lls obey

anot

her

We

still

do not kno w everyth ing about how they choose the necessary

order But we need to Because various diseases sta

rt

be

cau

se the cells get

mixed up and do not know which order to follow Perhaps by the lime

you grow up scient ists will have learned 10 manage the disobe dien

ce lls and to save people from many illnesses Maybe you will be the

one to do that

:

_


29/35

ow

U

unt

i to0 0

•

•

t

r

1 .. . .


30/35

HOW ARE CHILDREN MADE

You ca n pa rt ly answer this question yourself. T here was one

single cel l.

It

divided and divided and there were m

or

e a nd more

ce lls until f nally a child was made.

But where d

i

the

fi

r5 cell come f r

om

th

e one th at began

it

all? tcame from two - one from the mother and one from the

father.

Among the millions of cells whi

ch

you r

body

is made of there

are special cells. T hey

can

do things tha t other cells ca nnot.

Th

ey

ca n join and serve as the beginning of a new life. All animals and

all humans have these cells. The jo ining of two of these cells

one from your father and one from your mother created the

one which you began from. Bur before these cells joined into one

both of them had gotten rid of half of their chromosomes

otherwise... Otherwise you wou ld have twice as many as you

need. You would have 92 instead of 46. And that should not

happen.

Now you know that half the chromosomes in your cells came

from your mother and half from your father. But your mothe r got

half of her chromosomes from h

er

mother your grandmother

and half from he r father your grandfather And the same is true

of your father. So some of your chromosomes came from you r

grandmot

he

rs and your grandfathers. And one or two from

your

gr

ea t-grandmothe r. So you sti

ll

look a

l

nle

l

ke her.

And maybe in many years your great-grandson will look

like you.

See how wonderfully everyth ing is done

•


31/35


32/35

~ ~

A

BOY OR

A

GIRL

Who will co me f rom that cell, a oy o r a girl? T h is also depends on th e

chromosomes.

When you look at chro mosomes under the micr oscope, you can see

th at th ey are all d ifferent. Some a re sho rt while oth ers are long. So me a re

shaped like sling-sho ts, and ot he rs are straight

ke sticks.

Scientists have not discovered which ch ro mosomes dete rmine the

co lor of your eyes o r the shape

of

yo ur nose. But the chromosomes which

d

eter

mine whet h

er

a child

w

be a girl or a oy a re kn own and e ven ha ve

th eir own names. T hey a re called by letters of the alphabe t. One is the

leite r X, an d the oth er is the letter Y.

Like a ll e ther chromosomes, these two come to you fro m you r par

en

ts.

Th

e X chromosome ca me from you r mothe r. Later you will

e

ab le to say,

whic h c hromosome came from you r fathe r.

You see, both yo u r mother s cells and your father s cells have the X

ch ro mosome. But t he Y ch ro mosome

is only in your

fath

er s cells.

Th

is

c hromosome con ta ins the in

fonn

at ion which makes a boy diff

er

ent fr om

a

girl .

Yo u already kn ow that be for e two cells join togeth er, they ge t rid of

half their chromosomes. In t he moth

er

s cell, on ly an

c hro mosome re

mains because she does not have a Y chromosome ) . B UI in t he father s

cell the re can be either an or a Y chromosome. T h is is what decides who

will be born after a moth er s an d fa the r s cells join.

th e fathe r s

chro mosome joins with the mot

he

r

s, th en the child will be a girl.

But if the Y chro moso me was in th e father s cell, t he n a boy

will

be b

orn

.

Now you can say wh ich ch romosome yo u got from you r fa th er.


33/35


34/35

NOW WH T

O YOU KNOW

A great dea l You know that every ving thing is made of

cells.

Y

know tha t cells multiply by dividing in ha lf. You know

that you c me from one single cell that appea red when a cell from

you r fathe r joined with a cell fro m

your

mother. And you have

also lea

rne

d about how a cell is made: a membrane on the outside,

cytoplasm inside, and a nucleus in the cytoplasm. In the nucl

eu

s

re chromosomes containing all the information about what the

cell should do.

See how many interesting th ings you can learn by asking

just one simple question : Where did I come from? And think

how many i

nter

esting things you still do not know. Why does a

cell suddenly begin to divide? How does it

i

ght against h rmfu l

germs? How does a cell move? How do new animals ap pea r if

children always resemble their p rents? Why are plants green

nd

we

r

en

t? Why is a frog cold, while we have a tempera

ture

of

36.6 degrees Celsius if we do not have a feve r? And why do we get

fevers?

Some of these questions do not h ve answers yet. We still

have much to le rn. And 10 do that we must study.

you un-

derstood what was

wr

itten in this book, then you ca n say that you r

studies have begun. Even if you do not rememb

er

ev

er

ythi ng,

that is no problem. Read this book again afte r a wh

e. And maybe

you

will

fi

nd othe r books about the tiny cells which make up grass,

and trees, and you r gr ndmother, and you yourself, and even

(but this is just between us)

your

fathe r s nose.


35/35

p katin cells cells and more cells

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