Cell organelles.pptx

7/25/2019 Cell organelles.pptx

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Cell Organelles

LS1101 : Introduction to Biology

Anindita Bhadra

E-mail: abhadra@iiserol!ac!in


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Cells "nder a #icrosco$e


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A %enerali&ed Cell


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The cell/plasma membrane is the thin nearly invisible structure that

cytoplasm of the cell.

It also connects the endoplasmic reticulum, and the nuclear membr

In eukaryotic cells, organelles are bounded by plasma membranes.

The cell membrane encloses the cell, defines its boundaries, and maessential differences between the cytosol and the extracellular envir

All biological membranes have a common general structure: each i

film of lipid and protein molecules, held together mainly by noncov

interactions.

'he Cell #embrane


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'he Cell #embrane

ell membranes are structures, and most

molecules are able to

in the plane of the m

The (luid mosaic mmembrane was first

!. ". !inger and #. $

&'().

*hospholipids

*roteins*hospholipids

*roteins


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'he )luid #osaic #odel

+ydrocarbon tai

*hosphate group

double bonded o

epending on the temperature and lipid composition, phospholipid

transition between a -gel or more solid state0 and a li1uid or mor


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In a living organism, the composition of the phospholipid bilayer i

membrane is generally maintained in a li1uid state, which maximi3

proteins and the dynamic capabilities of the membrane.

The lipid molecules are arranged as a continuous double layer abou

The lipid bilayer serves as a relatively impermeable barrier to the p

water2soluble molecules.

5loating around in the cell membrane are different kinds of protein

generally globular proteins. They are not held in any fixed pattern

float around in the phospholipid layer.

'he )luid #osaic #odel


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'y$es o( *roteins:

&. Integral: trans2membrane proteins6

span the hydrophobic interior

a. hannels

b. arriers

). *eripheral: not embedded6 attached

to the surface

a. 7n3ymatic activity

b. !tructure

)unctions o( membr

&. Transport

). 7n3yme

8. 9eceptor sites

. Intercellular ;unctio

4. ell2cell recognitio


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arbohydrates c

associated with t

surface of the m

Cholesterol2 sti

membrane by co

phospholipids

%lycoli$ids2 sig

%lyco$roteins2

attached chain o

antibodies0

Other #olecules


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Channel *roteins:form small openings for

diffuse through

Carrier *roteins:regulate transport and dif

+ece$tor *roteins:molecular triggers that s

responses such as release of hormones or op

channel proteins0

Cell +ecognition *roteins:=arker proteins

the cell to other cells

En&ymatic *roteins:carry out metabolic re

#embrane *roteins


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Carrier $roteins are peripharal protein

not extend all the way through the mem

bond and drag molecules through the b

and release them on the opposite side,

'rans$ort *roteins

Channel $roteins extend through the bilipid layer.

They form a pore through the membrane that can

move molecules in several ways, including diffusion,

which re1uires no energy.


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Sym$orts also use the process of diffusi

a molecule that is moving naturally into diffusion is used to drag another molecu

5or example, glucose hitches a ride with

'rans$ort *roteins

!ome proteins actively use energy from the A'*sin the cell to drag

from area of low concentration to areas of high concentration work

against diffusion0 an example of this is the sodium/potassium pump

energy of a phosphate shown in red0 is used to exchange sodium a

potassium atoms.


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#arer *roteins

They play an important role in organ transplants. If the marker prot

transplanted organ are different from those of the original organ the

re;ect it as a foreign invader.

#arer $roteins extend across the ce

and serve to identify the cell.

The immune system uses these protei

friendly cells from foreign invaders.

They are as uni1ue as fingerprints.


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Endocytosis

An important group of peripheral membrane proteins are water2so

en3ymes that associate with the polar head groups of membrane ph

>ne well2understood group of such en3ymes are the phospholipas

hydroly3e various bonds in the head groups of phospholipids.

These en3ymes have an important role in the degradation of damacell membranes.

$arge molecules that are manufactured in the cell are released thro

membrane by the reverse process, called e,ocytosis.


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The cell membran

engulf structures ttoo large to fit thro

pores in the memb

This process is kn

endocytosis.

In this process the

itself wraps around

and pinches off a v

the cell.

Endocytosis


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Cell Organelles

LS1101 : Introduction to Biology

Anindita Bhadra

E-mail: abhadra@iiserol!ac!in


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'he Cell )actory


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'he Cell )actory

The cell membran

boundary to the cregulates what en

the cell.


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'he Cell )actory

The cytoplasm or

the factory floor, all the organelles.


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'he Cell )actory

The cytoskeleton is re

maintaining the shapethe beams and pillars o


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Cytoseleton

The cytoskeleton is a system of protein filaments in the cytoplasm

cell that gives the cell shape and the capacity for directed movemen

Intermediate (ilamentsprovide mechanical strength.

#icrotubules determine the positions of membrane bound organel

intracellular transport.

Actin (ilaments determine the shape of the cell?s surface and are n

whole2cell locomotion.

A large number of accessory $roteins are associated with these fil


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Cytoseleton

7ach type of cytoskeletal filament is constructed from smaller prot

The cell is able to build large cytoskeletal structures by the repetiti

large numbers of the small protein subunits.

@ecause these subunits are small, they can diffuse rapidly within cy

whereas the assembled filaments cannot.

In this way, cells can undergo rapid structural reorgani3ations, disa

filaments at one site and reassembling them at another site far away


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Cytoseleton

7ach type of cytoskeletal filament is constructed from smaller prot

The cell is able to build large cytoskeletal structures by the repetiti

large numbers of the small protein subunits.

@ecause these subunits are small, they can diffuse rapidly within cy

whereas the assembled filaments cannot.

In this way, cells can undergo rapid structural reorgani3ations, disa

filaments at one site and reassembling them at another site far away


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'he Cell )actory

The endoplasmic retic

assembly line of the ce


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Endo$lasmic +eticulum

The 79 consists of membranous channels that wind through the c

It is the transport network for molecules targeted for certain modi

specific final destinations, as opposed to molecules that are destin

freely in the cytoplasm.

There are two types of 79, rough and smooth. 9ough 79 has riboto it, and smooth 79 does not.

9ough 79 produces proteins, smooth 79 produces steroids.


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'he Cell )actory

The ribosomes are the wo

on the assembly line of th


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+ibosomes

The ribosomes are the sites of protein synthesis in the cell.

They are mostly attached to the 79, but some are also free, in the

A ribosome, formed from two subunits locking together, functions

1. 'ranslateencoded information from the cell nucleus provided

ribonucleic acid m9%A0,/. Lin together amino acids selected and collected from the cyt

transfer ribonucleic acid t9%A0,

. E,$ortthe polypeptide produced to the cytoplasm where it w

functional protein.


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The proteins produced by the free ribosomes are mostly used with

while those produced by the ribosomes on the 79 are transported

In a mammalian cell there can be as many as 10 million ribosome

!everal ribosomes can be attached to the same m9%A strand, this

called a $olysome.

9ibosomes have only a temporary existence. hen they have syn

polypeptide the two sub2units separate and are either re2used or br

+ibosomes


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9ibosomes can ;oin up amino acids at a rate of )BB per minute.

9ibosomes are organelles composed of ribosomal proteins ribopr

ribonucleic acids ribonucleoproteins0.

A eukaryotic ribosome is composed of ribosomal 9%A and about

and has a molecular mass of about ,)BB,BBB a.

9ibosomes are found in prokaryotic cells, eukaryotic cells, chloro

mitochondria.

+ibosomes


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There are about &B billion protein molecules in a mammalian cell

produce most of them.

The proteins and nucleic acids that form the ribosome sub2units ar

nucleolus and exported through nuclear pores into the cytoplasm.

The two sub2units are une1ual in si3e and exist in this state until ruse.

The larger sub2unit has mainly a catalytic function6 the smaller su

decoding one.

+ibosomes

'h C ll ) t


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'he Cell )actory

The #olgi apparatus is th

packaging department of

% i A


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'he %olgi A$$aratus

The #olgi apparatus looks similar to the 79. It is a set of ( or C fl

saccules between the 79 and the cell membrane.

It is involved in the formation of lysosomes and other en3yme2con

cellular inclusions, and in the formation of secretory granules in c

#olgi apparatus acts as a condensation membrane for the concentrproducts produced elsewhere into droplets or granules by losing w

transported to the cell surface for export.

The principal function of #olgi complex is secretion.

'h % l i A t


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#olgi apparatus has been shown to be a great intracellular centre o

formation in some cell types.

#olgi body in endocrine cells helps in secretion of hormones.

#olgi bodies of plant cells synthesi3e all polysaccharides such as

hemicellulose and microfibrils of a2cellulose. These are packagedsecretion.

#lycoproteins are formed in the #olgi complex by the attachment

carbohydrate to the protein products of the endoplasmic reticulum

'he %olgi A$$aratus

'he Cell )actor


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'he Cell )actory

Desicles in the cell act as

factories.

i l


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esicles

Desicles are double membrane bound sacs carrying different produ

part of the cell to another.

They are often associated with the #olgi apparatus.

They also carry food, en3ymes, waste products.

They are involved in storage, transport and phagocytosis.

$ysosomes and peroxisomes are two kinds of vesicles found in th

'he Cell )actory


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'he Cell )actory

The =itochondria are the

of cells.

#it h d i


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#itochondrion

The mitochondrion is the site of cellular res$iration.

The mitochondrion is a double membranebound structure filled

matri,.

The outer membrane is selectively permeable, ;ust like the cell me

The inner membrane is folded inward to provide extra surfaces fo

respiration.

These folds are known as cristae.

#itochondrion


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#itochondrion

The inner membrane is freely permeable only to oxygen, carbon d

water.

The inter2membrane space has an important role in the primary fu

mitochondria, which is oxidative phosphorylation.

The matrix contains dissolved oxygen, water, carbon dioxide, the intermediates that serve as energy shuttles, en3ymes etc.

=itochondria produce adenosine triphosphate AT*0 by systemati

extracting energy from nutrient molecules substrates0.

'he Cell )actory


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'he Cell )actory

The vacuoles are storage

cell.

acuole


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acuole

Dacuoles serve a variety of functions, including storage.

They have an irregular shape and are usually very large in plant ce

8B E 'BF of the cell volume.

They contribute to the rigidity of the plant using water to develop

pressure.

They also store nutrient and non2nutrient chemicals and break dow

molecules.

'he Cell )actory


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'he Cell )actory

The nucleus is the seat of con

2ucleus


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2ucleus

=ost eukaryotic cells contain a nucleus, which is seen under the m

dark mass inside the cell.

The nucleus is surrounded by a double membrane, known as the n

en3elo$e.

A fluid2filled space or $erinuclear s$ace is present between the twnuclear membrane.

The nuclear envelope is a highly regulated membrane barrier that

compartmentalisation of the nucleus from the cytoplasm.

2ucleus


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2ucleus

2uclear $ore com$le,es %*s0 are large proteinaceous channel

the nuclear membrane and allow transport of molecules in and ounucleus.

2ucleo$lasm, also known as karyoplasm, is the matrix present in

nucleus.

#enes are located in chromosomesinside the nucleus.

The nucleus is the site of %A re$licationand transcri$tion.

2ucleus


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2ucleus

The %A is transcribed into pre messenger 9%A pre m9%As0 in

nucleus. The mature m9%A after splicing is exported to the cytoptranslation.

The clearest substructure in the nucleus in most eukaryotes is the

which is the site of r%A transcription and ribosome biosynthesis

The nucleolus is the largest structure in the cell nucleus.

The nucleolus has numerous other functions including assembly o

recognition particles, modification of transfer 9%As and sensing c

2ucleus


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2ucleus

The nucleolus disappears when a cell undergoes division and is re

the completion of cell division.

2uclear s$ecles are highly dynamic, irregularly shaped nuclear

enriched with pre m9%A splicing factors.

>ne of the earliest ideas about the evolution of the eukaryotic cell

organelles formed when the plasma membrane grew into the cell a

walling off parts of the cell. This idea, called the autogenic hy$ot

correctly explain the origin of the nuclear membrane, endoplasmi

and #olgi apparatus.

2ucleus


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2ucleus

7xceptions to the rule:

#ultinucleated cells: =ammalian skeletal muscle cells6 plasmod

molds6 metastati3ing tumor cells.

Enucleated cells: =ammalian red blood cells.

olly was born from an enucleated oocyteG

Chromosomes


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Chromosomes

hromosomes are packaged forms of %A

inside the nucleus.

hromosomes are not visible in the cell?s

nucleusHnot even under a microscopeHwhen

the cell is not dividing.

=ost knowledge of chromosomes comes from

observations of %A during cell division.

The haploid human genome contains approximately 8 billion base

packaged into )8 chromosomes

Chromosomes


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Chromosomes

7ach chromosome has a constriction point

called the centromere, which divides the

chromosome into two sections, or -arms.

The short arm of the chromosome is labeled

the -p arm. The long arm of the

chromosome is labeled the -1 arm.

The location of the centromere on each

chromosome gives the chromosome its

characteristic shape, and can be used to help

describe the location of specific genes.

Chromosomes


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4istone $roteinsare involved in packaging chromosomal %A in

microscopic space of the eukaryotic nucleus.

The histone2%A complex is known as chromatin.

+istones are a family of small, positively charged proteins termed

+)@, +8, and +. %A is negatively charged, and thus binds to h

The basic repeating structural and functional0 unit of chromatin i

nucleosome, which contains eight histone proteins and about &<

%A

Chromosomes


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4istone $roteinsare not present in most prokaryotes.

*rokaryotes package their %A by supercoiling.

=ultiple proteins act together to fold and condense prokaryotic

particular, one protein called +, which is the most abundant prot

nucleoid, works with an en3yme called topoisomerase I to bind %

introduce sharp bends in the chromosome, generating the tension negative supercoiling.

>nce the prokaryotic genome has been condensed, %A topoisom

gyrase, and other proteins help maintain the supercoils.


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Cell organelles.pptx