(676547914) 5. Cell Structure n Functions

7/24/2019 (676547914) 5. Cell Structure n Functions

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8. CELL:THEUNITOF LIFE

- A cell is the fundamental structural and functional unit of all living organisms.

- All organisms are composed of cells. They include unicellular organisms and multicellular organisms.

- Robert Hooke: Discovered cell.

- Anton on Leeu!en"oek: First observed and described a live cell.

- The invention of the com#oun$ and electron microsco#es revealed all the structural details of the cell.

CELL

THEOR%

- &alt"ias 'c"lei$en ()8*8+ observed that all plants are

composed of different kinds of cells.

- T"eo$ore 'c"!ann ()8*,+ reported that cells had a thin

outer layer (now known as plasma membrane!". #e also

found that cell wall is a uni$ue character of plant cells.

#e proposed the hypothesis that the bodies of animals

and plants are composed of cells and products of cells.

- %chleiden & %chwann formulated the cell t"eor-.

- Ru$ol irc"o! ()8//+ first e'plained that cells divided

and new cells are formed from pre-e'isting cells (Omnis

cellula-e cellula". #e modified the cell theory.

- ell theory states that)

(i" All living organisms are composed of cells and

products of cells.

(ii" All cells arise from pre-e'isting cells.

AN OERIE0OFCELL

- All cells contain a semi-fluid matri' called c-to#lasm. *t

is the main arena of cellular activities and chemical

reactions. This keeps the cell in living state!.

- All cells contain non-membrane bound organelles called

Ribosomes. These are found in the cytoplasm+

chloroplasts (in plants"+ mitochondria and on rough ,.

- ells differ in sie+ shape and activities.

o 'mallest cells: /ycoplasmas (0. 2m in length"

o Largest isolate$ single cell: ,gg of ostrich.o Longest cells: ,.g. 3erve cell.

o %ie of bacteria) to 4 2m.

o #uman 5s are about 6.0 2m in diameter.

- 5ased on the functions+ shape of cells may be disc-like+

polygonal+ columnar+ cuboid+ thread like+ or irregular.

- ells are 7 types) 1rokar-otic cells 2 Eukar-otic cells.

1RO3AR%OTICCELL'

- They have no membrane bound nucleus and organelles.- They include bacteria4 blue5green algae4 m-co#lasma

2 11LO (1leuro 1neumonia Like Organisms+.

- They are generally smaller and multiply more

rapidly than the eukaryotic cells.

- They vary in shape & sie. ,.g. 5acteria have 8 basic

shapes) 6acillus (rod like"+ Coccus (spherical"+ ibrio

(comma shaped"+ and '#irillum (spiral".

Cell organelles in #rokar-otic cells

). Cell En7elo#e

- *t is a chemically comple' protective covering.- *t is made of tightly bound layers.

o l-cocal-9: 9uter layer. *t differs in composition and

thickness among different bacteria. *t may be a slime

la-er (loose sheath" or ca#sule (thick & tough".

o Cell !all: /iddle layer. %een in all prokaryotes. *t

gives shape to the cell and provides a structural

support to prevent the bacterium from bursting or

collapsing.

o 1lasma membrane: *nner layer. *t is semi-permeable

in nature and interacts with the outside. This is

structurally similar to that of the eukaryotes.

- 5ased on the types of the cell envelopes and response to

:ram staining (developed by :ram"+ bacteria are 7 types)

o ram #ositi7e: They take up and retain the gram stain.

o ram negati7e: They do not retain the gram stain.

. &esosome2 C"romato#"ores

(&embranousstructures+

- &esosome is formed by the infolding of plasma

membrane. *t includes 7esicles4 tubules 2 lamellae.

- Functions: /esosome helps

o *n cell wall formation.

o *n D3A (chromosome" replication.

o *n Distribution of chromosomes to daughter cells.

o *n respiration and secretion processes.

o To increase the surface area of the plasma membrane

and enymatic content.- C"romato#"ores are membranous infoldings in some

prokaryotes (e.g. cyanobacteria". They contain pigments.

*. Nucleoi$

- *t is formed of non-membranous (naked" circulargenomic

;NA (single chromosome; :enetic material" & protein.

- /any bacteria have small circular D3A (#lasmi$+

outside the genomic D3A. *t gives some uni$ue

phenotypic characters (e.g. resistance to antibiotics" to

bacteria.


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- 5acterial flagellum is made of parts < ilament4 "ook

and basal bo$-. The filament is the longest portion and

e'tends from the cell surface to the outside.

/. 1ili an$ Fimbriae

- These are surface structures that have no role in

motility.

- The #ili (sing. =ilus" are elongated tubular

structures made of a special protein (#ilin+.

- The imbriae are small bristle like fibres sprouting out

of the cell. *n some bacteria+ they help to attach the

bacteria to rocks in streams and also to the host tissues.

=.

Ribosomes

- *n prokaryotes ribosomes are associated with the

plasma membrane of the cell.

- They are about 14 nm by 70 nm in sie.

- They are made of two subunits - />' and *>' units.

They together form ?>'prokaryotic ribosomes.

(%> sedimentation coefficient? a measure of density &sie".

Function:

ibosomes are the site of translation (protein

synthesis". %everal ribosomes may attach to a single

m3A to form a chain called #ol-ribosomes

(#ol-some+. ibosomes of a polysome translate the

m3A into proteins.

?. Inclusion6o$ies

- These are non-membranous+ stored reserve material seen

freely in the cytoplasm of prokaryotic cells.

- ,.g. phosphate granules+ cyanophycean granules and

glycogen granules+ gas vacuoles etc.

- as 7acuoles are found in blue green and purple and

green photosynthetic bacteria.

EU3AR%OTICCELL'

- They have well organied membrane boun$

nucleus and organelles (endoplasmic reticulum (,"+

:olgi comple'+ lysosomes+ mitochondria+ microbodies

etc".

- There is a clear compartmentaliation of cytoplasm

due to the membrane bound organelles.

- They have comple' locomotory & cytoskeletalstructures.

- Their genetic material is organied into chromosomes.- ,ukaryotes include protists+ plants+ animals and fungi.

;i..erencesbet!een1lant an$ animal

cells

1lant cell Animal cell

1. ell wall present Absent

7. =lastids are present Absent

. A large central vacuole /any small vacuoles

8. entrioles are absent =resent

Cell organelles in eukar-otic cells

). Cell &embrane- hemical studies on the human 5s showed that

the cell membrane is composed of a li#i$ bila-er.

- The lipids are arranged within the membrane with the

outer #olar "ea$ and the inner "-$ro#"obic tails. This

ensures that the non-polar tail of saturated

hydrocarbons is protected from the a$ueous

environment.

- The lipid component of the membrane mainly consistsof

#"os#"ogl-ceri$es.

- ell membranes also possess protein and carbohydrate.- atio of protein and lipid varies in different cells. ,.g.

*n human 5+ membrane has 47@ protein and 80@

lipids.

- Depending on the ease of e'traction+ membrane

proteins are 7 types)

o Integral #roteins: =artially or totally buried in

membrane.

o 1eri#"eral #roteins: ie on the surface of membrane.

- Flui$ mosaic mo$el o cell membrane: =roposed by

'inger 2 Nicolson (1B67". According to this+ the $uasi-

fluid nature of lipid enables lateral movement of proteins

within the overall bilayer. This ability to move within the

membrane is measured as its fluidity.

Functions:o Transport of the molecules. The membrane is

selectively permeable to some molecules present on either

side of it.


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o Due to the fluid nature+ the plasma membrane can

help in cell growth+ formation of intercellular

Cunctions+ secretion+ endocytosis+ cell division etc.

T-#eso.Trans#ort

). 1assi7e trans#ort: *t is the movement of

molecules across the membrane along the

concentration gradient (i.e.+ from higher concentration

to the lower" without the e'penditure of energy. *t is 7types)

a. 'im#le $iusion: *t is the movement of

neutral solutes across the membrane.

b. Osmosis: *t is the movement of water by

diffusion across the membrane.

As the polar molecules cannot pass through the non-

polar lipid bilayer+ they re$uire a carrier protein of the

membrane to facilitate their transport.

. Acti7e trans#ort: *t is the movement of

molecules across the membrane against the

concentration gradient (i.e. from lower to the higher

concentration" with the e'penditure of energy (AT= is

utilied". ,.g. 3a;E

pump.

. Cell

0all

- *t is a non-living rigid structure found outer to the

plasma membrane of fungi and plants.

- ell wall of Algae is made of cellulose+

galactans+ mannans and minerals like a9. *n

other plants+ it consists of cellulose+ hemicellulose+

pectins and proteins.

- ell wall of a young plant cell (#rimar- !all+ is

capable of growth. *t gradually diminishes as the cell

matures and the secon$ar- !all is formed on the innerside (towards membrane" of the cell.

- The mi$$le lamella is a layer mainly of calcium pectate

which glues the different neighbouring cells

together. The cell wall and middle lamellae may be

traversed by #lasmo$esmata which connect the

cytoplasm of neighbouring cells.

Functions:

a. *t gives shape to thecell.

b. *t protects the cell from mechanical damage &

infection.c. *t helps in cell-to-cellinteraction.

$. *t acts as barrier to undesirable

macromolecules.

*. En$omembrane'-stem

- *t is a group of membranous organelles having

coordinated functions.

- They include endoplasmic reticulum (,"+ :olgi

comple'+ lysosomes and vacuoles.

En$o#lasmicReticulum(ER+

- These are a network of tiny tubular structures scattered in

the cytoplasm.

- , divides the intracellular space into 7 compartments)

luminal (inside ," & e9tra luminal

(cytoplasm".

- ,ndoplasmic reticulum is 7 types)

a. Roug" en$o#lasmic reticulum (RER+: 5ear

ribosomes on their surface. , is fre$uently

observed in the cells actively involved in protein

synthesis and secretion. They are e'tensive and

continuous with the outer membrane of the nucleus

b. 'moot" en$o#lasmic reticulum ('ER+: ibosomes

are absent. %, is the maCor site for synthesis of

lipid. *n animal cells lipid-like steroidal hormones are

synthesied in %,.

8olgia##aratus

- Densely stained reticular structures near the nucleus.

- First observed by Camillo olgi (1B".

- They consist of flat+ disc-shaped sacs (cisternae+ of 0.4

1.0 m diameter. These are stacked parallel to each other.

- isternae are concentrically arranged with conve' cis

(forming" face and concave trans (maturing" face. Cis &

trans faces are totally different+ but interconnected.

Function o olgi a##aratus:

o =ackaging materials+ to be delivered either to the

intracellular targets or secreted outside the cell.

/aterials to be packaged in the form of vesicles from the

, fuse with the cis face and move towards the maturing

face. This is why the :olgi apparatus remains in close

association with the endoplasmic reticulum.o =roteins synthesied by ribosomes on the ,

are modified in the cisternae of the :olgi apparatus

before they are released from its trans face.

o :olgi apparatus is the important site of formation

of glycoproteins and glycolipids.

L-sosomes

- These are membrane bound vesicular structures formed

by the process of packaging in the :olgi apparatus.

- ysosomal vesicles contain almost all types of hydrolytic

enymes (hydrolases< lipases+ proteases+ carbohydrases".

They are active at the acidic p#. These enymes can

digest carbohydrates+ proteins+ lipids and nucleic acids.

acuoles

- These are the membrane-bound space found in the

cytoplasm. *t contains water+ sap+ e'cretory product and

other materials not useful for the cell.

- Gacuole is bound by a single membrane called tono#last.

- *n plant cells+ the vacuoles can occupy up to B0@ of the

volume of the cell.


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- *n plants+ the tonoplast facilitates the transport of a

number of ions and other materials against concentration

gradients into the vacuole? hence their concentration is

significantly higher in the vacuole than in the cytoplasm.

- *n Amoeba, the contractile 7acuole is important for

e'cretion. *n many cells+ as in protists+ oo$ 7acuoles are

formed by engulfing the food particles.

'.

?. C-toskeleton

- *t is a network of filamentous proteinaceous structures

present in the cytoplasm.

- *t provides mechanical support+ motility+ maintenance of

the shape of the cell etc.

8. Cilia an$ Flagella- They are hair-like outgrowths of the cell membrane.

- ilia are small structures which work like oars+

causing the movement of either the cell or the

surrounding fluid.

- Flagella are comparatively longer and responsible for cell

movement.

- Flagella of prokaryotic bacteria and eukaryotes are

structurally different.

- ilium and flagellum are covered with plasma

membrane. Their core (a9oneme+possesses a number of

microtubules running parallel to the long a'is.

- The a'oneme usually has B pairs of doublets of radially

arranged peripheral microtubules+ and a pair of centrally

located microtubules. This is known as ,B arra-.

- The central tubules are connected by bridges and are also

enclosed by a central sheath+ which is connected to one

of the tubules of each peripheral doublet by a radial

spoke. Thus+ there are nine radial spokes. The peripheral

doublets are also interconnected by linkers.

- 5oth the cilium and flagellum emerge from centriole-like

structure called the basal bo$ies.

,. Centrosomean$ Centrioles

- Centrosome is an organelle usually containing two non-

membrane bound cylindrical structures called centrioles.

- They are surrounded by #ericentriolar materials.

- The centrioles lie perpendicular to each other. They are

made up of B evenly spaced peripheral fibrils of tubulin.

,ach of the peripheral fibril is a triplet. The adCacenttriplets are also linked.

- The central part of the centriole is also proteinaceous and

called the "ub+ which is connected with tubules of the

peripheral triplets by radial s#okes made of protein.


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- The centrioles form the basal body of cilia or

flagella+ and spindle fibres that give rise to spindle

apparatus during cell division in animal cells.

)>.

Nucleus

- 3ucleus was first described by Robert 6ro!n (11".

- ater the material of the nucleus stained by the

basic dyes was given the name c"romatin by

Flemming.

- 3ormally+ there is only one nucleus per cell.

Gariations in the number of nuclei are also observed.

%ome mature cells lack nucleus. ,.g. mammalian

erythrocytes and sieve tube cells of vascular plants.

- The interphase nucleus contains

o Nuclear en7elo#e: Double layered membrane with

a space between (10 - 40 nm" called the

#erinuclear s#ace. *t forms a barrier between the

materials present inside the nucleus and that of the

cytoplasm. The outer membrane usually remainscontinuous with the , and also bears ribosomes on

it.

The nuclear envelope has minute pores+ which are

formed by the fusion of its two membranes. These are

the passages for the movement of 3A and

protein between the nucleus and the cytoplasm.

o Nuclear matri9 (nucleo#lasm+

o C"romatin: A network of nucleoprotein fibres.

*t contains D3A and basic proteins ("istones++ some

non- histone proteins and 3A. During cell division+

chromatins condense to form c"romosomes.

o Nucleolus: 9ne or more non-membranous

spherical bodies. *t is continuous with the

nucleoplasm. *t is a site for ribosomal 3A synthesis.

C"romosomes:

- A single human cell has about 7 m long thread of D3A

distributed among its 8I (7 pairs" chromosomes.

- ,very chromosome has a primary constriction(centromere+ on the sides of which disc shaped

structures called kinetoc"ores are present.

- 5ased on the position of the centromere+

chromosomes are 8 types.

o &etacentric c"romosome: *t has middle

centromere forming two e$ual arms of the

chromosome.

o 'ub5metacentric c"romosome: *t has

centromere nearer to one end of the chromosome

resulting into one shorter arm and one longer arm.

o Acrocentric c"romosome: entromere is

situated close to its end forming one e'tremely short

and one very long arm.

o Telocentric c"romosome: *t has a terminal

centromere.

- %ome chromosomes have non-staining secondary

constrictions at a constant location. *t is called satellite.

)). &icrobo$ies

- These are many membrane bound minute vesicles that

contain various enymes.

- =resent in both plant and animal cells.


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CO&1ARI'ON6ET0EEN1RO3AR%OT ICAN; EU3AR%OT ICCELL'

1rokar-otic cells Eukar-otic cells

1. :enerally smaller arger

7. :enetic material is present in the form of nucleoid :enetic material is in the form of nucleus

. 3uclear membrane absent =resent

8. /embrane bound organelles absent =resent

4. ircular D3A inear D3A

I. ibosomes 60 % type 0 % type (60 % in plastids and mitochondria"

1. Match the columnsA,B, & C

M O D E L Q U E S T I O N S


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A B C

Mitochondria Sedimentation Spindle bers

Golgi bodies Hdroltic en!me "o#er house

$sosomes A%oneme Cisternae

ibosomes Centrioles Acidic "H

Cilia Glcoproteins George "alade

Centrosome Cristae '( )

). Bacterial cell en*elope is ha*ing a comple% structure. name the laers of the en*elope

+. pes of Chromosomes based on the position of centromere are gi*en. -ame the Chromosomes.

. /n cells glcoprotein & glcolipids are secreted b a

cell organelle. a. -ame the cell organelle

b. -eatl dra# its diagram

0. "lastids are found in all plant cells

a. $ist the three plastids found in plants.b. -ame the colorless plastids and specif its role.

. /dentif the characters of pro2arotic cells from the follo#ing

statements a. 3ndoplasmic reticulum present

b. ibosome present

c. Golgi bodies

absent d.

/ncipient nucleus

e. 4east is an

e%ample f. Mostl

anaerobes

5. Cop the follo#ing diagram and label th

e parts

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(676547914) 5. Cell Structure n Functions