Download MBBS Physiology Presentations 69 The Cell Lecture Notes

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Though chemical analysis of living things is

possible, because of its complex organization and

interaction of molecules Life in the form of living

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cell can not be produced

Cell is the smallest living entity which serves living

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building blocks for the immensely complicated

whole body.

THE CELL

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Life in the form of living cell can not be produced
Cell theory ? relation between cell and life

? Cell is the smallest structural & functional

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unit. Can carry out living processes

? Functional activities related to the specific

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structural property

? Living building blocks of animal or plant

? Organism's structure and function depends

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upon characteristics of its cells

? All new life & new cells are formed from

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preexisting cell

? Cells of one organism are fundamentally

similar in structure & function

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Observation of cell
?Cannot be seen by naked eye ? smallest visible

particle is 5-10 times larger than typical cell

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?Seen by microscope ? middle of 17th century
?Better vision of cells in tissues with `soapy mixture'

of fluid inside ? early 19th century
?Electron microscopy ? internal structure of cell ?

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1940
?Recently,- powerful microscopes, biochemical

techniques, cell culture technology, genetic

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engineering
Overview of Cell structure ?Total trillion cells

- 200 different cell types

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3 Subdivisions

Plasma membrane Nucleus

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Cytoplasm

Encloses

Contain cells

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Portion of

the cell

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genetic

cell interior

material

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not occupied

by nucleus
Plasma membrane ?

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?thin membranous structure enclosing each cell
?Oily barrier bet. ECF & ICF
?Holds contents of cell
?Gated wall ? selective movement of mol. Bet

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ICF & ECF

Nucleus ?
- Largest, single, organized compartment

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- Spherical or oval, near the centre
- surrounded by double layered

nuclear membrane having nuclear pores
allowing traffic between nucleus and

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cytoplasm
- Genetic material in nucleus ? DNA
Functions of nucleus

directs synthesis of proteins

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- serves as genetic

blue print during cell

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Structural and enzymes

duplication

controlling chemical reactions

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- Continue

DNA provides

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identical type of

`instructions' through

cell line within the

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3types of RNA

body and in

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reproductive cell

Messenger Ribosomal Transfer to transfer genetic

RNA

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RNA

RNA

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material to next

generation

Cytosol

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Cytoplasm

Organelles

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Complex gel

Site for compatible

like liquid

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chemical reactions

I Cytosol

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elaborate protein -gives shape

network

-Provides internal

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(cytoskeleton)

organization
-Regulates its

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movements
II Organelles

distinct,

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highly organized,
membrane enclosed,
occupies about ? of total

cell volume

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Each organelle

`Speciality shops' in cell
Separate compartment

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Separate contents

6 main types of organelles- similar in all cells

v Endoplasmic

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reticulum

- contain specific set

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of chemicals

v Rough ER

required for

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v Smooth ER

particular cellular

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function

v Golgi complex

- can carryout

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v Lysosomes

incompatible

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v Peroxysomes

chemical reactions

simultaneously

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v Mitochondria

v Vaults
Endoplasmic reticulum -- protein and lipid

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manufacturing factory.

Elaborate, fluid filled

extensively distributed,

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membranous system

SER

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RER

2 types continuous with each other and their

relative amount varies with the function of

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cell

SER ? network of tiny interconnected tubules

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RER ? project outwards from SER as stacks of
flattened sacks
- outer surface of membrane studded
with ribosomes ? rough granular appearance

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New protein on ribosomal RNA

Released in ER lumen

Exterior as

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Construction of

hormones or

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new cell

enzymes

membrane or

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organelles

Synthesis of lipids by enzymes present in the

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membrane released to lumen with protein

pressed attachment of carbohydrate buds off as

transport vesicle

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Smooth ER -No ribosome, so not involved in

protein synthesis,
- serve as a central packaging &

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discharge site for molecules which are

to be transported from ER
-formation of Transport vesicles which

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contain new protein and lipid and is

membrane bound and passes to Golgi

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complex , formation of peroxisomes
- Membrane used is replaced by newly

formed protein & lipid
Additional responsibilities in different cells

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1) Steroid secreting cells have abundant SER

2) Liver cells ? membrane of SER contain

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enzymes involved in detoxification

3) In muscle cells SER stores Ca++ which

plays imp. role in process of muscle

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contraction

Golgi Complex Stacks of flattened, curved,

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membrane bound sacs or cisterns
-may not be physically connected

with each other
-thin at the center and dilated at

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the periphery
- Number varies ?cells

specialized in pr. synthesis may

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have 100s of sacs
Mechanism of function

Transport vesicles containing Cargo from SER

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fuses with the inner most sac of Golgi complex

material travel through the layers of sacs to the

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outer sacs in the form of transport vesicles
During transit
1) raw material final finished product
2) sorting and directing the finished products
a) secretion to exterior of cell

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b) construction of new plasma membrane

c) incorporated in other organelles e.g. lysosomes

Secretory vesicles

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Membrane with

specific proteins

Recognition Coat proteins Docking

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marker for

for curling of marker on

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cargo on inner membrane

outer side

surface

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inside coat

protein ?

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Cargo ? conc. finished product with

v-SNARE

appropriate a.a. sequence acting as

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sorting signal
Exocytosis

Budding off vesicles in cytosol seperating

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specialized finished products from cytosol .

Movement towards membrane on appropriate signals

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Attachment with special pr. marker on target

membrane ? t SNARE

Fusion of membrane

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Opening of vesicle

Release of secretion

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Peculiarities of secretary process

1) Once pr. is synthesized does come in

contact with cytosol

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2) Synthesis and storage are well ahead

of time of requirement
3)Diffferent secretory vesicles for

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different destination
Lysosomes

?Membrane enclosed sacs containing powerful

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hydrolytic enzymes
?Average number ? 300 per cell
?No fixed structure- vary in size and shape
?0.2 ? 0.5 m in diameter
?Granular when inactive

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?Membrane protects rest of the cell
?Membrane and enzymes from Golgi complex

Extracellular material to be tackled by

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lysosome is brought into the cell by

endocytosis

3 types

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pinocytosis

phagocytosis

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Specialised

All cells

Receptor

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cells

mediated

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endocytosis
A.Pinocytosis - Cell drinking nonselective
B. continuous process seen in all

?Me ce

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m lls

brane deforming protein attached to membrane

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?Formation of pouch by dipping of membrane
?Sealing of ends
?Endocytic vesicle with ECF
?Vesicle is pinched off by protein Dynamin
?ECF to the cell and loss of extra plasma membrane

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added during exocytosis

Pinocytosis

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ECF

ECF

dynamin

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Membrane deforming

coat protein

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Endocytic

vesicle
B. Receptor mediated endocytosis ? highly

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selective process to import imp. specific large

molecules. Requires energy & Ca++

Coated pit Cathrin, actin,

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myosin

C. Phagocytosis

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? Internalization of large

multimolecular particles by

specialized cells e.g. certain

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types of w.b.c.s ( Professional

phagocytes)
bactebactium

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Pseudopodia

internalization

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Phagoso-

some

Fusion

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Residual

body

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absorption

digestion

Phagocytosis

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Autophagy ?
Role in regression of organ ? uterus, mammary glands
Removal of aged or damaged organelles
Rupture of lysosomal membrane CAUSES SELF

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DESTRUCTION but minimal damage because

optimum pH for hydrolytic enzymes is acidic.
Damage to nuclear DNA alters genetic properties

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Deficiency of one or more enzymes lead to

storage disease e.g. TAY SACHS disease-
Peroxisomes

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?Several hundreds
? to 1/3 size of lysosomes
?Transport of H+ across membrane so acidic pH
?Membrane enclosed sacs with powerful oxidizing

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enzymes which use O2 to remove hydrogen from

organic molecules and detoxify wastes produced in the

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cell or foreign toxic compound by formation of H2O2

which is oxidant but accumulation is prevented by

catalase which is antioxidant

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?H2O2 H2O + O2

Mitochondria

Outer membrane

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Electron

transport

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Inner membrane

protein

Crista

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Matrix

Intermembrane space

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Dissolved enzymes for citric

acid cycle

Chemiosmotic

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reactions
?100s-1000s in single cell

?Energy organelle or power plant

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?Extract energy from nutrient and transfer in to

usable form

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?Number and location in cell varies

?Round shaped or oval

?Possess their own DNA which produces molecules

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required for generating energy

?Defect in DNA lead to degenerative diseases or

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ageing

?Double membrane ? outer smooth, inner folded

forming cristae

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Energy release from the nutrients and its storage

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Dietary food

Energy in carbon bonds

digestion

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Smaller absorbable molecules

Through cell

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In the cell through membrane
1 mol. Of glucose

2 pyruvic acid

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2 ATP

Cytosol

mol.

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+

Anaerobic glycolysis

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2Acetyl co A

Matrix

Citric acid cycle 4NADH+2FADH2

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2 ATP

+

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Cristae

Low energy

-

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Electron transport

O

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compounds

2 + e

+

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-

+ electron

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H+ e

Intermembrane space

Chemiosmotic reaction ADP + Pi

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32 ATP

Synthesis of ATP- Oxidative phosphorylation
? Release of energy during electron transport

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reactions used for active uptake of H+ by inner

membrane
? Accumulation of H+ in intermembrane space

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? Transport of H+ through channels in inner

membrane
? Activation of ATP sythetase attached to

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channel protein
? ADP + Pi ATP (32mol) with utilization of

O2 from atm.
Chemiosmotic reactions

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H+ H+ H+ H+ H+ H+ H+ H+

H+ H+ H+

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H+

ATP

synthetase

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ADP + Pi

ATP

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Uses of ATP

1. Synthesis of new chemical compounds for

secretion and growth

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2. Membrane transport

3. Mechanical work
Vaults

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? 3 times larger than ribosomes
? Octagonal barrels with hollow interior
? Not seen with ordinary stain
? Pass through nuclear pore

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? transporting messenger RNA and other material
across nuclear membrane
? May be responsible for multi drug resistance in
cancer cells.

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Cytosol

? Semi liquid surrounding organelles
? Highly organized gel like mass with different
composition at diff. sites

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? Cytoskeleton is dispersed through out
? enzymes regulating intermediary reactions
? Ribosomal protein synthesis (used for cell)
? Storage of fats, glycogen ( Inclusions),
secretory vesicles

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Cytoskeleton

Complex protein network portion of cytosol which

act as `bones and muscles ` of the cell.giving shape ,

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support and control their movements

3 elements

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Microtubules microfilament intermediate filaments

Microtubules

Largest skeletal element, slender, long

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hollow unbranched tubes

Functions

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A) Maintains asymmetric cell shape e.g.

B) axon

B) Transport of secretary vesicles and

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other materials in any direction by

use of motor protein and energy

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? Movement of specialized cell

projection such as cilia, flagellum

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Tubulin

subunit ? Distribution of chromosomes during

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mitosis of spindles
Microfilament

- Smallest element of cytoskeleton
- Actin is present in most cells

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- 2 strands of globular actin

Actin - Role in the cell -

subunit Cellular contractile system

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Mechanical stiffener for
cellular projection-microvilli

Intermediate filaments

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Tough, maintain structure integrity of cell and

resist mechanical stress
e.g. microfilaments in axon
Keratin in skin cells

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Functional systems of cells

I. Ingestion
II. Digestion of foreign substances
III.Synthesis and formation of new

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structures

IV.Energy extraction
V. Locomotion ? ameboid movement,

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VI. ciliary movement