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PhysiologyofThe CELL (I)for pre-medic Mesir (July 2013)

DR. NUR FARIESHA MD HASHIM

MSc Radiation Biology (UCL), PhD Cancer Cell

Biology (KCL)

PHYSIOLOGY UNIT, DEPT. OF BIOMEDICAL SCIENCE, FACULTY OF MEDICINE

& HEALTH SCIENCES UPM

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Overview ofCELL PHYSIOLOGYat a glance

Cell Theory

Observation of cells

An overview of cell structure Endoplasmic Reticulum and Segregated Synthesis

Golgi Complex and Exocytosis

Lysosomes and Endocytosis

Peroxisomes and Detoxification

Mitochondria and ATP Production Centrosome, Centrioles and Microtubule Organization

Cytosol: Cell Gel

Cytoskeleton: Cell Bone and Muscle

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Learning OutcomesCell Physiology

At the end of the session, you will be able to :

1. Explain the parts of cells

2. Describe the functions of cell compartments

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Principles of the Cell Theory

The cell is the smalleststructural and functionalunit capable of carrying

out life processes

The functional activitiesof each cell depend onthe specific structuralproperties of the cell

Cells are the livingbuilding blocks of all

multicellular organisms

An organisms structureand function ultimately

depend on the collectivestructural characteristics

and functionalcapabilities of its cells

All new cells and new lifearise only from pre-

existing cells

Because of thiscontinuity of life,

the cells of all

organisms are

fundamentally

similar in

structure andfunction

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PART 1

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An Overview of Cell Structure- under an EM

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Cell Structure

Plasma

membrane

Encloses the cells

Nucleus

Contains the cells geneticmaterial

Cytoplasm

The portion of the cells interiornot occupied by the nucleus

Different cells share many common features. Most cells have 3 major subdivisions:

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The plasma membrane bounds the cell

Plasma

membrane

Very thin structurecomposed of mostly lipid

(fat)

It keeps the

intracellular fluid (ICF)within cells frommingling with the

extracellular fluid (ECF)outside the cells

Like gated walls that

enclosed ancient cities,the cell controls the entry

of nutrients and other

needed supplies and the

export of productsmanufactured within

Guard againstunwanted traffic into

or out of the cell

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The nucleus contains the DNA

1-Typically the largestsingle organized cell

component located nearthe center of the cell

2-Surrounded by nuclearenvelope- separates thenucleus from the rest of

the cell

3-Houses the cells geneticmaterial, DNA

4-DNA has 2 majorfunctions: directing proteinsynthesis and serves as

genetic blueprint during cellreplication

Nucleus

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Cytoplasm

Contains specialized organelles (cells little organs) and the cytoskeleton (ascaffolding of proteins , act as bone and muscle) dispersed within thecytosol

Organelles Highly organized structures. 2 categories: membranous and non-membranous organelles

Membranous organelles- 5 main types- endoplasmic reticulum, Golgicomplex, lysosomes, peroxisomes and mitochondria

Non-membranous organelles- ribosomes, vaults and centrioles

Cytoskeleton

Is an interconnected system of protein fibers and tubes that extendsthroughout the cytosol

Gives the cell its shape, provides for its internal organization, and regulatesits various movements

Cytosol

Semiliquid, gel-like mass.

Many chemical reactions that are compatible with one another are

conducted in the cytosol

The cytoplasm consists of various organelles, the cytoskeleton and cytosol

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PART 2

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Endoplasmic Reticulum and Segregated Synthesis

Endoplasmic Reticulum (ER) Fluid-filled membranous system distributed extensively throughout the

cytosol

Primarily a protein- and lipid-producing factory

Rough ER

Consists of stacks of relatively flattened interconnected sacs

Synthesizes glycoproteins and phospholipids that are transferred intocellular organelles, inserted into the plasma membrane, or secretedduring exocytosis

Smooth ER

Is a meshwork of tiny interconnected tubules

Synthesizes fatty acids and steroids, such as estrogens and testosterone;inactivates or detoxifies drugs and other potentially harmful substances;

removes the phosphate group from glucose-6-phosphate; and stores andreleases calcium ions that trigger contraction in muscle cells

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The roughendoplasmic reticulumsynthesizes proteins

for secretion andmembrane

construction

The outer surface of RER membrane is studded with smallparticles called ribosomes- the workbenches where

protein synthesis takes place

The RER synthesizes and releases a variety of newproteins which serve one of 2 purposes : 1-some proteinsare destined for export to the cells exterior as secretory

products, like protein hormones or enzymes 2- otherproteins are transported to sites within the cell for

constructing new cellular membrane

The RER is most abundant in cells specialized for proteinsecretion (i.e. cells that secrete digestive enzymes) or in

cells that require extensive membrane synthesis (i.e.rapidly growing cells like immature egg cells)

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The smoothendoplasmic

reticulum packagesnew proteins in

transport vesicles

No ribosomes. SER is rather sparse and primarily servesas a central packaging and discharge site for molecules

to be transported from the ER

Portions of the SER then bud off (balloon outward on thesurface, then are pinched off), forming transport vesiclesthat enclose the new molecules in a spherical capsule

derived from SER membrane

Vesicle= fluid-filled, membrane enclosed intracellularcargo container

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1-The RERsynthesizes

proteins to besecreted to the

exterior or to beincorporated intocellular membrane

2-The SER packagesthe secretory productinto transport vesicles,

which bud off andmove to the Golgi

complex

3-The transportvesicles fuse with

the Golgi complex ,open up, and emptytheir contents intothe closest Golgi

sac

4-The newly synthesized proteinsfrom the ER travel by vesiculartransport through the layers of theGolgi complex, which modifies the

raw proteins into final form andsorts and directs the finished

products to their final destination byvarying their wrappers

5-Secretory vesicles containingthe finished protein products

bud off the Golgi complex andremain in the cytosol, storingthe products until signaled to

empty

6-On appropriate stimulation,the secretory vesicles fuse withthe plasma membrane, open,

and empty their contents to thecells exterior. Secretion hasoccurred by exocytosis, withthe secretory products never

having come in contact with thecytosol

7-Lysosomesalso bud from

the Golgicomplex

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PART 3

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Golgi Complex

Consists of a stack of slightlycurved, membrane-enclosed sacs.

The vesicles at the dilated edges

of the sacs contain finished proteinproducts packaged for distribution

to their final destination

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Processing and packaging of proteins by the Golgi complex. All proteins exported fromthe cell are rocessed in the Gol i com lex

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(a) Exocytosis: A secretory vesicle

fuses with the plasma membrane,

releasing the vesicle contents to

the cell exterior. The vesicle

membrane becomes part of

the plasma membrane

(b) Endocytosis: Materials from the

cell exterior are enclosed in a

segment of the plasma membrane

that pockets inward and pinches off

as an endocytic vesicle

Exocytosis and endocytosis

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PART 4

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Lysosomes and endocytosis

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Endocytosis can be accomplished in 3 ways-pinocytosis,

receptor-mediated endocytosis and phagocytosis

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1- Pseudopods begin tosurround prey/solid

particle

2- Pseudopods closearound prey/ solid

particle

3- Prey/solid particle isenclosed in endocyticvesicle that sinks into

cytoplasm

4- Lysosome fuses withvesicle, releasing

enzymes that attackmaterial inside vesicle

Phagocytosis cell eating, large

multimolecular particles are internalised

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1- Solute moleculesand water molecules

are outside theplasma membrane

2- Membrane pocketsinward, enclosing

solute molecules andwater molecules

3- Pocket pinches offas endocytic vesiclecontaining sample of

ECF

Pinocytosis cell drinking, a drop of ECF is

taken up non-selectively

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1- Substances attachto membrane

receptors

2- Membrane pocketsinward

3- Pocket pinches offas endocytic vesicle

containing targetmolecule

A highly selective process that enables cells

to import specific large molecules that

it needs from its environment

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To be continued in CELL II