BASICS OF CELLULAR STUDY

Limits on Cellular Growth

• Cells must have enough cytoplasm to function!

• Can’t have too much!– Some

structural “leeway” in size

– Ability to compensate isn’t infinite

A Single Cell!

http://en.wikivisual.com/images/3/35/Raw_egg.jpg

THE FIRST KEY THE FIRST KEY DEFINITIONDEFINITION

•CELL:CELL: A mass of protoplasm A mass of protoplasm surrounded by a membrane surrounded by a membrane and containing a nucleus and and containing a nucleus and organellesorganelles– The fundamental unit of lifeThe fundamental unit of life

–CELLS DO NOT EXIST AS CELLS DO NOT EXIST AS INDEPENDENT ENTITIESINDEPENDENT ENTITIES

(No, not even in blood…as we’ll see later!)(No, not even in blood…as we’ll see later!)

THE SECOND KEY THE SECOND KEY DEFINITIONDEFINITION

• TISSUE:TISSUE: An aggregation of cells An aggregation of cells and intercellular materials and intercellular materials specialized for specific functionsspecialized for specific functions– Cells are Cells are alwaysalways part of a tissue part of a tissue– Tissue’s function determines what Tissue’s function determines what

cells are presentcells are present– Cells make tissue function possibleCells make tissue function possible– Structure of Structure of cellscells often predictable often predictable

based on based on tissuetissue function & function & vice vice versaversa

FOUR “BASIC

TISSUES”• EPITHELIUMEPITHELIUM• CONNECTIVE CONNECTIVE

TISSUETISSUE• MUSCLEMUSCLE• NERVOUS NERVOUS

TISSUETISSUE– OrgansOrgans made up made up

of theseof these– At least 2 basic At least 2 basic

tissues in any tissues in any organorgan

THE THIRD KEY THE THIRD KEY DEFINITIONDEFINITION

ORGANS: ORGANS: • Aggregations of Aggregations of

cells, tissues, and cells, tissues, and intercellular intercellular materials materials specialized for specialized for specific functionsspecific functions– Tissues Tissues are not are not

autonomousautonomous – AlwaysAlways integrated integrated

with with other tissuesother tissues to form organsto form organs

• Separation of Separation of tasks tasks and of cells and of cells & tissues& tissues is a is a hallmark of hallmark of organsorgans

DifferentiatioDifferentiationn

• Process by which Process by which cellscells come to have come to have different characteristics & capabilitiesdifferent characteristics & capabilities

• Differentiated Differentiated cells produce cells produce different different proteins than their progenitorsproteins than their progenitors– Not all capabilities expressedNot all capabilities expressed

• Not limited in timeNot limited in time– Continues throughout lifeContinues throughout life, , e.g.e.g., wound , wound

healing & hemopoiesishealing & hemopoiesis

• Usually a Usually a precursor or “stem” cell typeprecursor or “stem” cell type is involvedis involved– Reserve stem cells often present in Reserve stem cells often present in

tissues/organstissues/organs

• Differentiation of Differentiation of cells & cell lines cells & cell lines determines determines organorgan function & function & physiologyphysiology

Teased nerve fibers, OsO4 stain

SIZE RANGE IN ANIMAL CELLS

• Smallest: 3-4 m– Some cells of

blood, e.g. quiescent lymphocytes

• Largest: 100-150 m– Some neurons– Monocytes– Skeletal muscle

SMALL CELLS HAVE SMALL CELLS HAVE LIMITATIONSLIMITATIONS

• Typically very little cytoplasmTypically very little cytoplasm– Limits functionsLimits functions– May have inactive inclusionsMay have inactive inclusions– Nuclear material condensedNuclear material condensed– May be “transformed” to an active stateMay be “transformed” to an active state

Lymphocyte in a smear, Wright’s Stain, 1000x

Differentiation:How We Get From….

Here to Here

DifferentiatioDifferentiationn

• Process by which Process by which cellscells come to have come to have different characteristics & capabilitiesdifferent characteristics & capabilities

• Differentiated Differentiated cells produce cells produce different different proteins than their progenitorsproteins than their progenitors– Not all capabilities expressedNot all capabilities expressed

• Not limited in timeNot limited in time– Continues throughout lifeContinues throughout life, , e.g.e.g., wound , wound

healing & hemopoiesishealing & hemopoiesis

• Usually a Usually a precursor or “stem” cell typeprecursor or “stem” cell type is involvedis involved– Reserve stem cells often present in Reserve stem cells often present in

tissues/organstissues/organs

• Differentiation of Differentiation of cells & cell lines cells & cell lines determines determines organorgan function & function & physiologyphysiology

Teased nerve fibers, OsO4 stain

CELL DEATH• Many cells are pre-

programmed to die– Major mechanism of

morphogenesis– Shapes and sculpts limbs,

etc.– Timing is exact and

preprogrammed

• Many embryonic structures only temporary – Removes the “scaffold” from

the “building”

• Examples: – Formation of paws– Wound healing

Stem Cells

• A general term• A population of

“reserve” cells– Quiescent– Can be

stimulated – Undergo

differentiation– One stem may

produce several cell lines

THE PLASMA THE PLASMA MEMBRANEMEMBRANE

• Defines Defines cell’s limitscell’s limits

• Controls Controls passage of passage of materials materials between between interior & interior & exteriorexterior

• Site of Site of receptors, receptors, markers, markers, etc.etc.

• Can be Can be inferred but inferred but not directly not directly seen with seen with LMLM

• Easily Easily visible with visible with electron electron microscopymicroscopy

Two adjacent P.M.’s (arrows) define the limits of cells A & B. The space between is in neither cell: it’s the “intercellular compartment.

CONCEPTUAL MODEL OF THE P.M.

• A “fluid mosaic model”: a lipid bilayer with “islands” of protein to control movement; surface markers of protein, glycolipids & glycoproteins for recognition & signalling

Image from Histology by Gartner & Hyatt

PLASMA MEMBRANE

MICROVILMICROVILLILI

• In LM seen as “brush border”– Not individually

resolvable– Uniform length

& height– Intestine,

kidney, some other sites• Places where

absorption is vital

The refractile fringe of microvilli as seen in the light microscope is referred to as a “brush border”; this example is from the intestine

MICROVILLI

• Filled with cytoplasm, surrounded with PM• May contain actin filaments• May be arranged for maximum # per unit area• Fairly small structures

PM ADAPTATION FOR PM ADAPTATION FOR ABSORPTION/SECRETIONABSORPTION/SECRETION

• BASAL FOLDS • “Reverse” of

microvilli– Basal end of

cell, not apex– Infolds of PM

containing cytoplasm

• Often contain mitochondria

• Associated with active transport– Slower

transfer rate– Transporting

“finished goods”

P.M. ADAPTATIONS FOR P.M. ADAPTATIONS FOR MOVEMENT:CILIA & FLAGELLAEMOVEMENT:CILIA & FLAGELLAE

• Cell migration • Movement of materials

on cell surface• Always involves

microtubules– Cilia and flagellae– Amoeboid motion

• Entire cell or only parts of it may be affected

• Directional• Energy from ATP• Interact with aqueous

environment – Respiratory, reproductive

systems• An ancient development

– The only solution!

Cilia on the cells lining the tracheaCilia on the cells lining the trachea

CILIA & FLAGELLAE

STRUCTURE OF CILIA

Don’t Confuse Cilia & Don’t Confuse Cilia & Microvilli!Microvilli!

• An An order of magnitude difference in sizeorder of magnitude difference in size• Cilia can be 10-100 Cilia can be 10-100 m long, and at least 10 m long, and at least 10 m m

thickthick• Microvilli rarely exceed 1.0 Microvilli rarely exceed 1.0 m thick and 10 m thick and 10 m longm long

Cilia MV

Image from Bloom & Fawcett, A Textbook of Histology

ADAPTATIONS FOR MAINTAINING SHAPE

• Odd shapes crucial to function– Internal

“scaffolding”– May serve other

needs• Internal routing of

materials• “Wiring” for

information transfer

• Disruption causes problems– Chemotherapy

agents• e.g. Colchicine

MICROTUBULES & MICROTUBULES & MICROFILAMENTSMICROFILAMENTS

• Vital to movement normal architecture

• Ubiquitous and variable in makeup– May be contractile

• Cilia, flagellae, and amoeboid movement

– May be “stiff” – May be for internal

transport – Polymeric structures

• Shorten & lengthen by adding dimers

• Principal component is tubulin

• May contain ATPase, dynein

MICROTUBULES• 20-50 nm (200-500 Å)• Cytoskeleton

– Mitotic spindle, cilia, flagella

CYTOSKELETAL MICROTUBULES• Maintenance of shape of odd cells, e.g. neurons

MICROFILAMENTS

• Intermediate filaments– Internal

structural “scaffold”

– Anchor nucleus– Connect

cytoskeleton to PM

– Maintain shape of nuclear envelope

• Thin microfilaments– Mainly actin for

intracellular contractility• Amoeboid motion,

division, etc.

– Myosin usually involved as well

– Gel-like network in cytosol of other thin filaments

MICROFILAMENTS & INTERMEDIATE FILAMENTS

• Smaller than microtubules (6-10 nm) & associated with contractility– Actin & myosin

• May be involved with adhesion structures– Tonofilaments

of desmosomes

• Also a cytoskeletal element

• Variable in size, related to function

MICROFILAMENTS

Astroglial fibers in an astrocyte

MICROFILAMENTS

• Microfilaments & secretory vesicles, rat ovarian granulosa cells

MICROFILAMENTS

Actin & myosin in skeletal muscle

ADAPTATION FOR SURFACE PROTECTION

• Cells are susceptible to damage– May be

unavoidable, e.g. Intestinal cells eroded by digestive juices

– Strategy is to delay it

• Glycocalyx– Expendable &

renewable surface covering

– Resistant to erosion

– Can be “sacrificed”

GLYCOCALYX• Cell surface coat

– Carbohydrate in nature• Glyco = “sweet” calyx

= “husk”– Term coined by John

Luft in 1965• Found on all cells to

some extent• Usually heaviest at free

surface• Not quite “basement

membrane”• Functions usually

protective• Some enzymatic

activity• PAS+ / RR+ in EM• May not be obvious in

routine preps

GLYCOCALYX

• LM image courtesy of Dr. Ihab El-Zhogby

ADAPTATIONS FOR TISSUE INTEGRITY &

FUNCTIONAL COHESION

• Tissues are INTEGRATED both structurally & functionally

• Cells are not independent units• Cells must communicate• Cells must maintain contact

with each other• A whole series of PM

specializations

Occluding (“Tight”) Junctions

• Adjacent PM’s are fused together

OCCLUDING JUNCTION

• Function to separate “inside” from “outside”

• Control passage of materials; forces them to go through a cell

• Used to control osmotic pressure, ion flux, etc.

DESMOSOMES• Most common

membrane specialization

• Found in all types of tissues & organs

• Similar to adhering junction– Also for mechanical

integrity– Distinguished by

dense filamentous component

– Anchor cells to each other

• A “spot weld” versus a “bead weld”

SPECIALIZATIONS FOR COMMUNICATION

• Cells have to know what’s going on around them

• Tissue function depends on this– Smooth muscle– Cardiac muscle– Glandular epithelium– Many other examples

Gap Junction• Limited area of

plasma membrane• Found in all tissues • Not for adhesion but

for communication• Site of lowered or

variable resistance to passage of ions

• Membrane gap is 20Å or so

• “Pores” on either side

• Cell-to-cell communication

Gap Junctions

NUCLEUS & NUCLEAR ENVELOPE

• “Command & Control” center of cell

• All eukaryotic cells have the entire “blueprint”– MOST of it isn’t used– Degree of

specialization affects how much is accessible

– Physiological state determines appearance

• Broken down & reconstructed each cycle

• Nuclear morphology varies with function & state

• Envelope continuous with RER

• Nuclear envelope & RER are continuous– Ribosomes

found on NE outer surface

• Nuclear pores located at turnbacks of the NE

NUCLEUS NUCLEUS & RER& RER

NUCLEAR PORES

• Openings in nuclear envelope

• Allow passage of RNA

• Complex structure to control movement

NUCLEAR PORES

SYNTHESIS & SECRETION

• MOST cells have some synthetic capability

• SOME cells are specialized for it

• ALL use the same structures to do it– Endoplasmic

reticulum– Golgi apparatus

ENDOPLASMIC RETICULUM

• Two types:– Rough ER functions for protein

synthesis•Described many times from LM studies•EM reveals true nature•Porter coined term in 1950’s

– Smooth ER functions in various ways•Lipid synthesis•Enzymatic degradation pathways•Special role in muscle

RIBOSOME

• Functional unit of RER

• Bound & free types exist– Identical

structure– Large &

small subunits

– Entire ribosome complex about 300Å

ROUGH E.R.• Prominent

feature in secretory cells– Pancreatic cells– Plasma cells– Peptic cells

• Amounts vary with cell function

• Usually some present, may be minor amount

• Accounts for LM visible BASOPHILIA

BASOPHILIA & THE RER

GOLGI APPARATUS• Known since

19th Century– Visible in LM– Nature &

existence debated until 1960’s

• Functions to modify & package products of RER for release

• Camillo Golgi (1843-1926)

GOLGI APPARATUS

GOLGI APPARATUS

• Contains enzymes for attaching carbohydrate & lipid moieties to peptides

SMOOTH ENDOPLASMIC RETICULUM

• Visible only in EM• Prominent in cells

making steroids or lipids– Leydig cells– Luteal cells

• Role in detoxification– Large amounts in

hepatocytes

• Collection of interconnected tubules & vesicles

• Membranous but not “studded” with ribosomes

Summary of function

• Membran sel: eksositosis/endositosis• Mitokondria: energy production• RER:sintesa protein, enzym• SER : sintesa hormon,absorbsi/met lipid• Golgi complec:sintesa protein (ekskresi)• Ribosom: mengolah asam amino• Lysosome:fagositosis• Mikrotubuli: transportasi,kerangka sel,

gerakan sel• Sentriol: pembentuk mikrotubuli/mitosis

Thanks!