CELL AND CELL ORGANELLES

PRESENTED BY:

DR.NAVEEN PARVATHAREDDY, I MDS,NARAYANA DENTAL COLLEGE, NELLORE, AP.

CONTENTS INTRODUCTION

HISTORY

CLASSIFICATION

BASIC CELL STRUCTURE

CELL MEMBRANE

CYTOPLASM

CELL ORGANELLES - STRUCTURE & FUNCTIONS

CYTOSKELETON

PROJECTIONS FROM CELL SURFACE

CELL INCLUSIONS

REFERENCES

INTRODUCTION

Latin word ‘cella’Building blocksFunctionsCell biology

History

SCIENTIST YEAR DISCOVERYRobert Hooke 1655 CELLBrown 1831 NUCLEUSSchleiden 1838 CELL THEORY

Virchow 1858 “OMNIS CELLULA E

CELLULA”

Miescher 1871 DNA

James Watson & Francis

Crick1953 Double helix model of

DNA.

Singer & nicholson 1972 Fluid Mosaic model

CLASSIFICATION

Ex:animals, plants, protozoa, and fungi.

Ex :Bacteria, blue green algae

Size &shape• Spindle

shaped• Small &

disc shape• Long &

branched

number• Unicellular• multicellula

r

function• Movement• Synthesis &

secretion• Transport• Digestion• Absorption• Growth, repair

Based on cell

CELL STRUCTURE

CELL

CYTOPLASM NUCLEUSCELL MEMBRANE

CYTOSKELETON CYTOSOL CELL

ORGANELLES CELL INCLUSIONS

NUCLEAR MEMBRANE

NUCLEOLUS CHROMATIN NUCLEOPLASM

• Outer limiting membrane • Thickness• Functions as• Other names

HISTORY• Lipid bilayer• Sandwich model• Unit membrane

model• Fluid mosaic model

Cell membrane:

major constituents of plasma membrane are: lipids, proteins,

carbohydrates.

LIPIDS :

1. Phospholipids 2. Cholesterol. 3. Glycolipids.

Membrane ProteinsThey are mainly of two types:

Peripheral proteins

Integral proteins

Many Functions of Membrane ProteinsOutside

Plasmamembrane

InsideTransporter

Cell surfacereceptor

Enzymeactivity

Cell surface identity marker

Attachment to thecytoskeleton

Cell adhesion

Membrane carbohydrates Play a key role in cell-cell recognition

ability of a cell to distinguish one cell from another

important in organ & tissue development

basis for rejection of foreign cells by immune system

FUNCTIONS OF PLASMA MEMBRANE:

It maintains the shape of

cellHelps in

absorption of nutrients

Acts as Semipermeable membrane

Acts as Receptors for hormones &

enzymes

Regulates various

metabolic reactions

Helps in adhesion

between cells

Helps in exchange of

gases

Molecules move through plasma membrane by: Passive transporta) Diffusionb) Facilitated diffusionc) Osmosis

Active transport

Diffusion Move from HIGH to LOW concentration

No energy needed.

diffusion

Diffusion through phospholipid bilayermolecules that can get through directly are fats & other lipids

inside cell

outside cell

lipidsalt

aa H2Osugar

NH3

molecules can NOT get through

polar molecules H2O

Ions salts, ammonia large molecules starches, proteins

Channels through cell membrane

Membrane becomes semi-permeable with protein channels specific channels allow specific material across cell

membrane inside cell

outside cell

sugaraaH2O

saltNH3

Facilitated Diffusion Diffusion with the aid of protein channels

or carrier proteins. No energy is needed.

open channel = fast transporthigh

low

CARRIER PROTEINS:

The proteins move specific type of molecules through the membrane from one side to other side of membrane.

Active TransportCells may need to move molecules against concentration gradient.

Protein “pump”“costs” energy = ATP

conformational change

ATP

low

high

Transport summarysimplediffusion

facilitateddiffusion

activetransport

ATP

Transport of large molecules (bulk transport)

EndocytosisPhagocytosis Pinocytosis

Exocytosis

Phagocytosis: cell eating

Actin dependent endocytosis

Pinocytosis cell drinking endothelium clathrin independent endocytosis

EXOCYTOSIS

It is the process by which a vesicle moves from cytoplasm to the plasma membrane where it discharges its contents to the extracellular space.

CYTOPLASM

It is everything that is

present between the cell membrane and the nuclear envelope.

consists primarily of water. It includes:Factory area of cell site for

CYTOSOL

The cyoplasmic matrix is a concentrated aqueous gel consisting of molecules of different sizes and shapes.

Such as electrolytes, metabolites, RNA, and synthesised proteins.

Cytoplasmic cell Organelles Membranous organelles Mitochondria Golgi apparatus Rough surfaced endoplasmic reticulum Smooth surfaced endoplasmic reticulum

Coated vesicle Secretory vesicles Lysosomes Endosomes / Peroxisomes

Non Membranous organelles Ribosomes Microtubules Filaments

CELL ORGANELLES

MITOCHONDRIA-“powerhouse of the cell”

Bilayered organelle

“CRISTAE”.

“MATRIX”.

The outer membrane possess receptors

The inner membrane contains several enzymes, including phospholipase A2, monoamine oxidase and acetyl coenzyme A (coA) synthase.

Matrix contains

Elementary particles

The membrane forming the cristae contains proteins that have three major functions :

1.oxidative electron transfer.

2. Synthesis of ATP.

3.Regulating transport of metabolites .

CISTERNAE

Two types: r ER s ER

Present abundantly in

RER and Ribosomes are concerned with protein synthesis.

ENDOPLASMIC RETICULUM

Functions of rER: Segregation of proteins.

Helps in initial glycosylation of glycoproteins.

Synthesis of phospholipids.

The assembly of multi chain protein

Major reservoir of ca ions.

Functions of sER:Lipid and steroid

synthesis

Detoxification of drugs

Camillo Golgi.

Usually composed of 4 or more stacked layers of thin, flat, enclosed vesicles lying one side of nucleus.

Prominent in secretory cells.

It functions in association with ER,

GOLGI COMPLEX

STRUCTURE

Functionally Golgi complex is divided into 3 regions

1. The region nearest the nucleus is cis-face

2. The opposite face, nearest to cell membrane is trans-face

3. The intermediate part is medial Golgi.

Cis face: proteins are phosphorylated

Medial golgi : protein – carbohydrate complexes formed

Trans face : Inactive forms to active forms

Sugar residues are added and then

Sorting & packing into vesicles is done.

LYSOSOMES (Digestive bags, suicide sacks)

Lysosomes have unique membrane that is resistant to acidic internal PH.

They are fomed from region of golgi complex.

They are membrane limited vesicles and contain large variety of hydrolytic enzymes.

They are abundant in cells exhibiting phagocytic activity

Digestive organ of cell

Functions: Contains enzymes essential for for

intracellular digestion.

Kill and remove foreign bodies.

Acrosome

Autolysis.

PEROXISOMESsingle membrane bounded organelles with

oxidative enzymes Structure similar to lysosomesFormed by self replication or by budding

off from sERDetoxifying organs of cellLipid metabolism, myelin synthesisAbundant in hepatocytes

The enzymes in them react with other substances and produces H2O2 which is used to detoxify various substances by oxidising them.

ZELLWEGER SYNDROME

RIBOSOMES• Made up of a large and a

small subunit.

• Ribosomes are seen in 1.bound form 2.free form

• Mainly involved in protein synthesis

STRUCTURE

RNA molecules of both subunits are synthesized with in the nucleus

The individual ribosomes held together by strand of mRNA to form poly ribosomes.

The message carried by mRNA is a code for the amino acid sequence of proteins being synthesized by a cell and the ribosomes play a crucial role in decoding or translating this message during synthesis.

Centrosome is the area located near nucleus.

The two centrioles are located perpendicular to each other in the centrosome.

Each centrioles consists of nine bundles of tiny microtubules arranged in a circle.

Functions:

1. Basal body formation

2. Mitotic spindle formation

Centrosome:

CYTOSKELETON

The cytoplasm is permeated by a number of

fibrillar elements that collectively form a supporting network called the cytoskeleton.

Functions of cytoskeleton:-

Maintains the cellular architecture Cell motility Divides cytosol into functionally discrete areas Anchoring cells to each other.

25nm Protein is tubulin dimer(α and β

subunits). Polymerisation of microtubles in

centrioles constitute the microtubule organising centre (MTOC).

Act as conveyor belts

ROLE:

Intra-cellular vesicular transport.

Movement of cilia and flagella. Mitotic spindles Cell elongation and movement.

Microtubules

Microfilaments Diameter is 5 nm. It is composed of actin filaments.

Free actin = G –actin polymerised actin = F-actin.

FUNCTIONS: Anchorage and movement of

membrane protein Formation of core of microvilli. Cell division, locomotion. Extension of cell processes.

Intermediate filaments

Diameter: 10nm Connects adjacent cells through

desmosomes Made of fibrous proteins.

Proteins: Cytokeratin in epithelial cells Neurofilament proteins in neuronsDesmin in muscleGlial fibrillary acidic protein in astrocytesLaminin in nuclear laminaVimentin in various cells

PROJECTIONS FROM CELL SURFACE1. CILIA: These are minute

hair-like projections from free surface of some cells.

0.25μm in

diameter.

They are made up

of microtubules.

FUNCTIONS:Ciliary action moves :- -Secretions in the respiratory tract

-Ova through the uterine tube. -Spermatozoa through the male genital tract -Cells in embryogenesis

Abnomalities in cilia can lead to primary ciliary dyskinesia(PCD) or immotile cilia syndrome.

2) FLAGELLA

Similar in structure to cilia but longer.

Eg; tail of spermatozoan.

Movement starts at base of flagellum.

nearest segment--- one direction.

succeding segements--- opposite direction .

wave like motion passes down the flagellum.

3) MICROVILLI:

With EM: Finger like extensions of cell membrane. plasma memebrane and numerous actin filaments in it.

Increases the surface area for absorption of materials

CELL INCLUSIONS

Inclusions contain products of metabolic activity of the cell

Consists of pigment granules, lipid droplets and glycogen.

Considered as nonmoving and nonliving components of the cell.

characteristic staining properties

Commonly seen inclusions are Lipofuscin

Hemosiderin

Glycogen

Lipid inclusions

Crystalline inclusions

LIPOFUSCIN

Brownish gold pigment –H & E.

conglomerate of lipids, metals & organic molecules.

wear and tear pigment.

HEMOSIDERIN : Iron storage complex found in cytoplasm.

LM-deep brown granule.

GLYCOGEN:

Highly branched polymer.

may not be stained in H & E.

Liver and striated muscle cells shows unstained regions where glycogen is present.

In EM clusters of granules of 25 to 30nm.

LIPID INCLUSIONS: Are usually nutritive inclusions that provide energy for

cellular metabolism. May appear in cell for very short time but in Adipocytes they

constitute most of cytoplasmic volume and compress other organelles into thin rim at margin of the cell.

CRYSTALLINE INCLUSIONS: These contained in certain cells are recognised in light

microscope. In humans are found in sertoli and leydig cells of testis may contain storage material or cellular metabolite.

Significance is not clear.

REFERENCES: TEXT BOOK OF MEDICAL PHYSIOLOGY-

GUYTON & HALL 12TH EDITION CELL & MOLECULAR BIOLOGY- NALINI

CHENDAR & VISELLI BASIC HISTOLOGY- JUNQUERA HISTOLOGY 9TH EDITION- HAMS TEXT BOOK OF HUMAN HISTOLOGY, 4TH

EDITION – INDERBIR SINGH HISTOLOGY, A TEXT & ATLAS,5TH EDITION-

MICHAEL H.ROSS,WOJCIECH PAWLINA

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