AL-01 Cell (09-10)

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THE CELLTHE CELL

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Aims and Objectives

1. To review and interpret the microanatomy

of human cells as seen under the light andelectron microscope.

2. Give examples to demonstrate the diversity

of cell types in multicellular organisms suchas humans.

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Lecture Outline

Organisation of the cell:

Cytoplasm

Matrix Organelles

Inclusions

Nucleus

Review questions.

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THE CELLTHE CELL

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CELL

Cell is the basic structural and functional unit

of all multicellular organisms

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Cell

Nucleus

Cytoplasmic matrix

Organelles

Inclusions

Cytoplasm

Chromatin

Nucleolus

Nuclear envelope

Nuclear skeleton

Nucleoplasm

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Cell

Nucleus

Cytoplasmic matrix

Organelles

Membranous

Non-membranous

Inclusions Membranous

Non-membranous

Cytoplasm

Chromatin

Nucleolus

Nuclear envelope

Nuclear skeleton

Nucleoplasm

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Cytoplasmic matrix

Organelles Inclusions

CYTOPLASM

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Cytoplasmic matrix

Solution containing electrolytes, metabolites,

RNA and synthesized proteins.

CYTOPLASM

Organelles

Living structures with metabolic/synthetic

functions.

Inclusions

Non-living structures with no metabolic function.

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MEMBRANOUS ORGANELLES

1. Plasma/cell membrane

2. Endoplasmic reticulum

a. Smooth ER

b. Rough ER

3. Golgi apparatus

4. Mitochondria

5. Lysosomes6. Peroxisomes

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Plasma membrane

sER

rER

Mitochondrion

Lysosome

Golgi

apparatus

1. Plasma Membrane

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8-10 nm thick hence not visible with LM.

Trilaminarappearance when seen with TEM

(2 dark lines enclosing a clear band)

1. Plasma Membrane - Appearance

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1. Plasma Membrane - Composition

Proteins:

Integral proteins

(within lipid bilayer)

Peripheral proteins

(bound to surface)

Phospholipids:

Outer portion

(hydrophilic)

Inner portion

(hydrophobic)

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Proteins:

Integral proteins (within lipid bilayer)

Peripheral proteins (bound to surface)

Phospholipids:

Inner portion (hydrophobic)

Outer portion (hydrophilic)


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Glycocalyx:

A layer of glycoprotein-glycolipid molecules that covers the membrane.

Protects the cell from chemical/physical injuries

.


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Cell Junctions

Gap Junctions

Forjoining with adjacent

cells (to form tissues)

Allow communication

between adjacent cells.

1. Plasma Membrane - Modifications

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Gap Junctions

Consist of manycommunicating channels.

2 closely apposed plasma

membranes, 2nm apart.

Communication betweencytoplasmic compartments

of adjacent cells allow direct

passage of ions and small

molecules.

connexion

1. Plasma Membrane - Modifications

Each channel is made up of

2 connexions.

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Maintains the structural integrity of the cell.

Establishes transport system for some molecules.

Controls movements of substances in and out of the cell.

Acts as barrier between cytoplasm and external millieu.

Recognizes antigens, foreign cells, altered cells

(via receptors) Transduces extracellular signals into intracellular events.

Regulates interaction between cells.

1. Plasma Membrane - Functions

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Not visible with LM (8-10 nm thick).

Trilaminar appearance under TEM.

Formed by protein and bilayerphospholipids.

Covered by glycocalyx (a protective layer on its surface)

Cell junctionsjoin adjacent cells.

1. Plasma Membrane - Summary

Gap junctions allow communication betweenadjacent cells for direct passage of ions and

small molecules.

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a. Smooth ER

b. Rough ER

3. Golgi apparatus

4. Mitochondria


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Plasma membrane

sER

rER

Mitochondrion

Lysosome

Golgi

apparatus

2. Endoplasmic Reticulum

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sER

rER

A continuous membrane in the form of anastomosing network of tubules

2a. Smooth Endoplasmic Reticulum (sER)

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Devoid ofribosomes (not covered with ribosomes)

A continuous membrane in the form of anastomosing

network of tubules.

Responsible for cytoplasmic eosinophilia

2a. Smooth Endoplasmic Reticulum (sER)

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Particles of ribosomes stud the exterior surface of the membrane (EM)

2b. Rough Endoplasmic Reticulum (rER)

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arrows indicate

clear area

Basophilic part of cytoplasm (ergastoplasm) is the image of rER


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cells that contain large amounts ofplasma membrane

(e.g. nerve cells)

cells that synthesize proteins

(e.g. secretory and glandular cells, plasma cells,

fibroblasts, osteoblasts, odontoblasts, ameloblasts)

rERis well developed in:


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a. Smooth ERb. Rough ER

3. Golgi apparatus

4. Mitochondria


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Under LM, Golgi apparatus is

seen as a large clear area that

is surrounded by the basophilic

ergastoplasm (rER)

arrows indicates the clear area

3. Golgi Apparatus

Functions:

Synthesizes carbohydrate.

Modification, sorting and

packaging of proteins.

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Under EM, Golgi appears as

stacks of flat membrane-bound

sacs lying close to secretory

vesicles.

3. Golgi Apparatus

Functions:

Synthesizes carbohydrate.

Modification, sorting and

packaging of proteins.

cv = condensing vacuole; sv =secretory vacuole;

ff = forming face; mf = maturing face

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sER, rER and Golgi complex

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sER, rER and Golgi complex

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3. Golgi apparatus

4. Mitochondria


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Plasma membrane

sER

rER

Mitochondrion

Lysosome

Golgi

apparatus

4. Mitochondria

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Rod-shaped or rounded with double membrane

Inner membrane : folded shelves (cristae)

: studded with enzymes

Outer membrane : smooth

4. Mitochondria

Outermembrane

Innermembrane(cristae)

enzymes

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Rod-shaped or rounded with double membrane

Inner membrane : folded shelves (cristae)

: studded with enzymes

Outer membrane : smooth

4. Mitochondria

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Mitochondria, in large numbers, produce cytoplasmic

acidophilia (due to large amount of membrane they contain)

Mitochondria contain theirown DNA for protein synthesis

and replication independent of the cell nucleus.

Functions:

Formation of ATP (generate energy)

Synthesis of lipid

4. Mitochondria

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Found in which cells?

Cells that produce/spend large amount of energy

All cells except red blood cells, terminal keratinocytes

Found in which part of cell?

striated muscle cells

middle piece of spermatozoa proximal convoluted renal tubule cells

Region where energy usage is intense e.g.

apex of ciliated cells mid-piece of spermatozoa base of proximal convoluted renal tubule cells

4. Mitochondria

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3. Golgi apparatus

4. Mitochondria


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Plasma membrane

sER

rER

Mitochondrion

Lysosome

Golgi

apparatus

5. Lysosome

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Lysosomes (L) seen as dark stained

cytoplasmic granules in renal tubular

cells

L = Lysosome; N = Nucleus

Lumen of renal tubule seen as

a long slit

5. Lysosome

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EM showing 4 dark secondary lysosomes surrounded by mitochondria

5. Lysosome

Lysosomes

Mitochondria

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Digestive organelles, rounded in shape.

Functions:

Numerous in cells with phagocytic activity

(e.g. macrophages, neutrophil leucocytes,

renal tubular cells)

Intracellular digestion Recycling of cellular components

Lysosomal enzymes inactive at cytosol pH (~7.2)

(this prevents leakage of enzymes)

Contains hydrolytic enzymes

(e.g. protease, lipase, ribonuclease, acid phosphatase)

5. Lysosome

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Acid Vesicle System

Primary lysosomes

Lysosomes newly formed

from Golgi cisternae.

Secondary lysosomes

Primary lysosomes that

contains the material to be

digested.

Residual bodies(Tertiary lysosomes)

Vacuoles filled with hydrolytic

breakdown contents of

secondary lysosomes.

5. Lysosome

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3. Golgi apparatus

4. Mitochondria


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6. Peroxisomes (Microbodies)

Peroxisomes seen as small membrane-bound, spherical bodies (arrows)

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Spherical membranous structures containing oxidative

enzymes (peroxidases, catalases)

6. Peroxisomes (Microbodies)

Numerous in liver and kidney cells.

Functions:

Detoxify noxious agents

Kill microorganismsPeroxidases

Regulate H2O2 content of cells Catalases

F oxidation of fatty acids

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Membranous



a. Smooth ER

b. Rough ER

3. Golgi apparatus

4. Mitochondria

5. Lysosomes

6. Peroxisomes

CYTOPLASM

Non-membranous

1. Microtubule

2. Microfilaments

3. Centrioles

4. Ribosomes

Organelles

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NON-MEMBRANOUS ORGANELLES

1. Microtubules

2. Microfilaments

3. Centrioles

4. Ribosomes

Functions:

C

ytoskeleton

Maintains cell shape

Movement oforganelles or entire cell

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13

Basic subunits of protofilaments are

known as Tubulindimers/molecules

Each tubulin dimer is composed of

E-tubulin and F-tubulin molecules

EFTubulin

dimer

Protofilament Nonbranching hollow cylinders

(20-25 nm in diameter; 5nm thick)

Composed of 13 circularly arranged

globular protein subunits - protofilaments

Structure

1. Microtubules

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arrows = microtubules, LS arrows = microtubules, TS

1. Microtubules

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Provide rigidity of cell.

Functions:

Regulate movement of chromosomes.

(during mitosis and meiosis)

Regulate movement of organelles and vesicles.

Provide motion of cilia and flagella.

Maintain shape of cell.

1. Microtubules

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Axoneme of cilia and flagella (A)

Basal bodies of cilia (B) Centrioles (C)

Mitotic spindle fibers (M)

Microtubules are present in all cellsexceptred blood cells

AA

BB

CC

MM

Microtubules are found in the following regions of cells:

1. Microtubules

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1. Microtubules

2. Microfilaments

3. Centrioles

4. Ribosomes

Functions:

Cytoskeleton



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Actin filaments are thin filaments that interact with

myosin to produce intracellular or cellular movement

Actin microfilaments are found in all cell types

Muscle cell contains 2 types of microfilaments -

actin and myosin

2. Microfilaments (Thin filaments)

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AF = Actin (thin) filaments; M = Microtubules

EM of fibroblast cytoplasm showing actin filaments and microtubules

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Anchorage and movement of membrane proteins.

Functions:

Formation of structural core of microvilli.

Movement of plasma membrane

(e.g. endocytosis, exocytosis, cytokinesis)

Locomotion of cells.

Extension of cell processes.


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Intermediate Filaments

8-10 nm

Fibroussubunit

In addition to thin (actin) and thick (myosin) filaments,cells contain another class of intermediate-sized filaments

(10-12 nm diameter).

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Type ofIntermediate Filament Location

Cytokeratins (Keratins) Epithelial cells

Desmin Muscles (smooth and striated)

Glial Fibrillary Acidic Protein Astrocytes

Neurofilament protein Neurons (soma and processes)

Nuclear lamin Nucleus of all cells

Vimentin Mesenchymal cells


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Intermediate filaments in skin epithelial cell

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Provide structural framework/support for cell.

Functions:

Anchor the nucleus in place.

Provide structural framework of nuclear membrane.

Provide connection between cell membrane and

cytoskeleton


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Clinical Application

Antigens

Type ofIntermediate FilamentDiagnosis

Cytokeratins (Keratins)

Tumors of epithelial origin Desmin Tumors of muscles

Glial Fibrillary Acidic Protein Tumors of glial cells

Vimentin Tumors of connective tissue

Identification of specific type of intermediate filamentin tumors can reveal the origin of tumor.This information is important for diagnosis and treatment.

Identification of intermediate filament proteins is done

by immunocytochemical methods.

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1. Microtubules

2. Microfilaments

3. Centrioles

4. Ribosomes

Functions:

Cytoskeleton



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Each centriole is composed of 9 microtubule triplets

(linked by proteins)

3. Centrioles

Centrioles exist in pairs, arranged at right-angles to

each other.

Located near the nucleus of non-dividing cells

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Functions:

Organises formation ofmitotic spindle in both normal

and dividing (mitotic) cells.

Organises development of specialised microtubulesin motile cilia.

3. Centrioles

Centrosome

This region contains a pair of centrioles.

It is the site from which microtubules originate.

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1. Microtubules

2. Microfilaments

3. Centrioles

4. Ribosomes

Functions:

Cytoskeleton



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Composed of rRNA and proteins.

4. Ribosomes

Found as free form or membrane-bound.

Synthesize protein.

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Polysomes

are groups of ribosomes attached to a thread of

messenger RNA (mRNA)

Cytoplasmic basophilia

is due to the presence of numerous rRNA.

4. Ribosomes

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Functions

Types ofRibosome ProteinsSynthesized

Polysomes Proteins exported from cell.

Integral proteins of plasma membrane

Free ribosomes Proteins within cell (cytoplasmic

elements)

4. Ribosomes

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Primary componentsinvolved in protein synthesis

Ribosomes/polysomes

Golgi apparatus

Rough endoplasmic

reticulum (rER)

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Cytoplasmic matrix

Organelles Inclusions

CYTOPLASM

I l i

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Non-living components of the cell.

Inclusions

No metabolic activity.

Components ofInclusions

Membrane-bound Without membrane

Secretory granules

e.g. zymogen granules

Lipid deposits

(storage form of triglycerides)

Pigment deposits

e.g. Hb, melanin, lipofuscin

Glycogen deposits

(storage form of glucose)

I l i

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Inclusions

Secretory granules

Secretory granules seen in

association with Golgi complex and

vacuoles

C = Vacuoles; G = Golgi complex;

S = Secretory granules

G

CS

S

S

S

I l i

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Inclusions

Pigment deposits

Liver cells with pigment deposits

(Giemsa stain)

H = Hepatocyte; M = Macrophage;

PD = Pigment deposit

I l i

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Inclusions

Lipid deposits

L = Lipid droplets;

M = mitochondria (anomalous)

Lipid droplets appear as vacuoles

in the cytoplasm (underLM)

(as lipid was extracted by solvents

during tissue processing)

Lipid droplets as seen under EM

in adrenal gland

I l i

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Inclusions

Glycogen deposits

G = glycogen granules;

m = mitochondria; N = nucleus

appear as:

emptyregions underLM

(as they were lost during

routine tissue processing)

rosette-shapedgranules

underEM

found in large amounts in liver

and striated muscle cells

I l i

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Inclusions

Glycogen deposits

G = glycogen granules;

m = mitochondria

appear as:

emptyregions underLM

(as they were lost during

routine tissue processing)

rosette-shapedgranules

underEM

found in large amounts in liver

and striated muscle cells

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Cell

Nucleus

Cytoplasmic matrix

Organelles

Inclusions

Cytoplasm

Nuclear envelope

Nucleoplasm Nucleolus

Chromatin

Cell is the basic structural and functional unit

of all multicellular organisms

THE NUCLEUS

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THE NUCLEUS

Size Largest organelle of the cell

Shape Spherical

Spindle to oblong

Disk-shaped

Twisted

Lobulated

Number Single

Multiple (skeletal muscle, osteoclast)

Absent (mature RBC)

Position Central

Peripheral (skeletal muscle)

S th M l C ll N l i

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Oval shape

Single nucleus per cell

Central in position

Smooth Muscle Cell NucleiCharacteristic Features

Skeletal M scle Cell N clei

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Skeletal Muscle Cell NucleiCharacteristic Features

Flattened nuclei

More than one nucleus per cell

Peripheral in position

Skeletal Muscle Cell Nuclei

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Skeletal Muscle Cell NucleiCharacteristic Features

Flattened nuclei

More than one nucleus per cell

Peripheral in position

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The Nucleus

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The Nucleus

Outer nuclearmembrane

rER

ribosomes

Inner nuclearmembrane

Nuclear pore

nu

np

ch

Chromatin (ch)

DNA inside the nucleus inthe form of coiled strands.

Visible as chromosomes

during cell division.

Heterochromatin

Visible under LM ascondensed basophilic clumps.

At the periphery of nucleus.

Inactive form of chromatin.

Euchromatin Not visible as well defined

structure under LM.

Scattered throughout nucleus.

Active form of chromatin.

The Nucleus

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hetero-chromatin

euchromatin

nucleolus

Chromatin (ch)




Heterochromatin





structure under LM.



The Nucleus

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heterochromatinheterochromatin

euchromatineuchromatin

nucleolusnucleolus

Chromatin (ch)




Heterochromatin





structure under LM.



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What is the difference between organelle and

inclusion?

Review questions

Name:

4 membranous organelles

4 non-membranous organelles

Name 2 modifications of plasma membrane

stating the function of each.

Is the plasma membrane visible or not?

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For each organelle, state one function and one

location (cell) where it is found in abundance,.

State 2 main functions of cytoskeleton.

Name the largest organelle.

State the differences between euchromatin and

heterochromatin.

Review questions

Name 4 inclusions and state the content of each.

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END OF THE CELLEND OF THE CELL

AL-01 Cell (09-10)

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