CYTOLOGY & HISTOLOGYLecture three

DR. ASHRAF SAID

Review

Of the second lecture

Concept 3

The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes

Start

Of this lecture

Objectives of lecture threeThe Endoplasmic Reticulum: Biosynthetic FactoryLysosomes: Digestive Compartments

Concept 4

The endomembrane system regulates protein traffic and performs metabolic functions in the cell The endomembrane system

– Includes many different structures

The Endoplasmic Reticulum: Biosynthetic Factory

The endoplasmic reticulum (ER)–Accounts for more than half

the total membrane in many eukaryotic cells

The ER membrane Is continuous with the nuclear envelope

Smooth ER

Rough ER

ER lumenCisternae

RibosomesTransport vesicle

Smooth ER

Transitional ER

Rough ER 200 µm

Nuclearenvelope

Figure 1.12

The ER membrane

There are two distinct regions of ER–Smooth ER, which lacks

ribosomes

–Rough ER, which contains ribosomes

Functions of ER

The smooth ER– Synthesizes lipids

– Metabolizes carbohydrates

– Stores calcium

– Detoxifies poison

The rough ER– Has bound ribosomes

– Produces proteins and membranes, which are distributed by transport vesicles

Smooth Rough

The Golgi apparatus– Receives many of the transport vesicles produced in

the rough ER– Consists of flattened membranous sacs called

cisternae

The Golgi Apparatus: Shipping and Receiving Center

Functions of the Golgi apparatus include

Modification of the products of the rough ER

Manufacture of certain macromolecules

Golgiapparatus

TEM of Golgi apparatus

cis face(“receiving” side ofGolgi apparatus)

Vesicles movefrom ER to Golgi Vesicles also

transport certainproteins back to ER

Vesicles coalesce toform new cis Golgi cisternae

Cisternalmaturation:Golgi cisternaemove in a cis-to-transdirection

Vesicles form andleave Golgi, carryingspecific proteins toother locations or tothe plasma mem-brane for secretion

Vesicles transport specificproteins backward to newerGolgi cisternae

Cisternae

trans face(“shipping” side ofGolgi apparatus)

0.1 0 µm16

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2

3

4

Functions of the Golgi apparatus

Figure 1.13

Lysosomes:Digestive Compartments

A lysosome– Is a membranous sac of hydrolytic

enzymes

– Can digest all kinds of macromolecules

(a) Phagocytosis: lysosome digesting food

1 µm

Lysosome containsactive hydrolyticenzymes

Food vacuole fuses with lysosome

Hydrolyticenzymes digestfood particles

Digestion

Food vacuole

Plasma membrane

Lysosome

Digestiveenzymes

Lysosome

Nucleus

Lysosomes carry out intracellular digestion by phagocytosis

Figure 1.14 A

(b) Autophagy: lysosome breaking down damaged organelle

Lysosome containingtwo damaged organelles 1 µ m

Mitochondrionfragment

Peroxisomefragment

Lysosome fuses withvesicle containingdamaged organelle

Hydrolytic enzymesdigest organellecomponents

Vesicle containingdamaged mitochondrion

Digestion

Lysosome

Autophagy

Figure 1.14 B