the endomembrane system

Mr. Blithe

Endomembrane System:

Today, scientists know that the endomembrane system

includes the ENDOPLASMIC

RETICULUM(ER), GOLGI APPARATUS,

and LYSOSOMES.

The first Endomemembrane System was

discovered by Camillo Golgi in the late 1800s.

The endomembrane system is composed of the different inter-related membrane sacs within the cytoplasm of the cell.

Synthesis,

Modification,

Sorting and

Transport.

BIOMOLECULES

Introducing

the

Plant cell Animal Cell

"The police force of the cell"

"suicide bags“

“The cells' garbage disposal system.

It is the…

Lysosomes are spherical membranous bags that

contain enzymes (Acid Hydrolases).

size varies from 0.1–1.2 μm.

The lysosomal enzyemes are capable of digesting all

varieties of biological molecules.

Functions:

I. Digestion of worn out or non functional organelles.

II. Metabolic functions

III. Degradation of nonuseful tissue.

These membrane-bound organelles contain a variety of

enzymes called hydrolases that can digest proteins,

nucleic acids, lipids, and complex sugars.

Lysosomes break down all varieties of biological

molecules into their constituent parts, which are then

recycled.

Some important enzymes found within

lysosomes include:

All those hydrolytic enzymes are produced in the

endoplasmic reticulum, and to some extent in

cytoplasm are transported and processed through the

Golgi apparatus and through Golgi apparatus they

pinch off as single membrane vesicles.

adalan\endo_a.gif

In addition, vesicles that bud off from the plasma

membrane via endocytosis are also sent to lysosomes,

where their contents — fluid and molecules from the

extracellular environment — are processed. The

process of endocytosis is an example of reverse vesicle

trafficking, and it plays an important role in nutrition

and immunity as well as membrane recycling.

Lysosomal enzymes works best in an acid pH

approximately 5.

the lysosome membrane fuses with the membrane of a

food vacuole or Phagosome (particle containing vessel)

and squirts the enzymes inside.adalan\all about lysosomes\lysosomes at work.FLV

This action is called AUTOPHAGY…adalan\all about lysosomes\autophagy.avi - YouTube.FLV

The digested food can then diffuse through the vacuole

membrane and enter the cell to be used for energy or

growth.

Two Important Function:

1. maintain the organelles low pH level.

2. retains the dangerous acid Hydrolases

while permitting the final products of digestion

to escape so that they can be used by the cell

or excreted.

The only thing that keeps the cell itself

from being digested is the membrane

surrounding the lysosomes.

When the cell is injured or deprived of

oxygen and when excessive amount of

Vitamin A are present, the lysosomal

membrane becomes fragile. Such

ruptured results in Self-Digestion of the

cell, a process is called

AUTOLYSIS…

If the lysosomal enzymes do not reach the target it

causes Lysosomal Storage Disease..

Pompe's disease

an inherited disorder that is caused by the lack of the enzyme hydrolase acid alpha glucosidase (GAA) that is contained in lysosomes. GAA is responsible for breaking down glycogen to glucose.

Inclusion cell disease (I-cell disease)

this condition is caused by the failure to tag, by phosphorylation, all of the hydrolytic lysosomal enzymes with mannose-6-phosphate. This malfunction means that instead of the enzymes being transported to the lysosome, they are instead secreted from the cell.

Peroxisomes were first discovered by Christian de

Duve.

History…

Peroxisomes , also called microbodies,

are membranous sacs containing powerful

enxymes called PEROXIDASE..

Peroxisomes biogenesis has been unclear.

Recent experiments indicate that

peroxisomes originate or bud off

from the endoplasmic reticulum.

Peroxisomes are about the size of lysosomes (0.5–1.5

µm) and like them are bound by a single membrane.

They also resemble lysosomes in being filled with

enzymes.

contains a peroxisomal targeting signal (PTS).

contain about 50 different enzymes.

have crystalline and non-crystalline inclusions.

Peroxisomes stand out

in electronmicrographs

Urate Oxidase

crystalline core

major sites of oxygen utilization

Detoxify harmful or toxic substance like alcohol and

formaldehyde.

Disarm oxygen free radicals such as superoxide radical

by converting them to hydrogen peroxide (H2O2). And reduce Hydrogen peroxide to water and oxidizes

organic compounds (CH2)

2H2O2

2H2O+ O2

H2O2 + CH2 2H2O+ C

Breakdown (by oxidation) of excess fatty acids.

Breakdown of hydrogen peroxide (H2O2), a potentially dangerous product of fatty-acid oxidation. It is catalyzed by the enzyme catalase.

Participates in the synthesis of cholesterol. One of the enzymes involved is reductase.

Participates in the synthesis of bile acids.

Participates in the synthesis of the lipids used to make myelin.

Functions of the peroxisomes in the human liver:

Lack of peroxisomes or dysfunction may lead to:

A mutation in peroxin 2 (Pex2), a peroxisomal membrane protein involved in import process, causes one form of

Zellweger syndrome.It is a rare, congenital (present at birth) disorder characterized

by the reduction or absence of peroxisomes (cell structures that rid the body of toxic substances) in the cells of the liver,

kidneys, and brain. Zellweger syndrome is one of a group of genetic disorders called peroxisomal diseases that affect brain development and the growth of the myelin sheath,

the fatty covering-which acts as an insulator-on nerve fibers in the brain

Adrenoleukodystrophy (ALD) is a rare,

inherited metabolic disorder that afflicts the young boy Lorenzo Odone, whose story is told in the 1993 film "Lorenzo's oil." In this disease, the fatty covering (myelin sheath) on nerve fibers in the brain is lost, and the adrenal gland degenerates, leading to progressive neurological disability and death.

transport vesicles play a central role in the traffic of molecules between different membrane-enclosed compartments.

Vesicular transport is thus a major cellular activity, responsible for molecular traffic between a variety of specific membrane-enclosed compartments.

the formation of a vesicle by budding from the membrane. The cytoplasmic surfaces of transport vesicles are coated

with proteins.

Three kinds of coated vesicles1. clathrin-coated vesicles

are responsible for the uptake of extracellular molecules from the plasma membrane by endocytosis as well as the transport of molecules from the trans Golgi network to lysosomes.

2. COPII-coated vesicles-bud from the ER and carry their cargo forward along the

secretory pathway, to the Golgi apparatus.3. COPI-coated vesicles

bud from the ER-Golgi intermediate compartment or the Golgi apparatus and function in the retrieval pathways that serve to retain resident proteins in the Golgi and ER.

Clathrin (blue)

A protein called coat protein II (COPII; green)

A different protein called coat protein I (COPI; red)

clathrin-coated vesicles

are composed of two types of protein complexes clathrin and adaptor proteins.

Clathrin plays a structural role by assembling into a basketlike lattice structure that distorts the membrane and drives vesicle budding.

The binding of clathrin to membranes is mediated by a second class of proteins, called adaptor proteins.

COPI- and COPII-coated vesicles

composed of distinct protein complexes, which function analogously to clathrin and adaptor proteins in vesicle budding

The fusion of a transport vesicle with its target involves two types of events

1.the transport vesicle must specifically recognize the correct target membrane.

2. the vesicle and target membranes must fuse, thereby delivering the contents of the vesicle to the target organelle.

Transcription

Two groups of proteins are targeted to the ER: Proteins that are completely translocated into lumen of the

ER. These are soluble proteins destined for secretion, or for the lumen of another organelle.

Proteins that are inserted into membranes, and hence are only partially translocated into the endoplasmic reticuluum. These proteins may be destined for ER, another organelle, or the plasma membrane.

Lysosomal proteins from the rough endoplasmic reticulum (ER) must be further modified.

Modification of lysosomal

proteins called hydrolases

begins in the rough

endoplasmic reticulum

where a core oligosaccharide is added to the protein.

The hydrolases are then packaged into transport vesicles

and transferred to the cis-cisterna of the Golgi apparatus.

Inside the cis-cisterna of the Golgi, the core

oligosaccharide is phosphorylated.

One of the mannose residues in the oligosaccharide receives

a phosphate by way of two sequential reactions.

The modification of the core oligosaccharide on the hydrolase

enzyme results in the creation of an mannose 6-phosphate signal unique

to proteins destined for the lysosome. Other signals target other proteins for different destinations.

Upon reaching the trans-Golgi, the M6P portion of the

hydrolase binds to M6P receptors embedded in the

trans-Golgi membrane.

The membrane of the trans-Golgi then buds off into a

vesicle containing the receptors and the bound

hydrolases.AAA

Aspects of protein sorting

aaa

adalan\my report in cell bio\transport of protein from ER to its distination through golgiand sorting of protein.FLV

Special thanks to….

THANK

YOU

FOR YOUR

ATTENTION

!!!