endoplasmic reticulum class ix

DONE BY :-S.Durgashree

IX-A

KENDRIYA VIDYALAYA

KARAIKUDI

Discovered by Belgian biologist

Albert Claude (1899-1983).

Used the newly developed

electron microscope to explore

the interior of cells and along

with his associate Keith Porter in

1945 observed the presence of a

“lace-work structure.”

Rough ER appears as lumpy sheets of folded

membranes. The lumps are the ribosome. They

are not permanently attached, adhering only

when there is protein manufacturing work to

be done.

Smooth ER which isn't coated with ribosome's

looks like smooth tubes.

No specific base or point in a cell, as it extends

a network of membranes, tubules vesicles, and

sacs throughout the cell.

ER membranes are folded and stacked on top

of each other and connected to the nucleus.

Rough ER with ribosomes attached is closest

to the nucleus.

Endoplasmic - “within the cytoplasm”.

Reticulum - Latin for “a little net”.

-> Extensive network of folded membranes that

extends from the nuclear envelope to which it

is connected, throughout the cytoplasm.

-> Divided into two sub-compartments, rough

ER and smooth ER.

-> Defined by the presence of ribosomes bound

to its cytosolic surface.

-> Typically composed of a network of flattened

sacs (cisternae).

->Continuous with the outer

membrane of the nuclear

envelope, which also bears

ribosomes on its cytosolic

surface.

Secrete large quantities of proteins, such as

the :

(a) Acinar cells of the pancreas

(b) Mucus secreting cells of the lining of the

digestive tract.

Rough ER is the starting point of the

biosynthetic pathways of:

Proteins

Carbohydrate chains

Phospholipids

that journey through the membranous

compartments of the cell.

Lacks associated ribosomes.

Membranous elements are highly curved and

tubular, forming an interconnecting system of

pipelines curving through the cytoplasm.

Extensively developed in a number of cell

types, including those of skeletal muscle,

kidney tubules, and steroid-producing

endocrine glands FIGURE 1. The smooth ER (SER). Electron micrograph of a Leydig cell from

the testis showing the extensive smooth ER where steroid hormones are

synthesized.

Synthesis of fatty acids and steroid hormones,

such as estrogens and testosterone.

Detoxification in the liver of a wide variety of

organic compounds, including barbiturates and

ethanol.

Sequestering calcium ions within the

cytoplasm of cells.

Ribosomes on its

outer surface.

Not associated with

ribosomes.

Site of synthesis of

proteins destined for

secretion .

Involved in lipid

metabolism.

ON MEMBRANE - BOUND RIBOSOMES:

a. Secreted proteins

b. Integral membrane proteins

c. Soluble proteins in ER, Golgi complex, lysosomes,

endosomes, vesicles and plant vacuoles

ON FREE RIBOSOMES:

a. Cytosolic proteins

b. Peripheral proteins

c. Proteins transported to the nucleus

d. Proteins to be incorporated in peroxisomes,

chloroplasts and mitochondria

As each protein is synthesized

in the rough ER, it becomes

inserted into the lipid bilayer

in a predictable orientation

determined by its amino acid

sequence. This orientation is

maintained throughout its

travels in the endomembrane

system, as illustrated in this

figure.

I hope that you would

have gained knowledge

from this power point

presentation….