UNIT 5.1. MEMBRANE-BOUND ORGANELLES: ENDOPLASMIC RETICULUM

“within the cytoplasm”

Endoplasmic means

Latin: “a little net”

Reticulum means

ER

Extensive network of folded membranes that extends from the nuclear envelope to which it is connected, throughout the cytoplasm.

It is present in both animal and plant cells.

Albert Claude

ER was discovered by Belgian biologist

Keith Porter

Albert Claude used the newly developed electron microscope to explore the interior of cells and along with his associate _____________ in 1945 observed the presence of a “lace-work structure.”

1. Cisternae

2. Tubules

3. Vesicles

3 Parts of ER

Cisternae

3 Parts of ER:

• These are flattened, unbranched, sac-like element

• They lie in stacks parallel to one another

• They bear ribosomes on the surface

Tubules

3 Parts of ER:

• These are irregular branching element which form a network along with another element

• These are often free of ribosomes

Vesicles

3 Parts of ER:

• These are oval and rounded, vacuole like element

• These are also free of ribosomes

Cisternae

3 Parts of ER:

• Are flattened, membrane-bound sacs that make up the bulk of the ER structure.

• They provide a large surface area for biochemical processes

• Function: Protein synthesis and processing, Lipid synthesis

Vesicles

3 Parts of ER:

• Are small, membrane bound sacs that bud off from the ER and transport proteins and lipids to various destinations within the cell or outside it.

• Function: Transport & Secretion

Tubules

3 Parts of ER:

• Are elongated, tubular structures that extend from the ER and can connect to the cisternae or vesicles

• Function: Communication, Membrane extension

Endoplasmic Matrix

• The space inside the tubules and vesicles is filled with a watery medium that is different from the fluid in the cytosol outside the ER.

T

T or F
Endoplasmic reticulum membranes are folded and stacked on top of each other and connected to the nucleus.

RER

• This is an extensive organelle composed of a greatly convoluted but flattish sealed sac (cisternae) that is continuous with the nuclear membrane.

• site of protein synthesis is destined for secretion.

membranes & secretory proteins

The rough ER manufactures ____________ and ______________

antibodies

In certain leukocytes (white blood cells), the rough ER produces _____________.

insulin

In pancreatic cells, the rough ER produces ________.

protein translocation

• process by which peptides are transported across a membrane bilayer

• process by which proteins are transported to specific locations inside or outside the cell after they are synthesized.

RER

_____ is the starting point of the biosysthesis pathways of Proteins, Carbohydrate chains, and Phospholipids

F

Smooth ER is MORE TUBULAR than rough ER

T or F

Smooth ER is less tubular than rough ER

• Forms a separate sealed interconnecting network

• It is found fairly evenly distributed throughout the cytoplasm

• It is not studded with ribosomes hence ‘smooth ER’

SER

• allows increased surface area for the action or storage of key enzymes and the products of these enzymes

• site of lipid synthesis (including oils, phospholipids and steroids)

• It helps in metabolizing of carbohydrates

• It maintains regulation of calcium concentration.

• also help in the biogenesis of golgi complex and lysosomes

• helps in detoxification of drugs and poisons

• It serves as a transitional area for vesicles that transport Endoplasmic Reticulum products to various destinations.

• helps in muscle contraction mechanism.

male and female hormones

SER: In brain cells it synthesizes ________

sarcoplasmic reticulum

SER: In skeletal and cardiac muscle, smooth ER is modified to form _______________ — main role is to store and release calcium ions (Ca²⁺), which are essential for muscle contraction.

Proteotoxicity

Diseases Caused by Malfunctioning of ER:

• cellular damage caused by misfolded, damaged, or aggregated proteins.

- Cystic Fibrosis

- Hepatic disorders

- Multiple sclerosis

- Sickle cell disease

- Retinitis pigmentosa

- Alzheimer's disease

Proteotoxicity in ER can cause