Endoplasmic Reticulum

What is the endoplasmic reticulum (ER)?

A network of membranes in the cytoplasm that:
Synthesizes proteins and lipids
Folds and transports these molecules.

What are the two types of ER?

Rough ER (RER)
Smooth ER (SER).

Why is the rough ER called “rough”?

Surface is covered with ribosomes
Looks bumpy under a microscope.

Why is the smooth ER called “smooth”?

Lacks ribosomes
Has a smooth appearance.

Is the ER found in all cells?

Found only in eukaryotic cells
Not present in prokaryotes.

What is the main function of the rough ER?

Synthesizes proteins for:
Secretion
Membrane insertion
Transport to organelles.

What happens to proteins after they are made in the RER?

Folded and chemically modified (e.g., glycosylation)
Packed into vesicles
Sent to the Golgi apparatus.

Which cells have a lot of rough ER?

Pancreatic cells (make insulin)
Plasma cells (make antibodies).

What are the functions of the smooth ER?

Lipid synthesis (phospholipids, steroids)
Detoxification of drugs/poisons
Carbohydrate metabolism
Calcium ion storage (especially in muscles).

Which cells have lots of smooth ER?

Liver cells (detox)
Adrenal gland cells (hormone production)
Muscle cells (calcium storage).

How is the SER involved in detoxification?

Contains enzymes that break down toxins
Makes harmful substances easier to eliminate.

How is the ER connected to the nuclear envelope?

Continuous with the outer nuclear membrane
Allows easy transport of proteins/RNA between nucleus and ER.

How does the ER help maintain homeostasis in the cell?

Produces essential molecules (lipids, proteins)
Regulates ion levels (e.g., calcium)
Detoxifies harmful compounds.

What happens if protein folding in the RER goes wrong?

Misfolded proteins accumulate
Causes ER stress
Can lead to diseases like Alzheimer’s or cystic fibrosis.

How do substances move from the ER to the Golgi apparatus?

Packaged into transport vesicles
Vesicles bud off from ER and fuse with Golgi.

What is the sarcoplasmic reticulum?

Specialized smooth ER in muscle cells
Stores and releases calcium ions for muscle contraction.