Ch 12: Endomembrane System Flashcards

Questions and Answers

What are the components of the endomembrane system?

Endoplasmic reticulum, golgi complex, endosomes, lysosomes, peroxisomes

What is the endoplasmic reticulum?

A continuous network of flattened sacs, tubules, and vesicles important in protein and lipid synthesis.

What are the two types of ER?

Rough ER and Smooth ER

What are the functions of the rough ER?

Biosynthesis and processing of proteins, folding of polypeptides, protein quality control. Signup and view all the answers

What are the functions of the smooth ER?

Processing or storing nonprotein molecules, drug detoxification, carbohydrate metabolism, calcium storage, steroid biosynthesis. Signup and view all the answers

How does drug detoxification work?

By hydroxylation which adds hydroxyl groups to hydrophobic drugs to increase their solubility. Signup and view all the answers

How does carbohydrate metabolism work?

Glucose is stored as glycogen in the liver, broken down to glucose-6-phosphate, and then converted to free glucose. Signup and view all the answers

How does calcium storage work?

Involves pumping calcium ions into the ER lumen and releasing them during muscle contraction. Signup and view all the answers

How does steroid biosynthesis work?

Involves large amounts of smooth ER found in cells synthesizing cholesterol and steroid hormones. Signup and view all the answers

What is the role of the ER in the biosynthesis of membrane lipids?

Membrane phospholipids are primarily synthesized by the ER. Signup and view all the answers

What is the golgi complex?

An organelle that plays a central role in membrane and protein trafficking, processing glycoproteins and membrane lipids from the ER. Signup and view all the answers

What is the structure of the golgi?

Consists of flattened membrane-bounded cisternae with distinct faces: cis-Golgi network and trans-Golgi network. Signup and view all the answers

What are the two models that depict the flow of lipids/proteins across the golgi?

Stationary cisternae model and Cisternal maturation model. Signup and view all the answers

What is the difference between retrograde and anterograde transport?

Anterograde transport moves materials from the ER to Golgi and plasma membrane; retrograde transport returns vesicles to the ER. Signup and view all the answers

What are the roles of the ER and Golgi in protein glycosylation?

Glycosylation is the addition of carbohydrate side chains to proteins, occurring in the ER and Golgi. Signup and view all the answers

Study Notes

Components of the Endomembrane System

Includes endoplasmic reticulum (ER), Golgi complex, endosomes, and lysosomes.
Endosomes sort and transport materials brought into the cell.
Lysosomes digest ingested materials and unneeded cellular components.
Peroxisomes, associated with hydrogen peroxide reactions, are not part of the endomembrane system.

Endoplasmic Reticulum (ER)

A continuous network of flattened sacs, tubules, and vesicles.
Critical for protein and lipid synthesis.

Types of Endoplasmic Reticulum

Rough ER: Contains ribosomes on the cytosolic side; transitional elements (TEs) form transition vesicles that transport proteins to the Golgi.
Smooth ER: Lacks ribosomes; extensively found in cells that produce steroid hormones.

Functions of Rough ER

Primarily involved in protein biosynthesis and processing.
Ribosomes create both membrane-bound and soluble proteins.
Protein quality control is conducted through ER-associated degradation (ERAD).

Functions of Smooth ER

Involved in processing and storing nonprotein molecules.
Key roles include drug detoxification, carbohydrate metabolism, calcium storage, and steroid biosynthesis.

Drug Detoxification

Involves hydroxylation, adding hydroxyl groups to hydrophobic drugs to enhance solubility.

Carbohydrate Metabolism

Liver stores glucose as glycogen associated with smooth ER.
Glycogen breakdown produces glucose-6-phosphate, which is converted to free glucose for release into the bloodstream.

Calcium Storage

The sarcoplasmic reticulum in muscle cells specializes in calcium storage.
High calcium concentration achieved by ATP-dependent calcium ATPases and released during muscle contraction through calcium channels.

Steroid Biosynthesis

Large amounts of smooth ER found in cells synthesizing cholesterol and steroid hormones.

Role of ER in Membrane Lipids Biosynthesis

Membrane phospholipids synthesized by the ER and transferred to the luminal side via phospholipid translocators.
Vesicles bud off and fuse with other membranes, facilitated by phospholipid exchange proteins.

Golgi Complex

Functionally and physically connected to the ER; central to membrane and protein trafficking.
Processes glycoproteins and membrane lipids from the ER, sorting and packaging them for transport.

Structure of Golgi Complex

Composed of flattened membrane-bounded cisternae with biological polarity.
Cis-Golgi Network (CGN): Oriented toward the ER.
Trans-Golgi Network (TGN): Opposite side of the Golgi where sorting occurs.
Medial Cisternae: Located between CGN and TGN, where protein processing occurs.

Models of Lipid/Protein Flow in Golgi

Stationary Cisternae Model: Stable model where materials are transported from one cisternae to another using shuttle vesicles in a cis to trans sequence.
Cisternal Maturation Model: Transient model where cisternae gradually transform from CGN through medial to TGN.

Transport Mechanisms

Anterograde Transport: Movement of materials from ER to Golgi to plasma membrane.
Retrograde Transport: Flow of vesicles from the plasma membrane back to the ER, maintaining lipid flow balance and materials needed for new vesicle formation.

Roles in Protein Glycosylation

Glycosylation occurs in the ER and Golgi, involving the addition of carbohydrate side chains to proteins.
Two types of glycosylation: N-linked and O-linked; terminal glycosylation happens as glycoproteins transit through the Golgi.

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Description

Test your knowledge of the endomembrane system with these flashcards. Learn about the key components such as the endoplasmic reticulum, golgi complex, endosomes, and lysosomes. Understand their functions in protein synthesis, processing, and digestion within cells.