Week 9 lecture 3 - The endomembrane system

What organelles are in the endomembrane system?

Nuclear envelope, endoplasmic reticulum, golgi apparatus, lysosomes, vesicles, plasma membrane, vacuoles and endosomes.

What is not included in the endomembrane system?

Mitochondria, plastids (chloroplasts), and prokaryotic cells lack and ES.

What are the functions of the endomembrane system?

The endomembrane system functions in the synthesis, modification, packaging, and transport of proteins and lipids. It also carries out chemical reactions and material trafficking.

What are signal peptides/signal sequences?

Short amino acid sequences that direct proteins to specific locations within a cell. They facilitate the transport of proteins to the endoplasmic reticulum or other organelles. They act like a postcode.

How does post-translational translocation work?

1. Protein is translated entirely in the cytoplasm by a free ribosome

2. Signal sequence directs the protein to the appropriate compartment (nucleus, mitochondria, plastids).

How does Co-translational translocation work?

1. Protein is initially translated by a free ribosome

2. The entire ribosome moves to the membrane, becoming a bound ribosome

3. Protein translocates across the membrane while being translated

4. Goes into the ER where it is prepared to be secreted.

What is the structure of ER

Contains smooth ER and rough ER. Rough ER has ribosomes attached

What is the function of smooth ER?

Lipid synthesis, detoxification, and calcium storage.

What is the function of rough ER?

Protein synthesis and processing, sends proteins to the Golgi apparatus via vesicles, produces lipids, adds carbs to proteins (glycoproteins).

What is the structure and function of the Golgi apparatus?

The Golgi apparatus is made up of flattened membrane-bound sacs called cisternae. Its function is to modify, sort, and package proteins and lipids received from the rough ER for transport to their destinations.

What does exocytosis do?

Delivers proteins and carbs to the outside of the cell, lipids to plasma membrane and membrane proteins to plasma membrane.

What does endocytosis do?

Retrieves contents of vesicles, lipids from plasma membrane and membrane proteins. Its different forms are phagocytosis, pinocytosis and receptor-mediated endocytosis.

What is a lysosome?

A lysosome is a membrane-bound organelle that contains digestive enzymes to break down waste materials and cellular debris.

What are cisternae?

Flat, stacked membrane-bound structures within the endoplasmic reticulum and Golgi apparatus, involved in processing and transporting proteins.

What is the ER lumen?

The liquid inside the ER where protein and lipid synthesis occurs.