Cell Bio Exam 2 pt. 7: Endomembrane system and peroxisomes

What are the 5 parts of the endomembrane system?

1. ER 2. Golgi complex 3. Vesicles and Endosomes 4. Lysosomes 5. peroxisomes

What are the two kinds of ER?

smooth ER and rough ER

What is the function of the rough ER?

involved in biosynthesis and processing of proteins

Where are ribosomes attached to the rough ER?

the cytosolic side of RER membrane

What are the ribosomes attached to the RER responsible for?

synthesizing both membrane-bound and soluble proteins

What are the 4 functions of the smooth ER?

1. drug detoxification 2. carbohydrate metabolism 3. calcium storage 4. steroid biosynthesis

What is the ER the primary source of?

membrane lipids like phospholipids and cholesterol

What happens to the phospholipid membranes created in the ER?

they are transferred to other membranes (plasma membrane and membrane of chloroplast, mitochondria, peroxisomes, etc.)

What type of transfer protein is responsible for transferring the phospholipid molecules from the ER?

phospholipid exchange/transfer proteins - they are specific to the phospholipid type

What are the two faces of the Golgi complex stack?

cis-Golgi network (CGN) and trans-Golgi network (TGN)

What continuously arrives to the CGN?

transition vesicles carrying newly synthesized proteins and lipids from ER

What continuously buds from the TGN?

transport vesicles carrying processed proteins from golgi to secretory granules, endosomes, lysosomes, and the plasma membrane

What is anterograde transport?

movement of material from ER through golgi toward the plasma membrane

What is retrograde transport?

movement of material from golgi back toward ER

What does the protein processing in ER and golgi involve?

glycosylation (addition of carbohydrates)

Where does N-linked glycosylation occur?

at amino group of asparagine

Where does O-linked glycosylation occur?

at hydroxyl group of serine or threonine

Are all steps of glycosylation strictly dependent on the previous step?

Yes

What are the consequences of a defect in one stage of glycosylation?

it alters all downstream events and can lead to disease

What are the two main stages of glycosylation?

initial glycosylation and modification of the carbohydrate side chains

Where does initial glycosylation occur?

in the ER

Where does modification of the carbohydrate side chain occur?

in the Golgi

What is the function of secretory pathways?

transporting molecules to the exterior of the cell

What is exocytosis?

when proteins sequestered in a secretory vesicle are released to the exterior of the cell as the membrane of the vesicle fuses with the plasma membrane

What types of proteins are exported through exocytosis?

peptide and protein hormones, mucus, milk proteins, digestive enzymes

What is endocytosis?

import of extracellular molecules by forming vesicles from the plasma membrane

What is phagocytosis?

cellular eating

What is pinocytosis?

cellular drinking

What are the two main mechanisms of endocytosis?

1. clathrin-independent or fluid-phase endocyotsis

2. receptor-mediated or clathrin-dependent endocytosis

What is clathrin-independent endocytosis?

fluid phase endocytosis

What is the function of clathrin-independent endocytosis?

process for nonspecific internalization of extracellular fluid; does not concentrate ingested material

How often does clathrin-independent endocytosis occur?

it proceeds at a relatively constant rate in most eukaryotic cells

What is receptor-mediated endocytosis?

primary mechanism for specific internalization of macromolecules by eukaryotic cells

How does receptor-mediated endocytosis work?

extracellular molecules are concentrated and ingested by specific receptors on outer surface of plasma membrane

What are the extracellular molecules that undergo receptor-mediated endocytosis?

hormones, growth factors, enzymes, serum proteins, antibodies, iron, some viruses, and bacterial toxins

What is the function of lysosomes?

degradation of all major classes of biological macromolecules (proteases, peptidases, nucleases, lipases, glycosidases, phosphatases, etc)

What do lysosomes contain that help them with degradation?

digestive enzymes called acid hydrolases (active at low pH)

What maintains an acidic pH (4-5) for the enzymes to digest?

ATP-dependent proton pumps

What are the 4 functions of peroxisomes?

1. hydrogen peroxide metabolism by enzyme catalase 2. detoxification of harmful compounds (methanol, ethanol, formic acid, formaldehyde, nitrites, phenols)

3. catabolism of unusual substances (D-amino acids, Xenobiotics, Alkanes)

4. oxidation of fatty acids to provide energy to cells