Lecture 19 Flashcards
Where does glycosylation occur
within the lumen of the ER and the Golgi complex
What is the difference between the smooth and rough ER
Rough ER: contains ribosomes that produce/secretes proteins
Smooth ER: lacks ribosomes and is the primary site for lipid synthesis
What are the functions of the smooth ER (SER)
1) Lipid Synthesis (main function)
2) Production of steroid hormones (endocrine cells)
3) Detoxification: liver cells that contain enzymes that modify foreign compounds
4) Sequestration (storage) of Ca2+ [needed for muscle contraction/relaxation]
What are the functions of the rough ER (RER)
1) Synthesis of membrane phospholipids
2) Glycosylation of proteins (addition of carb chains to specific proteins)
3) Protein folding (quality control) - molecular chaperones that help with the folding process
4) Protein synthesis, modification, and transport - proteins targeted to ER, endocrine compartments and plasma membrane
Where does protein synthesis occur? What is the main function?
Occurs in the cytoplasm
ribosomes synthesize polypeptides from mRNA
What proteins/organelles are associated with translation of free ribosomes?
Cytosolic proteins
Peripheral membrane proteins
Proteins targeted to the nucleus, mitochondria, peroxisomes and chloroplasts
What proteins/organelles are related to ribosomes associated with the ER membrane
Secreted proteins
integral membrane proteins
soluble proteins associated with the lumen of the endomembrane system
(e.g ER, Golgi, lysosomes)
How is the site of translation determined?
Ribosomes are targeted to the ER membrane by a specific signal sequence
Describe the signal sequence for the site of translation
Is located in the amino-terminus (N-terminus)
Contains several consecutive hydrophobic amino acids
Directs synthesis to the ER compartment
Why does a protein move through a channel and into the ER
For cotranslational import
What are the steps of cotranslational protein import
1) after translation of the signal sequence, a signal recognition particle (SRP) binds to the sequence and stops translation
2) SRP binds to the SRP receptor and targets the whole translation complex to ER (SRP + ribosome + mRNA + new polypeptide)
3) SRP gets released adn the ribosome binds to the translocon, protein synthesis resumes
4) The polypeptide enters the ER through translocon and is translated. Signal peptide is cleaved off and the chaperone folds the protein
What is exocytosis
movement of cellular components to the plasma membrane
Through the biosynthetic/secretory pathway
What is endocytosis
movement of cellular components from the plasma membrane to an organelle (lysosome)
Through the endocytic pathway
What is an example of exocytosis
Secretion of a neurotransmitter from pre-synaptic neuronal cells
What is an example of endocytosis
Uptake of low density lipoprotein (LDL - in the blood contains cholesterol to make membranes) particle in liver cells
