Lecture 8: Intro to the endomembrane system

Question 1

Endomebrane system (2)

what it is+includes

Answer 1

• Cytoplasmic membrane system that works together to modify, package, and transport lipids and proteins.
• Functionlly and structurally interrelated group of membranous cytoplasmic organelles including: ER, Golgic complex, endosomes, lysosomes, vacuoles

Question 2

Transport materials from donor compartment to recipient compartment steps:

Answer 2

1. Membrane bound vesicles shuttle materials between organelles
2. Vesicles bud from the donor compartment
3. Transport in a directional manner with the help of motor proteins and the cytoskeleton network
4. Vesicles fuse with the membrane of the recipient compartment
5. Cargo is released in the destonation compartment
6. Vesicle membrane becomes a part of the recipient compartment’s membrane
7. Escaped resident proteins of the donor compartment can be returned

Question 3

Transport materials from donor compartment to recipient compartment: How do we know where to bud?

Answer 3

Proteins (secreted proteins, lysosomal enzymes, membrane proteins…) are directed to the correct designation with sorting signals:
1. Amino acid sequences
2. attached oligosaccharides

Signals are recogized by receptors in the membranes of budding vesicles.

Question 4

Secretory Pathway (3)

what is synthesized, what occurs after+two types of secretion

Answer 4

• Examples of biomolecules synthesized in the ER: lipids/cholesterol, steroid hormones, secreted proteins, integral membrane proteins, glycosolyation of protein
• Modification occurs in the golgi complex
• constitutive or regulated secretion

Question 5

Constitutive secretion (3)

occurs in + what happens+ membrane

Answer 5

• Most cells
• Materials are continously transported in secretory vesicles from trans golgi and immediately secreted. Because the vesicles does not have any signal that will direct them to direct intracellular location they are just secreted out of cell through the cell membrane.
• Vesicle lipids contributes to the formation of the plasma membrane

Question 6

Regulated secretion (2)

what it is+ ex

Answer 6

• Materials are stored in membrane-bound compartments and remain near the cell surface until a particular stimuli arrives to trigger the secretion
• Ex: in face of increased Ca2+, nerve cells release neurotransmitters

Question 7

Endosome (3)

Answer 7

• Materials are taken up are transported to early endosomes for sorting, pinching of cell membrane during endocystosis
• Late endosomes are more acidic than early endosomes
• Fuse with lysosomes to deliver cargo for degradation

Question 8

Lysosome (2)

about it+function

Answer 8

• Contain hydrolytic digestive enzymes that is activated under an acidic PH (established by V-type proton pumps)
• Have roles in breakdown of material and organelle turnover (cells continuously degrade and replace their organelles)

Question 9

Transport of materials into the cell (endocytic pathway)

Answer 9

• Materials move from the outer surface of the cell to compartments within the cell (endosomes and lysosomes)

Question 10

Autoradiography

Answer 10

Following the location of radioactively-labeled materials in a cell

Question 11

Pulse-chase experiment

Answer 11

1. Radio-labelled amino acids are incooporated in the digestive enzymes being synthesized: Exposed to the radio-labelled amino acids for only a short time PULSE
2. Transfer cells to media with only unlabelled amino acids: Enzymes synthesized during this time will not be radio-labelled CHASE
3. Monitoro movement of protein and see how much pulse (radioactively labelled) proteins are left (may at surface released) and where the proteins are