Lecture #7 - Endomembrane system etc

Question 1

Transport is required for

Answer 1

1. Processing cellular material (e.g. cells wanna build ish so need move around)
2. Mainting compartment integrity

Question 2

The endomembrane system involve which 7 things? What is it?

Answer 2

1. Nucleus/nuclear membrane
2. The ER (sER + rER)
3. Golgi Apparatus (cis is longer side and trans is circular side)
4. Lysosomes
5. Vesicles
6. Endosomes (membrane-bound vesicles)
7. Cell membrane

=A functionally integrated cellular unit

Question 3

Smooth ER has what 4 functions?

Answer 3

1. METABOLISM of carbohydrates
2. Lipid SYNTHESIS for membranes (for phospholipids etc)
3. DETOXIFICATION of drugs and poisons
4. STORAGE of calcium ions (organelles can store high conc of ish and sER stores Ca2+ and releases it to activate certain processes)

Extensive sER in cells active in these processes - the amount of sER can be increased or decreased to meet demand (if overdose usually then ↑ sER to deal with it)

Question 4

Rough ER has what function? + special note

Answer 4

1. Involved in PROTEIN SYNTHESIS (secreted and membrane-bound proteins enter the lumen (interior) of the rER - then processed via the endomembrane system)
   - Rough bc ribosomes

Note: Synthesis of cytoplasmic proteins occurs on free ribosomes

Question 5

Golgi complex/apparatus

1. What is it?
2. Vesicles from ER arrive at what face and processed vesicles leave at what face?

Answer 5

1. Series of membrane sacs and associated vesicles and it has polarity:- cis and trans face
2. Vesicles from ER arrive at the cis face and processed vesicles leave at the trans face

Question 6

Roles of Golgi? (3 of em)

Answer 6

1. GLYCOSYLATION of proteins - addition or modification of carbohydrates - important for cell surface proteins (e.g. adding sugars or modifying sugars?)
2. SORTING PROTEINS - adds molecular markers to direct proteins to the correct vesicles
   • e.g. a special phosphorylated sugar (mannose
   6-phosphate) identifies lysosomal enzymes (proteins arrive in random assortment in vesicle so needa sort)
3. DIRECTING VESICLE TRAFFICKING - adds molecular “tags” to direct vesicles to the
   correct target compartment
   • such tags are often short proteins exposed on
   the vesicle surface
   • have specific amino acid sequences

Question 7

Retrieval tag does what? Other tags do what?

Answer 7

Direct proteins back to ER or previous Golgi cisternae
- important to maintain compartment integrity and function

(Some essential enzymes travel with vesicles like supervisors and ER needs em back so compartment integrity and function is maintained)

-Other tags direct to secretory pathways - important for release of proteins outside cell and surface expression

Question 8

Exocytosis does what?

Answer 8

TRANSPORT material out of the cell and DELIVER material to the cell surface

Question 9

The proteins released in constitutive pathway (exocytosis type) make up what?

Answer 9

• Proteins secreted make up ECM
• This pathway is unregulated
• The surface proteins are within the vesicle and cell membrane so when vesicle fuses, it doesn’t like a blank space in the surface?

Question 10

Regulated exocytosis releases what?

Answer 10

-Releases hormones and neurotransmitters (at the precise time you require it)

Question 11

Endocytosis - three types

Answer 11

1. PHAGOCYTOSIS uptake of
   “food” particles
   • forms a phagocytic vacuole which is “digested” (not vesicle - vacuole)
2. PINOCYTOSIS
   • non-selective uptake of solutes
3. RECEPTOR MEDIATED
   ENDOCYTOSIS
   • collects and concentrates specific molecules (receptors bind to specific molecules)
   • e.g. low density lipoprotein (LDL) particles

Question 12

Endocytotic pathways are directed to……

Answer 12

The endosome-lysosome pathway

vacuole comes in, fuses with lysosome, lysosome digests the bacteria that was phagocytosde

Question 13

Lysosomes do what?

Answer 13

1. DIGEST cellular/endocytosed materials + unwanted intracellular structures
   • contain hydrolytic enzymes
   • degrade proteins, lipids, carbohydrates and
   nucleic acids
2. Important for whole cell destruction or AUTOPHAGY (programmed cell death)
3. Important for cell health

Question 14

How does lysosome know what to digest?

Answer 14

Golgi labelled everything so lysosome only digests and degrades labelled ish - doesn’t go around destroying errythang, ya know?

Question 15

What kind of unwanted intracellular structures would lysosome wanna digest?

Answer 15

The extra sER that was created to deal with the drug - it’s taking up space and resources so get rid of it.