BIOL 103 Lecture Notes - Lecture 12: Disulfide, Secretion, Protein Folding

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2 Dec 2020

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Consists of er, golgi apparatus, lysosomes, endosomes, and secretory vesicles. Involved in processing of proteins for export from the cell, proteins destined for lysosomes, proteins entering cell from cell surface. Once proteins enter the er they never return to the cytosol; they are carried by vesicle transport to the other compartments of the system. Proteins entering this set of organelles can only enter at the start of each pathway. Proteins destined for secretory or lysosomal pathways must enter at er and proteins going through endocytosis enter through plasma membrane. Proteins that enter the endomembrane never leave the pathway until they reach the final destination, and never go back to cytosol (unless misfolded and needs to be destroyed) Protein translation happens in the cytosol and all proteins are processed after translation by: Removal of first methionine (carried over by the start trna) Formation of disulfide bridges (most common in secreted proteins, added after folding)

Related Questions

1. The histones that form the core of the nucleosome get into the nucleus by which of the following?

a) Passive diffusion through nuclear pores

b) Selective and facilitated active transport through nuclear pores

c) Ribosomes located in the nucleus synthetize histones in the nucleus

d) Histones are made at the ER membrane and then diffuse to the nucleus

2. Membrane proteins that belong to the golgi, lysosome, or plasma membrane first pass through which organelle before reaching their final subcellular destination?

a) The golgi apparatus

b) The smooth ER

c) The nucleus

d) The ER membrane

e) The ER lumen

3. Where in the cell would a ribosomal protein be located if it has had its nuclear export signal inactivated (non-functional or non-existent).

a) The protein would be found in the ER lumen

b) The protein would remain in the nucleus

c) The protein would be secreted

d) The protein would remain in the cytoplasm

e) The protein would be in the ER membrane

4. Where would be the final destination of a protein if it contained a NLS anywhere in the protein sequence (and which is exposed to the cytoplasm after protein folding) but also contained an ER signal sequence at the carboxy terminus?

a) The ER lumen

b) The nucleus

c) The cytoplasm

d) The inner nuclear membrane

e) The ER membrane

5. The sequence K-D-E-L serves as a retention/retrieval signal for ER proteins.

a) True

b) False

6. The following are true for both cell membrane proteins and secretory proteins EXCEPT?

a) Precursors of the mature proteins contain signal sequence.

b) Both types of proteins contain stop-transfer sequences

c) Both types of proteins enter the ER while being synthetized

d) Both types of proteins pas through the golgi apparatus

e) Both are carried by clatherin-coated vesicles

7. If you isolate a regulated secreted protein from a secretory/storage vesicle and inject it into the cytosol, is will?

a) Be secreted through channels in the plasma membrane

b) Be taken up into secretory vesicle and secreted

c) Remain in the cytosol until it is degraded

d) Be taken up into the rough ER and follow the secretory pathway

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1. Name two similarities and two differences between thecellular processes of importing

protein into the ER and importing protein to the nucleus.

2. What proteins are directly involved in the transportation ofcargo in a clathrin-coated

vesicle?

a. Dynamin

b. Adaptins

c. Cargo receptors

d. t SNARES

3. Suppose a cell was treated with colchiine, a drug causingmicrotubule disassembly.

What would happen within the cell? Why?

Suppose there were a genetic defect in the genes that code forkinesins and dyneins.

What would happen within the cell? Why?

4. Which of the following are true about microtubules?

a. They are utilized by the disease causing bacteriaLysteria.

b. Instability in the minus-end of the microtubule is caused bythe hydrolization of GTP.

c. Centrosomes contain binding sites for microtubules composed atype of tubulin ring.

d. Cellular concentrations of tubulin are above the criticalconcentration for plus-end

polymerization.

e. Motor proteins can attach organelles to the microtubules.

5. Indicate which of the following statements are false:

a. Membrane fusion is energetically unfavorable and thusrequires ATP or similar high

energy molecule to occur

b. Clathrin is responsible for capturing specific molecules fortransport in coated vesicle

structures.

c. Receptor proteins that are incorporated into an endosome canbe retrieved back to the

membrane domain it originated from; can return to a new domainof the membrane; or

can enter the lysosome for digestion.

d. Transport vesicles occasionally bud from the trans Golginetwork to fuse with the

plasma membrane in a process called constitutive exocytosis.

e. Most components of the endocytic vesicle membrane eventuallyare returned to the

plasma membrane for reuse.

6. Match the following organelles with their function:

Organelle Bank:

a. Mitochondria

b. Endoplasmic reticulum

c. Nucleus

d. Lysosome

e. Endosome

f. Peroxisome

g. Golgi apparatus

_____ quality control of mRNA

_____ location of oxidative phosphorylation

_____ responsible for detoxifying organic molecules (livercells)

_____ houses and protects genetic material

_____ responsible for modification and sorting of proteins andlipids

_____ location of ATP synthesis

_____ responsible for sorting endocytosed materials

_____ site of degradation and digestion

_____ responsible for oxidizing toxic molecules

_____ location of lipid synthesis

_____ location of hormone synthesis (adrenal cells)

B. Which organelle(s) from the above list communicate(s) withother organelle(s)

through the use of vesicular transport? ________________

C. Which organelle(s) from the above list receive proteins madein the

cytosol?___________________

D. Through which organelle(s) must proteins pass to reach theorganelle(s) which do not

receive proteins made exclusively in thecytosol?______________

E. Entrance into which organelle(s) requires that proteinsunfold and snake through the

membrane? _________________

F. How do organelles maintain their position in the cytosol? Bespecific.

G. Give 2 advantages that eukaryotic cells gain by havingorganelles.

7. Which of the following statements are true regardingactin?

a. They are arranged in a

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BIOL 103 Lecture Notes - Lecture 12: Disulfide, Secretion, Protein Folding

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