BIOL 303 Lecture Notes - Lecture 5: Golgi Apparatus, Clathrin, Cell Membrane

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coffeesea-lion325

12 Jun 2018

School

Department

Biology

Course

BIOL 303

Professor

Nahmani

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Chapter 13

• Recall the secretory and endocytosis pathway order and functions of each compartment

(chapter 13, slide 6)

• Endocytosis: membrane faces outside and pulls vesicle into the cell.

• Vesicles must first ‘fuse’ with the compartment membrane and then

release their cargo into the lumen.

• Exocytosis: vesicle starting inside the cell and being pushed out the membrane.

• They bud off from compartments carrying cargo from the lumen and/or

membrane.

• Parts of secretory and endocytic pathways:

• ER: endoplasmic reticulum = protein synthesis

• Golgi: Golgi apparatus = packaging, transport

• Endosomes: late and early = recycling, repackaging, transport

• Lysosome = degradation

• Plasma membrane = cytosol regulation, cell-to-cell communication,

excitability, etc.

• Late endosomes become lysosomes.

• Match COP and clathrin vesicular coatings with the organelles that use them (chapter 13,

slides 7-9).

• Clathrin-coated: Golgi Apparatus, Endosomes and Plasma Membrane

• COPI&II: Golgi cisternae & Endoplasmic Reticulum

• Describe in detail the process of clathrin endocytosis (chapter 13, slides 10-19).

• Clathrin assembly drives vesicle formation

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• Each subunit of clathrin is made up of 3 large and 3 small polypeptides

that form a triskelion.

• Triskelions assemble in a basket to form coated pits on cytosolic surfaces

of membranes.

• Clathrin triskelions can self-assemble and form the polyhedral

shape of the clathrin coat.

• Light chains link to actin cytoskeleton which help generate and/or

relieve forces produced during vesicle budding.

• Adaptor proteins link the clathrin coat to the membrane and bind

transmembrane ‘cargo receptors’ in the process

• Specific adapter proteins for sets of cargo receptors

• AP2 in the cytosol is formed from multiple protein subunits and exists in a

“locked” form.

• To bind cargo receptors (to “open”), AP2 must first bind a

phosphatidylinositol phosphate (PIP) phospholipid.

• Binding to a PIP exposes receptor binding sites for the

cargo receptors and allows AP2 to act as a coincidence

detector.

• Specific PIPs are found in different organelles, bind

specific Aps & recruit specific proteins to regulate vesicle

formation.

• Vesicles are “pinched off” by cytoplasmic proteins

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Related Questions

Which compartments are involved in vesicular transport? How are transport vesicles formed and targeted appropriately? What proteins are involved and what are their roles? What kinds of modifications are added to proteins in the ER? What determines whether a protein stays in the ER or moves on? Be sure to understand how vesicles fuse with their target membranes, and the consequences of fusion for the vesicleâs cargo as well as the proteins and lipids that are in the membrane. Know the structure of the Golgi apparatus and its role in intracellular trafficking. Understand the secretory process, endocytosis, exocytosis, function of the endosomes, and function of the lysosomes. Understand why endocytosis happens and how it can be regulated to take up specific molecules.

1/What is the fate of a protein with no N-terminus Signal Sequence?

(a)Transport through the constitutive secretory pathway

(b)Dispersal throughout the cytoplasm

(c)Transport into the nucleus

(d)Transport to the rough endoplasmic reticulum (RER)

2/ In nerve cells, Botulinum toxin-A degrades a subunit of a T-snare localized on the plasma membrane, how would this affect vesicular trafficking?

(a) It blocks the co-translational import of neurotransmitter proteins into the Endoplasmic reticulum via the translocon.

(b) It prevents the addition of carbohydrates to translated proteins

(c)It blocks the fusion of neurotransmitter-containing vesicles with the plasma membrane because theT-snare would not be able tophysically interact with the V-snare.

(d) None of the above

What is the correct order of events of Clathrin-mediated endocytosis?

1. Uncoating of Clathrin- coated vesicle

2. Recruitment of Clathrin and selection of cargo

3. Fusion of vesicle with early endosome

(a) 1, 2, 3

(b) 2, 1, 3

(d) 3, 1, 2

4/ Vesicles traveling anterogradely will eventually fuse with the cell membrane.

Which of the following elements does NOT participate in the fusion event?

(a) v-snare

(b) t-snare

(d) clathrin coat protein

When a cell releases a hormone into the bloodstream and a number of cells in a

distal location respond, this type of signaling is...

(a) Autocrine signaling

(b) Endocrine signaling

(d) Juxtacrine signaling

taupereindeer397

The vesicles that transport materials from donor membranes to acceptor membranes include:

	1.	COP-II coated vesicles
	2.	COP-III coated vesicles
	3.	COP-I coated vesicles
	4.	Clathrin coated vesicles

2.5 points

QUESTION 11

During skeletal muscle contraction, the roles of ATP include:

	1.	ATP is not required for forming the crossbridges between myosin and actin filaments.
	2.	ATP is utilized as a structural linker to mediate the interaction between myosin and actin filaments
	3.	Hydrolysis of ATP provides energy for myosin head to move along actin filaments and the binding of ATP to myosin head allows the detachment of myosin fromactin filaments.
	4.	ATP binds to actin filaments to drive the power stroke of myosin head.

2.5 points

QUESTION 12

One of the functions of smooth endoplasmic reticulum is

	1.	Synthesizing steroid hormone in the endocrine cells of the gonad and adrenal cortex
	2.	Serves as the starting point of the biosynthetic pathway
	3.	Synthesizing secretory proteins
	4.	Degrading cell debris

2.5 points

QUESTION 13

The function of COP-II coated vesicles is mainly:

	1.	Transporting materials from endosomes to Golgi complex
	2.	Moving materials from the ER to the ERGIC and Golgi complex.
	3.	Transporting materials from Golgi complex back to endoplasmic reticulum.
	4.	Involved in receptor-mediated endocytosis.

2.5 points

QUESTION 14

Which of the following processes is completed in rough endoplasmic reticulum?

	1.	Chaperones help misfolded proteins fold correctly.
	2.	Proteins that target to nucleus are synthesized in rough endoplasmic reticulum.
	3.	O-linked glycosylation occurs in rough endoplasmic reticulum.
	4.	Misfolded proteins are destructed in rough endoplamic reticulum.

2.5 points

QUESTION 15

Kinesin is the motor protein that coorporates with microtubules. It has the following functions:

	1.	It uses GTP as energy source.
	2.	It can hydrolyze ATP and use the energy to drive cargo along microtubules from minus end to plus end.
	3.	It has a globular head that can act as GTPase
	4.	The tail of kinesin is more diverse and binds to cargo

2.5 points

QUESTION 16

For correct segregation and trafficking, lysosomal proteins are tagged in the cis-Golgi with phosphorylated mannose residues, and then the tagged lysosomal enzymes are recruited to clathrin coated vesicles by mannose 6-phosphate receptors.

True

False

2.5 points

QUESTION 17

The process that specialized cells, such macrophages, engulf relatively large particles is:

	1.	Called pinocytosis
	2.	Called phagocytosis
	3.	Mediated by COP-II coated vesicles
	4.	Called autophagy

2.5 points

QUESTION 18

Proteins synthesized on rough endoplasmic reticulum and smooth endoplasmic reticulum are imported co-translationally to their destinations

True

False

2.5 points

QUESTION 19

Treatment of cells with a drug that promotes microtubule disassembly disperses Golgi complex into separate stacks of membrane compartments, suggesting that:

	1.	Golgi complex is made of microtubules.
	2.	Microtubules are important for the organization of Golgi complex.
	3.	Microtubules are transported into Golgi complex
	4.	Golgi complex is composed of tubulin proteins

2.5 points

QUESTION 20

Which of the following is correct about signal sequence of a secretory protein?

	1.	It is an âaddress codesâ for protein trafficking pathways
	2.	It is usually located at the C-terminus.
	3.	It targets the ribosome and the protein that is being synthesized to endoplasmic reticulum.
	4.	It is removed in Golgi complex.

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BIOL 303 Lecture Notes - Lecture 5: Golgi Apparatus, Clathrin, Cell Membrane

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