BIOB10H3 Lecture Notes - Lecture 6: Clathrin, Endosome, Cell Membrane

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21 May 2018

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Lecture 6

Endocytosis and Phagocytosis

Cellular Uptake of Particles and Macromolecules

• materials too large to pass through membrane

o eg. uptake of transporters and signaling receptors no longer required

o uptake of extracellular materials (ligands)

• uptake occurs into cytoplasmic vesicles derived from invaginations of cell membrane

Two separate categories:

endocytosis

phagocytosis

Endocytosis

• uptake of dissolved solutes, macromolecules, signaling receptors, etc.

Receptor-mediated endocytosis (RME)

• uptake of specific extracellular macromolecules (ligands) that bind to receptors on external cell

membrane surface

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Take up hormones, growth factors, enzymes, plasma proteins by binding to receptors

Endocytic Pathway (receptor-mediated)

• receptors bind ligand- undergo conformational change, clathrin binds on cytosolic side

• PM pinches in (via clathrin) to form early endosome (EE)

• early endosome matures into sorting compartment (SC)

• sorting compartment lumen fluid acidified due to action of membrane H+ pumps

• in low pH, ligands are released from cell membrane receptors

• receptors are recycled back to cell membrane in vesicles

• edosoe carrier esicles ECV’s leae “C ad fuse ith late endosomes (LE)

➔mature into lysosomes where contents are digested (via acid hydrolases)

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Document Summary

Endocytosis uptake of dissolved solutes, macromolecules, signaling receptors, etc. Receptor-mediated endocytosis (rme: uptake of specific extracellular macromolecules (ligands) that bind to receptors on external cell membrane surface. Take up hormones, growth factors, enzymes, plasma proteins by binding to receptors. Mature into lysosomes where contents are digested (via acid hydrolases) Phagocytosis (cell eating: receptors cluster into lipid rafts, clustering signals recruitment of signaling proteins. Pi3k (phosphorylates pi"s: pi3k phosphorylates pi on plasma membrane to make pi3p. Phagocytosis (cell eating: pi3p recruits ph-domain containing proteins, ph-proteins bind to actin proteins and cause the underlying actin cytoskeleton to rearrange, actin rearrangement causes large membrane extensions which engulf particle, particle internalized into membrane-bound compartment called phagosome. Phagocytosis (cell eating: phagosome fuses with lysosomes. Phagolysosome acid hydrolases kill/digest bacteria: so(cid:373)e pathoge(cid:374)s (cid:862)escape(cid:863) lysoso(cid:373)es, consequently are not killed and can proliferate in macrophages eg. mycobacterium, salmonella, pathogens secrete factors which interfere with rab proteins so lysosomes are not targetted correctly to phagosomes.

Related Questions

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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BIOB10H3 Lecture Notes - Lecture 6: Clathrin, Endosome, Cell Membrane

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