Transport Part 2

ER lumen side

On which side of ER membrane is the receptor of the transmembrane protein located on?

Cytosol side

On which side of the ER membrane are the binding domains of the transmembrane protein located on?

plasma membrane

GPI anchor attaches proteins to the __________.

Glycosylphosphatidylinositol

What does GPI stand for?

ER enzymes

What catalyzes the GPI anchor?

the C-terminus of a protein

What is the GPI anchor covalently attached to?

In the ER lumen

Where does the linkage of the GPI to the C-terminus of the protein occur?

GPI

Protein cut free from the ER membrane and then attaches to the ________, which is membrane bound and eventually travels to the plasma membrane.

the plasma membrane

What does the GPI anchor attach proteins to?

dynamic

The plasma membrane is very _________, it's always forming and being recycled.

packaging proteins to leave the cell

What is exocytosis?

What is endocytosis?

Golgi apparatus

What is known as the mail office of the cell?

the lumen

What is the interior part of the vesicle called?

transport vesicle

What allows the travel of a substance without passing through the phospholipid bilayer/ membrane?

cargo

What are the components of the lumen called?

1. they must take up appropriate cargo (budding stage)
2. must fuse with appropriate target membrane (fusion stage)

What are the two rules of transport vesicles selectivity?

The budding stage

starting to take up the necessary cargo to bud off the vesicle

Fusion stage

The transport vesicle then buds off and after uncoating, tethering and docking, it will fuse to the target membrane.

secretory pathway

What pathway refers to the ER, Golgi apparatus and the vesicles that travel in between them as well as the cell membrane and lysosomes. It's the pathway by which the cell secretes proteins into the extracellular environment.

Exocytosis

a secretory pathway that delivers newly synthesized proteins, carbohydrates, and lipids to the plasma membrane

Endocytosis

the cellular process in which substances are brought into the cell.

Endocytic pathway

Takes things in through the plasma membrane.
The cells remove a region of the plasma membrane and delivers these to the lysosomes where they are degraded in internal compartments.
The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material. Includes pinocytosis and phagocytosis.

endosomes

What are these internal compartments called?

formed by the invagination of the plasma membrane and are triggered by the activation of cell surface receptor.

How are endosomes formed?

Invagination

the process of a surface folding in on itself to form a cavity, pouch or tube.

they control the sorting of activated cell surface receptors either to the plasma membrane for further use or to the lysosome for degradation.

Why are endosomes important?

endosomes

membrane bound organelles, internal compartments where things get degraded and can also be used to capture nutrients.

lysosome (digestive organelles)

start with the plasma membrane, which is then removed to bring in the vesicle. Often these vesicles will then fuse with a __________ where the content will then be degraded in the endosome.

coated vesicles

vesicles that bud from membranes and have a coat on their cytosolic surface (surface facing extracellular environment).

shed its coat

After budding, the vesicle will __________, which allows the membrane to interact directly with the target membrane to fuse with it.

where a vesicle is going to fuse

What is a target membrane?

clathrin coated vesicles

these are the most popular type of coated vesicles, their outer coat is made of clathrin

exocytosis of clathrin coated vesicle

they bud from the Golgi apparatus on the outward secretory pathway. What is this process called?

endocytosis of clathrin coated vesicles

bud also from the plasma membrane on the inward path, which creates a clathrin coated pit. What is this process called?

COP coated vesicles
(COPI or COPII)

Transport vesicles that transport molecules from the ER to the Golgi and the Golgi to the Golgi (exocytosis)

Clathrin
(dark green structure)

assemble into basket-like network on the cytosolic surface on the membrane and this starts to shape the membrane into a vesicle

Dynamin
(yellow structure)

GTP binding protein that assembles into a ring around the neck of the invaginated pit and pinches off/ constricts the vesicle from the parent membrane. Uses the power from the phosphate to constrict off of the plasma membrane.

adaptins
(light green structure)

second class of coat proteins that helps to select the cargo for transport

adaptin

binds to your cargo and these cargo receptors bind to ________ and helps deliver it to your transport vesicle.

adaptin

What binds to clathrin?

in the cytosol

When does the clathrin coat disassemble?

vesicle docking

once the naked vesicle is within the cell, you have to dock the vesicles at a different location. use motor proteins to move vesicles along the cytoskeleton.

Rab proteins

What are the markers on vesicles called?

tethering proteins

What are receptors on the organelle called that dock vesicles?

tethering protein

Rab proteins bind to _________ on the target membrane.

ensures that transport vesicles fuse with the correct membrane

Unique combination of rab proteins/ tethering proteins ensures what?

vesicle-SNARE

What does v-SNARE stand for?

tethering-SNARE

What does t-SNARE stand for?

SNARE

provides additional recognition as transmembrane proteins. The tethering protein captures a vesicles by grabbing hold of the Rab protein.

vesicle, target membrane

SNAREs are on the ___________ and the _______.

vSNARE, tSNARE

_______ and ______ work together to firmly dock the vesicle in place on the target membrane. They also make sure that the vesicle is binding to the correct membrane.

exocytosis

proteins delivered from the ER to the Golgi to the cell surface via transport vesicles

transport vesicles, ER

These ____________ then fuse with the plasma membrane, and are then covalently modified in the ______ before leaving the cell.

disulfide bonds, glycosylation, and protein folding

What are examples of some covalent modifications that take place in the ER?

Golgi apparatus

has a collection of flattened membrane enclosed sacs and each stack consists of two distinct faces

cisternae

What are these flattened membrane enclosed sacs called?

cis face

Which face of the Golgi apparatus is next to the ER and allows entry into the Golgi?

trans face

Which face of the Golgi apparatus points towards the plasma membrane and allows things to exit from the Golgi?

cis, ER

Proteins enter through the _______ face of the Golgi network via transport vesicles from the _______?

cisternae

Proteins then travel through the ________ through transport vesicles from one cisterna to the next.

trans, plasma membrane

Proteins exit through the _________ face of the Golgi network destined for the _________ or another organelle.

The secretory vesicle

What tells you to release the secretory protein?

constitutive exocytosis pathway

a steady stream of vesicles bud from the trans Golgi network to the plasma membrane, where the plasma membrane supplies the vesicles with newly made lipids and proteins.

secretion

The vesicle carries soluble proteins to the cell surface to be released in the extra cellular fluid, what is this process called?
*Keep in mind that the vesicle stays attached to the cell surface and that it contributes to the extracellular matrix.

ER, Golgi

For the constitutive exocytosis pathway to occur, there has to be vesicles coming from the _________ to the ________.

regulated exocytosis pathway

This pathway is not always on and is important for secretory cells. This pathway awaits signal instructions before the vesicle leaves the trans Golgi network with the cargo.

Golgi

The ___________ packages cargo at much higher concentrations.

regulated exocytosis pathway

This pathway is important for the secretion or release of hormones, mucus, and digestive enzymes (extracellular signals like hormones or neurotransmitters).

closest to the ER

Where is the cis face of the Golgi located?

after medial region

Where is the trans face of the Golgi located?

endocytosis

Cells that take up fluid and molecules, small portion of the plasma membrane buds inward and pinched off to form the endocytic vesicle, and many of these become endosomes. This process is called?

the endosome

Where is the ingested material delivered to?

plasma membrane, lysosomes

The ingested material delivered to the endosome is then recycled back to the ___________ or is sent to the ___________(digestive organelle) to be degraded.

Pinocytosis
Pino=drinking

cellular drinking for fluid molecules. The ingestion of liquid into a cell by the budding of small vesicles from the cell membrane.
One type of endocytosis.

Phagocytosis
Phago=eating

Cellular eating. A process by which a cell uses its plasma membrane to engulf a large particle, giving rise to an internal compartment called the phagosome.
One type of endocytosis.

Phagosomes
Phago = eating

large vesicles brought in, therefore creating this internal compartment

Phagocytotic cells
Phagocytes (neutrophils and monocytes)

Immune cells that play a critical role in both the early and late stages of immune responses.

Macrophages

defense mechanisms
engulf or take up smaller cells. They digest and break them down.
*Once they are in the cell, they are then delivered to the endosome.
One type of endocytosis.
a large phagocytic cell found in stationary form in the tissues or as a mobile white blood cell, especially at sites of infection.

Autophagy

the cell recycles components. The mitochondria breaks it down and the plasma membrane recycles it. It's also a lysosome dependent process (digestive organelle).

to promote cell survival

An autophagy performs self-eating ____________. Also known as canabolism of a cell.

development of autophagy

helps reconstruct cells that are differentiating and not dividing, but still need to be maintained

autophagosome

fusion of small vesicles into a double membrane around the organelle and can fuse with the lysosome.

receptor mediated endocytosis

a means to import macromolecules from the extracellular fluid that involves Clathrin coats on the vesicles.
Selectively concentrating material mechanism as the vesicles are brought into the cell.
Uptake of cholesterol needed to make new membranes.

Cholesterol

___________ depends on receptor mediated endocytosis.

low-density lipoproteins (LDL)

Cholesterol is extremely insoluble, transported to the bloodstream bound to ________________.

liver

Cholesterol-LDL is secreted by the _______ and binds to receptors on the cell surface.

Cholesterol

_____________ is essential to cell membrane health.

Receptor mediated endocytosis

Ingest receptor-LDL complexes and deliver them to the endosomes. LDL then dissociates from the receptor and the receptor is recycled back to the plasma membrane. What is this process known as?

lysosomes

LDL goes back to the _____________.

hydrolytic enzymes

LDL is broken down into ___________ in the lysosomes.

cytosol

Cholesterol is then released from the LDL and will translocate to the ________. Now the LDL is available for membrane synthesis.

cholesterol

The lysosomes release _______ to be used in the plasma membrane.

acidic

Lysosomes are very _________ with their hydrolytic enzymes that use water to break down bonds.

LDL gene

Genetic pre-disposition to high cholesterol means that individuals have inherited defective versions of the _______, which causes the receptor o be missing or non-functional.

atherosclerosis

Cells deficient in taking up LDL-bound cholesterol, causes cholesterol to stay in the blood or the buildup of cholesterol (leading to higher levels of cholesterol), which leads to a disease called _____________.

a lysosome-dependent process that recycles components of itself to survive

What is autophagy?

cellular eating
The process by which a cell uses its plasma membrane to engulf a large particle like bacterial cells or viruses, thus giving rise to an internal compartment called the phagosome.

What is phagocytosis?

lysosomes

Where can free cholesterol and hydrolytic enzymes be found?

lysosome

This organelle is very acidic, uses a pump to maintain its H+ environment (against the gradient, so it needs ATP).