03B Transport of Large Molecules

Another name for Transport of large molecules

Membrane Flow system

What is the main vehicle of transport of large molecules called

Vesicles

True or false: For a cell to maintain relatively constant plasma membrane surface area, the rate of processes of exocytosis and endocytosis should be equal [

True

Two major types of transport of large vesicles

Exocytosis (secretion) and endocytosis ( process of internalizing macromolecules from the Extracellular fluid

Difference between membrane adherence of endocytosis and exocytosis

endo - comes in apposition (invagination) , exo - vesicle will go near the plasma membrane

Difference between membrane fusion of endocytosis and exocytosis

endo - fusion forms a vesicle, when detached, plasma membrane looses a portion; exo - plasma membrane gains more materia

For exocytosis, where are secretory vesicles formed

Golgi Apparatus

In order secretory vesicles to adhere on the plasma membrane, it has to move a distance and go to the cell surface using

Motor proteins on cytoskeleton/microtubules

Responsible for making the secretory vesicles move a certain distance from the Golgi apparatus area and the plasma membrane area

motor proteins and microtubules

Fate of secreted materials for exocytosis

could either remain on the surface of the cell or be part of the extracellular matrix (ECM)

Fate of secreted hormone from exocytosis

If hormone, it is diffused into the blood

Process of exocytosis

1. Bilayer adherence 2. Bilayer joining or fusion 3. Rupture of the membrane 4. Discharge of vesicle contents outside 5. Incorporation of vesicle membrane in the plasma membrane

Two types of exocytosis and their difference

constitutive ( continuous vesicle release ) vs regulated ( stimules regulated vesicle release)

This type of exocytosis Once the secretory vesicle is formed, it will fuse with a membrane and release its contents

constitutive exocytosis

. In this type of exocytosis, There is formation of secretory vesicles but they will stay inside the cytosol until a signal stimulates them to release contents into the cytosol

regulated exocytosis

How is muscle contraction a regulated exocytosis process

Vesicles in the motor neuron that contain neurotransmitter acetylcholine will only release contents into the synapse in the presence of action potential

What facilitates the movement of vesicles inward during endocytosis

motor proteins moving along microtubules

Process of endocytosis

1. Invagination of the cell membrane 2. Membrane pocket formation 3. Closing of CM around invaginated material 4. Pinching off 5. Entry

What happens when a vesicle formed from endocytosis fuses with a lysosome

Contents will be digested

What happens when a vesicle formed from endocytosis contains proteins and fuses with lysosomes

it will be hydrolyzed to produce amino acids, Amino acids will be released into the cytosol to be reused

True or false: Vesicle can also be involved in transcytosis

True

This is regarded as cell eating, where One cell will engulf another whole cell or very large structure

Phagocytosis

Why would there be strain when performing phagocytosis

The cell membrane will be under so much strain during the process because it will try to internalize something large or even as big as it is. The microfilament network supporting the membrane adjusts to support the formation of phagosomes

What do you call the product vesicle of phagocytosis

Phagosomes

This is known as cell drinking, where The cell will engulf extracellular fluid which contains some dissolved substance

pinocytosis

True or false: Involvement of the microfilament network is not required for vesicle formation in pinocytosis, compared to phagocytosis

True

True or false: The vesicles formed are much smaller in pinocytosis than phagocytosis

True

True or false: pinocytosis does not strain the cell membrane compared to phagocytosis

True

This kind of endocytosis involves receptors making the process more specific or involved a concentrating mechanism

Receptor mediated endocytosis

Principle of receptor mediated endocytosis

A receptor will specifically recognize and bind its substrate, so no (or only a very small amount) extracellular fluid will enter

What protein would facilitate the formation of coat around the vesicle for receptor mediated endocytosis

clathrin monomer ( triskelia

What causes the membrane invagination in receptor mediated endocytosis

force of the aggregation of the clathrin on the cytosolic side of the membrane lead

What is formed after membrane invagination in receptor mediated endocytosis

clathrin-coated vesicle called endosomes

What binds to the receptor that would trigger the formation of the coated pit [ along with clathrin on the cytosolic ]

cargo or ligand, forming the cargo-ligand complex

How do you form the coated pit

Aggregation of clathrin on the cytosolic side, and having ligand-receptor complex at the extracellular side to diffuse in, causing invagination

Receptor-cargo complex will laterally diffuse and move into the coated pit to form this

coated vesicles

This protein facilitates the release or pinching of the coated vesicle in receptor mediated endocytosis (and what is this process called

dynamin, internalization

True or false: the receptor-ligand complex moves towards higher concentration of clathrinnthat facilitates the invagination of the cell

True

How is clathrin recycled into the surface of the cell membrane

uncoating happens or the dissociation of the coat from the vesicle, returns to the cytosolicnside of the membrane and aggregates to participate in another round of rme

Explain rme and its general steps

1. Initiation 2. Assembly 3. Scission/invagination 4. Uncoating

This is the process where endocytosis and exocytosis happens together to facilitate the transport of solutes from one side to another side

transcytosis

What organelle produces or synthesize the receptors and how does it get transported to the cell membrane

endoplasmic reticulum, gets transported by the golgi apparatus

Cholesterol is transported in the blood as part of what complex

LDL or Low density lipoprotein that gets ingested in the cell through RME by LDL receptors that are present in the cell membrane

What part of the LDL particle binds to the LDL receptor on the cell membrane to form the LDL-receptor complex

apo-B protein

What would happen if there was mutations in the apo-b protein

decreased binding to the LDL receptor, leading to increased cholesterol concentration - hypercholesterolemia

This protein is essential in the creation of the LDL particle

apo B

This protein acts as a ligand, located on the LDL surface

apo b protein

What stage in the endosome can allow for the recycling back of the receptors

early endosome, late endosomes typically have no or less receptors

What causes the detachment of the receptors in the early endosome

the acidic environment caused by a late endosome, with a low ph - pH 5. The LDL and its receptor has high binding affinity at pH 7, but inside the endosome, the binding affinity is decreased

Fates of LDL once it fuses with the lysosome

proteins  amino acids, lipids  fatty acid, cholesterol  released into the cytosol to be used by the cell

Explain the rme of cholesterol uptake

oki

Receptor abnormalities: what do you call the mutation where receptors are not synthesized and its effect

null mutations - such prevention of synthesis of receptors leads to impaired cellular uptake or response to ligands. May lead to high concentration of a specific ligands to be digested in the extracellular matrix

Receptor abnormalities: what do you call the mutation where receptors fail to transport by the golgi apparatus from the ER to the cell membrane and its effect

transport/ processing defective mutations - failure to reach the cell membrane also impairs cellular uptake and response to ligands

Receptor abnormalities: what do you call the mutation where receptors reaches the cell membrane but cannot bind to the proper ligands and its effects

binding defective mutations - initiation cannot proceed since binding sites are defective, thus internalization cannot proceed, ligand concentrations remain elevated in the bloodstream

Receptor abnormalities: what do you call the mutation where receptors cannot concentrate in the clathrin coated pits due to mutations in some amino acids

internalization defective mutations and its effects - prevention of receptors from being internalized since clathrin cannot be recruited into the pits , leading to elevated concentrations of ligands in the bloodstream

What amino acids are defective during internalization defective mutations

phenylalanine, tyrosine, asparagune, proline [F/Y]XNPXY motif signals

Receptor abnormalities: what do you call the mutation where receptors fail to dissociate from the LDL particles in the endosome (even in the presence of acidic environment) and its effects

recycling-defective mutations - the release is supposedly necessary for the recycling of the receptors into the cell membrane, however, since the defect, it would be sent to the lysosome to be degraded. This leads to few cellular intake , increasing of ligand concentrations in the bloodstream due to few receptors

It is the continuous endocytosis and exocytosis starting from one cell surface membrane leading to another

Transcytosis

True or false: Trancystosis can be receptor independent and receptor mediated

true

Process of transcytosis of immunoglobins from the intesinal lumen to the blood stream

•Binding: IgA in breast milk binds to receptors on intestinal epithelial cells.• Endocytosis: The IgA-receptor complex is internalized into the cell.• Transcytosis: The complex is transported across the cell to the basolateral side.• Release: IgA antibodies are released into the interstitial fluid.• Entry into Bloodstream: IgA enters nearby blood vessels, providing passive immunity to the infant.

Difference between ferrotransferrin and apotransferrin

presence and absence of iron

The transferrin receptors cannot recognize metal ions of iron itself, thus, it only recognizes

transferrin

At what pH does ferrotransferrin bind to receptor with high affinity

ph 7

The shift in pH from 7 to acidic, will cause what for iron rme to be released into the cytosol for use by the cell

iron

The shift in pH from 7 to acidic, will cause what for iron rme to be released into the cytosol for use by the cell

iron

What gets recycled in iron rme

iron

Exposure of the apotransferrin and receptor to what conditions allows it to decrease its binding ability for its release in the extracellular matrix for another round

neutral ph

Explain the iron rme

oki