Vesicular Transport Flashcards
How do small molecules travel across the membrane?
Water and small molecules enter and leave the cell by passing through the lipid bilayer of the cell membrane by means of passive and active transport
How do large molecules travel across the membrane?
Proteins and polysaccharides and larger particles cross the membrane using vesicles
How do the membranes of organelles communicate with each other?
They communicate through vesicular transport
What are the two key processes of vesicular transport?
Exocytosis
Endocytosis
What is exocytosis?
The secretion of macromolecules through fusion of vesicles with the plasma membrane
What is endocytosis?
The cell takes in macromolecules by forming new vesicles from the plasma membrane.
How does fusion of vesicles work?
6
Budding of a vesicle from donor organelle
Vesicle transported to target organelle in the cytoplasm
Fusion with target
Membrane is transferred
Proteins retain original configuration
Soluble components transferred
Write a note on vesicles.
6
They form part of the endomembrane system
They are small membrane-bound sacs
They transport or store substances
Their membrane is made of two layers = lipid bilayer
Can fuse with organelles to release their contents within the cell
Can fuse with plasma membrane and release contents out of cell
List the six types of vesicles.
Vacuoles
Lysosomes
Peroxisomes
Endosomes
Transport vesicles
Secretory vesicles
Write a note on how exocytosis works.
5
A transport vesicle buds from the golgi apparatus and moves to the plasma membrane
The vesicular membrane and plasma membrane then make contact
The bilayers then re-arrange to allow fusion
Vesicle’s cargo is then released into extracellular fluid
Vesicular membrane then becomes part of the plasma membrane
What are the two types of exocytosis?
Constitutive exocytosis
Regulated exocytosis
Explain constitutive exocytosis.
2
A steady stream of transport vesicles from trans Golgi to plasma membrane
New lipids and proteins are continuously supplied to the plasma membrane for membrane growth, rejuvenation and remodelling
In constitutive exocytosis, where do the transport vesicles come from?
They come from the trans face of the Golgi and they go to the plasma membrane
Why is constitutive exocytosis needed?
It is needed for a continuous supply of new lipids and proteins for the plasma membrane
Why does the plasma membrane need new lipids and proteins?
It needs them for membrane growth, rejuvenation and modelling
Explain regulated exocytosis.
3
This functions only in cells specialised for secretion
Lots of secretory vesicles are found in specialised secretory cells - hormones, mucous, digestive enzyme
An extracellular signal will stimulate their fusion with the plasma membrane and release into the extracellular fluid
Explain endocytosis.
3
New vesicles are formed by the plasma membrane
It is the reverse process of exocytosis, using different proteins
There are three types of endocytosis
How are endocytic vesicles formed?
Plasma membrane pinches in to form a vesicle containing extracellular material
What are the three types of endocytosis?
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis
Explain phagocytosis.
The engulfment of a particle (usually food or microorganisms), by wrapping cell membrane around it to form a vacuole
Explain pinocytosis.
The taking in of fluids into small vesicles (Cellular drinking)
Explain receptor-mediated endocytosis.
Receptors in a receptor-coated pit interact with a specific protein, initiating formation of a vesicle
How does a cell carry out phagocytosis?
2
A cell engulfs a particle by wrapping pseudopodia around it and packaging it into a membrane enclosed sac
The particle is then digested when the vacuole fuses with a lysosome
Explain how pinocytosis works.
2
The cell ‘gulps’ droplets of extracellular fluid in tiny vesicles
These pinocytic vesicles are returned to the cell surface after ingestion
