INTRCELLULAR TRANSPORT Flashcards
WHAT ARE THE 2 TYPES OF INTRACELLULAR TRANSPORT?
-transport via vesicles
-transport via packaging through organelles and nuclear envelope membranes
EXPLAIN TRANSPORT THROUGH NUCLEAR PORES
selective transport of proteins and RNAs into and from nucleus and cytoplasm
-gated transport
-use of GTP
-transport of mRNA from cell with the help of signal peptide
-pore has a nuclear recognisation center, nuclear transport receptor, nuclear basket and cytostolic fibrils
HOW IS THE TRANSPORT OF PROTEINS DIRECTED?
signal sequence / signal peptide
-> if proteins lack this then they remain in the cytosol
EXPLAIN THE IMPORT OF PROTEINS INTO THE NUCLEUS
- The protein in the cytosol binds to a nuclear localization signal/receptor.
- formation of protein complex + signal peptide + receptor
- It is then actively transported through nuclear pores in the membrane (catches on cytosylic fibrils)
- Inside the cell, the transported protein is cleaved from the receptor and released in the nucleus.
- The receptor returns to the cytosol through another nuclear pore to be reused
WHAT IS THE NAME OF THE NUCLEAR RECEPTOR PROTEIN?
ran GDP In the cytosol and Ran- GTP in nucleus
EXPLAIN THE EXPORT OF SUBSTANCES OUT OF THE NUCLEUS
-same process as the import of substances into the nucleus except the order is opposite, it is a cycle
DIFFERENT TYPES OF TRANSPORT WITHIN THE EUKARYOTIC CELL
EXPLAIN THE TRANSPORT ACROSS MEMBRANE ORGANELLES
transport via protein translocators
-next to which sit protein receptors which recognize signal sequences which allows the material to be transported inside
DISCUSS TRANSPORT INTO MITOCHONDRIA AND PEROXISOMES
involves transport of mitochondrial
proteins that are encoded by the DNA
of the cell (not mitochondrial DNA)
- precursor with receptor protein (signal peptide) in cytosol
- Receptor protein→ docks to protein translocator
- Proteins goes through and docs to second translocator
- Protein entered mitochondrial matrix and signal protein gets cleaved off
WHAT ARE THE PROTEIN TRANSLOCATORS OF THE INNER AND OUTER MEMBRANE?
DISCUSS TRANSPORT INTO THE ER AND CHLOROPLASTS
-Transport of soluble proteins: translocation channel same as mitochondria
1. Signal peptide is recognised
2. Protein travels through membrane until it reaches final destination
3. Signal peptidase Cleaves signal and keeps it into place
4. Is integrated via its hydrophobic region
WHAT IS A SIGNAL SEQUENCE?
– sequence of AA at the N-terminal of a polypeptide chain
DISCUSS TRANSPORT INTO THE ER AND CHLOROPLASTS
-Transport of soluble proteins: translocation channel same as mitochondria
-co-translational transport
1. Signal peptide is recognised
2. Protein travels through membrane until it reaches final destination
3. Signal peptidase Cleaves signal and keeps it into place
4. Is integrated via its hydrophobic region C
WHAT DIRECTS A RIBOSOME INTO THE ER MEMBRANE?
ER signal sequence and an SRP
DISCUSS TRANSPORT VIA VESICLES
transport between the compartments of endomembrane systems (ER, GA) - transport from these compartments out the cell (exocytosis = SECRETION) and transport into cell (endocytosis)
->vesicles bud from one membrane and fuse with another, carrying membrane components and soluble proteins between the cell compartments
EXPLAIN EXOCYTOSIS
secretion occurs through secretory vesicles which are cleaved from the Golgi apparatus
-> transport vesicle fuses with plasma membrane, contents released into extracellular space while vesicle membrane becomes continuous with plasma membrane
CONSTANT = not regulated, constitutive – secretion is constant
REGULATED = secretion occurs only after a signal is given (through hormones or neurotransmitters)
DISCUSS RECEPTOR MEDIATED ENDOCYTOSIS IN ENDOSOMES
-clathrin-dependent endocytosis because of involvement of the membrane-associated protein clathrin in forming membrane vesicles that become internalized into the cell. Clathrin plays a major role in formation of clathrin-coated pits and coated vesicles
- an external ligand binding to a specific receptor that spans the plasma membrane ( ligands include hormones, growth factors, enzymes, serum proteins, LDL, transferrin, antibodies, some viruses, and even bacterial toxins.
-after receptor binding, the complex diffuses laterally in the plasma membrane until it encounters a specialized patch of membrane called a coated pit. The receptor–ligand complexes accumulate in these patches as do other proteins including clathrin, adaptor protein, and dynamin.
-since coated pits occupy about 20% of the plasma membrane surface area, they are not minor membrane features.
-the collection of these proteins starts to curve the adjacent section of the membrane that eventually pinches off to form an internalized coated vesicle.
-Clathrin and dynamin then recycle back to the plasma membrane, leaving an uncoated vesicle that is free to fuse with an early endosome.
-After the early endosomes mature into late endosomes, they then go to the lysosome for digestion. RME is a very fast process. Invagination and vesicle formation take about 1 min.
EXPLAIN TRANSPORT VIA ORGANELLES
no transport vesicles used, it is due to receptors that mediate vesicular transport
EXPLAIN THE TRANSPORT OF WHOLE ORGANELLES
mediated via kinesin (moves into + end; into periphery) and dynein (moves into - end; into cell) which travel along microtubules
ALTERNATIVE: myosin I function as “legs” which carry vesicles towards the + end; into
periphery
Myosin II towards the - end
Travel along actin filaments
