Cellular Transport

Question 1

Organelles

Answer 1

Organelle has lumen and membrane
Specific lipid and protein in lumen and membrane (needed for sorting)
Organelle has same function in all cells
Organelle has specific position in cell
Abundance of organelle related to cell type (muscle - energy - mitochondria)

Question 2

Evolution organelles

Answer 2

Pinching off of plasma membrane, nucleus, Gogli

Endosymbiosis, mitochondria, chloroplasts

Question 3

Types of membrane associated proteins

Answer 3

Transmembrane (single-, double-, multipass)
Membrane associated (one side is hydrophobic)
Lipid-linked (lipid anchored)
Protein attached (non-integrated (peripheral membrane proteins)

Question 4

Single-pass membrane proteins

Answer 4

2 signals and one signal
Protein goes to translocation channel, signal peptide is removed, ribosome continues translating until signal sequence is reached (protein is pushed down into translocation channel), channel opens laterally and protein moves into the lipid bilayer

Question 5

Double-pass protein

Answer 5

2 signals
Targeting, moves towards hydrophobic start-transfer sequence, translocation stops, translation continues, protein moves out of tranlocation channel, translation is finished

Question 6

Without knowing anything about the protein, you know how it is positioned in the membrane

Answer 6

Hydrophobic in membrane, hydrophilic outside membrane (multipass)

Question 7

Fate of proteins that have entered the ER

Answer 7

Stay in ER via ER retention signals

Further routing in secretory pathway via vesicular transport

Question 8

Vesicle traffic

Answer 8

Endocytic pathway

Secretory pathway

Question 9

Endocytic pathway

Answer 9

Uptake of material from exterior
Degradation in lysosomes
Metabolites to cytosol

Question 10

2 kinds of vesicle traffic

Answer 10

Phagocytosis, pinocytosis (ordinary and RME)

Question 11

Phagocytosis

Answer 11

Particles bind to receptors (antibodies) before uptake (triggered process)
Uptake –> large endocytic vesicles (phagosomes) –> fusion with lysosomes –> degradation

Question 12

Pinocytosis

Answer 12

Uptake via clathrin coated pit –> clathrin coated vesicle –> uncoating –> fusion with early endosome –> late endosome –> lysosome
Ordinary: indiscriminate continuous uptake (retrieval of membrane material)
Receptor-mediated endocytosis): specific binding of macromolecules to receptors –> accumulation in clathrin coated pits –> uptake (LDL)

Question 13

Sorting in endosoems

Answer 13

Early endosomes –> late endosomes –> develop or fuse lysosomes
Gradual decrease in pH (lowest in lysosome), receptors are released at low pH, recycling, degradation or transcytosis
Cargo always goes to lysosomes for degradation

Question 14

Secretory pathway

Answer 14

Flow of material towards exterior
ER –> Golgi –> plasma membrane –> external milieu
All transport in secretory pathway via vesicles

Question 15

During secretory transport

Answer 15

Modification (folding, glycosylation)
Quality control (retention and degradation of misfolded proteins)
Sorting (movement of proteins to other compartments)

Question 16

Modification (folding, glycosylation)

Answer 16

In lumen of ER, during synthesis, trimming and processing of sugars continues in ER and Golgi –> structure, protection, folding and sorting

Question 17

Quality control (retention and degradation of misfolded proteins

Answer 17

Only correctly folded proteins can leave the ER

Unfolded proteins remain complexed with chaperones (folding or transfer to cytosol for degradation)

Question 18

Sorting (movement of proteins to other compartments)

Answer 18

Proteins can stay or move on towards Golgi (default)
Mechanisms to stay:
Aggregation or interaction with chaperones and retention in ER via recognition of retention signal in the protein (return signal)
NB. All ER resident proteins have the retention signal; if they “escape” to the Golgi, they are recognized by a receptor and shuttled back to the ER.

Question 19

Golgi Apparatus Stacks of cisternae and tubules

Answer 19

Cis golgi network (sorting platform)
Cis cisternae (“powerplant” of glycosylation)
Medial cisternae
Trans cisternae (“powerplant” of glycosylation)
Trans golgi network (sorting platform)

Question 20

2 pathways of exocytosis

Answer 20

Constitutive secretion (to counteract the uptake of proteins) (present in all cells)
Regulated secretion (proteins concentrate, aggregate and packed into vesicles and only fuse if there is a signal (present in specialized cells, storage in vesicles near plasma membrane

Question 21

Characteristics of vesicles

Answer 21

Transport of both soluble and membrane proteins
Different types of vesicles to ensure correct sorting
Transport must be specific and well-regulated

Question 22

Specificity of vesicles

Answer 22

Initial recognition by Rab protein that are recognized by tethering proteins, further specificity by v-SNARE in vesicles that docks at t-SNARE in target membrane;many different SNAREs for specific fusion
Undergo conformational modifications, tie vesicle to the membrane so it must fuse (spontaneous fusion)

Question 23

Steps vescular transport

Answer 23

Donor compartment - budding - fusion - target compartment

Question 24

Budding: vesicle has a thick protein coat to

Answer 24

shape to faciliate budding (triskelions): clathrin, football like structures that pinch off from donor membrane
Capture molecules to transport (coat assembly and cargo selection, bud formation, vesicle formation, uncoating)
Pinching off by dynamin
Different adaptins dependent on donor membrane

Question 25

Adaptin

Answer 25

Adapter between cargo receptors and clathrin

Question 26

Lysosomes

Answer 26

Degradation of macromolecules by acid hydrolases
Hydrolases have low pH optimum (energy for proton pumps)
One membrane (protect cytosol, contains many transporters, contains ATPase)
Membrane proteins are highly glycosylated for protection

Question 27

4 entry pathways for lysosomes

Answer 27

Pinocytosis/endocytosis
Phagocytosis
Autophagy (damaged organelles, material from the cell itself)
Vesicular traffic from Golgi