lectures 7-8

Question 1

what enzymes do lysosomes contain?

Answer 1

acid hydrolases

Question 2

what is responsible for pH control in lysosomes

Answer 2

H+ATPase serves as proton pump, pumping H+ into lysosome from cytoplasm

Question 3

what are the pathways for degradation in lysosomes

Answer 3

phagocytosis
pinocytosis and receptor-mediated endocytosis
autophagy

Question 4

describe the process of phagocytosis

Answer 4

• bacterium enters and surrounded by vesicle forming phagolysosome
• digested particles diffused or transported into the cytosol for use in other metabolic processes
• some pathogens can stop the process and escape the phagosome to infect the host cell

Question 5

what is the endosymbiont hypothesis

Answer 5

incomplete phagocytosis - free-living prokaryotes became incorporated inside larger prokaryotes and eventually became mitochondria and chloroplasts

Question 6

what is autophagy

Answer 6

• autophagosomes form membranes around cytosol and organelles and starve them
• autophagy recycles the organelle/cytosol for new cell formation

Question 7

what is receptor-mediated endocytosis

Answer 7

metabolites, hormones etc absorbed by inward budding of plasma membrane vesicles containing proteins with receptor sites specific to the molecules being absorbed

Question 8

what is pinocytosis

Answer 8

the ingestion of liquid into a cell by the budding of small vesicles from the cell membrane

Question 9

features of a peroxisome

Answer 9

single membrane
contains many enzymes in crystalline core -eg catalase
involved in lipid metabolism
make antibiotics in fungi
made in endoplasmic reticulum

Question 10

what role does a peroxisome play in lipid metabolism

Answer 10

breakdown of long chain fatty acids by b-oxidation

biosyntheis of cholesterol

Question 11

describe the process of peroxisome genesis

Answer 11

takes place in ER

• precursor molecule is grown by uptake of cytosolic proteins/lipids
• existing peroxisomes carry out fission and split into two

Question 12

why do liver cells contain lots of peroxisomes

Answer 12

for detoxification - peroxisomes contain catalase and oxidase enzymes

Question 13

properties of lipid droplets

Answer 13

fat storage droplets
enclosed by a monolayer membrane
associated proteins help regulate metabolism of fat
hydrophilic outer layer shields droplet from water

Question 14

how/where are lipid droplets made

Answer 14

endoplasmic reticulum

fatty acid deposited between bilayer

Question 15

what is the role of Fatty Acid Binding Proteins (FABP)

Answer 15

• make fatty acid water soluble by binding fatty acid in hydrophobic pocket
• mediate transport/transfer of lipids between organelles
• required for ‘burning’ fat

Question 16

what is the most prominent transport vesicle

Answer 16

vSNARE

Question 17

How do vesicles fuse with the membrane using SNARE receptors - 3 step process

Answer 17

1. TETHERING
   - long protein interacts with Rab-GTPase protein in inactivated form
   - ‘tethers’ vesicle to target membrane
2. DOCKING
   - tight interaction with vSNARE complex with tSNARE complex with force to bend the membrane
3. FUSION
   - vSNARE bound, ligand exposed to inner liquid phase of early endosome
   - ligand released from receptor
   - vesicle and vSNARE may return to cell membrane

Question 18

what are the 3 types of vesicle ‘coats’

Answer 18

(1) COP1 - Golgi vesicles
(2) COP2 - endoplasmic reticulum-to-Golgi
vesicles
(3) Clathrin - endocytic vesicles.

Question 19

what are vesicle ‘coats’

Answer 19

specific proteins concentrated in patches moulding the forming vesicle, just under the plasma membrane
provide some identity to vesicle

Question 20

what are extracellular vesicles

Answer 20

• “transport vesicles” released from cells
• involved in cell-to-cell communication
• Contain RNAs and proteins provided by donor cell

Question 21

where are extracellular vesicles found

Answer 21

bodily fluids - fluid around spine and brain, urine and blood

Question 22

which extracellular vesicles are involved in cell to cell communication

Answer 22

ectosomes (microvesicles) and exosomes

Question 23

where are ectosomes and exosomes formed

Answer 23

ecto - formed at plasma membrane of donor

exo - formed and released at early endosomes in multi-vesicular bodies (smaller)

Question 24

what is the cytoskeleton

Answer 24

give the cell its shape and provide tracks to link regions of cell

made of filamentous bioplolymers
- F-actin, microtubules and intermediate filaments

associated proteins modulate activity, dynamics and organization of cytoskeleton

Question 25

what are the properties and uses of cytoskeleton filaments

Answer 25

F-actin: -
-      short-range transport
-	cell migration – movement of cells
-	helix of two single strands, flexible
-	8nm
Microtubules: 
-      long-range transport
-	chromosome inheritance (mitosis)
-	thicker, stiffer, hollow
-	25nm
Intermediate filaments: 
-      mechanical strength
-	10 nm

Question 26

how are protofilaments made

Answer 26

Globular-actin polymerises into Filamentous-actin