2. Cytoplasmic organelles and vesicle trafficking

Question 1

What is the structure of the golgi apparatus

Answer 1

• several membrane-covered stacked, flattened sacs (or cisternae)
• sacs are disk-like and often slightly curved (convex and concave surfaces)

Question 2

What is the function of the golgi apparatus

Answer 2

• sorting system, delivers proteins synthesise in RER to membrane, organelles, outside the cell
• produces vesicles in which proteins/lipids are stored
• modifies proteins and lipids by glycosylation
• Activation of peptides by proteolysis or phosphorylation
• synthesis of gycosaminoglycans and mucin
• selection of enzymes to be delivered to lysosomes

Question 3

What is the difference between the cis and trans side of the GA

Answer 3

• the cis side = end of organelle where substances enter from ER for processing
• the trans face = where substances exit in smaller vesicles near the cell membrane

Question 4

What is the vesicle direction?

Answer 4

Vesicles come from the ER through the cis side and leave through the trans side to the cell membrane (transported out) or to other organelles

Question 5

What are the different types of cisternae

Answer 5

Cis, medial and trans

Question 6

What are the functions of cis, medial and trans cisternae

Answer 6

They are morphologically and biochemically different
cis = phosphorylation of proteins
medial = addition of sugar residues
trans = protein protelysis, lipid and protein sorting, addition of sugar residue

Question 7

The cell activity affects

Answer 7

• expansion of GA cisternae
• no. of GA cisternae
• more than one GA may be present in cell

Question 8

What are the 4 destinations of proteins synthesised in RER passing through GA

Answer 8

• return to RER
• remain in GA
• go to lysosomes
• undergo exocytosis (secreted from cell)

Question 9

How do proteins return to RER

Answer 9

• found in lumen of GOLGI
• have sequence AA (Lys-Asp-Glu-Leu called KDEL)
• recognised by receptor
• which then returns vesicles to RER

Question 10

How to proteins remain in GA

Answer 10

• lack KDEL

- may have other signal-sequences/bind to specific membrane sites

Question 11

How proteins are delivered to lysosome

Answer 11

• have lysosome enzyme: 6-phosphate mannose

Question 12

What are the 2 types of secretion

Answer 12

• constitutive secretion

- regulated secretion

Question 13

Constitutive secretion

Answer 13

• not dependent of specific stimulation
• secretion products produced and immediately secreted
• vesicles covered by coating proteins (COPs) to be recognised

Question 14

Regulated secretion

Answer 14

• Dependent on specific stimulation (ex: release of hormones, pancreatic enzymes, neurotransmitters)
• proteins to be secreted are stored into vesicles that accumulate into cell (maturation of vesicles)
• vesicles accumulate close to PM fuse w membrane after stimulation
• ## coated by clathrin-like proteins

Question 15

What are the 3 tyypes of vesicle trafficking

Answer 15

• endocytosis
• exocytosis
• gemmation

Question 16

Define endocytosis

Answer 16

vesicle orginates from PM, takes extra-cellular material & internalises it

Question 17

Defind exocytosis

Answer 17

vesicle originates in the cell, fuses with PM, release content outside cell (extracellularly) –> vesicle still in cell

Question 18

Define gemmation

Answer 18

vesicle originates from CM, vesicle + content goes released outside cell

Question 19

What is the function of coated vesicles

Answer 19

• Coating of proteins –> favours bending of membrane during vesicle formation
• allows selection of components that have to be inserted & transported into vesicle
• Direction + destination

Question 20

What is COPs Coating

Answer 20

coating proteins which surround vesicles and direct them

Question 21

COP2

Answer 21

vesicles move from RER to GA

*ANTEROGRADE TRANSPORT = towards OUTSIDE

Question 22

COP1

Answer 22

vesicles move from GA to RER

*RETROGRADE TRANSPORT = towards INSIDE

Question 23

Clathrin coated

Answer 23

GA to PM/endosomes (lysosomes)

Question 24

Example of how vesicles are directed towards specific cell compartment

Answer 24

• transmembrane protein v-SNARE present on vesicles, specifically recognised by sequences t-SNARE on target membrane

Question 25

What are the 4 types of endocytosis

Answer 25

• receptor mediated endocytosis
• pinocytosis
• phagocytosis
• autophagy

Question 26

receptor-mediated endocytosis

Answer 26

PM turns back on itself (invaginated) + specific molecules w/ receptors bind to specific membrane receptors. These molecules are then internalised