20. Golgi Apparatus

Question 1

Golgi A? Func? Structure?

Answer 1

Discovered by Camillo Golgi in 1898
Position b/w nucleus and apical plasma membrane

Main Functions of GA:

Occur in smooth membranous cisternae

• Modifying new proteins - for lysosomes, secretion and plasmas membrane
• Packaging enzymes - lysosomes/ proteins for secretion
• Sorts materials for lysosomes, secretion, for plasma membrane

Structure:

-Entry (cis face)
•Takes proteins from RER
-Exit (trans face)
•Larger saccules- condensing vacuoles accumulate by this end
•Pushes proteins out  to use in other areas of cell
-Stacks (cisternae) (3 -12 at sizes 50-200nm)- that contain enzymes that aid reactions w/in GA
-Vesicles (30-50nm)
-Lumen

Question 2

Relation b/w RER and GA?

Answer 2

RER allows vesicles containing newly synthesised proteins to approach the GA for further processing. They fuse with GA, and empty their contents into the lumen - modified - trans-Golgi network (TGN) – where proteins and sorted/shipped, it is dependent on the signal sequence they carry then the condensing vacuoles bud from the maturing saccules and generate vesicles- carrying the completed proteins products  organelles

Question 3

Exocytosis vesicles?

Answer 3

Exocytotic vesicles (constitutive)

• Vesicle contains proteins destined for extracellular release.
• After packaging, the vesicles bud off and immediately move towards the plasma membrane - where they fuse and release the contents into the extracellular space in a process known as constitutive secretion.

Example: Antibody release by activated plasma B cells

Question 4

Secretory vesicles?

Answer 4

Secretory vesicles (regulated)

• Vesicles contain proteins destined for extracellular release.
• After packaging, the vesicles bud off and are stored in the cell until a signal is given for their release.
• When the appropriate signal is received they move toward the membrane and fuse to release their contents.
• This process is known as regulated secretion.

Example: Neurotransmitter release from neurons

Question 5

Lysosomal vesicles?

Answer 5

Lysosomal vesicles

• Vesicles contain proteins and ribosomes destined for the lysosome/ lysosome-like storage organelles.
• Lysosome - a organelle containing many acid hydrolases
• These proteins include both digestive enzymes and membrane proteins.
• The vesicle first fuses with the late endosome, and the contents are then transferred to the lysosome via unknown mechanisms.

Example: Digestive proteases destined for the lysosome

Question 6

Vesicle Formation and Traffic?

Answer 6

• Vesicle formation is driven by the assembly of coat proteins (e.g. clathrin)
• These proteins helps to regulate vesicular traffic