The Golgi Apparatus

Question 1

What does an oxidising environment in the ER promote

Answer 1

Promotes disulfide (S-S) bond formation (between the side chains of cysteine residues)
These bonds don’t form in the cytosol
Disulfide bonds formed in the ER is important in the structure of secreted and cell surface proteins

Question 2

How are soluble proteins folded in the ER

Answer 2

Fold in lumen of ER
Disulphide bond formation
Sometimes modified by N-linked glycosylation or GPI anchor addition

Question 3

Where do proteins go after being folded in the ER

Answer 3

To the Golgi

Question 4

What is the cis and trans face of the golgi

Answer 4

Cis face- nearer to ER (receiving end) (vesicles from ER attach to cis face)
Trans face- nearer to Plasma Membrane (exit end)- pinch off vesicle containing proteins (can become a lysosome or exit cell) -> is concave

Question 5

What is meant by the structure of the Golgi having intrinsic directionality

Answer 5

Fused vesicular tubules with proteins and lipids from ER enter (pinch off ER regions)
Proteins and lipids exit to cell surface or other organelles
Backwards of forwards (dynamic)
Number of stacks varies on cell types

unidirectional flow of cargo through its cisternae, from the cis-Golgi network to the trans-Golgi network

Question 6

What is the role of the Golgi

Answer 6

Accepts proteins and lipids from ER
Post translational modifications happen here
Covalently modifies, labels, sorts and sends them off
Oligosaccharide modifications, further additions to N-linked glycosylation added to many proteins

Question 7

How is the Golgi organised

Answer 7

Enzymes are compartmentalised in the Golgi cisternae
Enzyme complexes for further N and O linked modification

Question 8

How is the cisternae specialised for its role (stages of modification in the cisternae of Golgi)

Answer 8

Question 9

How is N-linked glycosylation modified further in the Golgi

Answer 9

Already added in the ER and then further modified in Golgi
If exposed to Golgi enzymes- made more complex
Can be extremely variable

Question 10

What is N-linked glycosylation

Answer 10

N-linked glycosylation, is the attachment of an oligosaccharide, a carbohydrate consisting of several sugar molecules, sometimes also referred to as glycan, to a nitrogen atom

Question 11

What is O-linked glycosylation

Answer 11

Sugars added to OH groups of SER or THR side chains
Glycosylation transferases add the sugar nucleotides

Question 12

What are muffins

Answer 12

Core of proteins of most mucus’s are called muffins
Heavily O-linked glycosylated
This gives mucus its sliminess

Question 13

What are the two models which describe how proteins move through the Golgi

Answer 13

Vesicular transport model
Cisternal maturation model

Question 14

Why do some proteins go backwards through the golgi

Answer 14

Proteins that are misfolded or incorrectly modified in the Golgi need to be returned to the endoplasmic reticulum (ER) for proper folding or degradation
Some proteins have ER retrieval signals so need to be returned to the ER

Question 15

How do some proteins go backwards through the Golgi

Answer 15

Luminal proteins
Membrane proteins

primary mechanism for retrograde transport involves COPI

Proteins destined for retrograde transport often contain specific retrieval signals
The KDEL receptor, located in the Golgi, recognizes and binds to these KDEL-tagged proteins.

The binding of proteins with retrieval signals to their receptors triggers the recruitment of coat protein complex I (COPI) components to the membrane.

COPI proteins coat the budding vesicles. The COPI complex consists of seven subunits that form a coat around the vesicle, aiding in its formation and budding from the Golgi membrane.
Small GTPases, such as Arf1, play a crucial role in initiating the formation of COPI-coated vesicles by recruiting coat proteins to the Golgi membrane.

The coated vesicle buds off from the Golgi membrane. The scission of the vesicle from the membrane is facilitated by dynamin-related proteins.
The vesicle is now free to move toward its destination

Question 16

Why do some proteins go backwards through the Golgi/ back to ER

Answer 16

Prevent depletion of organelle-resident proteins
Prevent depletion of lipids
More energetically efficient

Question 17

What are the different destinations of proteins after they exit the golgi

Answer 17

Secreted out of cell via the plasma membrane
Transported to stay in the plasma membrane
Vesicular trafficking around celllysosomes

Question 18

What kind of proteins are delivered to lysosomes

Answer 18

Hydrolytic enzymes which vary in size/number

Question 19

What is the structure of the lysosome

Answer 19

40+ acid hydrolyses, proteases, nucleuses and glycosidases
Lipases, phospholipids, phosphatases, sulfatases often appear crystalline
Lysosome has a low internal pH- protects the cell if lysosome breaks as the enzymes inside the lysosome wont work at the cells pH
H+ ATPase acidifies and drives metabolite transport

Question 20

What is lysosome targetting *

Answer 20

Lysosome targeting refers to the strategies and mechanisms by which specific molecules, drugs, or proteins are directed to lysosomes within a cell

Effective lysosome targeting can enhance the degradation of unwanted or toxic materials within cells, improve drug efficacy, and contribute to the treatment of a variety of diseases.

Question 21

What is the mannose-6phosphate tag

Answer 21

Responsible for the transport of hydrolytic enzymes to lysosomes (which are produced in the golgi)

Question 22

What is the function of lysosomes

Answer 22

Lysosomes hold enzymes in active state
Fuse with target organelle
A hybrid forms
Enzymes digest content of lysosome
Proteins are delivered to mature at the lysosome
Debris, phagocytoses microorganisms, dead cells digested
nutrient production

Question 23

What is autophagy

Answer 23

Allows the orderly degradation and recycling of cellular components- allows cell to disassemble junk parts and reuse components
Targetted cytoplasmic constituents isolated from the rest of the cell within a double membraned vesicle known as an auto phagosome
Auto phagosome fuses with lysosome and the contents are degraded and recycled

Question 24

How do lysosomal storage disorders occur

Answer 24

Many LSDs arise from mutations in genes that encode enzymes but numerous other ways in which process can break down
Failure of the activity in the lysosome

Question 25

What are some treatments for lysosomal storage disorders (LSDs)

Answer 25

Enzyme replacement therapy- replace missing or defective enzymes
Substrate reduction therapy- help prevent the accumulation of the damaging product
Chaperone therapy- help protector retold mutant enzyme
Gene therapy- alter the fault gene
Bone marrow- replace the entire set of healthy stem cells

Question 26

What is the structure of the Golgi

Answer 26

Membrane bound- lipid bilayer
Lumen of Golgi= where reactions take place

Question 27

What are the alternative routes to the lysosome

Answer 27

Phagocytosis
Auophagy
Endocytosis
(So these are the other process in which material is delivered to the lysosome)

Question 28

What is the vesicular transport model

Answer 28

Each cisternae remains in one place with unchanging enzymes
Proteins move forward through the stack via vesicles that move from earlier to later cisternae

Question 29

What is the cisternal maturation model

Answer 29

As a new cis cisternae is formed it extends across the Golgi stack
Proteins stay in a given compartment and different enzymes arrive there to convert a cis cisterna to a middle (medial) cisterna or a trans cisterna to a medial cisterna