Lecture 5 - endomembrane system and bulk transport processes

Question 1

What is the endomembrane system?

Answer 1

A membrane system interconnected by direct physical contact or transfer by vesicles

Question 2

What does the endomembrane system include

Answer 2

Nuclear envelope 
Endoplasmic reticulum
Golgi apparatus
Vesicles
Lysosomes 
Vacuoles
Plasma membrane

Question 3

What is a vesicle?

Answer 3

A membrane bound pouch that stores or transports substances within the cell

Question 4

What is the endoplasmic reticulum?

Answer 4

A network of folded membrane that accounts for half the membrane

Question 5

What are the two regions of the ER?

Answer 5

Smooth ER

Rough ER

Question 6

What are the 4 functions of smooth endoplasmic reticulum (sER)?

Answer 6

Metabolism of carbohydrates
Lipid synthesis for membranes
Detoxification of drugs and poisons
Storage of calcium ions

Question 7

What are calcium ions used for?

Answer 7

Signalling in the cell

Question 8

Why is it important that the amount of sER can change?

Answer 8

Because some areas of the body will need more sER if it’s role is connected to the function of sER such as the liver

Question 9

What makes rough endoplasmic reticulum (rER) rough?

Answer 9

Ribosomes

Question 10

What is the function of rER?

Answer 10

Protein synthesis

Question 11

How does protein synthesis occur?

Answer 11

Secreted and membrane bound proteins enter the lumen (interior) of the rER and are processed by the rER and the rest of the endomembrane system. It is then ready for release from the cell of retention on the cell membrane

Question 12

What is the golgi complex?

Answer 12

The golgi complex is an extensive organelle that is used for packaging.

Question 13

What is the golgi complex made of?

Answer 13

Flattened tubules

Question 14

What is the function of the golgi complex?

Answer 14

To recieve, modify, sort and ship proteins arriving from the rER

Question 15

Explain the polarity of the golgi complex

Answer 15

The golgi complex has polarity so there is a cis and trans face.
Vesicles from the ER arrive at the cis face and the processed vesicles leave at the trans face.

Question 16

How are vesicles used in the golgi complex?

Answer 16

To deliver stuff in and out of the golgi complex

Question 17

What is glycosylation?

Answer 17

To add (or modify) carbohydrate to proteins.

Question 18

Why is the addition of carbohydrates to proteins important?

Answer 18

Carbohydrates tag proteins so they know where to go. This is important for secreted/cell surface proteins.

Question 19

How do non membrane bound proteins (cytoplasmic proteins) get synthesised?

Answer 19

On free ribosomes found in the cytoplasm

Question 20

What do sorting proteins do?

Answer 20

Add molecular markers to direct proteins to the correct vesicles before they bud off from the trans face

Question 21

What is involved in directing vesicle trafficking? And why is it important?

Answer 21

Molecular tags are added to vesicles leaving the trans face to direct them to the correct targets.
It is important for release and surface expression

Question 22

What are the tags in directing vesicle trafficking?

Answer 22

The tags are often short proteins exposed in the vesicle surface.

Question 23

What are the two types of bulk transport across the membrane?

Answer 23

Exocytosis

Endocytosis

Question 24

What is exocytosis?

Answer 24

Exocytosis is the transportation of materials (glycoproteins) out of the cell or delivers it to the cell surface.

Question 25

What is constitutive exocytosis?

Answer 25

Continuous exocytosis that releases ECM proteins.

Question 26

What is regulated exocytosis?

Answer 26

Regulated exocytosis is exocytosis that will only occur if the cell receives a signal to do so. Regulated exocytosis releases hormones and neurotransmitters.

Question 27

What is endocytosis?

Answer 27

Endocytosis is the process where the cell takes in molecules and particulate matter at the plasma membrane

Question 28

What is phagocytosis?

Answer 28

Phagocytosis is cell eating/uptake of food particles (solids). When this happens the cell forms a phagocytic vacuole which is then digested by lysosomes

Question 29

What is pinocytosis?

Answer 29

Pinocytosis is cell drinking/ uptake of extracellular fluid that contains various solutes such as proteins and sugars (liquids). The uptake vesicle is formed with the aid of coat proteins and the uptake is nonselective.

Question 30

What is receptor mediated endocytosis?

Answer 30

It is a specialised form of pinocytosis where the cell to select what to take in.

Question 31

Describe what happens in receptor mediated endocytosis?

Answer 31

Receptor proteins attach themselves to the desired solute and then the cell takes it in. This allows the cell to take in specific substances which may have low concentrations.

Question 32

What is a lysosome?

Answer 32

A lysosome is a membrane bound organelle made by the rER and Golgi body that contains enzymes.

Question 33

What is the function of lysosomes?

Answer 33

The lysosome digests and releases unwanted cellular materials. They degrade protein, lipids, carbohydrates and nucleic acids and then release the broken up products into the cell.
Programmed cell death.

Question 34

What is autophagy?

Answer 34

Autophagy is self eating within the cell

Question 35

What is a vacuole?

Answer 35

A large vesicle that is derived from the rER and Golgi.

Question 36

Why are vacuoles important in plants?

Answer 36

Vacuoles in plants perform lysosome like functions. Plants have a large central vacuole that absorbs water which allows plant cells to grow without a large increase in cytoplasm