Cells and organelles 2

Question 1

Describe the topology of the secretory pathway

Answer 1

The lumen of a membrane bound organelle is congruent to the exterior of the cell. The lumen of the ER is topologically equivalent to the exterior of the cell.

Question 2

How do vesicles move toward and away from the golgi

Answer 2

Transport vesicles are pulled by various motors, kinesin and dynein. These motors pull the vesicles along microtubules

Question 3

What is the function of kinesin

Answer 3

It transports vesicles away from an organelle

Question 4

What is the function of dynein

Answer 4

It transports vesicles back towards the organelle

Question 5

What is the function of lysosomes

Answer 5

They degrade obsolete membrane-bound organelles through a process called autophagy

Question 6

How are lysosomes made

Answer 6

They are formed via transport vesicles from trans-Golgi fusing with late endosome

Question 7

What are endosomes

Answer 7

They are the intersect between the secretory pathway and the endocytic pathway

Question 8

Describe the process of uptake and degradation

Answer 8

• Uptake is by endocytosis (large particles by phagocytosis, small molecules by pinocytosis)
• Cargo internalised is delivered to endosomes and then passed to lysosomes for degradation
• Portions of the cell are digested by lysosomes

Question 9

What is endocytosis

Answer 9

It is a process by which micro or macro-molecules are transported into the cell

Question 10

What is clathrin-mediated endocytosis

Answer 10

• The macromolecule to be transported binds to a specific receptor
• The receptors are concentrated within a plasma region called the clathrin-coated pit
• Formation of invaginated pits and budding from the membrane to form clathrin-coated vesicles
• Dynamin forms ring around the invaginated pits resulting in conformational change

Question 11

Describe protein degradation by proteasome

Answer 11

• Junk protein is tagged with ubiquitin protein molecules
• E1 activates the carboxyl terminal of ubiquitin, driven by ATP
• E3 recognises and binds to a target protein and moves to form a complex with E2
• Ubiquitin is transferred from E1 to E2 and from E2 to the targeted protein on E3
• The polyubiquinated protein is recognised and degraded by a proteasome
• Once the protein is degraded into small peptides, ubquitin is released in the process for re-use in another cycle

Question 12

What is the advantage of compartmentalisation in eukaryote cell evolution?

Answer 12

Specialised reactions can be separated, concentrated and optimised

Question 13

What is the advantage of mitochondria in eukaryote cell evolution?

Answer 13

It produces most of the ATP supply for the cell

Question 14

What is the function of microtubules

Answer 14

They are involved in intracellular movement of cell organelles and vesicles. They form the mitotic spindle in centrosomes

Question 15

What is the function of microfilaments

Answer 15

Double strands of actin. They are linked with membrane proteins which provides structural shape to cells. Provides contractile forces enabling cells to move around

Question 16

What is the function of intermediate filaments

Answer 16

Formed from a variety of proteins. They support nuclear envelope and provide support for cytoplasm