Eukaryotic Structure 3

Question 1

Describe co-translational translocation

Answer 1

It is the process by which newly synthesised proteins are translocates into the ER.
1. Peptide with signal sequence binds to signal recognition particle (SRP), pausing translation
2. SRP guides ribosome and RNA to translocator through binding to SRP receptor on plasma membrane
3. Protein translation occurs through translocator into ER lumen

Question 2

How do vesicles know where to go ?

Answer 2

1. Protein coats help to determine the destination
2. Rab GTPases guide the vesicles to the correct location
3. SNARE proteins ensure that vesicle-membrane fusion only occurs at the right place

Question 3

How do SNARE proteins ensure fusion ?

Answer 3

V-SNAREs pair with t-SNAREs
The ‘zippering’ mechanism pulls the vesicle and target membrane together and allows fusion.

Question 4

What is exocytosis ?

Answer 4

The process by which vesicles fuse with the plasma membrane to release their contents outside the cell.

Question 5

What are the 2 types of exocytosis ?

Answer 5

1. Constitutive exocytosis
   Continuous. Deliver proteins and lipids to the plasma membrane
2. Regulated exocytosis
   Secretory vesicles are stored and released in signal

Question 6

Describe examples of regulated exocytosis

Answer 6

1. Insulin secretion
   Glucose uptake increases ATP which inhibits potassium channel, causing depolarisation. This opens calcium channels that trigger exocytosis of vesicles storing insulin.
2. Histamine
   Stimulus received by mast cells to release vesicles containing histamine

Question 7

What is endocytosis ?

Answer 7

The process by which the cell engulfs material from the outside by folding in its plasma membrane, forming a vesicle that brings material into the cell.
Types:
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis

Question 8

What is phagocytosis?

Answer 8

Engulfing large particles like bacteria

Question 9

What is pinocytosis ?

Answer 9

The non-specific uptake of extracurricular fluid and small molecules

Question 10

What is receptor-mediated endocytosis?

Answer 10

Surface receptors bind specific molecules then form clathrin-coated vesicles for internalisation
Highly selective

Question 11

What are endosomes ?

Answer 11

Intracellular sorting organelles
Early endosomes: the first compartment that receives material after endocytosis
Late endosomes: material is moved from early endosomes for further processing

Question 12

What are lysosomes ?

Answer 12

They contain a variety of hydrolytic enzymes responsible for breaking down waste materials and foreign substances.
They degrade proteins, nucleic acids, lipids and oligiosaccharides.
The enzymes are most active in acidic environment.
They also have specialised transporters to export useful metabolites out to cytosol

Question 13

What are the functions of a plant vacuole ?

Answer 13

1. Storage of nutrients
2. Degradation compartment
3. Controller of turgor pressure

Question 14

What are peroxisomes ?

Answer 14

Single membrane-enclosed organelles formed by budding off the ER
Contain oxidative enzymes: catalase and urate oxidase
Produces hydrogen peroxide to detox harmful metabolites

Question 15

What is zellweger syndrome ?

Answer 15

Genetic disorder where peroxisomes are not properly formed