Cell And Molecular Biology

Question 1

What is the process of endocytosing LDLs from the bloodstream?

Answer 1

Recognition of packaged LDL by receptors -> R recruiting clathrin coat by mediators eg adductin -> dynein cleaves off vesicle by GTP hydrolysis -> clathry coat dissembled -> fusion to endocytic vesicle then endosome -> acidification and dissociation of receptor -> Rs recycled -> fusion to lysosome -> LDL gedraded by lipidases -> cholesterol secreted

Question 2

What are the names of the different clathryn-like proteins and where are they localised?

Answer 2

Clathryn - plansma membrane, early endosomes, endocytosis, trans Golgi
COPI - Golgi apparatus
COPII - sER

Question 3

What is the involvement of the sER in vesicle transport?

Answer 3

SER prepares lipids to be inserted into membranes by joining two fatty acids with a phosphate group in one of the doible membrane layers.
This is where prots synthetised in the rER are packaged and released

Question 4

What are the different versions of vesicular transport and what are they used for?

Answer 4

Phagocytosis: actin mediated vesicle formation usually around a foreign body to internalise it for degradation in the lysosome, useful proteins and sugars extracted are recycled
Autophagy: malfunctioning own components are surrounded by small vesicles and engulfed, delivered to lysosome for degradation eg mitochondria, components recycled
Exocytosis: release of proteins, neurotransmitters or mucus from the producing cells

Question 5

Describe SNARE-mediated vesicle fusion!

Answer 5

Direct fusion impossible bc of slight negative charge of serines
T and v-SNAREs facilitatee fusion by forming a coiled coil structure zipping the vesicle to the membrane with their hydrophobicity (2 snare pairs per vesicle)
In the space between the SNARE pairs, the membrane is forced to mingle and content can be released
SNAREs are separated then recycled
( in NT uptake, the vesicle gains a v-SNARE as a process of recycling)

Question 6

How is vesicular secretion regulated? What types are there?

Answer 6

Constituitive release: contents are secreted as they are made by simple diffusion of the vesicle to the membrane
Good for eg mucus release in the lung

Regulated secretion: contents are packaged and highly concentrated by the removal of excess lipid packaging when samller vesicles form (insulin creates crystals this way) vesicles wait closely related to the plasma membrane for a signal when to be released
Eg insulin and other enzymes that are only periodically needed.