Unit 2.3 Endomembrane System

Unit 2.3 Endomembrane System

by Dawn Sasek

Self assembly ​of a Lipid Bilayer

• Watch the self assembly of a lipid bilayer video cl​ip.

  • ​Note the constant collisions of blue,polar water molecules

  • ​The green portion of the phospholipid cannot attract to water

  • ​the red portion of the phospholipid remains towards the water as the slightly negative charge of the phosphate attracts to the slightly positive charge of water.

​Vesicles are Lipid Bilayers in a circle that will Fuse together in water

• ​As you watch the video, notice

  • ​The blue water molecules in constant motion

  • ​Pay attention to the small pink particles..they bounce around; can move through membrane but can't seem to stay anywhere there is water...what type of molecule is this pink particle ..polar or nonpolar

  • ​the many separate vesicles start to fuse with each other

  • ​the green portion of the phospholipid must be the polar end. Why???

​Vesicles can self assemble and trap polar molecules inside of it.

• ​Note the red polar molecules can be trapped as a lipid bilayer self assembles around it.

• ​If the red polar molecules represent polar proteins, this vesicle filled with these polar proteins can fuse with other cell membranes very easily to either form a larger vesicle or fuse with the outer cell membrane to dump the proteins outside of the cell.

Multiple Choice

The phospholipid molecule can self assemble into a bilayer because...

• The polar head will attract to the aqueous environment

• The non-polar portion can't attract to water and will be pushed away by the water.

• moving water molecules will hydrogen bond with each other pushing the lipids away and towards each other.

• All choices are correct.

Multiple Choice

Polar molecules such as the red ones show here become trapped in a vesicle because...

• the polar molecules can easily pass through the lipid portion of the membrane.

• The polar molecules cannot pass through the lipid portion of the membrane.

The Endomembrane System and Vesicle Transport

• All cells are protein producing factories.

• Problem: Proteins are polar molecules that can't pass through the membrane.

  • ​Example, in a complex organism like a human, the pancreas cells produce tons of insulin that have to be transported out of the cell into the blood stream. How do we do this if insulin is polar????

• ​Eukaryotic cells have a system of wrapping the proteins in fatty vesicles that can fuse with the cell's membrane.

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Multiple Select

As seen in the previous video, proteins that are made on ribosomes that are attached to the ROUGH ENDOPLASMIC RETICULUM, RER for short, will eventually....

CHECK ALL THAT APPLY

• be released inside of the membrane bound endoplasmic reticulum...

• bud off inside of a vesicle that breaks off of the rough endoplasmic reticulum.....

• the vesicle fuses with the Golgi apparatus that modifies the vesicle and theN buds off again...

• the vesicle moves to outer cell membrane and fuses with membrane dumping protein contents outside of cell.

Multiple Choice

After watching the video, choose the best description of protein excretion from a cell.

• The endomembrane system inside of a eukaryotic cell is rigid and non changing

• The endomembrane system inside of a eukarytotic cell is a flexible, every changing dynamic system that interacts with itself via constant membrane bound vesicle budding and fusion.