Chapter 11: Membrane Structure

Question 1

Lipid biylayer

Answer 1

• cell membrane
• form bilayers in water
• flexible two dimensional fluid
• membrane assembly begins in ER
• packed with phospholipids

Question 2

Phospholipids

Answer 2

• has hydrophilic head region(faces water) made up of choline, phosphate, and glycerol
• has hydrophobic tail(faces inward, away from water) made up of hydrocarbons
• many packed into cell membrane

Question 3

Cis double bonds

Answer 3

• found within phospholipids
• bends can happen in hydrocarbon tails, where a double bond is formed and changes the fluidity of membrane within one part of tail

Question 4

What is the role of cholesterol in membranes?

Answer 4

• it creates a stiffer membrane by filling space between a bent and a straight hydrocarbon tail part
• visualize: polar head region left alone, cholesterol-stiffened region until bend, more fluid region after bend

Question 5

Amphipatic nature in cells

Answer 5

amphipathic nature of membrane lipids is crucial for the formation and stability of cell membranes. The hydrophilic heads interact with the surrounding water molecules, while the hydrophobic tails avoid water, creating a barrier that separates the internal and external environments of the cell. This lipid bilayer structure is vital for various cellular processes, including maintaining cell integrity, regulating the passage of molecules in and out of the cell, and facilitating communication between cells.

Question 6

Why do membrane lipids spontaneously form a lipid bilayer?

Answer 6

• water is a polar molecule while 2-methyl propane is a nonpolar molecule(and hydrophobic)
• they will not form favorable interactions with each other
• water molecules create a cage like structure around the molecule to maximize the hydrogen bonds
• this leads to decreased entropy when hydrophobic molecules are in H20(more order), since lipid bilayers are the lowest free energy conformation; the water forms a more ordered structure

Question 7

Why do lipids form a bilayer?

Answer 7

• polar molecules (such as acetone) combined with water, also a polar molecule, will create a solution readily

(like dissolved like ROT)

Question 8

Why are lipids already in a bilayer creating no effect on water?

Answer 8

• the water is not in contact with the hydrophobic tails of the lipids when they are in a bilayer
• so water does not form a cage like structure around lipids when in a bilayer
• (lipid bilayer is lowest free energy state)
• water less ordered increases entropy

Question 9

Describe the assembly of the lipid bilayer

Answer 9

• ER begins assembly of membrane
• ER has enzymes to synthesize phospholipids
• made right in membrane
• bud off in vesicles to golgi, or cytoplasm
• newly synthesized phospholipids are added to cytosolic side of ER membrane, redistributed by transporters
• transporters carry from one half of lipid bilayer to the next

Question 10

Flippase

Answer 10

• helps establish and maintain the asymmetric distribution of phospholipids characteristic of animal cell membranes
• the lipid bilayer of the golgi apparatus and new membrane form a lipid bilayer together, new membrane squishes inbetween golgi parts
• the flippase catalyzes transfer of specific phospholipids to the cytosolic monolayer

Question 11

Describe the asymmetric distribution of phospholipids and glycolipids in animal cell plasma membrane

Answer 11

• various phospholipids can be found in the cytosolic monolayer or noncytosolic monolayer
• essential phospholipid sits in cytosolic monolayer to participate in cell signaling
• glycolipids have larger attached head groups that represent sugars found exclusively in noncytosolic monolayer
• cholesterol distributed almost equally between both monolayers

Question 12

Scramblase

Answer 12

• catalyzed transfer of RANDOM phospholipdis from one monolayer to another
• random distribution occurs in ER membrane

Question 13

Describe membrane transport

Answer 13

• process of vesicle budding and fusing
• oritentation of membrane lipids and proteins preserved during process (cytosolic surface remains facing cytosol, noncytosolic surface faces away from cytosol)

Question 14

Gycosylation

Answer 14

• addition of sugars
• occurs in golgi
• glycosylated proteins and lipids retain orientation and will be outside the cell

Question 15

Importance of glycolipids and glycoproteins

Answer 15

• for cell recognition with other cells
• for nuetrophils moving out of blood vessels to site of infection it needs to fix

Question 16

Describe how eukaryotic cells are coated with sugars

Answer 16

• all carbyhydrates are on the external/noncytosolic surface of plasma membrane
• carbohydrate rich layer made of oligosaccharide side chains, which are attached to glycolipids and glycoproteins
• glycolipids and glycoproteins also attached to membrane of proteoglycans
• glycoproteins made by this cell can be absorbed back to contribute
• neutrophils can use sugar here to get into blood stream towards infection

Question 17

Why are sugars on the extracellular membrane important?

Answer 17

• the recognition of cell surface carbohydrates on neutrophils allows these immune cells to migrate out of the blood ad into infected tissues
• lectin and neutrophils work together to make this happen
• lectins made from endothelial cells lining blood vessel and recognize glyco-groups on neutrophil surfaces
• neutrophils normally stick to blood vessel wall
• protein interaction between neutrophil and lectin allows neutrophil to slip between endothelial cells to migrate out of the blood stream and to an infection