Membrane Structure

Question 1

Roles of Membranes

Answer 1

• receiving information
• import and export of small molecules
• capacity for movement and expansion

Question 2

Flip-Flop

Answer 2

• phospholipids move from one side of the cell membrane to the other

Question 3

Common movement of phospholipids?

Answer 3

• lateral diffusion
• flexion and rotation

Question 4

Effect of cholesterol on cell membrane

Answer 4

• makes it less fluid/more rigid

Question 5

Where are phospholipids made?

Answer 5

• made in the ER
• initially deposited in the cytoplasmic half of the ER membrane
• scramblase randomly distributes new phospholipids to both sides

Question 6

Steps of phospholipids being added to the membrane

Answer 6

1. phospholipid synthesis add to cytosolic half of the bilayer
2. scramblase catalyzes transfer of random phospholipids from one monolayer to another
   (in the ER membrane, phospholipids are randomly distributed)

Question 7

Delivery of phospholipids to organelle membranes

Answer 7

• in other organelles, flippases selectively transport phospholipids to the cytoplasmic side
• this leads to membrane asymmetry

Question 8

Flippase

Answer 8

catalyzes transfer of specific phospholipids to cytosolic monolayer

Question 9

Glycolipids

Answer 9

• sugars with fatty acid tails
• pointed towards outside of cell
• part of the carbohydrate coat that surround/protects animal cells

Question 10

Types of cell membrane proteins associations

Answer 10

• transmembrane
• monolayer associated
• lipid-linked
• protein-attached
• peripheral membrane proteins (proteins attached)
• ## integral membrane proteins

Question 11

Why might it be important that red blood cells have a strong cell cortex

Question 12

FRAP (Fluorescent Recovery After Photobleaching)

Answer 12

• can shine a certain wavelength of light on a green flourenscent protein and it will glow

Question 13

Why might it be important to create a separate apical vs basal side?

Question 14

Why are membranes important cellular barriers?

Answer 14

• allow specific molecules to cross
• enables the cell to concentrate nutrients and substrates
• creates gradients

Question 15

What holds together the phospholipid membrane?

Answer 15

• hydrophobic forces
• phospholipids spontaneously cluster into a bilayer to minimize contact of hydrophobic tails with water

Question 16

Increased fluidity
- what increases fluidity in membranes?

Answer 16

shorter fatty acid tails, unsaturated fatty acid tails, less cholesterol

Question 17

What causes membrane asymmetry?

Answer 17

flippases selectively transport phospholipids to the cytoplasmic side

Question 18

Where are glycolipids found?

Answer 18

only found in the non-cytosolic half of the plasma membrane (oriented outside of the cell)

Question 19

How do transmembrane proteins pass through the cell membrane?

Answer 19

using an alpha-helix with hydrophobic side chains sticking out

Question 20

Single pass transmembrane protein

Answer 20

a single polypeptide chain spans the lipid bilayer only once

Question 21

multi-pass transmembrane protein

Answer 21

a single polypeptide chain spans the lipid bilayer multiple times

Question 22

Beta barrels

Answer 22

are made of a beta sheet that twists and coils to form a barrel like structure in the cell membrane

Question 23

Detergents

Answer 23

amphipathic molecules that can disrupt hydrophobic associations, which can destroy molecules
- can also solubilize membrane proteins in a solution

Question 24

Cell walls

Answer 24

plants, yeast, and bacteria have cell walls made of protein, sugar, and more that provides increased resilience

Question 25

Cell cortex

Answer 25

a meshwork of filamentous proteins underneath the membrane that can disrupt hydrophobic associations, which can destroy membranes

Question 26

Cell fusion experiments

Answer 26

• proteins from human cell and mouse cell combined in a hybrid cell
• at 0 minutes proteins remain separated
• 40 minutes after cell fusion proteins are mixed

Question 27

apical side

Answer 27

the apical faces external environment or lumen

Question 28

basal side

Answer 28

closest to basal lamina or the lumen of the tissue
-mediates attachment to underlying tissue or surface via integrins

Question 29

Glycocalyx

Answer 29

Carbohydrate the coats the outside of the plasma membrane

Question 30

What is glycocalyx made up of?

Answer 30

• glycolipids
• glycoproteins: proteins with short, highly branched sugar chains
• proteoglycans: proteins with long sugar chains of repeated disaccharides (long sugar chains with no branching)

Question 31

What is the function of glycocalyx?

Answer 31

• “sugar coating”
• protects against mechanical damage
• attracts water->makes cells slimy/lubricated
• important part of cell to cell recognition

Question 32

What does recognition of carbohydrates on immune cells allow?

Answer 32

recognition of cell-surface carbohydrates on immune cells allows them to migrate out of the blood at the site of infected tissue

Question 33

Intravital Microscopy

Answer 33

• take living mouse (put it under)
• tape it down
• make incisions and pull desired organ out and place slide against organ to get flat surface and look at tissue.

Question 34

membrane domains

Answer 34

many proteins are anchored at specific membrane domains