Membrane Structure Flashcards
Roles of Membranes
- receiving information
- import and export of small molecules
- capacity for movement and expansion
Flip-Flop
- phospholipids move from one side of the cell membrane to the other
Common movement of phospholipids?
- lateral diffusion
- flexion and rotation
Effect of cholesterol on cell membrane
- makes it less fluid/more rigid
Where are phospholipids made?
- made in the ER
- initially deposited in the cytoplasmic half of the ER membrane
- scramblase randomly distributes new phospholipids to both sides
Steps of phospholipids being added to the membrane
- phospholipid synthesis add to cytosolic half of the bilayer
- scramblase catalyzes transfer of random phospholipids from one monolayer to another
(in the ER membrane, phospholipids are randomly distributed)
Delivery of phospholipids to organelle membranes
- in other organelles, flippases selectively transport phospholipids to the cytoplasmic side
- this leads to membrane asymmetry
Flippase
catalyzes transfer of specific phospholipids to cytosolic monolayer
Glycolipids
- sugars with fatty acid tails
- pointed towards outside of cell
- part of the carbohydrate coat that surround/protects animal cells
Types of cell membrane proteins associations
- transmembrane
- monolayer associated
- lipid-linked
- protein-attached
- peripheral membrane proteins (proteins attached)
- ## integral membrane proteins
Why might it be important that red blood cells have a strong cell cortex
FRAP (Fluorescent Recovery After Photobleaching)
- can shine a certain wavelength of light on a green flourenscent protein and it will glow
Why might it be important to create a separate apical vs basal side?
Why are membranes important cellular barriers?
- allow specific molecules to cross
- enables the cell to concentrate nutrients and substrates
- creates gradients
What holds together the phospholipid membrane?
- hydrophobic forces
- phospholipids spontaneously cluster into a bilayer to minimize contact of hydrophobic tails with water
Increased fluidity
- what increases fluidity in membranes?
shorter fatty acid tails, unsaturated fatty acid tails, less cholesterol
What causes membrane asymmetry?
flippases selectively transport phospholipids to the cytoplasmic side
Where are glycolipids found?
only found in the non-cytosolic half of the plasma membrane (oriented outside of the cell)
How do transmembrane proteins pass through the cell membrane?
using an alpha-helix with hydrophobic side chains sticking out
Single pass transmembrane protein
a single polypeptide chain spans the lipid bilayer only once
multi-pass transmembrane protein
a single polypeptide chain spans the lipid bilayer multiple times
Beta barrels
are made of a beta sheet that twists and coils to form a barrel like structure in the cell membrane
Detergents
amphipathic molecules that can disrupt hydrophobic associations, which can destroy molecules
- can also solubilize membrane proteins in a solution
Cell walls
plants, yeast, and bacteria have cell walls made of protein, sugar, and more that provides increased resilience
Cell cortex
a meshwork of filamentous proteins underneath the membrane that can disrupt hydrophobic associations, which can destroy membranes
Cell fusion experiments
- 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
apical side
the apical faces external environment or lumen
basal side
closest to basal lamina or the lumen of the tissue
-mediates attachment to underlying tissue or surface via integrins
Glycocalyx
Carbohydrate the coats the outside of the plasma membrane
What is glycocalyx made up of?
- glycolipids
- glycoproteins: proteins with short, highly branched sugar chains
- proteoglycans: proteins with long sugar chains of repeated disaccharides (long sugar chains with no branching)
What is the function of glycocalyx?
- “sugar coating”
- protects against mechanical damage
- attracts water->makes cells slimy/lubricated
- important part of cell to cell recognition
What does recognition of carbohydrates on immune cells allow?
recognition of cell-surface carbohydrates on immune cells allows them to migrate out of the blood at the site of infected tissue
Intravital Microscopy
- 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.
membrane domains
many proteins are anchored at specific membrane domains
