Lipids and Membranes Flashcards
1
Q
What are the cellular functions of lipids?
A
- Essential components of membranes
- Energy storage
- Signaling events
2
Q
What are the properties of lipids?
A
- Not true polymers
- Soluble in organic solvents and detergents
- Mostly amphipathic
- Huge variety of structures
3
Q
What are fatty acids?
A
- Carboxylic acid followed by long hydrocarbon chains
- 14-40 carbon long in plants and animals
- C16 and C18 are the most common
- Can have saturated or unsaturated bonds (affects physical properties)
4
Q
Stearic acid
A
18 carbons, 0 double bonds (fully saturated)
5
Q
Oleic acid
A
18 carbons, 1 double bond (one degree unsaturated)
6
Q
Linoleic acid
A
18 carbons, 2 double bonds (2 degrees unsaturated)
7
Q
alpha-Linoleic acid
A
18 carbons, 3 double bonds (3 degrees unsaturated)
8
Q
Palmitic acid
A
16 carbons, 0 double bonds (fully saturated)
9
Q
What are triacylglycerols?
A
- Aka triglcerides
- Basis for storage fat in animal tissues
- Glycerol backbone
- 3 fatty acids connected to backbone by ester linkages
- Nonpolar
10
Q
What are glycerophospholipids?
A
- Aka phospholipids
- Major component of biological membranes
- Glycerol-3-phosphate backbone
- 2 fatty acids (C1 and C2) connected by ester linkages
- Head group connected to phosphate group is polar
- Amphipathic (hydrophobic tails and hydrophilic head)
- C1 fatty acid is fully saturated C16-C18
- C2 fatty acid is unsaturated C14-C20
11
Q
Phosphatidic acid
A
H head
12
Q
Phosphatidylethanolamine
A
Ethanolamine head (CH2-CH2-NH3+)
13
Q
Phosphatidylserine
A
Serine head CH2-CH(NH3+)COO-
14
Q
Phosphatidylcholine
A
Choline head CH2-CH2-N(CH3)3+
15
Q
Phosphatidylinositol
A
Inositol head group
16
Q
What are sphingolipids?
A
- Have a sphingosine backbone
- Fatty acid at C2 attached by amide linkage
- Trans double bond in C3
- Important for membranes (axons)
- Made of ceramides (sphingosine with fatty acid residue)
17
Q
What are sphingomyelins?
A
- Importatnt in plasma membrane
1a. Wrap axon sheath to insulate electrical signals/create myelin sheath - Cerminde + phosphocholine or phosphoethanolamine group
18
Q
What are cerebrosides?
A
A type of sphingomyelin made of ceramide and 1 sugar residue
19
Q
What are gangliosides?
A
- Most complex sphingolipid made of ceramide and multiple carbohydrate groups
- Important in brain lipids
- Receptors for certain toxins
20
Q
What are steroids and sterols?
A
- Lipids mostly found in eukaryotes
- Made of 4 fused rings
- Most common is cholesterol
- Sterol is steroid with hydroxy group on C3
- Sterols are weakly amphipathic
- Steroids are precursors for many hormones
- Steroids are a major part of animal plasma membrane (fluidity)
21
Q
What are isoorenoids?
A
- 5 carbon unit lipids
ex. ubiquinone/coenzyme Q in mitochondrial membrane, plant pigments, vitamins A, K and E
22
Q
What are the 3 ways lipids assemble in water?
A
- Micelles (single membrane spheres)
- Bilayers (enclosed double membrane)
- Liposomes or vesicles (closed bilayer with solvent in center)
23
Q
What are biological membranes?
A
- Bilayer for phospholipids that encloses cells and organelles
- Formed by hydrophobic effect
- Fluid mosaic (2D fluid)
3a. Lateral diffusion common, transverse diffusion rare (needs help)
3b. Constant movement
3c. Transition temperature - Made of different combinations of lipids
4a. Lipids are asymmetrically distributed in each leaflet of a bilayer
24
Q
Why is PI an important phospholipd?
A
-Different PI (modified at specific locations with extra phosphate groups) identify different types of membranes
25
What can membrane-associated proteins do?
1. Catalyze reactions (enzymes)
2. Transport molecules (channels, pores, pumps)
3. traffic molecules (cargoes, coats, adaptors)
4. Relay signals (G proteins and receptors)
26
What are the 3 types of membrane proteins?
1. Transmembrane (integral)
2. Peripheral
3. Lipid-linked
27
What are the properties of transmembrane proteins?
1. Tightly assocaited with bilayers
2. Require detergents for removal
3.Most fully transverse membrane
3a. single or multiple alpha helices
3b. Beta barrel structures
3c. Need minimum of 25 amino acids to span 35 angstrom bilayer
4. usually amphiphillic
5. Can be glycosylated
5a. Glycoproteins are formed via a glycosidic bond
5b. Can be O linked (Ser and Thr)
5c. Can be N linked (As, beta linkage)
5d. Very hydrophilic (found in surface loops and turns)
5e. Common in secreted and transmembrane proteins
ex. GPCr
28
What are the properties of peripheral proteins?
1. Loosely associated with bilayer by electrostatic interactions or H bondings
2. Can be dissociated from membrane using extreme pH or high salt concentration solution
3. Can bind phosphoinostitide head groups
ex. G protein
29
What are the properties of lipid-linked proteins?
1. Protein is covalently attached to a lipid
a. through prenylation (bind isoprenoid/prenyl group to protein at C-X-X-Y/Y is aliphatic)
b. fatty acid linkage (myritstic acid or palmitic acid)
—Fatty acids can insert themselves in bilayer
30
What is myristolation? (lipid-linked protein)
Amide linkage to N-terminal Gly in protein
31
What is palmitoylation? (Lipid-linked protein)
Thioester linkage of Cys residue in protein
32
What are the functions of a membrane?
1. Structure and support
2. Separate cellular processes
3. Sequester chemical reactions
4. Provide platform or staging area for cellular processes
All membranes are connected by trafficking
33
What is membrane trafficking?
1. Movement of protein and lipids between different organelles
2. often occurs in small membrane-bound vesicles
3. Protein orientation is preserved (Er lumen and Golgi cisternae= outside cell)
34
What are coat proteins?
1. Proteins that surround vesicles
2. Large multi-subunit protein complexes (4-9 proteins)
3. Mediate trafficking pathways
4. Bind PI head group of membrane, transmembrane protein cargo, and other proteins needed to build vesicle
35
What is the APII/clathrin complex?
1. AP2 are adaptor proteins that bind clathrin scaffold to vesicle membrane, accessory proteins, and cargo proteins
1. Beta 2 subunit binds clathrin, sigma 2 and N mu 2 subunits binds cargo)
2. AP2is a heterotetramer with flexible and unstructured regions
3. AP2 binds PIP2 head groups = peripheral protein
4. Binds short/linear amino acid motifs in transmembrane protein cargo C terminus (YxxO, O=bulky, hydrophobic residue) with C-mu2 subunit
4a. C-mu2 subunit creates Beta sheet banana and motif binds deep hydrophobic grooves on coat protein surface (Y and O plug into grooves)
5. AP2 exists in 2 conformations: open and closed
5a. Closed in cytoplasm (cargo binding site is deep in protein/blocked"
5b. AP2 binds PIP2 in plasma membrane and undergo conformation change to open state
