Lipids and Membranes Flashcards
1
Q
Fatty Acid Structures
A
- Amphipathic Molecules that are mainly hydrophobic and water-insoluble
- Long akyl chain
- Acid at group at end
- Can contain cis double bonds
- Length of chain can vary from 12-24 carbons, usually an even number of carbons
- Unsaturated if there is a C-C double bond
- Saturated has higher melting point
2
Q
Trans Fatty Acids
A
- Trans fatty acids form by partial dehydrogenation of unsaturated fatty acids
- A trans double bond allows a given fatty acid to adopt an extended conformation
- Occur only in small amount naturally
- Have little nutritional value
- Stimulate cholesterol synthesis and release it into circulation
3
Q
Storage Lipids: Triacylglycerols
A
- 3 fatty acids esterified to a glycerol molecule
- Majority of fatty acids in biological systems are found in this form
- Solids are fats
- Liquids are oils
- Primary storage form of lipids (body fat)
- Less soluble in water than fatty acids due to lack of charged carboxylate group
- Less dense than water, fats and oils float
- Not commonly components of cell membranes
4
Q
Fats Provide Efficient Fuel Storage
A
- Fatty acid carry more energy per carbon because they are more reduced
- Fatty acids carry less water along because they are non-polar
- Glucose and glycogen are for short-term energy needs and quick delivery
- Fats are for long term energy needs, good storage, slow delivery
5
Q
Phospholipids
A
- Major component of membranes
-Primary Constituents of cell membranes - Two fatty acids form ester linkages with first and second hydroxyl group of L-glycerol-3-phosphate
6
Q
Sphingolipids
A
- Second most abundant lipids in plant and animal cell membranes
- Backbone is not glycerol
- Backbone is a long chain amino alcohol sphingosine
- A fatty acid is joined to sphingosine via an amide linkage rather than an ester linkage as usually seen in lipids
- Polar head group is connected to sphingosine by a glycosidic or phosphodiester linkage
- Found largely in the outer face of plasma membranes
7
Q
Ceramides
A
- Potent signal for apoptosis
- Regulate Kinase Activity
- All head groups are extra cellular and are involved in signal transduction
- Make up 30-40% of the cell membranes in skin
8
Q
Cerebrosides
A
- Make up 12% of white matter in the brain
- Head groups can be elaborate: gangliosides
9
Q
Glycosphingolipids and Blood Groups
A
- Blood groups determined in part by the type of sugars located on the head groups in glycosphingolipids
- Structure of sugar is determined by an expression of specific glycosyltransferases
10
Q
Steroids/Sterols
A
- 4-ring fused ring structure
- common structure found in cholesterol, plant sterols and hormones
- Present in membranes of most eukaryotic cells
- Modulate fluidity and permeability
- Thicken plasma membrane
- Most bacteria lack sterols
11
Q
Cardiolipin
A
- Around 20% of the lipids int he mitochondrial inner membrane
- Associated with proteins of the electron transport system and may serve as a proton trap
- Helps organize super complexes of electron transport proteins
12
Q
Functions of Membranes
A
- Define the boundaries of the cell
- Allow import and export
- Sense external signals and transmit information into the cell
- Provide compartmentalization within the cell
- Produce and transmit nerve signals
- Store energy as a proton gradient and support synthesis of ATP
13
Q
Membranes
A
- Individual fatty acids form micelles in water and do not form a lipid bilayer because they don’t have the right shape
- Phospholipids and sphingolipids have a more box-like shape and do form a bilayer
- Extending this structure in all directions you get a cell
- Very important characteristic is its fluidity: ability of the lipids to move around in the membrane
- At low temps, tails stack and membrane structure is rigid
- At high temps, tails have more freedom, greater mobility of lipids
14
Q
Membrane Tm
A
- Characteristic transition temperature or melting temperature at which the lipids become more mobile
- Influenced by length of the tails, longer the tails, higher the Tm
- Influenced by degree of saturation, the more unsaturated the lipids are, the lower the Tm
15
Q
Roles of sterols in the membrane
A
- Above the Tm, rigid ring structure reduces the movement of lipids in the membrane which decreases the fluidity
- Below the Tm, acts as an impurity and prevents the lipids from stacking which increases fluidity
- Serves to broaden the Tm of the bilayer
16
Q
Asymmetric Lipids
A
- Very slow transverse diffusion can lead to asymmetric bilayers
- Example is red blood cell membranes
17
Q
Bilayer Dynamics
A
- Movement of lipids in a bilayer
- Lateral diffusion (lateral movement) is OK
- Transverse Diffusion is unlikely (flip-flop)
18
Q
Fluid Mosaic Model of Membrane Structure
A
- Proteins moving around in a sea of lipids
- membranes also contain proteins which are critical to the function of the membrane
- Amount and types of proteins in membranes can vary
19
Q
Plasma Membrane
A
- Lipid components form a bilayer that can be split apart by “freeze-fracture”
- Mobility of proteins in the bilayer can be critical for many membrane functions
- Dependent on fluidity hence the need to maintain the correct degree of fluidity
- vast majority of membrane proteins are asymmetric in the membrane
20
Q
Nature of membrane proteins
A
- 1,2 and 4: integral (intrinsic) membrane proteins
- 3: peripheral (extrinsic) membrane protein
21
Q
Anchored Membrane Proteins
A
- N-myristoylation at N-terminus Gly (amide)
- S-palmitoylation at Cys0-residue near C-terminus (thioester)
- S-prenylation at Cys residue of C-terminus (thioether)
- GPI at C terminus
22
Q
How to tell difference between the types of membrane proteins
A
- Remove peripheral proteins with change in salt concentration chelating agents or change in pH
- Remove anchored proteins with enzymes that the specific bond
- Remove integral membrane proteins with detergents
23
Q
Membrane Proteins vs Soluble Proteins
A
- Different distribution of hydrophobic amino acids
- Hydrophobic amino acids are also on the outside of the protein structure where they come in contact with the alkyl chains of the membrane
24
Q
Transmembrane helices
A
- Membrane is 7-10 nm thick
- 3.6 residues in a-helical conformation to span the membrane
- Approximately 40 residues
