Unit 3.3 (lipids) Flashcards
What is a Lipid?
A hydrophobic biological substance that has a much higher affinity for an organic solvent than for water (many lipids are amphipathic)
What are the 7 classes of lipds?
(1) Fatty Acids
(2) Biological Waxes
(3) Triacylglycerols (TAGs)
(4) Glycerophospholipids
- Ether Glycerophospholipds
- Plasmalogens
- Liposomes (man made)
(5) Sphingolipids
- Sphingomyelins
- Gangliosides
(6) Terpenoids
(7) Steroids
- Cholesterol
- Bile Salts
Define (1) Fatty Acids
Long chain carboxylic acids (usually an even # of carbons)
Can be saturated or unsaturated
Define (2) Biological Waxes
What are some examples of biological waxes?
Waxes are nonpolar esters of fatty acids and long chain alcohols
Ex. Animal skin, leaves of plants, bird feathers, beeswax
Define (3) Triacylglycerols
Are these molecules hydrophobic?
Made from esterification of 3 fatty acids + glycerol
Charges neutralized = completely hydrophobic
What kinds of cells store fat?
Adipocytes
Describe the difference between “Delta Nomenclature” and “w Nomencalture” for Fatty Acids
What is significant about Linoleic acid and Linolenic Acid?
They are both essential fatty acids (EFAs) & must be obtained from diet
Are saturated or unsatured fats “more healthy” for you?
Unsaturated fats
Describe Triglyceride (TAG) Nomenclature
What enzymes store Triglycerides (TAGs)?
What process produces energy for the glycerol portion of TAGs? What about the Fatty Acid portion?
What are advantages/disadvantages for TAGs relative to carbohydrates?
Lipases store TAGs (break TAG ester bond)
Glycerol - Glycolysis ….. Fatty Acids - TCA
Advantages Relative to Carbs:
More energy/gram (9 vs. 4 kcal/g)
Can store without water in adipocytes
Disadvantages relative to Carbs:
Takes longer to “access” the stored energy
Describe the Process of Saponification
Result in 1-tail amphipiles! (forms micelles)
Define (4) Glycerophospholipids
Like TAGS, but have C3 phosphoester instead of acyl ester (2 tailed amphipiles)
In general …. C1 esterified to saturated fatty acid & C2 esterified to unsaturated fatty acid (C2 is longer)
What is one very important Glycerophospholipid? Why is it important?
Dipalmitoylphosphatidylcholine (DPPC)
Lung Surfactant!
- Decreases the surface tensions of the liquid
coating the alveoli
- Prevents alveoli from collapsing due to water
tension
What is the difference between (4) Glycerophospholipids and “Ether Glycerophospholipids”?
“Ether Glycerophospholipids have an ether group instead of an acyl group at C-1
What are two examples of “Ether Glycerophospholids”? Why are important?
(1) Platelet Activating Factor
Short acetate chain at C2
Potent & versatile biochemical signal molecule
(2) Plasmalogens
~50% of the heart phospholipids are plasmalogens
Most common head groups are phosphoserine, phosphocholine, and phosphoethanolamine
Which kind of lipids are most abundant in bilayer membranes? Why?
(4) Glycerophospholipids (aka phosphoglycerides)
They are 2-tailed amphipiles (these make bilayer membranes)
What are Liposomes? What are they used for? What are they made of?
Liposomes = artificial bilayer vesicles
Often made from glycerophospholipids
Delivery vehicle: Can be used to get hydrophilic drugs into cell
Define (5) Sphingolipids
Weird! (have Nitrogen and TRANS bonds)
18 Carbon AMINO alcohol
What are the 5 major types of Sphingolipids?
- Ceramide
- Sphingomyelin
- Cerebroside
- Globoside
- Ganglioside
Describe “Sphingomyelins” (a type of (5) sphingolipid)
What are they useful for?
Contain phosphocholine or phosphoethanolamine as their polar head group
Prominent in the MYELIN SHEATH - the membrane that surround and insulates the axons of neurons
Where are Cell Membrane Carbohydrates attached to? What is their purpose?
Attached to cell membrane proteins (glycoproteins) and cell membrane lipids (glycolipids) - Face outside of cell
*Mediate cell-cell interactions & serve as attachment points for bacteria, viruses, toxins, signaling hormones, etc.
What kinds of genetic diseases are associated with (5) Sphingolipids? Describe how these work.
- Sphingolipids are broken down by catabolic enzymes
- Genetically acquired absence of one of these enzymes (hexoaminadase) leads to disease
- This leads to accumulation of gangliosides in the cell, with severe medical consequences (Tay-Sacchs Disease)
Define (6) Terpenoids
Lipids built from ISOPRENE units, rather than fatty acids
Where are Terpenoids typically found in nature?
- Archael Cell Membranes (extremephiles)
- Many Vitamis (A, D, E, K) are isoprenoids
What are Vitamins?
Isoprenoids
Vitamins are compounds that are essential to the health of humans and other vertebrates that cannot be synthesized and must be obtained in the diet
Describe (in detail) Cholesterol Biosynthesis
Define (7) Steroids
Characterized by “steroid nucleus” (cholesterol)
*Mostly nonpolar, mostly water insoluble
*Planar Rings (steric rigidity)
What kinds of lipids are used for Endocrine Signaling? Describe Endocrine Signaling.
(7) Steroids
Endocrine Signaling - messengers secreted by glands and carried through the bloodstream to DISTANT target tissues
Where are (7) Protein receptors located?
On the CYTOPLASMIC side of the cell membrane
Are bacteria able to synthesize (7) Steroids?
No, bacteria do not have cholesterol
What is Vitamin D3? What is its function?
A steroid hormone (thus terpenoid)
Regulates Ca2+ metabolism
Describe “Bile Salts”
Oxidative derivatives of Cholesterol (7 - steroid)
Bile salts are amphipathic detergents (have a polar head and steroid backbone)
What are “Bile Salts” important for?
Aid in DIGESTION by dissolving fats in the small intestine and allowing absorption into the blood
What is important for Cholesterol Transport in the blood stream? (be specific, describe this mechanism)
What are Lipoproteins? What are they used for? How do they work?
Lipoproteins: Lipid Transport in blood circulation
TAGs & Cholesterol are insoluble in plasma …….
Lipoproteins are hydrophobic proteins that engulf TAGS and cholesterol so they can be transported in the blood stream
How are Lipoproteins classified? What is the order of this classification?
By Density!!!
Where is the role of Chylomicrons in TAG/chol transport?
Transport TAG + Chol from intestines to liver
Transport TAGs from intestines to muscle & adipose
What is the difference between “Low Density Lipoproteins” and “High Density Lipoproteins”?(particularly regarding their function)
Describe how a heart attack is caused.
Summarize (in detail) the transport of cholesterol in the blood
What are Phospholipases?
Enzymes that hydrolize the ester/phosphoester bonds of phospholipids (named by which ester bond hydrolyzed)
Where are Phospholipases found in nature? How do these work?
Venoms of poisonous snakes contain phospholipases
Reaction produces a lysophospholipid - acts as a detergent that dissolves RBC membranes, causing them to rupture
What are Eicosanoids? What is their function?
Eicosanoids are derivatives of arachidonic acid released by enzymatic cleavage from membrane phospholipids
Eicosanoids are PARACRINE HORMONES
= Hormones that have an effect on cells near where they have been synthesized (localized signaling)
What are NSAIDs? Give examples.
Non-steroidal Anti-inflammatory Drugs (Ibuprofen, Naproxen, etc.) - These are REVERSIBLE competitive inhibitors of COX (PGH2 Synthase)
How doe COX receptors work?
Whenever COX receptors bind to Eicosanoids, they produce increased body temp, inflammation, and pain
However, when COX is bound by NSAIDS, these symptoms are relieved
Which NSAID is an IRREVERSIBLE inhibitor of COX?
Aspirin (can be either a suicide inhibitor or a reactive substrate analog, depending on who you ask)
Who proposed the Fluid Mosaic Model?
Singer and Nicolson
What 2 phases is a biological membrane composed of?
- Continuous phase (fluid bilayer matrix)
- Discontinuous phase (proteins “floating” in the lipids)
What are the 3 different kinds of membrane proteins? How do you remove each one from the bilayer?
- Peripheral Membranes - bind via non-covalent interactions to membrane surface (easy to seperate from membrane … can be done by changing salt concentration, pH, or urea)
- Integral Membrane Proteins - have hydrophobic region that associated with membrane (hard to remove and difficult to solubize … can be done with detergents)
- Lipid Linked Proteins - Can be released from membrane by phospholipase
What are the 2 types of detergents that are used for studying membrane proteins? What is the difference between the two?
- SDS - ionic detergent that dissolves membranes and denatures proteins (removes both integral and peripheral proteins)
- Triton X-100 - Mild nonionic detergent that dissolves membranes without unfolding proteins (can sometimes be used to remove only peripheral proteins)
What is a Porin?
Porins act as pores through which small molecules can diffuse. Are prevalent in mitochondria and in the outer membrane
Describe Lipid & Protein Movement in the Fluid-Mosaic model
Lipids & Proteins can diffuse laterally & rotate, but CANNOT diffuse transversally through membrane (proteins move slower than lipids)
What experiment proves that lipids can diffuse laterally?
FRAP (Fluorescence Recovery After Photobleaching)
What are Flippases?
Enzymes that facilitate the lipids flipping from one layer to the other
Define “Transverse Asymmetry” of the Membrane Bilayer
Carbohydrates, lipids, and protein composition is different on either side of the membrane bilayer (all contribute to transverse asymmetry)
What phenomena contributes to Lateral Asymmetry in the membrane bilayer?
Lipid rafts - Unique domains of sphingolipids and steroids in the membrane (participate in recognition, signaling, etc)
What 3 factors contribute to lower melting point (less stable) Fatty Acids?
- Double bonds (unsaturation)
- Cis Bonds (less stable than trans)
- Shorter chains (less van der wals interactions)
Describe the Partial Hydrogenation of Unsaturated Fats. What does this lead to?
Partial Hydrogenation gives semi-solid fats, but leads to isomerization of the double bonds to give unnatural TRANS fatty acids
These increase LDLs and increase Coronary heart disease
Describe how Bilayer Membrane Fluidity is related to melting temperature.
How do cold-blooded animals & bacteria control their membrane fluidity?
They modify their membrane fatty acid composition with changing temperature to maintain fluidity.
How does Cholesterol affect membrane fluidity? Does this work in bacteria?
Describe the membrane permeability of small hydrophobic molecules, small uncharged polar molecules, larger uncharged polar molecules, and ions
What are Transport Proteins?
Span membrane & facilitate exclusive entry/exit of specific molecules (different membranes have different transport proteins which determine what can enter/exit)
What are the 3 “families” of Translocation Systems within membrane bilayers?
Define Passive Transport. What are the 2 kinds of Passive Transport? Define Active Transport
Describe how +/- Hydropathy values are related.
(+) = Hydrophobic
(-) = Hydrophilic
Describe how to read a Hydropathy Plot
(+) Hydropathy value indicates a Hydrophobic side chain. This means that the alpha helix associated with the membrane protein spans the bilayer
Define Lipid Linked (Anchored) Proteins
Lipid anchor is within the membrane, and it is able to reversibly anchor/de-anchor molecules
This is extremely important in controlling signaling pathways
