Lipids Flashcards
Fatty acids are
- water-insoluble hydrocarbons used for cellular energy storage.
- highly reduced and thus provide a rich source of stored chemical energy for cells.
- Storage of hydrophobic fats as triacylglycerols is also highly efficient because water is not needed to hydrate the stored fats.
Membrane lipids are:
- composed of hydrophobic tails attached to polar head groups.
- Cellular membranes are composed of a variety of lipids, including glycerophospholipids and sterols.
- These lipids are used for structuring membranes as well as for displaying molecules on the membrane surfaces for signaling and molecular recognition.
Many lipids are present in the cell at ________ amounts than those making up membranes or being stored as fat.
These lipids can function as:
smaller;
- cellular messengers
- hormones
- electron carriers
- pigments
The chemical properties of lipids are related to their __________ and _____________
structure and composition
Biological Lipids Features:
Lipids function are also diverse:
Biological lipids:
- Chemically diverse
- Generally insoluble in water.
Lipids functions are also diverse:
- Stored energy
- Components of biological membranes.
Other lipid functions:
- electron carriers
- hydrophobic anchors for proteins
- emulsifying agents in the digestive tract
- hormones
- intracellular messengers
Fatty acids are:
- Water-insoluble hydrocarbons with attached _______used for cellular energy storage
- Generally ________and thus provide a rich source of________
- Storage of hydrophobic fats (fatty acids) as triacylglycerols is not _______highly_______ because water is not needed to hydrate the stored fats
- COO-
- highly reduced; stored chemical energy
- hydrated; efficient
- fatty acids = ____________
- oxidation of fatty acids (to CO2 and H2O) is highly ______________
- hydrocarbon derivatives
- exergonic (energy producing)
fatty acids = __________ with hydrocarbon tails ranging from __ to ___ carbons long
- can be _______ or ______
- can be _______ or _______
carboxylic acids; 4 to 36 (C4 to C36)
- saturated or unsaturated
- branched or unbranched
Poor solubility in water dur to the ____________
- increased chain length _______ solubility
- decreased double bond number ________ solubility
carboxylic acid group is _______ and _______ at neutral pH
nonpolar hydrocarbon chain
- decreases
- decreases
polar and ionized
Nomenclature for Unbranched Fatty Acids
- the chain length and number of bonds, separated by a colon
- numbering begins at the carboxyl carbon
- positions of double bonds are indicated by ∆ and a superscript number
Common Patterns in Fatty Acids
- even numbers of carbon atoms (12 to 24 carbons)
- mostly straight chains
- Can be unsaturated
- if monounsaturated, the double bond is usually between C-9 and C-10 (∆9)
- if polyunsaturated fatty acids:
- the double bonds are usually ∆12 and ∆15
- double bonds are usually separated by a methylene group
- double bonds are usually in the cis configuration
Polyunsaturated Fatty Acids (PUFAs)
Contain more than one double bon in their backbone
- omega-3 (w-3) fatty acids= double bond between C-3 and C-4 relative to the most distant carbon (w)
- omega-6 (w-6) fatty acids= double bond betweeen C-6 and C-7 relative to w
humans must obtain the omega-3 PUFA α-linolenic acid (ALA; 18:3(∆9,12,15)) from_________
their diet
humans use ALA to synthesize:
- eicosapentaenoic acid (EPA; 20:5(∆5,8,11,14,17))
- docosahexaenoic acid (DHA; 22:6(∆4,7,10,13,16,19))
the optimal dietary ratio of omega-6 to omega-3 PUFAs is between _____ and _____
1:1 and 4:1
triacylglycerols are fatty acid esters or glycerol
- composed of three fatty acids in ester linkage with a single glycerol
- May consist of
- (one kind of fatty acid)
- mixed (two or three different fatty acids)
- non-polar, hydrophobic
Triacylglycerols Provide ________________
- Stored Energy and Insulation
- vertebrates store triacylglycerols as lipid droplets in adipocytes (fat cells)
- plants store triacylglycerols in the seeds
Advantages of Using Triacylglycerols as Stored Fuels
- Generally highly or more reduced state
- Stored in unhydrated form
Lipases
enzymes that catalyze the hydrolysis of stored triacylglycerols, releasing fatty acids for export to sites where they are required as fuels
adipocytes and germinating seeds contain lipases
Dietary intake of _________ is linked to a higher incidence of cardiovascular disease
trans fatty acids
trans fatty acids do what?
- raise the level of triacyglycerols in the blood
- raise the level of LDL (“bad”) cholesterol in the blood
- lower the level of HDL (“good”) cholesterol
- increase the body’s inflammatory response
- Double layer of lipids that acts as a barrier to polar molecules and ions
- amphipathic
- hydrophobic regions associated with each other
- hydrophilic regions associate with water
- biological membranes
- membrane lipids
Four general types of membrane lipids
- phospholipids = have hydrophobic regions composed of two fatty acids joined to glycerol or sphingosine
- glycolipids = contain a simple sugar or a complex oligosaccharide at the polar ends
- archaeal tetraether lipids = have two very long alkyl chains ether-linked to glycerol at both ends
- sterols = compounds characterized by a rigid system of four fused hydrocarbon rings
Derivatives of phosphatidic acid
glycerophospholipids
glycerophospholipids
- two fatty acids are attached in ester linkage to the first and second carbons of glycerol
- a highly polar or charged group is attached through a phosphodiester linkage to the third carbon
The Fatty Acids in Glycerophospholipids
- can be any of a wide variety
- in general, glycerophospholipids contain:
- a C16 or C18 saturated fatty acid at C-1
- a C18 or C20 unsaturated fatty acid at C-2
In glycerophospholipids a phosphodiester bond joins the head group to __________
The phosphate group can bear a __________ charge
glycerol
negative, neutral, or positive charge
ether lipids
one of the two acyl chains is attached to glycerol in ether
- chain may be saturated
- chain may contain a double bond between C-1 and C-2 as in plasmalogens
platelet-activating factor
an ether lipid that serves as a potent molecular signal
- releases from leukocytes called basophils
- stimulates platelet aggregation and serotonin release
- plays a role in inflammation and the allergic response
sphingolipids
class of membrane phospholipids and glycolipids
- have a polar head group and two nonpolar tails
- contain no glycerol
- contain one molecule of the long-chain amino alcohol sphingosine or one of its derivatives
ceramide
compound resulting when a fatty acid is attached in amide linkage to the NH2 on C-2
structurally similar to a diacylglycerol
Ceramides are the structural parent of all sphingolipids
C-1, C-2, and C-3 of sphingosine are structurally analogous of the three carbons of glycerol in glycerophospholipids
sphinogomyelins
subclass of sphingolipids that contains:
- phosphocholine or
- phosphoethanolamine as their polar head group
glycosphingolipids
have head group consist of one or more sugars connnected directly to the -OH at C-1 of the ceramide moiety
- do not contain phosphate
- occur largely in the outer fce of plasma membranes
cerebrosides
have a single sugar linked to ceramide
- those with galactose are found in the plasma membranes of cells in neural tissue
- those with glucose are found in the plasma membranes of cells in nonneural tissues
globosides
glycosphingolipids with 2 or more sugars, usually D-glucose, D-galactose, or N-acetyl-D-galactosamine
sometimes called neutral glycolipids, as they have no charge at pH 7
gangliosides
- oligosaccharides as their polar head groups and
- 1 or more residues of N-acetylneuraminic acid (Neu5Ac), a sialic acid, at the termini
- 1 sialic acid residue = GM (M for mono-) series
- 2 sialic acid residues= GD (D for di-) series
- 3 sialic acid residues= GT (T for tri-) series (and so on)
Sphingolipids at cell surfaces are sites of
biological recognition
- prominent in the plasma membranes of neurons
- human blood groups (O, A, B) are determined in part by the oligosaccharide head groups of these glycosphingolipids
Phospholipids and Sphingolipids Are Degraded in Lysosomes
Phospholipid degradation…
- phospholipases of the A type remove one of the two fatty acids
- lysophospholipases remove the remaining fatty acid
- lysosomal enzymes catalyze the stepwise removal of sugar units of gangliosides
Abnormal Accumulations of Membrane Lipids
genetic defects in any of these hydrolytic enzymes leads to the accumulation of gangliosides in the cell
Sterols:
Steroid nucleus:
structural lipids present in the membranes of most eukaryotic cells
- Steroid nucleus:
- consists of four fused rings
- almost planar
- relatively rigid
cholesterol
major sterol in animal tissues
- amiphipathic
- polar head group
- nonpolar hydrocarbon body
- membrane constituents
polar derivatives of cholesterol that emulsify dietary fats in the intestine to make them more readily accessible to digestive lipases
bile acids
Sterols Serve as Precursors for Products with Specific Biological Activities
- steroid hormones
- regulate gene expression
- bile acids
steriods
oxidized derivates of sterols
- lack the alkyl chain attached to ring D of cholesterol
- more polar than cholesterol
steriod hormones move through the bloodstream (on protein carries) to target tissues binding to highly specific receptor proteins in the nucleus which triggers changes in
gene expression
Steroids derived from cholesterol
- Testosterone
- Male sex hormone produced in the testes
- Cortisol
- Hormone produced in the adrenal cortex; regulates glucose metabolism
- Prednisone
- Synthetic steroid used as an anti-inflammatory agent
- Beta-Estradiol
- Female sex hormone produced in the ovaries and placenta
- Aldosterone
- Hormone produced in the adreanl cortex; regulates salt excretion
- Brassinolide ( a brassinosteroid)
- Growth regulator found in vascular plants
Vitamin D3 (cholecalciferol)
formed in the skin from 7-dehydrocholesterol in a photochemical reaction driven by the UV component of sunlight
- not biologically active
- converted by enzyme in the liver and kedney to calcitriol
calcitrol
hormone that regulates calcium uptake in the intestine and calcium levels in the kidney and bone
Phosphatidylinositols and Sphingosine derivatives act as _____________
intracellular signals
phosphatidylinositol (PI) and its phosphorylated derivatives regulate cell structure and metabolism
in the cytoplasmic face of plasma membranes ____________serves as a reservoir of messenger molecules that are released in response to extracellular signals
Phosphatidylinositol 4,5-Bisphosphate (PIP2)
phospholipase C hydrolyzes PIP2 to IP3 and diacylglycerol (intracellular messengers)
ceramide and sphingomyelin are potent regulators of __________
ceramide or its derivatives are involved in the regulation of:
protein kinases
- cell division
- differentiation
- migration
- programmed cell death
Eicosanoids Carry Messages to Nearby Cells
eicosanoids =
involved in:
paracrine hormones, substances that act only on cells near the point of synthesis instead of being transported in the blood
involved in:
- reproductive function
- inflammation, fever, and pain associated with injury or disease
- formation of blood clots
- regulation of blood pressure
- gastric acid secretion
Eicosanoids are derived from
arachidonic acid
four major classes of eicosanoids
- prostaglandins
- thromboxanes
- leukotrienes
- lipoxins
prostaglandins (PG)
functions:
class of eicosanoids that contain a five-carbon ring
array of functions:
- stimulate contraction of the smooth muscle of the uterus
- affect blood flow to specific organs, the wake-sleep cycle, and the responsiveness of certain tissues to hormones
- elevate body temperature and cause inflammation and pain
thromboxanes (TX)
class of eicosanoids that have a six-membered ring containing an ether
produced by platelets (also called thrombocytes)
act in the formation of blood clots and reduction of blood flow to the site of a clot
Leukotrienes (LT)
- class of eicosanoids that contain three conjugated double bonds
- powerful biological signals
- leukotriene D4 induces contraction of the smooth muscle lining the airways to the lung
Lipoxins (LX)
- class of eicosanoids that are linear and contain several hydroxyl groups along the chain
- potent anti-inflammatory agents
