Ch. 5: Lipid Structure and Function Flashcards
lipids are a major component of one of the most important structural parts of the cell, which is …
the phospholipid bilayer
what 2 things does the unique ability of phospholipids to form a bilayer allow for?
- allows our cell to function as they do
- separates the cell interior from the surrounding environment
each of the membrane components is an amphipathic molecule, define amphipathic
it has both hydrophilic and hydrophobic regions
for membrane lipids, what is the hydrophilic region and what is the hydrophobic region
hydrophilic: polar head
hydrophobic: fatty acid tails
what happens to membrane lipids when placed in aqueous solution?
they spontaneously form structures that allow the hydrophobic regions to group internally while the hydrophilic regions interact with water
this leads to the formation of various structures, including liposomes, micelles, and the phospholipid bilayer
what are phospholipids composed of? (4)
- a phosphate + 2. an alcohol –> comprise the polar head group
joined to a 3. hydrophobic fatty acid tail by 4. phosphodiester linkages
one or more fatty acids are attached to a backbone to form the hydrophobic tail region
how can phospholipids be further classified?
according to the backbone on which the molecule is built
are all sphingolipids phospholipids?
no
what are lipid properties determined by?
the degree of saturation in fatty acid chains and the functional groups to which the fatty acid chains are bonded
how do the hydrocarbon chains (long-chain fatty acids) of lipids differ? (2)
what do these characteristics determine?
- degree of saturation
- length
determine how the overall molecule will behave
how will fully saturated fatty acids behave? (4)
- will only have single bonds
- have greater van der Waals forces
- have a more stable overall structure
- they form solids at room temperature
when is the carbon atom in a fatty acid considered saturated?
when it is bonded to four other atoms, with no pi bonds
how do unsaturated fatty acids behave? (3)
- includes one or more double bonds
- double bonds introduce kinks into the fatty acid chain, making it difficult for them to stack and solidify
- tend to be liquids at room temperature
how do unsaturated fatty acids behave in the phospholipid bilayer?
phospholipids with UNsaturated fatty acid tails make up more FLUID regions of the phospholipid bilayer
what determines the properties of phospholipids, glycerophospholipids, and sphingolipids at the surface of the cell membrane? (2)
- a variety of fatty acid tails
- different head groups
defn + aka + 2 ex + char (2) + diagram: glycerophospholipids
aka: phosphoglycerides
defn: the phospholipids that contain a glycerol backbone bonded by ester linkages to two fatty acids and by a phosphodiester linkage to a highly polar head group
ex: phosphatidylcholine is a glycerophospholipid with a choline head group; phosphatidylethanolamine is a glycerophospholipid with a ethanolamine head group
char: 1. the head group can be positively charged, negatively charged, or neutral
2. their membrane surface properties make them very important to cell recognition, signaling, and binding
3. fatty acid chains of varying length and saturation, results in a variety of functions
what is the ABO blood typing system based on?
cell-surface antigens on red blood cells
what group of lipids do these cell-surface antigens belong to?
they are some of the most well-known sphingolipids!
defn + char: sphingolipids
defn: have a sphingosine or sphingoid (sphingosine-like) backbone and have long-chain, nonpolar fatty acid tails and polar head groups
char: 1. sites of biological recognition at the cell surface
2. can be bonded to various head groups and fatty acids
what makes a sphingolipids also a phospholipid?
containing a phosphodiester linkage
defn: glycolipid
any lipid linked to a sugar
why are some sphingolipids considered to be glycolipids?
because they contain glycosidic linkages to sugars
what are the four major subclasses of sphingolipids and what do they differ by? + diagram
differ by head group
- ceramide
- sphingomyelins
- glycosphingolipids
- gangliosides
what is the simplest sphingolipid? what is its head group?
ceramide
a single H is its head group
char (5): sphingomyelins
- the major class of sphingolipids that are also phospholipids (sphingophospholipids)
- have either phosphocholine or phosphoethanolamine as a head group
- contain a phosphodiester bond
- head groups have no net charge
- are major components in the plasma membranes of cells producing myelin (oligodendrocytes and Schwann cells)
char (3) + aka: glycosphingolipids
aka: glycolipids
- head groups composed of sugars bonded by glycosidic linkages
- not phospholipids (do not contain a phosphodiester linkage)
- found mainly on the outer surface of the plasma membrane
how can glycosphingolipids be further classified? (2)
- cerebrosides
- globosides
defn: cerebroside vs. globoside
cerebroside = has a single sugar
globoside = has 2 or more sugars
what else are cerebrosides and globosides referred to as?
neutral glycolipids because they have no net charge at physiological pH
char (3) + func: gangliosides
- the most complex sphingolipids
- have polar head groups composed of oligosaccharides with one or more N-acetylneuraminic acid (NANA; aka sialic acid) molecules at the terminus and a negative charge
- considered glycolipids because they have a glycosidic linkage and no phosphate group
func: major role in cell interaction, recognition, and signal transduction
mnemonic for gangolioside structure
GANGLIosides are the GANGLY sphingolipids with the most complex structure and functional groups (oligosaccharides and NANA) in all directions
defn: waxes
esters of long-chain fatty acids with long-chain alcohols
char + func: waxes
form pliable solids at room temp (what we think of as wax)
function as protection for plants and animals
how do waxes work in plants and in animasl?
plants: secreted as a surface coating to prevent excessive evaporation and to protect against parasites
animals: secreted to prevent dehydration, as a water-repellant to keep skin and feathers dry, and as a lubricant
what about waxes makes them good for structure building? (such as bees building honeycombs)
the solid and plastic nature of waxes which contain esters with long alkyl chains
what active roles do lipids have? (5)
- serve as coenzymes in the electron transport chain and in glycosylation reactions
- function as hormones that transmit signals over long distances
- function as intracellular messengers responding to extracellular signals
- certain special lipids with conjugated double bonds absorb light
- certain special lipids act as pigments
what 4 important categories of signaling lipids should we focus on?
- steroids
- prostaglandins
- fat soluble vitamins
- precursors (like terpenes)
defn: terpenes
defn: a class of lipids built from isoprene (C5H8) moieties and share a common structural pattern with carbons grouped in multiples of 5
odiferous chemicals that are the metabolic precursors to steroids and other lipid signaling molecules and have varied independent functions
char (3): terpenes
- produced by plants and some insects
- generally strong scented
- sometimes part of the plant or insect’s protective mechanism
how are terpenes grouped?
according to the number of isoprene units present
a single terpene unit contains 2 isoprene units
defn + func: monoterpenes
C10H16
terpenes that contain two isoprene units
abundant in essential oils and turpentine
defn: sesquiterpenes
terpenes that contain 3 isoprene units
sesqui- = one and a half
defn + example: diterpene
terpenes that contain 4 isoprene units
vitamin A
defn + func: triterpenes
terpenes with 6 isoprene units
can be converted to cholesterol and various steroids
defn + aka + 2 ex: carotenoids
aka: tetraterpenes
terpenes with 8 isoprene units
ex: beta-carotene, lutein
what type of terpene is natural rubber and why?
a polyterpene
because it has isoprene chains between 1000 and 5000 units long
defn + aka: terpenoids
aka: isoprenoids
derivatives of terpenes that have undergone oxygenation or rearrangement of the carbon skeleton
char (4): terpenoids
share similar characteristics with terpenes
- biological precursor function
- aromatic properties
- contribute to steroid biosynthesis
- contribute to the scents of cinnamon, eucalyptus, camphor, turmeric, and others
how are terpenoids named?
in the same fashion as terpenes (diterpenoids derive from 4 isoprene units, etc.)
defn + char (2) + structure: steroids
metabolic derivatives of terpenes
- characterized by having 4 cycloalkane rings fused together (3 cyclohexane, 1 cyclopentane)
- nonpolar because of the large number of C’s and H’s
what is steroid functionality determined by?
the oxidation status of these rings and the functional groups they carry
defn: steroids vs. steroid homrones
STEROID = a group defined by a chemical structure
STEROID HORMONES = steroids that ACT as hormones
defn + func: steroid hormones
steroids that act as hormones (they are secreted by endocrine glands into the bloodstream and then travel on protein carriers to distant sites, where they can bind to specific high-affinity receptors and alter gene expression levels)
potent biological signals that regulate gene expression and metabolism, affecting a wide variety of biological systems even at low concentrations
what are 4 important steroid hormones to remember?
- testosterone
- various estrogens
- cortisol
- aldosterone
defn + func (3) + char + diagram: cholesterol
defn: an important steroid that is func: 1. a major component of the phospholipid bilayer and 2. is responsible for mediating membrane fluidity
char: it is an amphipathic molecule containing both hydrophilic and hydrophobic components
func: 3. also serves as a precursor to many important molecules including steroid molecules, bile acids, and vitamin D
what do interactions with both the hydrophobic tails and hydrophilic heads of phospholipids allow cholesterol to do? how does this alter with temperature?
to maintain relatively constant fluidity in cell membranes
LOW temp: it keeps the cell membrane from solidifying
HIGH temp: holds the membrane intact and prevents it from becoming too permeable
defn: prostaglandins
20-C molecules that are unsaturated carboxylic acids derived from arachidonic acid and contain one 5-C ring
func (2): prostaglandins
- act as paracrine or autocrine signaling molecules
- regulate the synthesis of cAMP in many tissues (which then mediates the actions of many other hormones)
what are some downstream effects of prostaglandins?
- powerful effects on smooth muscle function
- influence over the sleep-wake cycle
- elevation of body temperature associated with fever and pain
how does NSAIDs (nonsteroidal anti-inflammatory drugs) like aspirin affect the production of prostaglandins?
NSAIDs inhibit the enzyme cyclooxygenase which aids in the production of prostaglandins
defn: vitamin
an essential nutrient that cannot be adequately synthesized by the body and therefore must be consumed in the diet
defn: water-soluble vs. lipid-soluble vitamins
lipid-soluble vitamins = can accumulate in stored fat
water-soluble vitamins = excreted through urine
what are the 4 fat-soluble vitamins?
- A
- D
- E
- K
defn + aka: vitamin A
aka: carotene
an unsaturated hydrocarbon that is important in vision, growth and development, and immune function
defn: retinal
the most significant metabolite of vitamin A, the aldehyde form
a component of the light-sensing molecular system in the human eye
defn: retinol
the storage form of vitamin A
defn: retinoic acid
the oxidized form of retinol
a hormone that regulates gene expression during epithelial development
defn + aka: vitamin D
aka: cholecalciferol
can be consumed in a UV light-driven reaction in the skin
what is vitamin D converted to in the liver and kidneys?
calcitriol (1,25-(OH)2D3)
defn + func: calcitriol
defn: the biologically active form of vitamin D
func: increases calcium and phosphate uptake in the intestines which promotes bone production
what can a lack of vitamin D result in?
rickets, a condition seen in children characterized by underdeveloped, curved long bones as well as impeded growth
mnemonic: carotene
carrots are high in vitamin A, which is why eating carrots is colloquially suggested to improve vision
mnemonic: vitamin D
regulates calcium
it is frequently added to milk in order to aid in the absorption of calcium
defn: vitamin E
a group of closely related lipids called tocopherols and tocotrienols characterized by a substituted aromatic ring with a long isoprenoid side chain and are characteristically hydrophobic
defn: tocopherols
biological antioxidants
what happens to the aromatic rings of tocopherols? what is the impact of this?
the aromatic ring reacts with free radicals, destroying them
this, in turn, prevents oxidative damage, an important contributor to the development of cancer and aging
mnemonic: vitamin K
vitamin K is for Koagulation
defn + func (2): vitamin K
a group of compounds including phylloquinone (K1) and the menaquinones (K2)
func: 1. vital to the posttranslational modifications required to form prothrombin, an important clotting factor in the blood
- required to introduce calcium-binding sites on several calcium-dependent proteins
what happens to the aromatic ring in vitamin K?
it undergoes a cycle of oxidation and reduction during the formation of prothrombin
defn: triacylglycerols
a class of lipids specifically used for energy storage
what are the 2 reasons for which lipids in general are a fantastic way for the body to store energy?
- the C atoms of fatty acids are more reduced than those of sugars, which contain numerous alcohol groups –> thus the oxidation of triacylglycerols yields twice the amount of energy per gram as carbohydrates, making this a far more energy-dense storage mechanism compared to polysaccharides like glycogen
- triacylglycerols are hydrophobic –> they do not draw in water and do not require for hydration for stability –> this helps decrease their weight, especially in comparison to hydrophilic polysaccharides
what is an added benefit of lipids as a way to store energy for vertebrates surviving in colder temperatures?
the layer of lipids serves a dual purpose of energy storage and insulation –> it helps to retain body heat so that less energy is required to maintain a constant internal temperature
aka + structure + diagram + char (3): triacylglycerols
aka: triglycerides
composed of 3 fatty acids bonded by ester linkages to glycerol
char: 1. overall nonpolar
2. overall hydrophobic
3. insoluble in water
are the 3 fatty acids that make up a triacylglcyerol the same?
for most naturally occurring triacylglycerols, it is rare for all 3 fatty acids to be the same
why are triacylglycerols insoluble in water?
the polar hydroxyl groups of the glycerol component and the polar carboxylates of fatty acids are bonded together, decreasing their polarity
how are triacylglycerol deposits observed in cells? what is the function of these deposits?
as oily droplets in the cytosol
func: serve as depots of metabolic fuel that can be recruited when the cell needs additional energy to divide or survive when other fuel supplies are low
defn + func + loc (3): adipocytes
special cells in animals
store large amounts of fat
are found primarily under the skin, around mammary glands, and in the abdominal cavity
how are triacylglycerol desposits found in plants?
in seeds as oils
how do triacylglycerols travel in the bloodstream?
bidirectionally between the liver and adipose tissue
what are the physical characteristics of triacylglycerols determined by?
the saturation (or unsaturation) of the fatty acid chains that make them up
defn + how do they move in the body: free fatty acids
unesterified fatty acids with a free carboxylate group
circulate in the blood bonded noncovalently to serum albumin
defn: saponification
the production of soap through fatty acids
chem: the ester hydrolysis of triacylglycerols using a strong base
defn/func + chem name: lye
the base that is used in saponification
sodium or potassium hydroxide
process (4) + diagram: saponification
- the ester hydrolysis of triacylglycerols using a strong base
- this results in the basic cleavage of the fatty acid
- which leaves the sodium salt of the fatty acid and glycerol
- this fatty acid salt is soap
defn: surfactant
lowers the surface tension at the surface of a liquid, serving as a detergent or emulsifier
Soap can act as a surfactant. Explain how soap works.
- If we try to combine an aqueous solution and oil, as with vinegar and olive oil in salad dressing, theses solutions will remain in separate phases
- if we were to add soap, however, the two phases would appear to combine into a single phase, forming a colloid
- this occurs because of the formation of micelles: tiny aggregates of soap with the hydrophobic tails turned inward and the hydrophilic heads turned outward, thereby shielding the hydrophobic lipid tails and allowing for overall solvation
