Chapter 5: Lipid Structure and Function Flashcards
What is an amphiphatic molecule?
Contains hydrophilic and hydrophobic regions
What are the three types of structures membrane lipids can form in aqueous solutions?
- Liposome
- Micelle
- Phospholipid bilayer
What do phospholipids contain?
- Polar head group: phosphate and alcohol
- Hydrophobic tail: fatty acid
What is the linkage that joins the polar head group to the fatty acid tail in phospholipids?
Phosphodiester linkage
If a phospholipid has a glycerol backbone, what is its name?
Phosphoglyceride or glycerophospholipid
If a phospholipid has a sphingosine backbone, what is its name?
Sphingolipids
Can all sphingolipids be defined as phospholipids?
No
Differentiate saturated and unsaturated fatty acids.
Saturated: only single bonds
Unsaturated: one or more double bonds
When is a carbon atom considered to be saturated?
When it is bonded to four other atoms, with no pi bonds
Which type of fatty acid has greater Van der Waals force? Which type of fatty acid has kinks? Which type of fatty acid is liquid at room temperature?
- Van der Waals: saturated
- Kinks: unsaturated
- Liquid: unsaturated
Are all glycerophospholipids phospholipids?
Yes
What is the structure of glycerophospholipids?
- Glycerol backbone bound by ester linkages to two fatty acids
- Glycerol backbone bound by a phosphodiester linkage to a highly polar head group
How are glycerophospholipids named?
According to their head group since they determine the membrane’s surface properties
What is phosphatidylcholine?
Glycerophospholipid with a choline head group
Are all sphingolipids phospholipids?
- Many, but not all (sphingophospholipids containing a phosphodiester bond)
- Can also be glycolipids (glycosidic linkages to sugars)
What is the simplest sphingolipid? What is its head group?
- Ceramide
- Single hydrogen atom at its head group
Which sphingolipid is a major component of myelin sheaths?
Sphingomyelin
What are sphingomyelins? What are their head groups? What is their linkage? What is the charge of the head group?
- Major class of sphingophospholipids
- Phosphatidylcholine or phosphatidylethanolamine head group
- Phosphodiester bond
- Head group has no net charge
What are glycosphingolipids? What are their head groups? What is their linkage?
- Glycolipids
- Sugars
- Glycosidic linkage
Where are glycosphingolipids mainly found in terms of the plasma membrane?
Outer surface of the plasma membrane
What are the two classification of glycosphingolipids?
- Cerebrosides
- Globosides
Differentiate cerebrosides and globosides.
Cerebrosides: one sugar connected to sphingosine
Globosides: two or more sugars connected to sphingosine
Why can cerebrosides and globosides be referred to as neutral glycolipids?
They have no net charge at physiological pH
What are gangliosides? What is their head group composed of? What is the charge of the head group?
- Glycolipids
- Polar head groups composed of oligosaccharides with one or more NANA molecules at the terminus
- Negative charge
Do gangliosides possess a glycosidic linkage or a phosphodiester linkage?
Glycosidic
Which sphingolipid is the most complex?
Gangliosides
What does NANA mean? What is it also called?
N-acetylneuraminic acid (sialic acid)
ABO blood typing system is based on cell-surface antigens on red blood cells, which are examples of which lipid?
Sphingolipids
What are the major roles of gangliosides?
Major role in cell interaction, recognition, and signal transduction
What are waxes?
Long-chain fatty acids esterified to long-chain alcohols
What is the major role of waxes?
Used as protection against evaporation and parasites in plants and animals
What components of membrane lipids contribute to their function?
- Polar head group
- Degree of unsaturation of fatty acid tails
What is the difference between a sphingolipid that is also a phospholipid and one that is NOT?
- The bond between the sphingosine backbone and the head group
- Phospholipid: phosphodiester bond
- Glycolipids: glycosidic bond
What would happen if an amphiphatic molecule were placed in a nonpolar solvent rather than an aqueous solution?
The opposite of what would happen in water: polar part of molecules on the inside, nonpolar part on the outside
In what way do lipids serve as coenzymes?
In the electron transport chain and in glycosylation reactions
What kind of special lipids can absorb light?
Lipids with conjugated double bonds
Terpenes are a class of lipids build from ______ moieties and share a common structural pattern with carbons grouped in multiples of ____
- isoprene (C5H8)
- 5
Which odiferous chemicals are the metabolic precursors to steroids and other lipid signaling molecules?
Terpenes
What does odiferous mean? Give an example of an odiferous compound.
- Something that carries a smell
- Terpenes
What is one terpene unit called? How many isoprene units does it contain?
- Monoterpene
- 2 isoprene units
How are terpenoids derived from terpenes?
- Via oxygenation or backbone rearragement
- Similar odorous characteristics
What are terpenes mainly produced by?
- Plants and some insects
- In some cases, pungent chemicals are part of the plant or insect’s protective mechanism
How many isoprene units do sesquiterpenes, diterpenes and triterpenes?
Sesquiterpenes: 3
Diterpenes: 4
Triterpenes: 6
Vitamin A is a ______ from which retinal is derived
diterpene
Carotenoids are _______ and have eight isoprene units
tetraterpenes
Terpenes get their name from their original discovery in what?
Turpentine
What is the general structure of a steroid? What are they derivates of?
- Derivatives of terpenes
- Three cyclohexane rings and one cyclopentane ring
What is steroid functionality determined by? (2)
- The oxidation status of the rings
- The functional groups that the rings carry
What are steroid hormones? Give examples.
- High-affinity receptors, work at low concentrations, and affect gene expression and metabolism
- Testosterone, various estrogens, cortisol, aldosterone
What is cholesterol a major component of? What is its role?
- Major component of the phospholipid bilayer
- Responsible for mediating membrane fluidity
Is cholesterol a hydrophilic or hydrophobic molecule?
Neither, it is amphiphatic
What allows cholesterol to maintain relatively constant fluidity in cell membranes?
Interactions with both the hydrophobic tails and hydrophilic heads of phospholipids
What does cholesterol do at low temperatures? What does it do at high temperatures? With this in mind, what is it also referred as?
- Fluidity buffer
- Low temperature: keeps the cell membrane from solidifying
- High temperature: holds the membrane intact and prevents it from becoming too permeable
Steroid hormones, bile acids, and vitamin D are derived from which precursor?
Cholesterol
How did prostaglandins acquire their name?
They were first thought to be produced by the prostate gland
Where are prostaglandins produced from?
Produced by almost all cells in the body
How many carbons do prostaglandins contain? What are they derived from?
- 20 carbons
- Arachidonic acid
What is the general structure of prostaglandins?
- Unsaturated carboxylic acids
- Contain one five-carbon ring
Prostaglandins act as ____ or _____ hormones
paracrine or autocrine
What is the biological function of prostaglandins? What does it regulate?
Regulates the synthesis of cyclic adenosine monophosphate (cAMP)
What is cAMP? What is its role?
Ubiquitous intracellular messenger that mediates the actions of many other hormones
What is the relationship between aspirin and prostaglandins?
Aspirin inhibits the enzyme cyclooxygenase (COX), which aids in the production of prostaglandins
Which lipid has powerful effects on muscle contraction, body temperature, the sleep-wake cycle, and pain?
Prostaglandins
What are the fat-soluble vitamins? Where do they accumulate?
- A, D, E, K
- Accumulate in stored fat
What is vitamin A important in? What is its other name?
- Carotene
- Important in vision, growth and development, and immune function
What is the most significant metabolite of vitamin A? What form is it in?
- Retinal
- Aldehyde form
What is the role of retinal?
Component of the light-sensing molecular system of the human eye (vision)
What are the two metabolites of vitamin A?
- Retinal
- Retinoic acid
What is the storage form of vitamin A?
Retinol
How is retinoic acid derived?
Retinol is oxidized to retinoic acid
What is the function of retinoic acid?
Hormone that regulates gene expression during epithelial development
What is vitamin D also called? How can it be acquired?
- Cholecalciferol
- Consumed or formed in a UV-driven reaction in the skin
How is vitamin D converted to calcitriol?
The liver and kidneys convert vitamin D to calcitriol, the biologically active form of vitamin D
What is the role of calcitriol?
Increases calcium and phosphate uptake in the intestines, which promotes bone production
What does a lack of vitamin D result in?
Rickets, seen in children and characterized by underdeveloped, curved long bones as well as impeded growth
Vitamin E characterizes a group of closely related lipids called __________ and _________.
tocopherols and tocotrienols
What are tocopherols and tocotrienols characterized by in terms of structure? Are they hydrophilic or hydrophobic?
Substituted aromatic ring with a long isoprenoid side chain and are usually hydrophobic
What is the role of tocopherols?
- Biological antioxidants
- Aromatic ring reacts with free radicals, destroying them
- Prevents oxidative damage (contributor to the development of cancer and aging)
Vitamin K is a group of compounds. Which compounds are included in this group?
- Phylloquinone (K1)
- Menaquinone (K2)
What is the major function of vitamin K?
- Vital to the posttranslational modifications required to form prothrombin; important factor in blood clotting
- Aromatic ring of vitamin K undergoes a cycle of redox reactions during the formation of prothrombin
What is vitamin K’s role in bone health?
Required to introduce calcium-binding sites on several calcium-dependent proteins
How many carbons are in diterpene?
20 carbons
Why are lipids a fantastic way to store energy, from the body’s point of view? (2)
1) Carbon atoms of FA are more reduced than those of sugars, which contain numerous alcohol groups (2x as much energy per gram) - dense energy store
2) Triacylglycerols are hydrophobic; decrease their weight
* Also serves as insulation for animals living in colder temperature
Which lipid is the preferred method of storing energy for long-term use?
Triacylglycerols
What is the general structure of triacylglycerols? What linkages are used?
One glycerol attached to three fatty acids by ester bonds
Animal cells specifically used for storage of large triacylglycerol deposits are called _______
adipocytes
Where are triacylglycerol deposits found in plants?
In seeds as oils
Triacylglycerols travel bidirectionally in the bloodstream between the ______ and _______
liver and adipose tissue
What are free fatty acids?
Unesterified fatty acids with a free carboxylate group
How do free fatty acids circulate in the body?
In the blood bound noncovalently to serum albumin
Which lipid make up soap?
Fatty acid salt
What is saponification? What is the compound that is used?
- The ester hydrolysis of triacylglycerols using a strong base
- Lye (sodium or potassium hydroxide)
What can act as surfactants?
Soap
What are surfactants? What do they form to do so?
- They lower the surface tension at the surface of a liquid, serving as a detergent or emulsifier
- Forming micelles
What can micelles dissolve? Why does it wash away?
- Can dissolve a lipid-soluble molecule in its fatty acid core
- Washes away with water because of its shell of carboxylate head groups
What is a micelle in terms of soap?
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
How does the human body store energy?
As glycogen and triacylglycerols
If you are washing dishes with soap, where do fat-soluble particles dissolve? Where do water-soluble compounds dissolve?
- Fat-soluble: dissolve inside micelles in the soap-water solution and wash away
- Water-soluble: freely dissolve in water
