Biochem - lipid structure and function Flashcards
What are lipids characterized by?
Insolubility in water and solubility in nonpolar organic solvents
What is the major component of the phospholipid bilayer?
Lipids
Define amphipathic molecule.
A molecule with both hydrophilic and hydrophobic regions
What are the two regions of membrane lipids?
- Polar head (hydrophilic region)
- Fatty acid tails (hydrophobic region)
What structures do lipids form in aqueous solutions?
- Liposomes
- Micelles
- Phospholipid bilayer
What determines the behavior of lipids?
The degree of saturation and length of the long-chain fatty acids
What are saturated fatty acids characterized by?
Single bonds connected to four other atoms and no pi bonds
What is the effect of unsaturated bonds in fatty acids?
They introduce kinks which make it hard to stack
What elements do phospholipids contain?
- Phosphate
- Alcohol (polar head group)
- Hydrophobic fatty acid tail
What is a glycerophospholipid?
Phospholipids with a glycerol backbone bonded to two fatty acids
What is phosphatidylcholine?
A glycerophospholipid with a choline head group
What distinguishes sphingolipids from glycerophospholipids?
Sphingolipids have a sphingosine backbone
What is the simplest sphingolipid?
Ceramide
What are sphingomyelins?
Sphingolipids that are also phospholipids with either phosphocholine or phosphoethanolamine as a head group
What are glycolipids?
Sphingolipids with head groups composed of sugars bonded by glycosidic linkages
What are cerebrosides?
Glycosphingolipids with a single sugar
What are gangliosides?
Glycolipids with polar head groups composed of oligosaccharides and a negative charge
What are waxes?
Esters of long-chain fatty acids with long-chain alcohols
What role do waxes play in plants?
Prevent excessive evaporation and protect against parasites
What are terpenes?
Lipids built from isoprene moieties with carbon groups in multiples of five
What is the structural characteristic of steroids?
Four fused cycloalkane rings: three cyclohexane and one cyclopentane
What is the role of cholesterol in membranes?
Mediates membrane fluidity and serves as a precursor to many important molecules
What are prostaglandins derived from?
Arachidonic acid
What are the two classes of vitamins?
- Water-soluble vitamins
- Fat-soluble vitamins
What is Vitamin A important for?
- Vision
- Growth and development
- Immune function
What is the biologically active form of Vitamin D?
Calcitriol (1,25-(OH)2D3)
What is the function of Vitamin E?
Biological antioxidant preventing oxidative damage
What is the role of Vitamin K?
Vital for posttranslational modifications required to form prothrombin
What are triacylglycerols used for?
Energy storage
Why are lipids effective for energy storage?
- More reduced carbon atoms than sugars
- Hydrophobic and do not require hydration for stability
What is the relationship between triacylglycerols and carbohydrates in terms of energy yield?
Triacylglycerols yield twice the amount of energy per gram as carbohydrates
What is the primary storage mechanism of triacylglycerols compared to polysaccharides?
Triacylglycerols are a more efficient storage mechanism than polysaccharides like glycogen.
How do triacylglycerols affect weight compared to hydrophilic polysaccharides?
Triacylglycerols are hydrophobic and do not require hydration for stability, decreasing their weight.
What contributes to the insolubility of triacylglycerols in water?
Their nonpolar and hydrophobic nature, which decreases polarity due to bonded polar groups.
What role do triacylglycerols serve in the body?
They serve as depots of metabolic fuel for energy during cell division or low fuel supplies.
Where are adipocytes primarily located in animals?
Under the skin, around mammary glands, and in the abdominal cavity.
In plants, where are triacylglycerol deposits commonly found?
In seeds as oils.
How do triacylglycerols travel in the bloodstream?
Bidirectionally between the liver and adipose tissue.
What primarily determines the physical characteristics of triacylglycerols?
The saturation or unsaturation of the fatty acid chains.
Define free fatty acids.
Unesterified fatty acids with a free carboxylate group.
How do free fatty acids circulate in the body?
Bonded noncovalently to serum albumin.
What is saponification?
The ester hydrolysis of triacylglycerols using a strong base.
What traditional base is used in saponification?
Lye, which is sodium or potassium hydroxide.
What are the products of saponification?
The sodium salt of the fatty acid and glycerol.
What is adipocere?
The result of natural saponification occurring in corpses, known as grave wax.
What function do soaps serve as surfactants?
They lower the surface tension at the surface of a liquid.
What happens when soap is added to an aqueous solution and oil?
The two phases appear to combine into a single phase, forming a colloid.
What are micelles?
Tiny aggregates of soap with hydrophobic tails inward and hydrophilic heads outward.
What is the role of micelles in cleaning?
They allow cleaning agents to dissolve both water-soluble and water-insoluble messes.
What vitamins are absorbed with the help of micelles?
Fat-soluble vitamins A, D, E, and K.
What forms micelles in the body for fat absorption?
Fatty acids and bile salts secreted by the gallbladder.
True or False: Triacylglycerols are polar compounds.
False
