Week 8-Lipids, Phospholipids, Their Biological Importance, and Solution Preparation

Lipids

main biological function of

• includes energy storage along

• the building blocks of living cells.

• Lipids are insoluble in water

  • but are soluble in organic solvents

  • like ether and chloroform.

two categories of lipids:

• Hydrolyzable lipids

  • MADE OF fatty acids

    • polor/hyrdophilic end with carboxylic group

    • non-polar/hydrophobic end; the long hydrocarbon chain 

• Nonhydrolyzable lipids

Hydrolyzable Lipids

lipids that can be converted to small molecules by hydrolysis with water.

• are derived from fatty acids

• Fatty acids are carboxylic acids (R-COOH) with long hydrocarbon chains of 12 to 20 carbon atoms.

• They are the building blocks of fat in our body and in the food we eat.

Nonhydrolyzable Lipids

lipids that cannot be converted to small molecules by hydrolysis with water.

Fatty acids are of two types:

Naturally occurring fatty acids may be from plant or animal sources.

• They have an

  • even number of carbon atoms in the chain,

  • and can -be either saturated or unsaturated

Some fatty acids cannot be produced by the body and are referred to as essential fatty acids

• Linoleic (Omega-6 fatty acid) and Linolenic acids (Omega-3 fatty acid)

  • unsaturated fatty acids.

  • required for the growth and development of the body.

  • omega numbering is based on the appearance of the double bond on the carbon chain. The first carbon with a double bond in the chain is called the omega carbon.

1. Saturated fatty acids have no double bonds (C=C) in their long hydrocarbon chains.

   1. Saturated fatty acids are solid at room temperature and are generally obtained from animal source.

2. Unsaturated fatty acids have one or more double bonds (C=C) in their long hydrocarbon chains.

   1. Unsaturated fatty acids are liquid at room temperature and are generally obtained from plant source.

   2. As the number of double bonds in the fatty acid increases, the melting point decreases

Triacylglycerols (Hydrolyzable Lipids)

• are the building blocks of fat in our body and in the food we eat.

• Fats and oils are made of triglycerides.

  • Hence fat and oil molecules are also known as triacylglycerol or triglycerides.

• are formed when a glycerol molecule and three molecules of fatty acids are combined.

Glycerol

• also known as glycerin

• a three-carbon simple organic molecules, having three Hydroxyl (-OH) groups in the same molecule

• It has a sweet taste.

Simple Triglyceride

• If the side chains (R, R’ and R’’) from the three fatty acid molecules are of the same kind

mixed triglyceride

if two or three fatty acids side chains are different,

Saturated triglycerides

• contain only saturated fatty acids

• They make up for most animal fat and are solid at room temperature.

• They have a high melting point and are generally from animal source.

Unsaturated triglycerides

• contain at least one unsaturated fatty acid.

• They make up most vegetable oils and are liquid at room temperature.

• They have a lower melting point are generally from plant source.

• Oils are derived from fatty acids that have a larger number of double bonds.

• Increasing the number of double bonds in the fatty acid chain decreases the melting point of the triglyceride.

monounsaturated triglycerides.

Triglycerides that have one carbon double bond (C=C)

polyunsaturated triglycerides.

Triglycerides that have two or more carbon double bonds (C=C)

Clinical Importance of Triglycerides

1. Fats are used to

   1. build cell membranes

   2. insulate the body

   3. store energy for later use.

2. Humans store energy as triglycerides in adipose cells

   1. below the surface of the

      1. skin

      2. breast area

      3. surrounding internal organs.

3. The number of adipose cells is constant; weight gained or lost causes them to swell or shrink, but not decrease or increase in number

4. In order for the triglycerides to be used for energy in the body, they have to be hydrolyzed.

   1. The esters in the triglycerides are hydrolyzed by enzymes called lipases.

   2. Hydrolysis takes place in the presence of water molecules.

   3. Triglycerides are hydrolyzed into glycerol and fatty acids as shown in the diagram below.

• It is said that a high intake of saturated triglycerides is linked to heart disease.

  • Saturated fats stimulate cholesterol synthesis, which can lead to cholesterol building up inside arteries, known as cholesterol plaques.

  • This results in high blood pressure, heart attack, and even stroke

• Triglycerides are usually measured along with cholesterol as part of a blood test known as Lipid Profile.

Phospholipids (Hydrolyzable lipids)

• can be broken into simple molecules by hydrolysis with water

• are lipids that contain a phosphate molecule

• resemble triacylglycerols

  • Except in phospholipids,

    • the third fatty acid is replaced with a phosphate group, which is bonded to the glycerol

      • The phosphodiester/hydrophilic head of the molecule has a nitrogen-containing molecule in the R position, which is attached to the oxygen of the phosphate group.

      • nitrogen-containing molecule can be of different kinds, such as Choline molecule, as shown in the following image.

    • also referred to as phosphoacylglycerols.

    • Phosphoacylglycerols are the main component of most cell membranes.

• is made of a hydrophobic tail and a hydrophilic head,

  • two fatty acid side chains form two nonpolar “tails” that lie parallel to each other.

    • This is known as the non-polar end or the hydrophobic (water not-liking) tail

  • The phosphodiester end of the molecule is a charged or polar “head”

    • also known as the hydrophilic (water-liking) head.

Cell Membrane Structure and the Role of Phospholipids

• Phospholipids, the major component of cell membranes, contain a hydrophilic polar head and two hydrophobic nonpolar tail, which is often drawn as shown in the picture below.

• cell membranes are composed of two adjacent layers of phospholipids called phospholipid bilayers.

• When phospholipids are mixed with water, they assemble in such a way that the hydrophobic (water-not liking) or nonpolar tails are towards the interior of the bilayer and the hydrophilic (water-liking) or polar heads are towards the exterior of the bilayer as seen in the diagram below.

• Alongside the phospholipids, the cell membrane also has other molecules like proteins, carbohydrates and cholesterol embedded in the lipid bilayer.

glycolipids

carbohydrates are attached to the exterior of the cell

purpose of cell membrane

• stop the passage of ions and molecules into or out of the cell.

• transport of oxygen, carbon dioxide and other molecules through the membrane.

  • small molecules like O₂ and CO₂ can diffuse through the cell membrane, traveling from higher to lower concentration

  • larger polar molecules and ions like Cl⁻ or HCO₃⁻, travel through integral protein channels would facilitate their transport to cross the membrane efficiently.

  • For the movement of other ions such as Na⁺, K⁺, and Ca²⁺, some energy input is required and this is called active transport.

Steroids (Non Hydrolyzable Lipid)

• are a type of non-hydrolyzable lipids that cannot be converted to small molecules by hydrolysis with water.

• are a group of lipid characterized by a carbon skeleton with four fused rings (tetracyclic)

• contain a significant amount of hydrocarbon character,

• but unlike other lipids, they are not esters

• Different steroids have different functional groups attached to this group of rings.

  • The most common steroid in the body is cholesterol.

    • Many steroid hormones are produced from cholesterol.

Cholesterol as a Steroid

• is present in the cell membrane and is one of the most prominent steroids.

• It is synthesized in the liver

• is found in almost all body tissues.

• obtained in the diet

  • meat

  • cheese

  • butter

  • eggs

• is insoluble in the aqueous medium of blood.

• transported through the bloodstream by lipoproteins,

  • are granules of phospholipids and proteins.

  • Two types

    • LDL (Low-density lipoproteins)

    • HDL (High-density lipoproteins).

• Elevated levels of cholesterol in the bloodstream can lead to

  • coronary artery disease, heart attack, etc.

  LDL (Low-density lipoproteins)

•  Transports cholesterol from the liver to the tissues

• Deposits cholesterol on the walls of arteries,

  • when it carry more than is needed to form cell membranes.

  • This deposit forms plaque, which restricts blood flow;

  • thus, LDL cholesterol is called “bad” cholesterol.

HDL (High-density lipoproteins)

• Transports cholesterol from tissues back to the liver

• Reduces the level of cholesterol in the blood-stream by bringing excess back to the liver

• thus HDL cholesterol is called “good” cholesterol

   Steroid Hormones

• Hormones are chemical molecules that are synthesized in one part of the body.

• They are secreted directly in the blood, which carries them to other organs and tissues of the body.

• There, they get attached to steroid receptors to form the hormone receptor compleX

  • allows the hormone to carry out its function

Two important classes of steroid hormones:

• Sex hormones

• Adrenal cortical steroids, also known as corticosteroids

Sex hormones

• important role in the

  • sexual development

  • reproduction

  • general health.

• They include

  • female sex hormones

    • estrogen

    • progesterone

  • male sex hormones

    • androgen.

    • They are typically made in the gonads or placenta.

Adrenal cortical steroids, also known as corticosteroids

• are natural hormones and important in maintaining good health.

• There are two types of corticosteroids which are

  • aldosterone

    • regulates blood pressure by controlling sodium and potassium levels in the blood and tissues

  • cortisol

    • Regulate metabolism, manage stress, and suppress the immune system

• They are typically made in the adrenal cortex.