CHAPTER THREE: Lipids summary

Lipids are:

  • Insoluble in water
  • Soluble organic solvents
  • Utilized by living cells

Classification of lipids

Simple lipids – These are fats and oils with glycerol and waxes which have alcohol or glycerol.

Complex lipids – These have alcohol and other groups such as phosphates. There are three main types of complex lipids:

  • Phospholipids which include Glycerolphospholipids, and sphingolipids.
  • Glycolipids which has fatty acid, carbohydrate, and a nitrogenous base
  • Lipoproteins which have lipids and proteins
  • Other types of lipids which include amino lipids, lipopolysaccharide, and sulfates.
  • Derived lipids which are formed by hydrolysis of simple and complex lipids
  • Miscellaneous lipids e.g. carotenoids

Functions of lipids

  • Act as concentrated fuel reserves for the body
  • Are constituents of cell membrane structure and regulates the permeability of the lipid bilayer
  • Are a source of fat-soluble vitamins: A, D, E, and K
  • Regulate cellular metabolism e.g. Steroid hormones
  • Insulates body organs

Fatty acids

  • These are carboxylic acids with hydrocarbon side chains
  • They can be either esterified or unesterified
  • Saturated fatty acids are those which contain no double bond in their structure
  • Unsaturated fatty acids are those which contain at least a single double bond in their structure

Fatty acids can be categorized into three types in terms of the carbon chain length:

  • Short-chain – Less than 6 carbons
  • Medium-chain – 8 to 14 carbon atoms
  • Long-chain – 16 to 24 carbon atoms
Essential and non-essential fatty acids

The essential fatty acids are not synthesized by the body and hence must be provided in the diet. The most important essential fatty acids are linoleic acid and linolenic acid which transport cholesterol, helps in the structure and function of the cell membrane and form lipoprotein.


  • Triglycerides are esters of glycerol with fatty acids
  • They are the most abundant group of lipids functioning as fuel reserves
  • These are primarily found within the adipose tissue as adipocytes.
Properties of triacylglycerols
  • -Saponification forms glycerol and soaps
  • -Hydrolysis forms fatty acids and glycerol
  • -Rancidity is a property of fatty acids when left exposed to water, air, bacteria, e.t.c.
  • -Oxidation forms peroxides and free radical

Phospholipids can be glycerophospholipids which are made up of glycerol and alcohol or sphingolipids made up of sphingosine and glycerol

Functions of phospholipids

  • They are structural components of membranes
  • In mitochondria, they help maintain the conformation of ETC components for cellular respiration
  • They participate in the absorption of fat in the intestine
  • Aids in the synthesis of lipoproteins
  • Removes cholesterol from the body
  • Acts as surfactants that lower surface tension
  • Involved in the signal transmission across the membranes
  • Cepharins are a special type of phospholipids that helps in blood clotting.


Cholesterol is insoluble in water but soluble in organic solvents like benzene

Functions of cholesterol include:
  • Insulation of the nervous tissue
  • Synthesis of bile acids
  • Amphipathic lipids – These are lipids possessing both polar and nonpolar chains.
  • The non-polar (hydrophobic) side chain is the hydrocarbon chain while the polar (hydrophilic) is the carboxylic acid chain.
  • Liposomes are another important phospholipids type when amphipathic lipids in aqueous solution are subjected to sonification
  • Emulsions – These are formed when non-polar lipids mixed with water


Ch. 6 Lipids Summary Assignment
Leave the first rating
The presence of many C-C and C-H bonds causes fats to be ..
rich in energy and insoluble in water
In fat synthesis,__and fatty acids combine to make fats plus__.
glycerol; water

Created by
Key concepts:
Phospholipids And Triglycerides Both
Cell Membrane
Integral Membrane Protein
Terms in this set (27)

The presence of many C-C and C-H bonds causes fats to be ..
rich in energy and insoluble in water

In fat synthesis,__and fatty acids combine to make fats plus__.
glycerol; water

In the reaction that builds a fat, groups react with groups.
hydroxyl; carboxyl

Triglycerides vary with respect to the number of …
C atoms in the tails. and double bonds in the tails.

A food company hydrogenated a barrel of fat. The treatment …
made the fat less fluid.

The most unsaturated fats have …
the most double bonds

What do DNA, proteins, and fats have in common?
carbonyl groups

Which statement most accurately explains why cholesterol and phospholipids are amphipathic but fats are not?
Cholesterol and phospholipids contain both hydrophilic and hydrophobic regions; fats are primarily hydrophobic.

A phospholipid is a _.
nonpolar lipid molecule that is made amphipathic by the addition of a phosphate

What region of a steroid is hydrophilic?
the terminal hydroxyl group

Phospholipids and triglycerides both _.
have a glycerol backbone

Lipids _.
are insoluble in water

Steroids are considered to be lipids because they _.
are not soluble in water

Molecules that are amphipathic must contain _.
both hydrophilic and hydrophobic regions

Lipids are insoluble in water because_____.
they contain nonpolar C-C and C-H bonds

Which of the following is true of membrane lipids?
They contain a hydrophilic head group and a hydrophobic tail.

In an experiment involving planar bilayers, a solution of table salt (sodium and chloride ions in water) is added on the left side of the membrane while pure water is added on the right side. After 30 minutes the researchers test for the presence of ions on each side of the membrane. The right side tests negative for ions. What can you conclude?
ions cannot cross planar bilayers

Which aspect of phospholipids is most important to the formation of bilayers?
They are amphipathic.

Which of the following increases the strength of the hydrophobic interactions in lipid bilayers and thus makes them less permeable to polar molecules?
increasing length of the hydrocarbon chains

Which of the following crosses lipid bilayers the fastest?
a small, nonpolar molecule like oxygen (O2)

Which of the following crosses lipid bilayers the slowest?
a sodium ion

Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?

Decreasing the saturation of the fatty acid chains on a particular type of phospholipid would result in the formation of _.
more fluid bilayers

Where would you most likely find an integral membrane protein?
spanning the cell membrane, with parts of the protein visible from both the inside and the outside of the cell

When biological membranes are frozen and then fractured, they tend to break along the middle of the bilayer. The best explanation for this is that _.
the hydrophobic interactions that hold the membrane together are weakest at this point

When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are _.
integral proteins

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