<< Chapter < Page Chapter >> Page >
By the end of this section, you will be able to:
  • Describe the four major types of lipids
  • Explain the role of fats in storing energy
  • Differentiate between saturated and unsaturated fatty acids
  • Describe phospholipids and their role in cells
  • Define the basic structure of a steroid and some functions of steroids
  • Explain the how cholesterol helps to maintain the fluid nature of the plasma membrane

Lipids include a diverse group of compounds that are largely nonpolar in nature. This is because they are hydrocarbons that include mostly nonpolar carbon–carbon or carbon–hydrogen bonds. Non-polar molecules are hydrophobic (“water fearing”), or insoluble in water. Lipids perform many different functions in a cell. Cells store energy for long-term use in the form of fats. Lipids also provide insulation from the environment for plants and animals ( [link] ). For example, they help keep aquatic birds and mammals dry when forming a protective layer over fur or feathers because of their water-repellant hydrophobic nature. Lipids are also the building blocks of many hormones and are an important constituent of all cellular membranes. Lipids include fats, oils, waxes, phospholipids, and steroids.

Photo shows a river otter swimming.
Hydrophobic lipids in the fur of aquatic mammals, such as this river otter, protect them from the elements. (credit: Ken Bosma)

Fats and oils

A fat molecule consists of two main components—glycerol and fatty acids. Glycerol is an organic compound (alcohol) with three carbons, five hydrogens, and three hydroxyl (OH) groups. Fatty acids have a long chain of hydrocarbons to which a carboxyl group is attached, hence the name “fatty acid.” The number of carbons in the fatty acid may range from 4 to 36; most common are those containing 12–18 carbons. In a fat molecule, the fatty acids are attached to each of the three carbons of the glycerol molecule with an ester bond through an oxygen atom ( [link] ).

The structures of glycerol, a fatty acid, and a triacylglycerol are shown. Glycerol is a chain of three carbons, with a hydroxyl (OH) group attached to each carbon. A fatty acid has an acetyl (COOH) group attached to a long carbon chain. In triacylglycerol, a fatty acid is attached to each of glycerol’s three hydroxyl groups via the carboxyl group. A water molecule is lost in the reaction so the structure of the linkage is C-O-C, with an oxygen double bonded to the second carbon.
Triacylglycerol is formed by the joining of three fatty acids to a glycerol backbone in a dehydration reaction. Three molecules of water are released in the process.

During this ester bond formation, three water molecules are released. The three fatty acids in the triacylglycerol may be similar or dissimilar. Fats are also called triacylglycerols or triglycerides because of their chemical structure. Some fatty acids have common names that specify their origin. For example, palmitic acid, a saturated fatty acid    , is derived from the palm tree. Arachidic acid is derived from Arachis hypogea, the scientific name for groundnuts or peanuts.

Fatty acids may be saturated or unsaturated. In a fatty acid chain, if there are only single bonds between neighboring carbons in the hydrocarbon chain, the fatty acid is said to be saturated. Saturated fatty acids are saturated with hydrogen; in other words, the number of hydrogen atoms attached to the carbon skeleton is maximized. Stearic acid is an example of a saturated fatty acid ( [link] )

The structure of stearic acid is shown. This fatty acid has a hydrocarbon chain seventeen residues long attached to an acetyl group. All bonds between the carbons are single bonds.
Stearic acid is a common saturated fatty acid.

When the hydrocarbon chain contains a double bond, the fatty acid is said to be unsaturated . Oleic acid is an example of an unsaturated fatty acid ( [link] ).

Questions & Answers

a complete virus particle known as
Darlington Reply
These are formed from identical protein subunitscalled capsomeres.
Pushpam
fabace family plant name
Pushpam Reply
in eukaryotes ...protein channel name which transport protein ...
Pushpam Reply
in bacteria ...chromosomal dna duplicate structure called
Pushpam
what is a prokaryotic cell and a eukaryotic cell
Matilda Reply
There are two types of cells. Eukaryotic and Prokaryotic cells. Prokaryotic cells don't have a nucleus or membrane enclosed organelles (little organs within that cell). They do however carry genetic material but it's not maintained in the nucleus. Prokaryotic cells are also one celled.
juanita
Prokaryotic cells are one celled (single celled).
juanita
Prokaryotic cells are Bacteria and Archea
juanita
Prokaryotic cells are smaller than Eukaryotic cells.
juanita
Eukaryotic cells are more complex. They are much bigger than Prokaryotic cells.
juanita
Eukaryotic cells have a nucleus and membrane bound organelles.
juanita
Eukaryotic cells are animals cells which also includes us.
juanita
Eukaryotic cells are also multicellular.
juanita
nice explaination
Amna
eukaryotic cells are individual cells .. but eukaryotes are multicellular organisms which consist of many different types of eukaryotic cells
Will
also eukaryotic cells have mitochondria. prokaryotic cells do not
Will
Good
John
in prokaryotes only ribosomes are present... in eukaryotes mitochondria ...glogi bodies ..epidermis .....prokaryotes one envelop but eukaryotes compartment envelop....envelop mean membrane bound organelles......
Pushpam
we have 46 pair of somatic cell and 23 pair of chromosomes in our body, pls can someone explain it to me. pls
Matilda Reply
we have 22 pairs of somatic chromosomes and one pair of sex chromosome
Amna
thanks
Matilda
we have 23 pairs of chromosomes,22 pairs of somatic and one pair of sex chromosomes
Amna
23 chromosomes from dad & 23 chromosomes from mom 23 +23=46 total chromosomes
juanita
X & Y chromosomes are called sex cells, the very presence of a Y chromosome means the person is Male.
juanita
XX Female XY Male
juanita
If a Karyotype has more than 46 Chromosomes then nondisjunction occured. For example, having an extra chromosome 21 will cause Down Syndrome.
juanita
in mammal state the different vertebrae and their location in the body
Igbinigie Reply
what is a somatic cell
Senam Reply
somatic cells are body cells
juanita
somatic cell organised whole plant body part
Pushpam
what is biology
lilian Reply
what is biology
Dada Reply
The scientific study of life.
juanita
the virus that causes mumps in humans is composed of a protein outer Shell containing a core of DNA
Daniel Reply
Basic science and applied science question about cancer
Joyce Reply
what are the importance of ATPs
Olatunji Reply
How can biology be studied from a microscopic approach to a global approach
Joyce Reply
The large central opening in the poriferan body is called
Chynna Reply
You go for a long walk on a hot day. Give an example of a way in which homeostasis keeps your body healthy.
Joyce Reply
You sweat.
juanita
sweating is your bodies way of keeping you from overheating.
juanita
Thank you
Joyce

Get the best Biology course in your pocket!





Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?

Ask