Lipids are a diverse group of biological molecules that do not mix with water. The key groups of lipids encompass fats, phospholipids, steroids and waxes. Lipids serve energy storage functions, are the major components of biological membranes, and act as precursors for hormones.
Many lipids can be synthesised by human cells. However, some essential lipids such as omega-3 and omega-6 fatty acids have to be obtained from diet.
Some dietary sources of essential lipids
Fats
A typical fat molecule is a triglyceride consisting of a glycerol part and three fatty acid tails. The long fatty acid tails provide fats with their hydrophobic properties.
Fats are synthesised by dehydration synthesis
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OpenStax College - Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013., CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=30131156
In animals, fats serve as long-term energy storage molecules. Fats are mainly deposited in adipose tissue cells that provide thermal insulation and cushion the body's organs.
Fat is stored in adipose tissue cells
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OpenStax College - Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013., CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=30131287
Phospholipids
Phospholipids are the key components of cell membranes. Phospholipids are structurally similar to fats but only have two fatty acid tails. Instead of the third tail, phospholipids have a negatively charged phosphate group. This arrangement results in a dual nature: a strongly hydrophobic part ("tails") that repels water and a hydrophilic part ("head") that attracts water.
The structure of a phospholipid
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In an aqueous environment, phospholipids tend to form a bilayer: the hydrophilic heads face outward, interacting with water, while the hydrophobic tails are concealed within. Phospholipid bilayers comprise the plasma membrane and the internal membranes of eukaryotic cells.
Phospholipid bilayer
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OpenStax - https://cnx.org/contents/[email protected]:fEI3C8Ot@10/Preface, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=30131169
Steroids
Steroids are lipid molecules that have four fused hydrocarbon rings. A typical steroid is cholesterol – the component of animal cell membranes and a precursor of such hormones as estradiol and testosterone.
Cholesterol
Summary
The videos below provide the summary of the topic and some additional details:
