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DENF 1521 Biochemistry

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Fatty Acid Metabolism

Lesson 9.1
Nomenclature and Structure of Fatty Acids

Instructions
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  3. After studying Lesson 9.1, and responding to all practice exercises, follow instructions at the end to submit your responses for Lesson 9.1 participation credit.
NAME:
Dental Biochemistry Brush
DB Bullet Lesson 9.1 Fatty acid structure

Lesson 9.1
Fatty acid structure

9.1A Lesson objectives

The objectives of this lesson are to understand:

  1. The basic structure of saturated and unsaturated fatty acids
  2. The numbering systems used to designate the carbon atoms in fatty acids
  3. The effects of chain length and saturation on the properties of fatty acids
  4. That triacylglycerols are the storage form for fatty acids

9.1B What are fatty acids?

Fatty acids are a class of compounds composed of a long hydrocarbon chain and a terminal carboxylic acid group. Fatty acids may be saturated in which they contain no double bonds, or unsaturated in which case they have one or more double bonds. There are four major functions of fatty acids in the body.

  1. Serve as building blocks for phospholipids and glycolipids
  2. Covalent attachment to proteins to make the protein more hydrophobic.
  3. Source of fuel
  4. Derivatives serve as hormones and second messengers

One common fatty acid is palmitic acid. Palmitic acid is a fatty acid containing 16 carbon atoms and no double bonds. The corresponding unsaturated fatty acid is palmitoleate which contains 1 double bond.

Common fatty acids
Name Number of carbons; double bonds Structure
Palmitate

16; 0

palmitate
Stearate 18; 0 stearate
Palmitoleate 16; 1 palmitoleate
Oleate 18; 1 oleate

The numbering system for fatty acids follows the following conventions. The carboxylic acid carbon is carbon 1 with numbering continuing until the terminal methyl group. Carbons 2 and three are often called the and carbons as indicated by the red in the diagram. The terminal methyl group is referred to as the omega carbon indicated in blue. This convention is often used when referring to unsaturated fatty acids. In the example above, oleic acid is also called an omega-9 fatty acid because the double bond is located 9 carbons in from the terminal methyl group. An important class of dietary fatty acids are the omega-3 fatty acids containing a double bond in position 3 as shown below. These fatty acids are abundant in cold water fish (such as salmon, herring, mackerel) oil and flaxseed and soy oil. Alpha-linolenic acid is an omega-3 fatty acid that is used by the cell to make other omega-3 fatty acids.

numbering

omega fa

.

Dental Biochemistry Brush
DB Bullet Lesson 9.1 Fatty acid structure
Fatty acid structure
Practice
Exercise 1:

Which of the following fatty acids contains 16 carbon atoms and no double bonds?

No Response
Stearate
Palmitate
Acetate
Palmitoleate
Practice
Exercise 2:

A saturated fatty acids has at least one double bond.

No Response
True
False
Dental Biochemistry Brush
DB Bullet Lesson 9.1 Fatty acid structure

 

9.1C Melting Point of fatty acids

The melting point of a fatty acid is the temperature at which fatty acids go from an ordered, rigid state to a relatively disordered, fluid state. This is a very important property of biomembranes. We mention it in the context of fatty acid structure because the chain length and degree of unsaturation influence the melting point. For example, a fatty acid composed of 16 carbons has a lower melting point than one with 20 carbons. Also, a fatty acid with 16 carbons and 1 double bond will have a lower melting point than a fatty acid with 16 carbons and no double bonds. To summarize, increasing the chain length of a fatty acid, increases its melting point. Increasing the number of double bonds, decreases the melting point.

Dental Biochemistry Brush
DB Bullet Lesson 9.1 Fatty acid structure
Melting point
Practice
Exercise 3:

In general, increasing the chain length of a fatty acid increases its melting point.

No Response
True
False
Dental Biochemistry Brush
DB Bullet Lesson 9.1 Fatty acid structure

 

9.1D The storage form of fatty acids

Fatty acids are stored in the form of triacylglycerols often referred to as TAGs. Triacylglycerols are highly concentrated stores of energy with the yield for the complete oxidation of fatty acids about 9 kcal/g. TAGs are stored in a nearly anhydrous form in contrast to proteins and carbohydrates which are highly hydrated. The major site of accumulation of triacylglycerols in mammals is the cytoplasm of adipose (fat) cells. Large globules of triacylglycerols in the adipose cell can take up most of the cytoplasmic space. Adipose cells are specialized cells which synthesize and store TAGs. The TAGs can be mobilized in the form of fatty acid molecules which are transported to other tissues through the bloodstream.

A model TAG and its hydrolysis to free fatty acids is shown below. The enzyme which carries out this hydrolysis is called a lipase. The products of the reaction are glycerol and 3 free fatty acids . The activity of these lipases is regulated by hormones using cAMP as a second messenger. The mechanism is similar to that described in lesson 8.5 for the hormone activation of glycogen breakdown. TAG breakdown, called lipolysis is stimulated by epinephrine, glucagon, and adrenocorticotropin hormone. Insulin inhibits lipolysis. The fatty acids released by lipolysis undergo -oxidation while the glycerol NAD is converted to pyruvate or glucose in the liver.

The Lipolysis Reaction
Dental Biochemistry Brush
DB Bullet Lesson 9.1 Fatty acid structure
Triacylglycerols
Practice
Exercise 4:

Triacylglycerols are stored in a highly hydrated form in adipose cells.

No Response
True
False
Practice
Exercise 5:

The activation of lipolysis requires an increase in which of the following in the cell?

No Response
Insulin
cAMP
Glycerol
Oxygen
Practice
Exercise 6:

The highest energy stores in the body are found in

No Response
Protein
Carbohydrate
Triacylglycerols
Glucose
Dental Biochemistry Brush
DB Bullet Lesson 9.1 Fatty acid structure

 

9.1F Summary

After completing this lesson you should understand the following about the nomenclature and structure of fatty acids.

  1. Know the basic structure of saturated and unsaturated fatty acids
  2. Understand the numbering systems used to designate the carbon atoms in fatty acids
  3. Chain length and saturation of the fatty acid influences its properties
  4. The storage form of fatty acids is triacylglycerols

Final Instructions


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End Lesson 9.1
Nomenclature and structure
of fatty acids


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