Lipids - Types of Fat and Function

Question 1

Lipids in the Body

Answer 1

Lipids exist in the body in various forms with each form having a different structure and function. Lipids include:
* Individual fatty acids.
* Triglycerides.
* Phospholipids —in every cell membrane.
* Cholesterol and steroid-based compounds (e.g. oestrogen).
* Sphingolipids —found in nerve cell membranes, e.g. myelin.
* Glycolipids—involved in cell identity (like a cell ‘passport’).
* Cerebrosides — glycosphingolipids found in the brain.
* Fat-soluble vitamins —A, D, E, K.

Question 2

Phospholipid

Answer 2

= phosphate + fatty acids

Question 3

Glycolipid

Answer 3

= carbohydrate + lipid

Question 4

Cerebroside

Answer 4

= waxy lipid + sugar

Question 5

Sphingolipid

Answer 5

= long chain amino alcohol + fatty acid + sugar

Question 6

Function of Lipids:

Answer 6

• Energy (ATP) production
• Storage of energy reserves
• Cell membrane structure
• Thermal insulation
• Steroid hormones
• Formation of eicosanoids
• Growth and development
• Constituents of nervous tissue structure
• Aid to cell-signalling processes.
• Absorption of fat-soluble vitamins.
  Eicosanoids= signalling molecules

Question 7

Function: Energy (ATP) production

Answer 7

• Energy (ATP) production — each gram of fat supplies the body with about nine calories.

Question 8

Function: Storage of energy reserves

Answer 8

• Storage of energy reserves —fats are a more efficient form of storage energy than carbohydrates or proteins, so the body stores any excess energy as fat.

Question 9

Function: Cell membrane structure

Answer 9

• Cell membrane structure —phospholipids and cholesterol stabilise cell membranes, whilst allowing a degree of fluidity, which is crucial to the function of every cell.

Question 10

Function: Thermal insulation

Answer 10

• Thermal insulation in subcutaneous tissue and protection around organs.

Question 11

Function: Steroid hormones

Answer 11

• Steroid hormones —progestogens, androgens, glucocorticoids, mineralocorticoids and oestrogens are derived from cholesterol

Question 12

Function: Formation of eicosanoids

Answer 12

• Formation of eicosanoids —signalling molecules involved in a range of processes such as blood coagulation and inflammation.

Question 13

Function: Growth and development

Answer 13

• Growth and development —the brain is rich in arachidonic acid (AA) and docosahexaenoic acid (DHA).

Question 14

Function; nervous tissue structure

Answer 14

• Constituents of nervous tissue structure (sphingomyelin).

Question 15

Function: cell-signalling

Answer 15

• Aid to cell-signalling processes.

Question 16

Function: Absorption of vitamins.

Answer 16

• Required for the absorption of fat-soluble vitamins.

Question 17

Fatty Acids:
(short, medium, long chain)

Answer 17

• Fatty acids are hydrocarbon chains with an acid group at one end and a methyl group at the other.
• Short-chain fatty acids (up to 5 Cs) and medium-chain fatty acids (6–12 Cs) travel directly to the liver where they can be used to create energy or ketones. Medium-chain triglycerides (MCTs) can be used as a source of energy before exercise (e.g.1 tbsp).
• Long-chain fatty acids (14–22 Cs) and very long chain fatty acids (> 22 Cs) are used to build cell membranes.
  (C= Carbon)

Question 18

Short-Chain Fatty Acids (SCFA)

Answer 18

• Short-chain fatty acids (SCFAs) have fewer than six carbon atoms.
• SCFAs are produced when dietary fibre is fermented in the colon.
• Acetate, propionate and butyrate are the most common SCFAs.
• Butyrate is particularly important for colon health because it is the primary energy source for colonocytes. It supports the intestinal tight junctions.
• SCFAs are speculated to have a role in microbiota-gut-brain axis crosstalk.
• Butyrate is thought to have an anti-inflammatory effect on the colon.

Question 19

Fatty Acids:
Omega nomenclature system

Answer 19

• Fatty acids are named using their common names and the omega nomenclature system.
• The omega system uses the number of carbon atoms, the number of double bonds, and the number of carbons from the omega end to the first carbon in the double bond.
• The omega-6 fatty acid, arachidonic acid, is referred to as 20:4 w6 (20 = No. of carbons, 4 = No. of double bonds, w6 = No. carbons to first double bond)

Question 20

Unsaturated fats and Hydrogenation

Answer 20

• Unsaturated fats can be saturated by the addition of hydrogen —as in hydrogenation when oils are made into solid spreads.
• Hydrogenation turns the natural fatty acid into unnatural forms (i.e. trans fats) which are damaging to health.
• Hydrogenation= addition of hydrogen

Question 21

Fatty Acids (Types):

Answer 21

There are different types of fatty acids:
1. Saturated
2. Unsaturated
3. Monosaturated
4. Polysaturated
The more double bonds there are in a fatty acid, the less stable it is, increasing susceptibility to oxidation.

Question 22

Saturated fatty acids

Answer 22

Saturated fatty acids:
* Contain no C-C double bonds. All the carbons are completely saturated with hydrogen bonds.
* Solid at room temperature.

Question 23

Unsaturated fatty acids

Answer 23

Unsaturated fatty acids:
* Contain one or more double bonds between carbons.
* Liquid at room temperature.

Question 24

Monosaturated fatty acids

Answer 24

Monounsaturated fatty acids:
* Have one double bond in the chain.

Question 25

Polysaturated fatty acids

Answer 25

Polyunsaturated fatty acids:
* Have several double bonds

Question 26

Unnatural Trans Fats

Answer 26

• Unnatural trans fatty acids are produced by high temperatures and hydrogenation.
• They are found in margarine, processed foods and refined vegetable oils.
• Trans fats stiffen cell membranes, making them prone to oxidation. This also alters their protective action and permeability, impeding normal cell function.
• Trans fats alter blood triglyceride and cholesterol profiles and are linked to an increased risk of cardiovascular disease, insulin resistance and cancer.
  hydrogenation = the addition of hydrogen to solidify an unsaturated fat

Question 27

Cis and Trans Fatty Acids

Answer 27

• At each double bond, two possible isomeric forms exist.
  o Cis configuration = the H atoms are on the same side of the double bond. The majority of natural fats are cis.
  o Trans configuration = the H atoms are on separate sides of the double bond.
• Conjugated linoleic acid (CLA) is a natural trans fat found in grass-fed meat and dairy products. Studies indicate CLA helps increase lean muscle mass and decrease body fat.

Question 28

Triglycerides

Answer 28

• Triglycerides (TGs) are the major form of dietary fat, and the form in which fat is stored in the body. They circulate in the blood when released for energy.
• TGs are lipid molecules made up of one unit of glycerol and three fatty acids.
• The three fatty acids can differ in length (number of carbon atoms) and degree of saturation (number of hydrogen molecules attached).
• High levels of triglycerides in the blood have been linked to atherosclerosis, and hence heart disease and stroke.
  Triglycerides are also referred to as triacylglycerols (TAGs)