Lecture Notes

Fatty acid oxidation
Learning objectives:

1. Importance of triacylglycerol (TAGS or TGS)
2. Overview of fatty acid metabolism
3. Mobilisation of fatty acids
4. Metabolism glycerol
5. Describe 3 stages of fatty acid metabolism (with reference to the committed steps of the process)
6. Strategy for metabolism of odd chain and unsaturated fatty acids
7. Ketone body formation
8. Role in normal physiology and diseases

CTP IS AN ENERGY SOURCE FOUND IN LIPID METABOLISM

Fatty acid: what are they & biological roles?

 What is a fatty acid?
- Molecules that contain a long linear (unbranched) hydrocarbon chain and a terminal carboxylate group.
 4 major biological roles of fatty acids
1. Building block form phospholipids & glycolipids: important components of biological membranes
2. Covalent attachment to proteins- targets them to membrane locations (prenylation)
3. Fuel molecules: stored as triacylglycerol (also called triglycerides) uncharged ester of fatty acids with glycerol
4. Derivatives serve as hormones & intracellular messengers


Caloric value of fats and carbohydrates

 Why store fuel as a fatty acid?
- High concentrated food supply (as completely reduced and anhydrous i.e. no water attached)
- Complete oxidation fats = 9Kcal/g
- Complete oxidation carbohydrates/protein =4kcal/g
- As non-polar are not hydrated
- Unlike carbohydrates - 1g glycogen binds 2g water
- Hydrated carbohydrate 1.3kcal/g
- Thus can store more energy in less weight

Fuel reserves and energy needs

 An average human has the following fuel reserves:
- Approx. 1600 kcal of glycogen in liver and muscle
- Approx. 24,00 kcal as protein
- Approx. 13,000 kcal as fat
 Typically humans need about 2000-2500 kcal/day
- Fat reserve will last for ~ 2 months
- Average body weight is ~160 Ib (equivalent to 72 Kg)
- Fat weight is ~ 20% (32Ib equivalent to 14 kg)
- Same amount of energy stored as hydrated glycogen would weigh ~220 Ib (equivalent to 99 kg)

Fats provide energy during fasting & starvation

 Fasting
- The first source of energy is stored glycogen
 Starvation
- Glycogen stores depleted within 24 hours
 Brain need glucose as fuel and gets it from 2 sources
1. Protein →AA → glucose

, 2. Triglycerides → glycerol → glucose
- No glucose from FA
 Prolonged starvation:
- Proteins preserved for muscle activity
- Fatty acid converted to ketone bodies
- Brain fuel shifted to ketone bodies

Fatty acids (FA)

 Long chain linear hydrocarbons carboxylic acids
- usually even number of C atoms ~ 12 to 20
- The C are numbered starting from carboxylic C
 They are amphillic
- Have a polar end
- Rest of the molecule is nonpolar
 FA may be saturated (no double bonds) or unsaturated (1 or more double bonds)
 All naturally occurring double bonds have a cis-configuration longer chain and saturation increases melting point
of FA and FA are ionised at physiological pH




How to get FA?

 FA Are the direct source of energy from lipids
 FA are oxidised by a process called β-oxidation
 When excess fats or calories are consumed in the diet they are condensed into triglycerides
 TG are stored in specialised fat-storage called adipocytes
 These special cells allow triglycerides to coalesce to form large globules that take up most of cells
 Adipose tissue accumulates subcutaneously and in different body cavities of obese people
 Liposuction removes this adipose tissue

Sources of fatty acids

1. Dietary lipids processed by the intestinal cells
2. Newly synthesised lipids, mostly by the liver
3. Lipids mobilised from adipocyte stores

LO1. IMPORTANCE OF TRIAGLYCEROLS (TAGS OR TGS)