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Lecture notes of 12 pages for the course Metabolic Pathways at QMUL
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Fatty acid oxidationLearning 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)
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