Describe the structure of fatty acids and the two different types.
Long hydrocarbon chains with a carboxyl (-COOH) group at one end. They vary in chain length and saturation (saturated = no double bonds, unsaturated = with double bonds).
Describe the structure and fats/triglycerides.
Composed of three fatty acids bound to a glycerol backbone.
Describe the structure of phospholipids.
Made of two fatty acids, a glycerol backbone, and a phosphate group.
Describe the structure of glycolipids.
Similar to phospholipids but with a carbohydrate moiety replacing the phosphate group.
Describe the structure and function of cholesterol.
A sterol structure with four carbon rings and a hydroxyl group. It contributes to membrane fluidity and serves as a precursor for steroid hormones.
What are the 5 main biological roles of lipids?
- Energy storage
- Structural components e.g. phospholipids and cholesterol in cell membranes
- Insulation and protection
- Signalling molecules
- Transport of fat-soluble vitamins
Describe lipid digestion in monogastrics.
- Lipids are emulsified by bile salts in the small intestine.
- Pancreatic lipase breaks down triglycerides into free fatty acids and monoglycerides.
- These products are absorbed in the small intestine and assembled into chylomicrons for transport.
Describe lipid digestion in ruminants.
- Rumen microbes (mostly bacteria) transform dietary fats by lipolysis, breaking down triglycerides into free fatty acids (FFAs) and glycerol.
- After lipolysis, free fatty acids undergo biohydrogenation, a process where microbes add hydrogen to unsaturated fatty acids, converting them into more saturated forms.
How are lipids transported from the small intestine?
Absorbed lipids are packed into chylomicrons and enter the lymphatic system, eventually reaching the bloodstream.
How do fatty acids enter cells from the blood stream?
Lipoprotein lipase breaks down triglycerides in chylomicrons to allow fatty acids to enter cells.
What is the role of the liver in lipid transport?
Converts excess fatty acids to triglycerides and assembles them into very-low-density lipoproteins (VLDL) for distribution to other tissues.
What is the role of adipose tissue?
Stores fatty acids as triglycerides for later use; releases them back into the blood as free fatty acids when energy is needed.
What is the role of insulin in adipocytes?
Promotes lipid storage by increasing glucose uptake and triglyceride synthesis.
How are lipids released from adipocytes?
- When energy is needed, hormone-sensitive lipase breaks down triglycerides into free fatty acids and glycerol.
- These free fatty acids enter the bloodstream and are transported to other tissues (e.g., muscle) for oxidation and energy production.
Define beta-oxidation and name the key products.
The process by which fatty acids are broken down in the mitochondria to generate acetyl-CoA, NADH, and FADH₂.
How is beta-oxidation linked to the Kreb’s cycle?
- The acetyl-CoA produced enters the cycle.
- In the TCA cycle, acetyl-CoA is oxidized, producing additional NADH and FADH₂, which then feed into the electron transport chain (ETC) to produce ATP.
- Therefore beta-oxidation provides substrates that drive the TCA cycle and ETC.
Compare energy release from carbohydrates vs fats.
The oxidation of fatty acids yields more ATP than carbohydrates, as fatty acids contain longer carbon chains, resulting in more acetyl-CoA and greater NADH and FADH₂ production.
How are ketone bodies generated?
When carbohydrate availability is low, the liver converts excess acetyl-CoA (from fatty acid oxidation) into ketone bodies: acetoacetate, beta-hydroxybutyrate, and acetone.
Where does ketone body formation occur?
The mitochondrial matrix of liver cells.
Where does beta-oxidation occur?
Mitochondria
What is the role of ketone bodies?
Serve as an alternative energy source e.g. during prolonged fasting, low-carbohydrate diets, or untreated diabetes.
Why would ketone bodies be formed?
Liver gluconeogeneis uses up TCA intermediates –> ketone bodies way of shuttling energy from the liver to places where acetyl coA can be used.
Where does fatty acid synthesis occur?
Occurs in the cytoplasm, primarily in the liver and adipose tissue.
Describe how fatty acids are synthesised.
Acetyl-CoA is converted into malonyl-CoA, which serves as the building block for fatty acid chains in a process facilitated by fatty acid synthase.
