Fat Catabolism

Chapter 17

Fatty Acid Catabolism

– How fats are digested in animals– How fats are mobilized and transported in tissues– How fats are oxidized as a source of energy– How “ketone bodies” are produced and used

Key topics: To Know

Oxidation of fatty acids is a major energy source in many organisms

• About one-third of our energy needs comes from dietary triacylglycerols

• About 80% of energy needs of mammalian heart and liver are met by oxidation of fatty acids

• Many hibernating animals, such as grizzly bears, rely almost exclusively on fats as their source of energy

• Some animals (camels) store fat as an eventual source of water

Fats provide efficient fuel storage

• The advantage of fats over polysaccharides:

– Fatty acids carry more energy per carbon because they are more reduced

– Fatty acids carry less water along because they are nonpolar

• Glucose and glycogen are for short-term energy needs, quick delivery

• Fats are for long-term (months) energy needs, good storage, slow delivery

Fat Storage in White Adipose Tissue

Lipid Digestion

Chylomicron

Mobilization of Fat from Adipose Tissue

Guinea Pig Adipocytes

Entry of Glycerol into Glycolysis

Energetics of Glycerol as An Energy Source

Glycerol kinase - ATP

Glycerol-3-P DH + NADH

3-P-Gyld DH + NADH

3-PGA Kinase + ATP

Pyr Kinase + ATP

Total = 1 ATP + 2 NADH

Can GLYCEROL be FERMENTED? Explain

Major Fatty Acid Oxidation = β-Oxidation Occurs in the Mitochondrion

β-OxidationOverall Flow

One Round (a) and Further Rounds (b) of β-Oxidation

EOC Problem 4: explores numbers of round of β-oxidation.

EOC Problem 9: Compartmentalization of β-oxidation.

EOC Problem 3 Compares β-oxidation with the Citric Acid Cycle

Hibernating Animals Rely upon β-Oxidation for their Sleep

EOC Problems 13, 26 and 28: Deals with Fat as Storage of Water and Energy. Please keep in mind Prof

Makemson spent a good portion of his life in the Middle East…fat as storage of water!!

*Assumes 1 NADH = 2.5 ATP, and 1 FADH2 = 1.5 ATP from Respiratory Electron Transport

Energetics of Oxidation of Palmitic Acid

EOC Problems 1 and 2 deals with amount of energy stored in fat and how long it can last?

Oxidation of Unsaturated Fatty Acids (Remember they are cis!)

Multiple points of unsaturation can require

energy to get them through β-Oxidation

β-Oxidation of Odd Numbered Fatty Acids Results in Propionyl-SCoA

Peroxisomes in Animals – mainly different in First Step and Usually use >20 C and branched chain fatty acids.

Peroxisomes in Plants are main fatty acid oxidation (not in mitochondria)

Plant vs Animal β Oxidation

Seeds are Loaded with Fats and Oils

Arrangement of the β-Oxidation Enzymes

Eukaryotes Also have 2 Arrangements of these Enzymes

ω-Oxidation in the ER of Liver Cells

ω = Omega, the last letter in the Greek alphabet

Minor pathway in mammals, more important in invertebrates

α-Oxidation of Branched Chain Fatty Acids Takes Place in Peroxisomes

β-oxidation of Odd Numbered Fatty Acids … last round produces 1 Ac-SCoA and 1 Propionyl-SCoA

Formation of Ketone Bodies Occurs in the Liver

Isoprenes and Steroids

Oxidation of Ketone Bodies by Non-hepatic Tissues

Requires Glucogenic Intermediates, Glucose can not be made from Ac-SCoA

EOC Problem 16: About use of fatty acids in Diabetics.

Things to Know and Do Before Class

1. Review structure of fat, general concepts of digestion of fat.

2. Role of glucagon to mobilize fat utilization.3. Activation of fatty acids in cytoplasm for their

oxidation in the mitochondrion.4. Know the steps of β-oxidation…and what is

involved for the complete oxidation of the fatty acids to CO2 and water.

5. Know that unsaturated fatty acids are oxidized, but energy output is different (which way?).

6. Know that other forms of fatty acid oxidation exist.

7. Know how ketone bodies are made and used.8. EOC Problems: 1-4, 9, 10, 13, 16, 26, 28.