Chapter 3 - Fat Metabolism

Sources of Fat During Exercise

intramuscular triglycerides, plasma FFA

Intramuscular Triglycerides

primary source during higher intensity

Plasma FFAs

from adipose tissue lipolysis

• tricglycerides → glycerol + 3 FFAs

FFA Converted To

acetyl-CoA and enters Krebs Cycle

When Are FFAs Important

• primary source during low-intensity exercise

• as muscle glycogen levels decline in long-duration exercise

Oxidation of Fat

fat stored in muscle and fat cells can supply 70,000 kcal in a lean adult

Only Useful Form of Fat For Energy

a triglyceride containing

• glycerol and 3 FFAs

Lipolysis

body breaking down triglycerides

• uses enzymes called lipases

During Formation of Triglycerides

• water is released

• Fatty acids needs to be free from hydrogen

Main Triglyceride Sources

• adipocytes

• intramuscular TG

• blood lipoproteins

What Happens When FFAs are Freed

they enter the blood and are transported to the muscle via diffusion

• increase FFAs in blood → increase their transport into muscle

Stages of Lipid Catabolism

1. mobilization

2. transport

3. uptake

4. activation

5. B-oxidation

6. mitochondrial oxidation

Mobilization (lipolysis)

triglyceride breakdown

• TG → 3 FFAs + glycerol (- 1 ATP)

• FFA → muscle → catabolized for energy

• glycerol → liver → converted to glucose

Mobilization Hormone

HSL → uses ATP to clean off an individual FFA

• 1 ATP used activating this

Transport

FAs released into the blood and bound to carrier protein (albumin)

• once in the cell FAs are activated then transported into the mitochondria

Uptake

enter muscle cytosol (active transport)

• FAs require special transport proteins to get across muscle cell membrane

Activation

fatty acids are converted into fatty acyl-CoA using ATP

• lose 1 ATP

Long Chain Fatt Acyl-CoA

enters the mitochondria using the carnitine shuttle

Carnitine Palmitoyltransferase (CPT) System

take fatty acyl-CoA and move it across mitochondrial membrane

B-Oxidation Occurs In

the mitochondrial matrix

B-Oxidation

Fatty Acyl-CoA broken down into acetyl-CoA

• produces NADH and FADH2

• then acetyl-CoA enters the Krebs Cycle to produce ATP

Acyl CoA Dehydrogenase

fatty acyl-CoA to unsaturated acyl-CoA

• generates one FADH2

B-hydroxyacyl CoA Dehydrogenase

B-hydroxy acyl-CoA to B keto acyl-CoA

• generates one NADH + H+

B-Oxidation Simplified

• # of carbons the FA has

• #C/2 - 1 = # of cycles

• # of acetyl CoA = # of C/2

Mitochondrial Oxidation

products of B-oxidation go to Krebs Cycle and ETS

• FADH2 and NADH+ goes to ETS

• acetyl-CoA go to Krebs Cycle

Each Cycle of B-Oxidation Produces

• 1 NADH → 2.5 ATP

• 1 FADH2 → 1.5 ATP

• 1 Acetyl-CoA → 10 ATP

• Total = 14 ATP

Glycerol Can Be Used As

an energy source

• must be converted to a form that can enter glycolysis

• does not contribute much during exercise

1 ATP Necessary to Phosphorylate Glycerol

to glyeraldehyde 3-phosphate (G3P)

• reduces NAD+ to NADH

• then proceeds through glycolysis to pyruvate

Glycerol Metabolism

glycerol = glyceraldehyde 3-phosphate

glyceraldehyde 3- phosphase

• 2 ATP + 2 NADH + Acetyl CoA

• 1 glycerol = 17 ATP (but - 1) so 16!

Protein

contributes but very little (<5%)

• amino acids

• must be converted

• enter energy pathways

CHO vs Fat

CHO is 20% more O2 efficient

• allowing us to exercsie at higher pace

• CHO gives less ATP than fat