lipid metabolism

lipid metabolism

• triglyceride is a molecule that is made up of a glycerol molecule and fatty acids

• only triglycerides routinely oxidized for energy

• two building blocks oxidized separately:
  - glycerol —> glycolysis glycerol can go through glycolysis
  - fatty acids —> B oxidation fatty acids go through process where they get broken down and energy is extracted by beta oxidation

Energy density of macronutrients

• greater energy yield:
  - fat= 9 kcal per gram (9000 calories per gram)
  - CHO= 4kcal per gram (4000 calories per gram)
  - protein= 4 kcal per gram (4000 calories per gram)

• lipids are energy dense relative to carbs and protein

Triglyceride formation

• made up of a glycerol molecule plus the three fatty acids attached to each carbon of the glycerol

• glycerol is a three carbon molecule and associated with each carbon there is a fatty acid
  - three fatty acids give it the name triglyceride

• you can get triglycerides through your diet or it can be made in your body

• large molecule

• how we store lipid inside cells

• structure of cooking oil and lard

Similarities and differences between phospholipid and triglyceride

• one of the fatty acids of the triglyceride is replaced with a phosphorus containing group or vice versa
  - the phospholipid is produced at the border of the smooth and rough ER
  - triglyceride is produced in the smooth er

• similarities: both synthesized inside cells within the endoplasmic reticulum

• very similar to phospholipid where you have two fatty acids, each attached to a separate carbon and you have a phosphorus containing group attached to the third carbon
  - phospholipid make up plasma membrane

How does a triglyceride get across the the plasma membrane

• lipase: enzyme that breaks down the triglyceride into its components (a glycerol and its three fatty acids)

• once this is done the glycerol and fatty acids can be transported across the plasma membrane

• once they are in the interstitial fluids we can recombine them to form a triglyceride

cell uses triglyceride as energy source

• glycerol ends up being broken down in glycolysis

• but the fatty acids enter beta oxidation

Beta (B) Oxidation

• glycerol is a three carbon molecule and can enter glycolysis as glyceraldehyde 3 phosphate
  - the glyceraldhyde 3 phosphate is important because that is the molecule that we extract electrons from the synthesis of ATP via substrate level phosphorylation
  - in the process we produce pyruvate

• this is where we extract those electrons and hydrogens and synthesize ATP via substrate level phosphorylation

• the pyruvate that was produced can be transported across the mitochondria, broken down, producing more NADH and synthesizing acetyl CoA

• then acetyl CoA can then enter into the Krebs cycle which generate more high energy electron carriers and ATP via substrate level phosphorylation

Products in glycolysis from glycerol **KNOW THESE NUMBERS**

• how many NADH are produced from a glycerol molecule?
  - in glycolysis: 1

• How many ATP do we produce in glycolysis from this glycerol?
  - 2

• How many pyruvate molecules do we produce from a glyceraldehyde three phosphate?
  - 1
  - glyceraldehyde 3 phosphate is a 3 carbon molecule and so is pyruvate, since we started with three carbons, we are ending with three carbons

Metabolism of fatty acids

• enter into beta oxidation

• can require energy for activation

• CoA is involved

• in beta oxidation we produce a lot of high energy electron cerriers and acytel CoA

differences between fatty acids and glycerol

• fatty acids enter a different metabolic pathway
  - beta oxidation

Similarities between glycerol and fatty acids

• they both strip off hydrogens and electrons and produce NAD

• aerobic metabolism of a glycerol molecule and metabolism of fatty acids can produce acetyl CoA

Fatty acid

• long chain of carbons with a bunch of hydrogens

• as the 18 carbon fatty acid makes its way through beta oxidation and we strip off hydrogens and electrons, this produces acetyl CoA
  - Acetyl CoA has 2 carbons from one cycle

• that produces Acetyl CoA

• now down to a 16 carbon fatty acid and it passes through beta oxidation taking more hydrogens and electrons