METABOLISM OF LIPIDS AND PROTEINS

Physiology Unit 1

In Physiology Today

Metabolism Quiz 2 Protein metabolism Lipid metabolism Lab Exam 1

Exam I

Alternate Fuel Sources

DistribuDon of Fuel Sources

PepDde Bond FormaDon DehydraDon Synthesis

Amino Acids as Fuel

When glucose levels are low, amino acids will be catabolized

Amino acids can be classified into 2 groups Glucogenic amino acids

Pyruvate - - -> glucose, glycogen, faOy acids Ketogenic amino acids

Acetyl CoA - - -> Krebs cycle, ketone bodies, faOy acids

Can not be converted to glucose

OxidaDve DeaminaDon The amine group from an

amino acid is removed and gives rise to NH3 (ammonia)

Oxygen replaces the nitrogen

Oxygen comes from spliYng H2O

Gives rise to a keto acid Result

convert to energy through Krebs cycle

convert to glucose or fat

Pyruvic acid is a keto acid!

Keto Acids

3 types of keto acids keto acid - pyruvic acid keto acid - acetoaceDc acid keto acid

An amino acid can be deaminated in the liver, producing an keto acid

keto acids are primarily used by hepatocytes as a fuel source and in lipogenesis

TransaminaDon

Alanine deaminaDon via transaminase yields pyruvate

Purpose: To make another type of amino acid by transferring an amine (NH2) from an exisDng amino acid to a keto acid

Amino Acid Pools

FaOy Acids as Fuel

Under resDng condiDons about 50% energy used comes from faOy acid catabolism Muscle Liver Kidneys

FaOy Acids as a Fuel Reserve

Adipose Dssue main source of faOy acids Intramuscular triglycerides (IMTG) contribute 5-50% CirculaDng lipoproteins minimal

Endogenous triglycerides Lipoproteins Formed by the liver Largest fuel reserve in body

DistribuDon in lean male adipose Dssue = 17,500 mmol skeletal muscle (IMTG) = 300 mmol plasma (VLDL) = 0.5 mmol

Lipolysis

Triglyceride catabolism Digests triglycerides into 3 faOy acids and glycerol

Glycerol Gluconeogenesis, Glycogenesis

In liver Glycolysis

Glycerol enters glycolysis as PGAL FaOy Acid

-oxidaDon = breakdown of faOy acid chain Produces ketones (acetyl CoA) - - -> many fates, dependant on the needs of the body

-OxidaDon Occurs in the matrix of mitochondria Enzymes remove 2-carbon (aceDc acid) molecules from COOH (carboxyl) end of faOy acid chain -Forms acetyl CoA

Acetyl CoA -Enters Krebs Cycle

ATP, NADH + H+ and FADH2 produced

Other uses of Acetyl CoA in the cell (or other cells)

FaOy Acid Structure

How Much ATP is Formed???

Example: Triglyceride with three 18-C faOy acid chains

G L Y C E R O L

FATTY ACID

FATTY ACID

FATTY ACID

New diagram showing carboxyl attachment to glycerol

For Each 18 C FaOy Acid Chain: 8 bonds

1 NADH + H+ + 1 FADH2 per bond

9 acetyl CoA

each acetyl CoA -----> Krebs cycle 1 ATP X 9 = 9 ATP

3 NADH + H+ X 9 = 27 NADH + H+ 1 FADH2 X 9 = 9 FADH2

CC CC CC CC CC CC CC CC CC

ATP From OxidaDon of One FaOy Acid Chain

ATP = NADH + H+

8 + 27 = 35 NADH + H+ 35 X 3 =

FADH2 8 + 9 = 17 FADH2 17 X 2 =

105 ATP

9 ATP

34 ATP 9 ATP 105 ATP +34 ATP 148 ATP -1 ATP 147 ATP

Cost of ini*a*ng -oxida*on

How Much ATP for the EnDre Triglyceride?

Glycerol converted back to PGAL total ATP produced = 20

Three 18-C faOy acid chains 3 x 147 ATP = 441 ATP

Grand total 441 + 20 = 461 ATP

Ketone Bodies

Products of faOy acid catabolism Produced at the branch point if sufficient ATP Produced if Krebs can not keep up with the amount of Acetyl CoA that is being produced

Formed by joining together 2 acetyl There are three ketone bodies:

acetone (3C) acetoaceDc acid (4C) -hydroxybutyric acid (4C)

Can be metabolized by the brain if necessary