Metabolism of Nutrients

Eko Widodo

Metabolism◦The sum total of all the chemical reactions that go on in living cells

Energy Metabolism◦Includes all the reactions by which the body obtains & spends energy from food

Metabolism

Metabolic reactions take place inside cells, especially liver cells

Anabolism is the building up of body compounds and requires energy.

Catabolism is the breakdown of body compounds and releases energy.

The Site of Metabolic Reactions

The Site of Metabolic Reactions

From CHO → glucose From fats → glycerol & FA From proteins → AA

4 basic units used in metabolic pathway

Alcohol can disrupt normal metabolic pathways (Highlight 7)

Energy Yielding Nutrients

ATP – adenosine triphosphate◦ High-energy storage compound◦ Captures some energy released during breakdown

of glucose, glycerol, fatty acids, and amino acids

The Transfer of Energy in Reactions - ATP

Adenosine Triphosphate (ATP)

Hydrolysis of ATP occurs simultaneously with reactions that will use that energy◦ Coupled reactions◦ Energy released from breakdown of one

compound used to create bond in formation of another

The Transfer of Energy in Reactions - ATP

Co-enzymes are organic molecules that work with enzymes to facilitate their activity.

Enzymes & co-enzymes are helpers in metabolic reactions.

Some B vit serve as coenzymes to enzymes that release energy from glucose, glycerol, FA & AA.

Enzymes & Co-enzymes – Helpers in Metabolism

Basic units enter metabolic pathways. During catabolism, the body separates atoms of basic units.◦ Glucose: 6 C◦ Glycerol: 3 C◦ FA: even number of C (commonly 16 or 18)◦ AA: 2, 3 or more C, with N attached

While each starts down a different path – 2 by-products are common ◦ pyruvate & acetyl-coA

Eventually all enter the TCA cycle & electron transport chain

Breaking Down Nutrients for Energy

Glucose splitting 6-C Glucose → two 3-C compounds →

Pyruvate

Glucose

anaerobic

Pyruvate

Glycolysis

If cell needs energy (& O2 is available), it removes COOH group from pyruvate to produce 2 C compounds that bonds with CoA to form Acetyl CoA

Pyruvate

Acetyl CoA

Absence of sufficient O2 (or mitochondria) pyruvate is converted to lactic acid

Pyruvate

anaerobic

Lactate Lactate recycled to

glucose in liver by Cori cycle

Pyruvate to Acetyl CoA

aerobic

Paths of Pyruvate & Acetyl CoA

3-C glycerol is easily converted to pyruvate Also easily converted to glucose

Glucose

Glycerol

Pyruvate

Glycerol to Pyruvate

FA are taken apart in 2-C units through fatty acid oxidation.

2-C units split off & combine with CoA to form Acetyl CoA.

If cell doesn’t need energy, acetyl CoA molecules combine to create TG.

Fatty Acids to Acetyl CoA

Deaminated first (lose N)

Catabolized in a variety of ways: ◦ Pyruvate glucose◦ Acetyl CoA more energy or body fat◦ Directly into TCA Cycle generate energy

Amino Acids Breakdown

Amino Acids◦ Deamination results in two products:

Keto acid Ammonia

◦ Transamination is the transfer of the amino group from an amino acid to a keto acid.

◦ Ammonia is converted to urea—a much less toxic compound—in the liver.

◦ Urea is excreted through the kidneys to rid the body of unused nitrogen.

Amino Acids Breakdown

In Summary◦ Glucose and fatty acids are primarily used for

energy, amino acids to a lesser extent.◦ Glucose is made from all carbohydrates, most

amino acids and the glycerol portion of fat.◦ Protein is made from amino acids.◦ Glucose can be made into nonessential amino

acids if nitrogen is present.◦ All energy-yielding nutrients consumed in

excess can contribute to fat storage.

Breaking Down Nutrients for Energy

TCA Cycle – tricarboxylic acid cycle (akaKreb’s cycle)

Oxaloacetate picks up acetyl CoA & drops off 2-C & returns to pick up another acetyl CoA.

As acetyl CoA breaks to CO2, H atoms with their electrons are removed.

Coenzymes made from B vitamins take H & electrons & transfers them to ETC.

Breaking Down Nutrients for Energy – the final steps

Electron Transport Chain (ETC) Consist of a series of proteins that serve as

electron carriers. These carriers are inside inner membrane of mitochondria.

In ETC, energy is captured in bonds of ATP molecules.

ATP leaves mitochondria & enters cytoplasm, where it can be used for energy.

Breaking Down Nutrients for Energy – the final steps

Kcal/gram Each ATP holds energy & Kcal measures

energy, so the more ATP generated the more Kcal collected. ◦One glucose molecule yield 36-38 ATP

when oxidized completely.◦One 16 carbon FA yield 129 ATP when

oxidized completely.

When energy intake exceeds energy output, there is a gain in weight.

Fat cells enlarge & multiply regardless of whether the excess comes from protein, CHO or fat.

Most direct & efficient pathway to body fat is dietary fat.

Energy Balance - Surplus

Body needs energy all the time Relies on energy stores between meals

◦ glycogen◦ fatty acids◦ lean mass tissue .. least preferred

Energy Balance

Fasting—Inadequate Energy◦ Glucose needed for the brain◦ Protein meets glucose needs◦ The shift to ketosis

Ketones are produces when glucose is not available.◦ Ketosis causes a suppression of the appetite.◦ Slowing of metabolism

Energy Balance – Fasting/Starvation

Fasting—Inadequate Energy◦ Symptoms of starvation

Muscle wasting Decreased heart rate, respiratory rate, metabolic

rate, and body temperature Impaired vision Organ failure Decreased immunity Depression, anxiety, and food-related dreams

Energy Balance – Fasting/Starvation

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