Concepts

ATP

Adenosine triphosphate, the main energy currency of the cell, generated from the metabolism of carbohydrates, fats, and proteins.

Hydrophobic

Lacking affinity for water; tending to repel and not absorb water. Lipids are hydrophobic.

Triglyceride

A glycerol-based lipid made when three fatty acids link with a glycerol backbone by ester bonds. It is the most predominant lipid form in nature.

Ester bond

The chemical bond that links fatty acids to the glycerol backbone in lipids like triglycerides.

Saturated fatty acid

A fatty acid having all single bonds between carbon atoms in its hydrocarbon chain.

Unsaturated fatty acid

A fatty acid having at least one double bond between carbon atoms in its hydrocarbon chain.

Omega-3 fatty acid

An unsaturated fatty acid with the first double bond from the methyl end at the third carbon, examples include ALA, EPA, and DHA.

Omega-6 fatty acid

An unsaturated fatty acid with the first double bond from the methyl end at the sixth carbon, examples include Linoleic acid and arachidonic acid.

Chylomicron

A large lipoprotein that transports triglycerides absorbed from the small intestine to other tissues.

Lipoprotein lipase (LPL)

An enzyme secreted by blood capillaries that breaks down triglycerides in chylomicrons, releasing fatty acids.

Lipolysis

The breakdown of triglycerides into glycerol and fatty acids.

Beta-oxidation

The breakdown of fatty acids into acetyl-CoA in the mitochondria to subsequently produce ATP.

Fed state

The metabolic state characterized by high blood glucose concentration, typically immediately after a meal.

Fasted state

The metabolic state characterized by low blood glucose concentration, occurring during fasting.

Insulin

A hormone secreted by the pancreas in response to high blood glucose, promoting anabolic processes.

Glucagon

A hormone secreted by the pancreas in response to low blood glucose, promoting catabolic processes.

Glycogenesis

The synthesis of glycogen from glucose, primarily in the liver and skeletal muscle.

Glycogenolysis

The breakdown of glycogen into glucose, releasing glucose into the bloodstream.

Gluconeogenesis

The synthesis of new glucose from non-carbohydrate precursors, primarily in the liver.

Acetyl-CoA

A central two-carbon molecule in metabolism that enters the Krebs cycle for ATP production.

Gross Energy

The total energy present in the diet, representing the energy in organic matter.

Digestible Energy

The gross energy minus the energy lost in feces.

Metabolizable Energy

The digestible energy minus the energy losses in urine and gases.

Net Energy

The metabolizable energy minus the heat produced by the animal.

Volatile Fatty Acids (VFAs)

Short-chain fatty acids produced by the fermentation of carbohydrates by rumen microorganisms.

Biohydrogenation

The process by which rumen microorganisms convert unsaturated fatty acids into more saturated fatty acids.

Isomerization

The first step in biohydrogenation where some cis double bonds are converted to trans double bonds.

Hydrogenation

The second step in biohydrogenation where hydrogen is added to the double bonds of fatty acids.

Pre-gastric esterase (lingual lipase)

A lipase secreted before the stomach that breaks down ester bonds in lipids.

ATP citrate lyase

An enzyme that catalyzes the conversion of citrate to acetyl-CoA in the cytoplasm.

Hexokinase

An enzyme that catalyzes the phosphorylation of glucose to glucose-6-phosphate.

Protein synthesis

The process of building proteins from amino acids, occurring in ribosomes.

Deamination

The removal of the amino group from an amino acid.

Urea cycle

A series of biochemical reactions that convert toxic ammonia into urea.

Anabolism

The branch of metabolism involving the synthesis of complex molecules from simpler ones.

Catabolism

The branch of metabolism involving the breakdown of complex molecules into simpler ones.

Glycolysis

The metabolic pathway that converts glucose into pyruvate, producing a small amount of ATP.

Krebs cycle

A series of biochemical reactions that oxidize acetyl-CoA, generating ATP, NADH, and FADH2.

Electron transport chain

The final stage of aerobic cellular respiration where electrons drive ATP synthesis.

Lactose synthesis

The production of lactose from glucose and galactose in the mammary gland.

Emulsification (of fat)

The process of breaking down large fat globules into smaller droplets for digestion.

Mixed micelles

Structures formed from monoglycerides, fatty acids, and bile salts in the small intestine.

Enterocyte

An absorptive cell lining the wall of the small intestine.

Glycerol-3-phosphate

An activated form of glycerol that serves as the backbone for triglyceride synthesis.

Fatty acyl-CoA (activated fatty acid)

A fatty acid molecule linked to coenzyme A, required for triglyceride synthesis and beta-oxidation.