2.2 Macronutrients: structure, properties, and functions
3 min read•august 7, 2024
Macronutrients are the building blocks of our diet. , , and each play unique roles in our bodies, from to . Understanding their properties is key to grasping how food fuels us.
This section dives into the nitty-gritty of macronutrients. We'll explore their basic units, like and , and how they combine to form complex structures. We'll also look at how they behave and change in different conditions.
Macronutrient Classes
Types of Macronutrients
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- Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen atoms, usually with a 2:1 ratio of hydrogen to oxygen (empirical formula Cm(H2O)n)
- Proteins are large biomolecules consisting of one or more long chains of amino acid residues
- Proteins perform a vast array of functions within organisms, including catalyzing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells and organisms, and transporting molecules from one location to another
- Lipids are a diverse group of compounds that are united by a common feature of being hydrophobic ("water-fearing") due to their predominantly hydrocarbon makeup
- Lipids serve many functions in living organisms, including energy storage, signaling, and acting as structural components of cell membranes
Macronutrient Building Blocks
Carbohydrate Building Blocks
- Monosaccharides are the simplest carbohydrates and are often called single sugars
- They are the building blocks from which all bigger carbohydrates are made (glucose, fructose, galactose)
- are polymeric carbohydrate molecules composed of long chains of monosaccharide units bound together by
- This carbohydrate can be digested to release energy for the body (starch) or serve as structural components (cellulose, chitin)
Protein and Lipid Building Blocks
- Amino acids are organic compounds that contain both amino and carboxyl functional groups, along with a side chain (R group) specific to each amino acid
- Amino acids can be linked in varying sequences to form a vast array of proteins
- are long-chain hydrocarbon molecules with a carboxylic acid group at one end
- Fatty acids are the building blocks of many complex lipids such as , , and
Macronutrient Properties and Changes
Protein Denaturation and Amino Acid Essentiality
- is a process in which proteins lose their folded structure by application of some external stress or compound such as a strong acid or base, a concentrated inorganic salt, an organic solvent, radiation or heat
- Denaturation disrupts the normal alpha-helix and beta sheets in a protein and uncoils it into a random shape
- Denaturation results in the loss of protein function and can lead to aggregation and precipitation of the unfolded protein
- are amino acids that cannot be synthesized from scratch by the organism fast enough to supply its needs, and must therefore be supplied in the diet
- The nine amino acids humans cannot synthesize are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine
Lipid Properties
- is the oxidative degradation of lipids, a complex process whereby free radicals "steal" electrons from the lipids in cell membranes, resulting in cell damage and rancidity of fats
- Antioxidants can protect against lipid oxidation by neutralizing free radicals
- have no double bonds between the carbon atoms of the fatty acid chain and are thus "saturated" with hydrogen atoms
- Saturated fats are typically solid at room temperature (butter, lard)
- have one or more double bonds in the fatty acid chain
- have only one double bond (olive oil) while have two or more double bonds (fish oil)
- Unsaturated fats are typically liquid at room temperature
Carbohydrate Properties
- The is a value assigned to foods based on how slowly or quickly they cause increases in blood glucose levels
- Foods low on the glycemic index (≤55) release glucose slowly and steadily (whole grains, legumes)
- Foods high on the glycemic index (≥70) release glucose rapidly (white bread, candy)
Key Terms to Review (21)
Amino acids: Amino acids are organic compounds that serve as the building blocks of proteins, composed of an amino group, a carboxyl group, and a unique side chain. They play essential roles in various biological processes, including enzyme function, hormone production, and the formation of neurotransmitters, making them crucial macronutrients for all living organisms.
Carbohydrates: Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, typically found in foods as sugars, starches, and fibers. They play a vital role as a primary energy source for the body and have a significant impact on food science, food chemistry, and nutrition.
Cell structure: Cell structure refers to the organized arrangement of various components within a cell that contribute to its function and integrity. These components include the cell membrane, cytoplasm, organelles, and genetic material, all of which play crucial roles in the overall functioning of living organisms. Understanding cell structure is essential for grasping how macronutrients interact with cells to provide energy, support growth, and facilitate metabolic processes.
Energy storage: Energy storage refers to the process of capturing and holding energy for later use, primarily in the form of lipids in biological systems. This stored energy is crucial for various physiological functions, enabling organisms to survive during periods of low food intake or high energy demand. Lipids serve as a concentrated source of energy and play a significant role in overall nutrition, impacting metabolic processes and health.
Essential Amino Acids: Essential amino acids are amino acids that cannot be synthesized by the body and must be obtained through diet. They play a crucial role in protein synthesis, tissue repair, and nutrient absorption, making them vital for overall health and well-being. Understanding these amino acids helps clarify their importance in protein structure, functional properties in food, and their role as macronutrients that provide energy and support bodily functions.
Fatty acids: Fatty acids are long hydrocarbon chains with a carboxylic acid group at one end, serving as the building blocks of lipids. These molecules can be saturated or unsaturated, influencing their physical properties and functions in biological systems, such as energy storage and membrane structure.
Glycemic Index: The glycemic index (GI) is a ranking system that measures how quickly carbohydrate-containing foods raise blood glucose levels after consumption. Foods with a high GI are rapidly digested and absorbed, causing a swift rise in blood sugar, while those with a low GI are digested more slowly, resulting in a gradual increase. This concept is vital for understanding how different carbohydrates can affect energy levels and overall health, particularly in relation to sweeteners and sugar alternatives, the functional properties of carbohydrates in foods, and the role of macronutrients in nutrition.
Glycosidic linkages: Glycosidic linkages are covalent bonds that connect monosaccharides to form disaccharides and polysaccharides, playing a crucial role in the structure and function of carbohydrates. These linkages are formed through a dehydration reaction, where a water molecule is released as two sugar molecules bond together. The type of glycosidic linkage, whether alpha or beta, affects the properties and digestibility of the resulting carbohydrate.
Lipid oxidation: Lipid oxidation is a chemical process where lipids, primarily unsaturated fats, react with oxygen, leading to the degradation of fats and the formation of off-flavors, odors, and potentially harmful compounds. This process is significant in food science as it impacts flavor, nutritional quality, and the shelf-life of food products.
Lipids: Lipids are a diverse group of hydrophobic organic compounds that are insoluble in water but soluble in organic solvents. They play crucial roles in energy storage, cellular structure, and signaling within biological systems. As one of the primary macronutrients, lipids are essential for maintaining proper physiological functions and contribute to the flavor, texture, and nutritional value of foods.
Monosaccharides: Monosaccharides are the simplest form of carbohydrates, consisting of single sugar molecules that cannot be hydrolyzed into smaller carbohydrates. These basic units serve as the building blocks for more complex carbohydrates and play essential roles in energy metabolism and cellular functions.
Monounsaturated fats: Monounsaturated fats are a type of dietary fat that contains one double bond in its fatty acid chain, which makes it liquid at room temperature but solid when chilled. These fats are known for their health benefits, including improving heart health and lowering bad cholesterol levels, connecting them to essential functions of macronutrients and the classification of lipids.
Phospholipids: Phospholipids are a class of lipids that are a major component of all cell membranes, consisting of two fatty acids, a glycerol unit, and a phosphate group. They play crucial roles in the structure and function of cellular membranes, affecting permeability and fluidity, while also serving as important emulsifiers in food systems.
Polysaccharides: Polysaccharides are complex carbohydrates formed by long chains of monosaccharide units linked together by glycosidic bonds. They play vital roles in energy storage and structural support within living organisms, highlighting their importance in the classification and structure of carbohydrates as well as in the functions of macronutrients.
Polyunsaturated fats: Polyunsaturated fats are a type of dietary fat that contain more than one double bond in their chemical structure. These fats are typically liquid at room temperature and play a crucial role in overall health, as they can help reduce bad cholesterol levels and provide essential fatty acids that the body cannot produce on its own.
Protein Denaturation: Protein denaturation is the process in which proteins lose their natural structure and function due to the unfolding of their three-dimensional shape. This can occur due to factors such as heat, pH changes, or chemical exposure, disrupting the non-covalent interactions that maintain protein structure. Understanding protein denaturation is essential as it affects protein functionality in food and biological systems, leading to changes in texture, solubility, and biological activity.
Proteins: Proteins are large, complex molecules made up of amino acids that play critical roles in the structure, function, and regulation of the body's tissues and organs. They are essential macronutrients in food that contribute to bodily functions such as growth, repair, and immune response, making their study crucial in understanding food science, chemistry, and nutrition.
Saturated fats: Saturated fats are a type of fat molecule that contains no double bonds between carbon atoms, resulting in a straight-chain structure. This structure allows saturated fats to pack closely together, making them solid at room temperature. They are primarily found in animal products and some plant oils, playing a significant role in nutrition and health discussions.
Sphingolipids: Sphingolipids are a class of lipids that contain a backbone of sphingosine, a long-chain amino alcohol. They play critical roles in cellular structure and function, particularly in the formation of cell membranes, signaling pathways, and as components of lipid rafts, which are specialized areas in membranes that organize signaling molecules.
Triglycerides: Triglycerides are a type of fat (lipid) found in the blood, composed of three fatty acid molecules attached to a glycerol backbone. They are the most common form of fat in the body and serve as a significant energy source, while also playing a role in various physiological functions and being important for the structure of cell membranes.
Unsaturated fats: Unsaturated fats are a type of fatty acid that contain one or more double bonds in their carbon chains, which results in fewer hydrogen atoms compared to saturated fats. These fats are usually liquid at room temperature and can be classified into monounsaturated and polyunsaturated fats. Unsaturated fats play a crucial role in health, contributing to improved cholesterol levels and overall heart health.