What is NOT a Function of Lipids? Fats' Role

Lipids, a diverse group of molecules that include fats, oils, and waxes, play essential roles in various biological processes, yet understanding what is not a function of lipids is equally crucial for a comprehensive view of their significance. The American Heart Association, for example, emphasizes the importance of distinguishing between the established roles of lipids in energy storage and structural support, and misconceptions about their capabilities, like directly participating in DNA replication. While lipid metabolism, a process often studied using tools like gas chromatography-mass spectrometry (GC-MS), generates energy, lipids are not primarily involved in enzymatic catalysis, a function more attributable to proteins, as highlighted in the research of lipid expert Dr. Johanna Claeson. Furthermore, though lipids contribute to the formation of cellular membranes, specifically within the endoplasmic reticulum, they do not dictate the genetic code, a role reserved for nucleic acids.

The World of Lipids Unveiled: An Essential Overview

Lipids represent a structurally diverse class of biological molecules indispensable for life. Encompassing a wide array of compounds, including fats, phospholipids, steroids, and waxes, lipids are characterized by their insolubility in water and solubility in organic solvents.

Defining Lipids and Their Diversity

Unlike carbohydrates or proteins, lipids aren't defined by a single repeating monomer. Instead, they're grouped based on their shared physical property: hydrophobicity. This characteristic stems from their predominantly hydrocarbon structure.

This leads to a vast structural diversity, resulting in a correspondingly vast range of biological functions. From energy storage to cell membrane formation, the sheer variety of lipid forms is paramount to consider.

The Hydrophobic Imperative: Solubility and Implications

The hydrophobic nature of lipids arises from their predominantly nonpolar covalent bonds. These bonds share electrons equally, leaving no partial charges to attract water molecules.

This "water-fearing" property dictates their solubility. Lipids readily dissolve in nonpolar organic solvents like chloroform or ether, but not in water. This insolubility is essential for their role in forming biological barriers.

This principle underpins cellular compartmentalization and controls molecular interactions.

Biological Functions: A Multifaceted Role

Lipids participate in a remarkably broad spectrum of biological processes. Their functions extend far beyond simple energy storage, including structural roles, signaling pathways, and even enzymatic activity.

Energy Storage and Insulation

Triglycerides (fats) serve as the primary long-term energy storage molecules in animals. They store more energy per gram than carbohydrates or proteins. Additionally, subcutaneous fat layers provide insulation against cold temperatures.

Membrane Structure and Integrity

Phospholipids are the fundamental building blocks of cell membranes. Their amphipathic nature—possessing both hydrophilic and hydrophobic regions—allows them to spontaneously form lipid bilayers in aqueous environments.

Cholesterol, another lipid, inserts itself into the lipid bilayer, modulating its fluidity and stability.

Hormones and Signaling

Steroid hormones, such as testosterone and estrogen, act as chemical messengers, regulating a diverse array of physiological processes including growth, development, and reproduction.

These hormones bind to specific receptors, triggering changes in gene expression and cellular function.

Other Vital Roles

Beyond these major functions, lipids play a role in vitamin absorption, protecting surfaces, and thermal regulation. Understanding their diverse functionalities is critical for comprehending the complexity of biological systems.

Fats (Triglycerides): Powerhouse of Energy Storage

Having introduced the broader world of lipids, we now turn our attention to one of its most vital components: fats, also known as triglycerides. These molecules serve as the body's primary mechanism for long-term energy storage, as well as providing crucial insulation. Understanding their structure and function is paramount to grasping their biological significance.

The Structure of Triglycerides: Glycerol and Fatty Acids

Triglycerides are constructed from two fundamental building blocks: a glycerol molecule and three fatty acids. Glycerol is a simple three-carbon alcohol, serving as the backbone to which the fatty acids are attached.

Fatty acids, on the other hand, are long chains of carbon atoms, typically ranging from 12 to 24 carbons in length. A carboxyl group (-COOH) is attached to one end of the chain.

The carbon atoms are linked together by single or double bonds. This crucial aspect dictates whether a fatty acid is saturated (single bonds only) or unsaturated (one or more double bonds).

Energy Storage: The Primary Function of Fats

The primary role of triglycerides is to serve as a concentrated energy reservoir. The long hydrocarbon chains of fatty acids are rich in chemical energy. When the body needs energy, triglycerides are broken down through a process called lipolysis.

This releases the fatty acids, which are then oxidized to generate ATP (adenosine triphosphate), the cell's main energy currency.

Fats offer a distinct advantage over carbohydrates and proteins in terms of energy density. Gram for gram, fats yield more than twice the energy compared to carbohydrates or proteins. This efficiency makes triglycerides an ideal form of long-term energy storage.

This is particularly important for organisms that need to store energy reserves for periods of fasting, hibernation, or migration.

Insulation: A Secondary, but Important, Role

In addition to energy storage, triglycerides also play a significant role in insulation. Adipose tissue, which is primarily composed of fat cells containing triglycerides, is located beneath the skin and around vital organs.

This layer of fat provides thermal insulation. It helps to reduce heat loss from the body in cold environments. The insulation provided by fat is crucial for maintaining a stable body temperature, particularly in endothermic animals (warm-blooded animals) that generate their own body heat.

Furthermore, the fat surrounding organs also acts as a cushion. It protects them from physical trauma and injury. This protective function is especially important for delicate organs such as the kidneys and liver.

In conclusion, triglycerides are critical lipids with dual functions. They serve as the body's primary energy reserve and providing thermal and physical insulation. Their unique structure allows for efficient energy storage and release, making them indispensable for survival.

Phospholipids: Architects of the Cell Membrane

Having explored the structure and function of triglycerides, our attention now shifts to another class of lipids, phospholipids. These molecules are essential components of cell membranes and possess unique structural properties that dictate their function. Understanding the architecture of phospholipids is fundamental to grasping how cells maintain their integrity and interact with their environment.

Decoding the Phospholipid Structure

Phospholipids share a structural backbone with triglycerides but with a crucial modification: one of the fatty acids is replaced by a phosphate group.

This phosphate group is further modified with a polar molecule, such as choline or serine, rendering it hydrophilic (water-loving).

Therefore, a phospholipid molecule is comprised of three primary components:

• Glycerol Backbone: A three-carbon alcohol that serves as the foundation for the molecule.

• Two Fatty Acids: These long hydrocarbon chains are hydrophobic (water-fearing) and are typically saturated or unsaturated.

• Phosphate Group: A negatively charged group attached to the glycerol, modified with an additional polar molecule, giving the "head" its hydrophilic character.

The Amphipathic Nature: A Dichotomy of Interactions

The most distinctive characteristic of phospholipids is their amphipathic nature. This means that a single molecule possesses both hydrophobic and hydrophilic regions.

The fatty acid tails are nonpolar and repel water, while the phosphate head group is polar and readily interacts with water.

This dual nature is critical to their function in forming biological membranes.

The Lipid Bilayer: A Foundation of Cellular Life

The amphipathic properties of phospholipids drive them to self-assemble into a lipid bilayer in an aqueous environment.

The hydrophobic tails of the phospholipids align inward, shielded from water, while the hydrophilic heads face outward, interacting with the surrounding water molecules.

This arrangement forms a stable, selectively permeable barrier that encloses cells and defines their boundaries.

The lipid bilayer is not merely a static structure; it is a fluid mosaic, allowing for lateral movement of phospholipids and embedded proteins.

The Importance of Membrane Fluidity

Membrane fluidity is crucial for various cellular processes, including:

• Protein Function: Enabling proteins embedded in the membrane to diffuse and interact with each other.

• Cell Signaling: Facilitating the movement of signaling molecules within the membrane.

• Membrane Trafficking: Allowing for the fusion and budding of vesicles during endocytosis and exocytosis.

Cholesterol's Modulating Role

Cholesterol, another type of lipid, is also found within cell membranes. It acts as a fluidity buffer, maintaining membrane integrity over a range of temperatures.

At high temperatures, cholesterol reduces fluidity, preventing the membrane from becoming too permeable. At low temperatures, it prevents the membrane from solidifying.

In summary, phospholipids, with their unique amphipathic nature, are fundamental to the architecture of cell membranes.

Their ability to form a lipid bilayer provides a selectively permeable barrier that is essential for cellular life.

Steroids: More Than Just Hormones

Having explored the structure and function of phospholipids, our attention now shifts to another class of lipids, steroids. These molecules, often recognized for their hormonal roles, possess a unique structural blueprint and far-reaching influence within biological systems. Understanding the architecture of steroids unveils their diverse functionality, from maintaining membrane integrity to orchestrating complex physiological processes.

The Core Structure: Four Fused Rings

Steroids are distinguished by their characteristic structure: four interconnected carbon rings. This tetracyclic structure, consisting of three cyclohexane rings (six-carbon rings) and one cyclopentane ring (five-carbon ring), forms the foundation upon which various functional groups are attached.

These functional groups, such as hydroxyl (-OH) or carbonyl (=O) groups, dictate the specific properties and biological activity of each steroid molecule. The arrangement and nature of these attachments create the diversity that allows steroids to perform such varied roles in the body.

Key Players: Cholesterol, Testosterone, and Estrogen

Several steroids hold prominent positions in biological systems. Cholesterol, arguably the most well-known steroid, is an essential component of animal cell membranes. Testosterone and estrogen are critical sex hormones responsible for the development and maintenance of secondary sexual characteristics and reproductive functions.

Cholesterol: A Structural Cornerstone

Cholesterol is not only a precursor for steroid hormone synthesis, but also plays a crucial role in modulating the fluidity of cell membranes. By inserting itself between phospholipid molecules, cholesterol helps to maintain membrane integrity and prevent drastic changes in fluidity due to temperature fluctuations.

Testosterone and Estrogen: Hormonal Regulators

Testosterone, the primary male sex hormone, is responsible for the development of male secondary sexual characteristics such as muscle mass, bone density, and hair growth. Estrogen, the primary female sex hormone, governs the development of female secondary sexual characteristics, regulates the menstrual cycle, and supports pregnancy. These hormones exert their effects by binding to specific receptors within cells, initiating signaling cascades that alter gene expression and ultimately influence cellular function.

Beyond Hormones: Diverse Functions

The role of steroids extends beyond hormonal regulation. They also function as signaling molecules involved in various physiological processes, including inflammation, immune responses, and metabolic regulation. Certain steroids, for example, act as anti-inflammatory agents, helping to reduce swelling and pain in conditions such as arthritis.

The versatility of steroids stems from their unique structure and the ability to interact with a wide range of cellular targets. This capacity allows them to exert fine-tuned control over a multitude of biological pathways, solidifying their importance in maintaining homeostasis and overall health.

Waxes: Nature's Protective Coatings

Building upon our examination of steroids, we now turn to waxes, a class of lipids often overlooked but indispensable in the natural world. These molecules, characterized by their unique ester structure, serve as protective barriers for a diverse array of organisms. Let us delve into the structural and functional attributes of waxes and their crucial roles in providing waterproofing and defense.

The Chemistry of Waxes: Ester Linkages

Waxes are esters formed through the combination of long-chain fatty acids and long-chain alcohols. This esterification process yields a molecule that is highly hydrophobic, owing to the extensive nonpolar hydrocarbon chains.

The length and saturation of these chains determine the melting point and hardness of the wax. This also explains the solid consistency typically observed at room temperature. This is a critical attribute for their protective function.

Protective Functions: A Natural Shield

Waxes play a critical role as protective coatings across various biological systems. Their primary function stems from their exceptional water-repellent properties.

Waterproofing in Plants

Plants utilize waxes, often secreted by epidermal cells, to form a waxy cuticle on their leaves and stems. This cuticle minimizes water loss through transpiration, a process vital for survival, especially in arid environments.

Furthermore, the waxy coating protects against the entry of pathogens and herbivores, providing a physical barrier against external threats.

Protection in Animals

In the animal kingdom, waxes serve similar protective roles. Insects, for instance, secrete waxes to create a waterproof layer on their exoskeletons.

This layer prevents desiccation and offers protection against environmental hazards. Beeswax, secreted by honeybees to construct honeycombs, is a notable example. This offers both structural integrity and protection for the developing bee larvae and stored honey.

Defense Mechanisms

Beyond waterproofing, waxes contribute to defense mechanisms in certain organisms. Some plants employ waxes containing irritant compounds. This then deter herbivores, adding another layer of protection.

Beyond Protection: Other Roles

While their primary function is protection, waxes also play other roles. In some aquatic organisms, waxes contribute to buoyancy. Certain marine birds and mammals secrete waxes that enhance insulation against cold temperatures.

These additional functions highlight the versatility of waxes and their adaptation to diverse environmental conditions.

Waxes, though often taken for granted, are vital lipids that play crucial roles in protecting organisms from environmental stressors. Their unique ester structure and hydrophobic properties make them indispensable in providing waterproofing and defense. As we continue to explore the world of lipids, the importance of these often-understated molecules becomes increasingly clear.

Fatty Acids: Saturated, Unsaturated, and Essential

Lipids, in their diverse roles, owe much of their functionality to the specific fatty acids that comprise them. The type of fatty acid – whether saturated or unsaturated – profoundly impacts the lipid's properties and its subsequent biological effects. Furthermore, the crucial role of essential fatty acids, those that the body cannot synthesize, underscores the dietary significance of these molecules.

Saturated vs. Unsaturated Fatty Acids: A Structural Distinction

The fundamental difference between saturated and unsaturated fatty acids lies in their chemical structure, specifically the presence or absence of double bonds between carbon atoms within the hydrocarbon chain.

Saturated fatty acids possess a linear structure because they consist of carbon atoms entirely bonded to hydrogen atoms with single bonds. This linearity allows saturated fatty acid molecules to pack tightly together, resulting in solids at room temperature. Common examples include palmitic acid and stearic acid, frequently found in animal fats and some plant oils like coconut oil.

Unsaturated fatty acids, conversely, contain one or more double bonds. Each double bond creates a "kink" or bend in the hydrocarbon chain, disrupting the tight packing observed in saturated fatty acids. These kinks result in weaker intermolecular forces and lower melting points. Consequently, unsaturated fatty acids are typically liquids at room temperature, exemplified by oleic acid in olive oil and linoleic acid in sunflower oil.

Cis and Trans Unsaturated Fatty Acids

It's important to note that unsaturated fatty acids can exist in cis or trans configurations. Cis double bonds, the more common configuration found naturally, result in a more pronounced bend in the fatty acid chain. Trans double bonds, often formed during industrial processing (partial hydrogenation) of vegetable oils, create a less severe bend, somewhat resembling the shape of a saturated fatty acid.

Trans fats have been linked to adverse health effects, prompting regulations aimed at reducing their presence in processed foods.

Essential Fatty Acids: A Dietary Imperative

The human body can synthesize most of the fatty acids it needs. However, certain polyunsaturated fatty acids (PUFAs), termed essential fatty acids, cannot be synthesized endogenously. These must be obtained from the diet.

The two primary essential fatty acids are:

• Alpha-linolenic acid (ALA), an omega-3 fatty acid.
• Linoleic acid (LA), an omega-6 fatty acid.

The Importance of Omega-3 and Omega-6 Fatty Acids

These essential fatty acids serve as precursors for the synthesis of other important fatty acids and signaling molecules involved in a wide range of physiological processes, including:

• Inflammation: Omega-6 fatty acids tend to promote inflammation (necessary for immune response), while omega-3 fatty acids often have anti-inflammatory effects. Maintaining a balanced ratio of omega-6 to omega-3 is considered important for optimal health.
• Brain function: DHA (docosahexaenoic acid), an omega-3 fatty acid derived from ALA, is a major structural component of brain cell membranes and plays a vital role in cognitive function and neurological development.
• Cardiovascular health: Omega-3 fatty acids have been shown to reduce triglycerides, blood pressure, and the risk of heart disease.
• Cell membrane structure and function: Essential fatty acids contribute to the fluidity and integrity of cell membranes, impacting cellular communication and nutrient transport.

Dietary Sources of Essential Fatty Acids

Good sources of ALA include flaxseeds, chia seeds, walnuts, and canola oil. LA is abundant in vegetable oils such as sunflower, safflower, and corn oil. Fatty fish, such as salmon, tuna, and mackerel, are excellent sources of pre-formed DHA and EPA (eicosapentaenoic acid), other omega-3 fatty acids derived from ALA. A balanced and varied diet rich in these sources is essential for ensuring adequate intake of these critical nutrients.

Fat-Soluble Vitamins: Riding the Lipid Wave

Lipids, in their diverse roles, owe much of their functionality to the specific fatty acids that comprise them. The type of fatty acid – whether saturated or unsaturated – profoundly impacts the lipid's properties and its subsequent biological effects. Furthermore, the crucial role of essential fatty acids in the diet highlights yet another facet of lipid importance: their involvement in the absorption and utilization of fat-soluble vitamins, which are absolutely essential for various physiological processes.

The A, D, E, K Quartet

Four vitamins – A, D, E, and K – are classified as fat-soluble, meaning they require the presence of lipids for their proper absorption from the digestive tract and subsequent transport throughout the body. Unlike water-soluble vitamins, these cannot be readily dissolved in aqueous environments. Consequently, they rely on dietary lipids to facilitate their journey from the gut to the tissues where they exert their effects.

The Lipid-Dependent Absorption Process

The absorption of fat-soluble vitamins is intricately linked to lipid digestion and metabolism.

Dietary lipids, including triglycerides, cholesterol, and phospholipids, are emulsified by bile salts in the small intestine. This emulsification process increases the surface area available for enzymatic action by pancreatic lipases.

These lipases break down triglycerides into monoglycerides and free fatty acids, which then form micelles.

Micelles are small, spherical aggregates of lipids and bile salts that effectively solubilize the hydrophobic fat-soluble vitamins.

These vitamin-laden micelles then diffuse through the aqueous environment of the intestinal lumen and come into contact with the enterocytes, the absorptive cells lining the intestinal wall.

Within the enterocytes, the fat-soluble vitamins, along with the digested lipids, are packaged into chylomicrons.

Chylomicrons are large lipoprotein particles that are specifically designed for transporting dietary fats and fat-soluble vitamins through the lymphatic system and, eventually, into the bloodstream.

Why Lipids are Indispensable

The reliance of vitamins A, D, E, and K on lipids for absorption underscores the critical importance of adequate dietary fat intake.

Diets severely restricted in fat can lead to malabsorption of these essential nutrients, potentially resulting in a range of health problems.

Vitamin A deficiency, for example, can impair vision and immune function. Vitamin D deficiency can compromise bone health.

Vitamin E deficiency can damage cells through oxidative stress.

Finally, Vitamin K deficiency can impair blood clotting.

Therefore, understanding the interplay between lipids and fat-soluble vitamins is essential for maintaining optimal health and preventing nutrient deficiencies. This understanding further emphasizes the multifaceted and indispensable role of lipids in human physiology.

Biological Roles: Energy, Structure, and Regulation

Lipids, in their diverse roles, owe much of their functionality to the specific fatty acids that comprise them. The type of fatty acid – whether saturated or unsaturated – profoundly impacts the lipid's properties and its subsequent biological effects. Furthermore, the crucial role of essential fatty acids and the structural importance of glycerol backbones underscore their significance. Let's delve into the core biological functions where lipids reign supreme.

Energy Storage: The Triglyceride Advantage

Triglycerides, the most abundant type of lipid, are the body's primary means of long-term energy storage. This makes them a critical fuel reserve. Their ability to pack more energy per gram compared to carbohydrates or proteins is due to their highly reduced carbon atoms.

This compact energy density is essential for survival. It allows organisms to store large amounts of energy without significantly increasing body mass. When energy is needed, triglycerides are broken down via lipolysis, releasing fatty acids that can be oxidized to produce ATP, the cell's energy currency.

Structural Integrity: Phospholipids and Cell Membranes

Phospholipids are indispensable components of cell membranes. These amphipathic molecules spontaneously form a lipid bilayer in aqueous environments. This creates a selectively permeable barrier. The hydrophobic tails of the phospholipids cluster together, while the hydrophilic heads face outwards, interacting with the surrounding water.

Cholesterol, another lipid, is embedded within the phospholipid bilayer. It modulates membrane fluidity. At high temperatures, cholesterol reduces fluidity, while at low temperatures, it prevents the membrane from solidifying. This ensures proper membrane function over a wide range of temperatures.

Insulation: Protecting Against the Elements

The insulating properties of lipids are crucial for maintaining body temperature. Adipose tissue, composed primarily of fat cells (adipocytes) containing triglycerides, is found beneath the skin and around vital organs.

This layer of fat acts as a thermal barrier, reducing heat loss in cold environments. It helps conserve energy. Marine mammals, such as whales and seals, rely heavily on thick layers of blubber for insulation, enabling them to survive in frigid waters.

Steroid Hormones: Chemical Messengers

Steroid hormones, derived from cholesterol, are potent signaling molecules that regulate a wide range of physiological processes. These processes include reproduction, metabolism, and immune function. Examples include testosterone, estrogen, cortisol, and aldosterone.

These hormones bind to specific receptor proteins inside cells. This triggers changes in gene expression. This alters cellular function. Their influence is far-reaching, affecting growth, development, and overall homeostasis.

Facilitating Vitamin Absorption: A Lipid-Dependent Process

Lipids play a crucial role in the absorption of fat-soluble vitamins (A, D, E, and K). These vitamins are hydrophobic and require lipids for efficient absorption from the small intestine.

Dietary fats are emulsified by bile salts, forming micelles that transport the fat-soluble vitamins to the surface of the intestinal cells. Once absorbed, these vitamins are packaged into chylomicrons. Chylomicrons are lipoproteins that transport them through the lymphatic system and into the bloodstream. Without adequate dietary fat, the absorption of these essential vitamins is compromised, leading to potential deficiencies.

What Lipids Don't Do: Clearing Up Common Misconceptions

Lipids, in their diverse roles, owe much of their functionality to the specific fatty acids that comprise them. The type of fatty acid – whether saturated or unsaturated – profoundly impacts the lipid's properties and its subsequent biological effects. Furthermore, the crucial role of essential fatty acids highlights their importance for overall health. However, despite their significance, there exist several misunderstandings regarding the functions that lipids actually perform within biological systems. It is therefore imperative to clarify what lipids do not do, dispelling misconceptions that can lead to inaccurate understandings of their biological roles.

Lipids Are Not Primary Carbohydrate Storage Molecules

While both lipids and carbohydrates serve as energy storage molecules, their roles differ significantly. Carbohydrates, primarily in the form of glycogen in animals and starch in plants, serve as a rapidly accessible energy source.

Lipids, particularly triglycerides, are the body's primary means of long-term energy storage. They store more energy per gram than carbohydrates, but their energy is not as readily available for immediate use. The body prefers using carbohydrates for quick energy boosts and relies on lipids for prolonged activity or periods of fasting.

Lipids and Genetic Information: A Clear Distinction

It is crucial to emphasize that lipids do not play a role in encoding or transmitting genetic information. The molecules responsible for these critical functions are nucleic acids: DNA and RNA.

DNA contains the genetic blueprint for all living organisms, while RNA plays various roles in gene expression and protein synthesis. Lipids, with their hydrophobic nature and structural roles, are completely unrelated to these information-carrying processes. Misunderstanding this difference can lead to a flawed grasp of basic molecular biology.

Lipids Generally Lack Enzymatic Activity

Enzymes, the biological catalysts that accelerate biochemical reactions, are almost exclusively proteins. While some lipids can influence enzyme activity by modulating the cellular environment or acting as signaling molecules, they do not directly function as enzymes themselves.

Therefore, lipids do not possess the specific three-dimensional structures and active sites necessary to catalyze reactions. This distinction is vital for understanding how metabolic processes are regulated within cells.

Lipids and Direct Protein Synthesis: An Unrelated Pathway

Protein synthesis, the complex process of translating genetic information into functional proteins, is orchestrated by ribosomes, mRNA, tRNA, and various protein factors. Lipids do not participate directly in this process.

While lipids might influence the cellular environment where protein synthesis occurs, they are not directly involved in the steps of transcription, translation, or post-translational modification. Therefore, lipids play a structural and regulatory role, not an enzymatic one.

Hydrophobic Nature Prevents Water Transport

Lipids, by definition, are hydrophobic, meaning they repel water. This property makes them essential for forming barriers, such as cell membranes, that separate aqueous environments.

However, this hydrophobicity also means that lipids are not directly involved in the transport of water or water-soluble substances across these barriers. Water transport is primarily facilitated by specialized protein channels and aquaporins that allow controlled movement of water molecules through cell membranes.

In summary, while lipids are essential for various biological processes, it is important to have a clear understanding of what they do not do. By dispelling these common misconceptions, a more accurate and complete appreciation of their true roles in maintaining life is possible.

So, while lipids are powerhouses when it comes to energy storage, insulation, hormone production, and cell structure, remember that one thing they don't do is directly build muscle. You'll need protein for that! Hopefully, this cleared up any confusion on what is not a function of lipids, and you've got a better understanding of these essential fats and their real role in your body.