Biology I Unit 2

Didactic unit

Unit 2. The Chemistry of Life

Start!

CONTENT

2. Biogenic Elements

1. Unit presentation

3. Water Properties

6. Conclusions

4. Biomolecules

5. Vitamins and Nutrition

8. References

9. Chemistry Review

7. Unit Summary and Self-evaluation

1. Unit presentation

UNIT 2 PRESENTATION

In this unit, we will study the primary molecules that make up living organisms, including biogenic elements, carbohydrates, lipids, proteins, and nucleic acids. We will examine their structure, function, and presence in food. By understanding how these biomolecules affect our bodies, you can make informed choices about maintaining a balanced diet and improving quality of life.

1. Unit presentation

Introduction

"What you eat today can determine how you'll feel tomorrow: from the energy you have to how your body ages."

Have you ever wondered why certain foods give us energy while others make us feel tired? How do our daily food choices relate to aging and the development of chronic degenerative diseases like diabetes or hypertension? The answers to these questions can be found in the chemical components of food and how they interact with our bodies. In this unit, we will examine the essential molecules in living organisms and food, such as carbohydrates, lipids, and proteins, and understand their role in maintaining our vital functions. Understanding the chemical components of living organisms will help us understand their nutritional properties and make more informed decisions about what we eat, leading to a healthier and more sustainable lifestyle.

1. Unit presentation

Primary

Biogenic Elements

Secondary

Trace Elements

The Chemistry of Life

Physicochemical properties

Water

Role of water in living thing processes

Carbohydrates

Lipids

Structure and role of biomolecules

Proteins

Nucleic acids

Water-soluble vitamins

Vitamins and nutritional properties

Fat-soluble vitamins

Nutrition and diet

1. Unit presentation

Objectives

This second unit will allow you:

Recognize

Describe

Distinguish

Identify

biogenic elements in biological processes.

the nutritional properties of chemical components in foods.

the physicochemical properties of water.

the structure and function of organisms' biomolecules and vitamins.

2. Biogenic Elements

Are we really made of star stuff?

When we look at the stars, we may not realize that the matter we are made of originated from them. The atoms that make up living beings come from the Earth and its atmosphere, which were once part of a nebula in space. Renowned astronomer Carl Sagan correctly said we are "star stuff." Although the elements that make us are the same as those found throughout the universe, their proportions in living organisms are not exactly the same due to differences in their chemical properties.

Watch the following video and answer the questions

What are the four most abundant elements in the human body, and what percentage of our body do they represent?

How do oxygen and hydrogen combine to form a molecule crucial for life, and where is it primarily found in the body?

Why is carbon essential for forming macromolecules like DNA and proteins?

2. Biogenic Elements

BIOGENIC ELEMENTS

The table below displays the percentage of elements in the universe and living organisms. Which elements are abundant in the universe but not significant in living organisms?

Why are elements like helium and neon not found significantly in living organisms? What sets them apart from the other elements in the mentioned table?

2. Biogenic Elements

Primary biogenic elements

Out of the 92 naturally occurring elements known, around 25 are involved in the composition of living organisms and carry out functions within them. These elements are called biogenic elements.

The primary biogenic elements are essential for creating fundamental biomolecules like carbohydrates, lipids, proteins, and nucleic acids. They make up approximately 96% of living matter and include carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus.

1. General characteristics

2. Role in biological processes

2. Biogenic Elements

Secondary biogenic elements

Secondary biogenic elements, also known as essential secondary bioelements, comprise all biogenic elements with an abundance between 0.1% and 4.5%. Their presence is crucial in all living organisms.

Role in biological processes:

• Calcium is essential for forming bones, teeth, mollusk shells, coral skeletons, and sponges. It is also an essential element for muscle contraction and pollen tube formation.
• Potassium is involved in many cellular functions. Together with sodium, it creates the sodium-potassium pump, providing the cell membrane's electrical potential and regulating membrane permeability. Muscle and nervous system functions also require potassium.
• Magnesium participates in protein and nucleic acid synthesis, transporting substances across the cell membrane, muscle contraction, nerve impulse transmission, and oxidative phosphorylation.
• Like potassium, sodium, and calcium, chlorine influences the cell membrane potential, affecting electrical potential and permeability.

2. Biogenic Elements

Trace elements, also known as oligoelements, have concentrations below 0.1% in organisms and are not found in all living beings. This does not mean they are insignificant, as even a small amount is essential for survival. However, the absence of some can lead to the death of the organism.

Trace elements

Role in biological processes:

• Fluorine (F): Strengthens bones and teeth by forming fluorapatite, which makes them more resistant to decay and damage.
• Boron (B): Important in plant cell walls and believed to play a role in bone health and the regulation of mineral metabolism in animals.
• Cobalt (Co): A key component of vitamin B12, which is essential for the production of red blood cells and the functioning of the nervous system.
• Copper (Cu): Involved in iron metabolism, the formation of hemoglobin, and acts as a cofactor in many enzymes important for energy production and antioxidant defense.
• Iodine (I): Necessary for the synthesis of thyroid hormones, which regulate metabolism, growth, and development.
• Iron (Fe): A vital component of hemoglobin, which carries oxygen in the blood, and plays a role in cellular respiration and energy production.
• Manganese (Mn): Acts as a cofactor for enzymes involved in metabolism, bone formation, and the detoxification of free radicals.

• Silicon (Si): Believed to contribute to the formation of connective tissues, bones, and cartilage, and has a role in the strength and flexibility of these structures.
• Selenium (Se): An important antioxidant that helps protect cells from oxidative damage and supports the immune system.
• Zinc (Zn): Plays a role in DNA synthesis, cell division, protein synthesis, wound healing, and immune function. It also acts as a cofactor for various enzymes.
• Molybdenum (Mo): Acts as a cofactor in enzymes that metabolize sulfur-containing amino acids and other substances.
• Chromium (Cr): Enhances the action of insulin and helps regulate blood sugar levels.
• Tin (Sn): Thought to be involved in some enzymatic functions, although its biological role is not fully understood.
• Vanadium (V): May play a role in bone and tooth formation and has been shown to influence insulin activity.

2. Biogenic Elements

Biogenic Element's Deficiency and Excess Diseases in the Human Body

Deficiency

2. Biogenic Elements

Biogenic Element's Deficiency and Excess Diseases in the Human Body

Excess

3. Water Properties

WATER AND ITS IMPORTANCE FOR LIFE

Water is the most crucial inorganic molecule for living organisms. It is the most abundant substance in living beings and is essential for the development of life on the planet. This vital liquid covers two-thirds of the earth's surface (approximately 71%). However, only 3% of the water on earth is freshwater, most of which is frozen, and the rest is saltwater. As you may know, the water molecule has a molecular formula of H2O and is made up of two hydrogen atoms and one oxygen atom. It is formed through a covalent bond in which the atoms share electrons without gaining or losing them. The water molecule is polar because its internal charge is unevenly distributed, with the end where oxygen is located being somewhat negative and the end where the hydrogen atoms are located being somewhat positive. This polarity creates attraction between water molecules, forming brief hydrogen bonds.

ACID AND BASES

WATER IN LIVING THINGS

PROPERTIES

3. Water Properties

Physicochemical properties

3. Water Properties

Four emergent properties of water contribute to Earth’s suitability for life

Cohesive behavior

• Cohesion due to hydrogen bonding contributes to the transport of water and dissolved nutrients against gravity in plants. Therefore, it is a good component to give plants turgidity and maintain their shape.

• Adhesion, the clinging of one substance to another, also plays a role. Adhesion of water by hydrogen bonds to the molecules of cell walls helps counter the downward pull of gravity.
• Related to cohesion is surface tension, a measure of how difficult it is to stretch or break the surface of a liquid. At the interface between water and air is an ordered arrangement of water molecules, hydrogen-bonded to one another and to the water below. This gives water an unusually high surface tension, making it behave as though it were coated with an invisible film.

3. Water Properties

Four emergent properties of water contribute to Earth’s suitability for life

Moderation of temperature by water Water moderates air temperature by absorbing heat from air that is warmer and releasing the stored heat to air that is cooler. Water is effective as a heat bank because it can absorb or release a relatively large amount of heat with only a slight change in its own temperature.

• The specific heat of a substance is defined as the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1°C. Thus, because of water high specific heat, the water that covers most of Earth keeps temperature fluctuations on land and in water within limits that permit life.
• Water’s high heat of vaporization is another emergent property resulting from the strength of its hydrogen bonds, which must be broken before the molecules can exit from the liquid in the form of water vapor. As water evaporates, the surface of the liquid that remains behind cools down, that is called evaporative cooling. Evaporative cooling of water contributes to the stability of temperature in lakes and ponds and also provides a mechanism that prevents terrestrial organisms from overheating.

3. Water Properties

Four emergent properties of water contribute to Earth’s suitability for life

Floating of ice on liquid water Water is one of the few substances that are less dense as a solid than as a liquid. In other words, ice floats on liquid water. While other materials contract and become denser when they solidify, water expands.

• The ability of ice to float due to its lower density is an important factor in the suitability of the environment for life. If ice sank, then eventually all ponds, lakes, and even oceans would freeze solid, making life as we know it impossible on Earth.

3. Water Properties

Four emergent properties of water contribute to Earth’s suitability for life

Water: The Solvent of Life Water is a very versatile solvent, a quality we can trace to the polarity of the water molecule. As you observe the video, you will notice that water molecules surround the individual sodium and chloride ions, separating and shielding them from one another. The sphere of water molecules around each dissolved ion is called a hydration shell.

• Any substance that has an affinity for water is said to be hydrophilic.
• There are other substances that do not have an affinity for water. Substances that are nonionic and nonpolar actually seem to repel water; these substances are said to be hydrophobic.

3. Water Properties

Role of water in living things

Due to its properties, water plays highly significant roles in living organisms. These functions are described below:

• Solvent for substances: practically all biological reactions take place in an aqueous medium.
• Biochemical: water participates in many chemical reactions; for example, in hydrolysis during food digestion and as a source of hydrogen in photosynthesis, etc.
• Transport: water serves as the transport medium for substances from the outside to the inside of organisms and within the organism itself, sometimes involving considerable effort, as in the ascent of raw sap in trees.
• Structural: the volume and shape of cells that lack a rigid membrane are maintained thanks to the pressure exerted by the water inside them.
• Thermoregulation: this is due to water's high specific heat and heat of vaporization. For example, when animals sweat, they release water, which absorbs heat from the body to evaporate, causing the body to cool down as a result.
• Osmoregulation: It is the active regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content; that is, it maintains the fluid balance and the concentration of electrolytes to keep the body fluids from becoming too diluted or concentrated.

4. Biomolecules

THE STRUCTURE AND FUNCTION OF ORGANIC BIOMOLECULES

Biomolecules are divided into four groups based on their chemical structure and function. The groups and their respective roles are as follows:

• Carbohydrates - structure and energy
• Lipids - energy storage
• Proteins - cellular functioning
• Nucleic acids - reproduction and coding of proteins.

Organic biomolecules are complex molecules essential for living organisms' proper functioning. They are composed of C, H, O, N, and sometimes other elements. These molecules are critical in various biological processes, such as metabolism, growth, and reproduction. Understanding the structure and function of organic biomolecules is crucial in fields such as biochemistry, pharmacology, and medicine.

Carbon is the molecular "skeleton" in these biomolecules, providing great potential for structural variability. Each of these biomolecules is explained in detail later.

4. Biomolecules: Carbohydrates

Carbohydrates

The carbon skeletons of both glucose and fructose are six carbon atoms long. Other monosaccharides may have three to seven carbons. Five-carbon sugars, called pentoses, and six-carbon sugars, called hexoses, are among the most common. Functions

• They are necessary for chemical energy production, making them essential for the energy metabolism of living organisms.
• They play a role in forming structures like cell walls and membranes.
• They are components of cartilage, bones, and tendons.
• They are also present in nucleic acids.
• They are produced during the process of photosynthesis.

The name carbohydrate refers to a class of molecules ranging from the small sugar molecules dissolved in soft drinks to large polysaccharides, such as the starch molecules we consume in pasta and potatoes. If you count the numbers of different atoms in the fructose molecule in the figure above, you will find that its molecular formula is C6H12O6, identical to that of glucose. Thus, glucose and fructose are isomers.

Polysaccharides

Disaccharides

Food Sources

4. Biomolecules: Lipids

Simple lipids

Derived lipids

Lipids

These lipids are made of C, H and O. Their structure are comprised of two simple molecules: fatty acids and –OH groups.

There are obtained from the transformation or degradation of simple/complex lipids. They include substances such as sterols and fat-soluble vitamins.

Lipids are diverse compounds that are grouped together because they share one trait: They do not mix well with water. Lipids consist mainly of carbon and hydrogen atoms linked by nonpolar covalent bonds. Some of the may contained sulfur or phosphorus. Lipids also differ from carbohydrates, proteins, and nucleic acids in that they are neither huge macromolecules nor polymers built from similar monomers.

• Structural components of membranes and cellular tissues.
• Energy reserve
• They act as thermal insulator and protect certain organs from physical blows.
• Functional components of hormones
• Catalytic activities.

Cholesterol

Progesterone

Complex lipids

These are composed of C, H, and O and may contain other elements such as N, P, or S. They serve more specific structural and metabolic functions in organisms.

Testosterone

Estrogen

Food Sources

Aldosterone

Cortisol

4. Biomolecules: Proteins

Proteins

• Proteins are macromolecules made up of long chains of amino acids. Amino acids are the basic building blocks of proteins, and each one consists of the following chemical groups:
• Amino Group (–NH2): A basic functional group.
• Carboxyl Group (–COOH): An acidic functional group.
• Side Chain or R-group: The variable part of each amino acid that determines its chemical and physical properties.
• Hydrogen Atom (–H): Attached to the alpha carbon, which is the central carbon atom to which the other groups are bonded.

Amino acids are linked together by peptide bonds, which form between the amino group of one amino acid and the carboxyl group of another, releasing a molecule of water (dehydration synthesis).

FUNCTION

CHEMICAL COMP.

STRUCTURE

SOLUBILITY

4. Biomolecules: Nucleic acids

RNA

RNA is a single-stranded molecule composed of nucleotides. Each nucleotide consists of a phosphate group, a ribose sugar, and a nitrogenous base (adenine, uracil, cytosine, or guanine). Uracil replaces thymine found in DNA.

Role

• Messenger RNA (mRNA): Carries genetic information from DNA in the nucleus to the ribosome, where it is translated into proteins.
• Ribosomal RNA (rRNA): Part of the ribosomes, where protein synthesis occurs.
• Transfer RNA (tRNA): Transports amino acids to the ribosome during protein synthesis, matching its anticodons with mRNA codons.

VS

DNA

DNA is a double-helix molecule composed of two nucleotide chains. Each nucleotide consists of a phosphate group, a deoxyribose sugar, and a nitrogenous base (adenine, thymine, cytosine, or guanine).

Role

DNA stores and transmits genetic information that guides the development, function, and reproduction of organisms. It is located in the nucleus of eukaryotic cells and in the cytoplasm of prokaryotic cells. Additionally, DNA is found in the mitochondria and chloroplasts of eukaryotic cells.

5. Vitamins and nutrition

VITAMINS

Role of vitamins

Vitamins are organic compounds essential for the body, as they cannot be synthesized in sufficient quantities and must be obtained through diet. Vitamins have a wide variety of chemical structures but are categorized into two major groups based on their solubility:

• Cofactors and Coenzymes: Many vitamins act as coenzymes or precursors of coenzymes that assist enzymes in catalyzing biochemical reactions. For example, B-complex vitamins are essential for energy metabolism.
• Antioxidants: Some vitamins, such as vitamin C and vitamin E, act as antioxidants, protecting cells from damage caused by free radicals.
• Tissue Maintenance and Growth: Vitamin A is vital for vision, tissue growth, and skin health. Vitamin D regulates calcium metabolism, essential for bone maintenance.
• Blood Clotting: Vitamin K plays a key role in synthesizing proteins involved in blood clotting.
• Immune System: Several vitamins, such as vitamin C, help strengthen the immune system.

4. Week 2

Water-soluble vitamins

Fat-soluble vitamins

B Vitamins:

• Vitamin B1 (Thiamine): Helps in carbohydrate metabolism and the functioning of the nervous system.
• Vitamin B2 (Riboflavin): Participates in energy production and in the health of the skin and eyes.
• Vitamin B3 (Niacin): Contributes to energy metabolism and the health of the skin, nervous system, and digestive tract.
• Vitamin B5 (Pantothenic Acid): Involved in the synthesis of coenzyme A, crucial for metabolism.
• Vitamin B6 (Pyridoxine): Important for amino acid metabolism and brain function.
• Vitamin B7 (Biotin): Participates in the metabolism of fats, carbohydrates, and proteins.
• Vitamin B9 (Folic Acid): Essential for DNA formation and cell synthesis, especially important during pregnancy.
• Vitamin B12 (Cobalamin): Necessary for red blood cell formation and nervous system function.

Vitamin C (Ascorbic Acid): Acts as an antioxidant, helps in collagen synthesis, and improves iron absorption.

Vitamin A: Essential for vision, skin health, and immune system function. Found in the forms of retinol and beta-carotene (provitamin A). Vitamin D: Aids in the absorption of calcium and phosphorus, promoting bone health. Can be obtained through sunlight exposure and certain foods. Vitamin E: Acts as an antioxidant, protecting cells from damage caused by free radicals and participating in immune system health. Vitamin K: Crucial for blood clotting and bone health. There are two main forms: K1 (phylloquinone), found in green leafy vegetables, and K2 (menaquinone), found in animal products and fermented foods.

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Reflexiona

Sphingolipids

Sphingolipids are lipid-containing sphingosine, an amino alcohol, instead of glycerol. They are mainly found in cell membranes, especially in nerve cells. Sphingolipids help form the cell membrane structure, protect the cell surface, and play a role in signaling processes for cell communication, especially in the nervous system. They are crucial for maintaining membrane stability and ensuring proper cell communication, particularly in tissues like the brain and nervous system.

Glycolipids

Glycolipids are lipids with one or more carbohydrate groups attached. They are usually located in the outer layer of the cell membrane. Glycolipids are crucial for cell recognition and communication. They assist in the identification of cells, which is vital for immune system function and tissue formation.

Estrogens

Estrogens are a group of steroid hormones primarily involved in the development and regulation of the female reproductive system and secondary sexual characteristics. The three main types of estrogens are estradiol, estrone, and estriol.

• Reproductive function: Estrogens regulate the menstrual cycle and are essential for the growth and development of the uterine lining (endometrium), preparing it for potential pregnancy.
• Sexual development: During puberty, estrogens are responsible for the development of female secondary sexual characteristics, such as breast development, widening of the hips, and body fat distribution.
• Bone health: Estrogens help maintain bone density by slowing down the process of bone breakdown, which is important for preventing osteoporosis.
• Cardiovascular protection: Estrogens contribute to maintaining healthy blood vessels and reducing the risk of cardiovascular diseases by regulating cholesterol levels.

Disaccharide

Cells construct a disaccharide from two monosaccharide monomers by a dehydration reaction (one monomer gives up a hydroxyl group and the other gives up a hydrogen atom from a hydroxyl group). As H2O is released, an oxygen atom is left, linking the two monomers through a glycosidic bond. The most common disaccharide is sucrose, which is made of a glucose monomer linked to a fructose monomer. Transported in plant sap, sucrose provides a source of energy and raw materials to all the parts of the plant.

The chemistry of life is sensitive to

acidic and basic conditions

In aqueous solutions, a very small percentage of the water molecules actually break apart (dissociate) into ions:

• H+ Hydrogen ions
• OH– Hydroxide ions

A compound that donates hydrogen ions to soutions is called an acid. A base is a compound that accepts hydrogen ions and removes them from solution. The pH of human blood plasma (the fluid portion of the blood) is very close to 7.4. A person cannot survive for more than a few minutes if the blood pH drops to 7.0 or rises to 7.8.

Aldosterone

Aldosterone is a steroid hormone produced by the adrenal glands, specifically in the outer section called the adrenal cortex. It is part of a group of hormones known as mineralocorticoids. Aldosterone is essential for maintaining electrolyte balance (particularly sodium and potassium) in the blood, fluid levels, and blood pressure, all of which are critical for normal body function and homeostasis.

Chemical properties

VS

Physical properties

Polysaccharides

Polysaccharides are macromolecules, polymers of hundreds to thousands of monosaccharides linked together by dehydration reactions. Polysaccharides may function as storage molecules or as structural compounds.

• Starch: Starch granules serve as carbohydrate “banks” from which plant cells can withdraw glucose for energy or building materials.
• Glycogen: Animals store glucose in a different form of polysaccharide, called glycogen. Most of your glycogen is stored as granules in your liver and muscle cells.
• Cellulose: It is a major component of the tough walls that enclose plant cells. Cellulose is not a nutrient for humans, although it does contribute to digestive system health.

The human body comprises about 63% water, the human embryo about 94% water, and algae around 95% water. The amount of water in the body is directly related to its physiological activities, with lower percentages found in organisms with dormant life stages, such as seeds, where it makes up approximately 20%. Water exists in living matter in three forms:

• Circulating water: for example, in blood and sap.
• Interstitial water is found between cells, sometimes adhering firmly to the intracellular substance, as in connective tissue.
• Intracellular water is found in the cytosol and inside cellular organelles.

Living beings can obtain water directly from external sources or other biomolecules through various biochemical reactions. One example of this is the water obtained from the oxidation of glucose.

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Protein Functions

• Enzymes: Catalyze chemical reactions in the organism. Examples: amylase, lipase.
• Structural Proteins: Provide support and shape to cells and tissues. Examples: collagen, keratin.
• Transport Proteins: Transport substances throughout the body or within cells. Examples: hemoglobin (oxygen transport), albumin (hormone and fatty acid transport).
• Contractile Proteins: Involved in muscle movement. Examples: actin, myosin.
• Regulatory Proteins: Regulate biological processes, such as gene expression. Examples: hormones like insulin, transcription factors.
• Defensive Proteins: Defend the organism against pathogens. Examples: antibodies, immune system proteins.

Carbon has several important properties:

• It forms stable covalent bonds that store a lot of energy.
• It can form bonds with up to four different elements, providing molecular variability.
• It can form single, double, or triple bonds.
• It can bond with other carbon atoms, forming long chains.
• Compounds, while stable, can also be transformed through chemical reactions.
• Carbon bonded to oxygen forms gaseous compounds.

All these properties derive from its small atomic radius and the presence of 4 electrons in its outer shell. Hydrogen, Oxygen, and Nitrogen can form stable covalent bonds. They are part of the carbon chains that make up the molecules of living organisms.

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Waxes

Waxes are a type of lipid composed of long-chain fatty acids esterified to long-chain alcohols (ester bond). Unlike fats and oils, waxes are generally non-polar and hydrophobic, making them water-repellent. Functions

• Waterproofing: In plants, the wax layer prevents excessive water loss through evaporation. In animals, it helps protect and insulate.
• Protection: Waxes can protect plants and animals from environmental factors, such as bacteria, fungi, and parasites.

Testosterone

Testosterone is the primary male sex hormone, though it is also present in females in smaller amounts. It is produced mainly in the testes and, to a lesser extent, in the adrenal glands. It is responsible for the development of male secondary sexual characteristics, such as muscle growth, facial hair, and a deeper voice. It also plays a role in sperm production and maintaining bone density.

Cortisol

Cortisol is a steroid hormone produced by the adrenal glands. It is often referred to as the “stress hormone” because its levels increase in response to stress. Cortisol helps regulate metabolism, control blood sugar levels, and reduce inflammation. It also plays a role in the body’s response to stress by providing energy and helping to manage the immune response during stressful situations.

• Animal Products: Butter, cheese, fatty cuts of beef, pork, lamb, and poultry with skin.
• Processed Foods: Sausages, bacon, baked goods like cakes and cookies made with butter or shortening.
• Coconut Oil and Palm Oil: Plant-based but high in saturated fat.

Saturated fats

• Olive Oil
• Avocados
• Nuts: Almonds, peanuts, and cashews.
• Seeds: Pumpkin and sesame seeds.
• Fish: Rrich in omega-3 fatty acids
• Vegetable Oils: Sunflower oil, corn oil, and soybean oil.
• Walnuts, Flaxseeds and Chia Seeds

Unsaturated fats

• Processed Foods: Fried foods, margarine, store-bought baked goods, and snacks containing partially hydrogenated oils.

Trans fats

Phospholipids

Phospholipids are molecules consisting of a phosphate "head" (hydrophilic, water-attracting) and two fatty acids "tails" (hydrophobic, water-repelling). They organize into a bilayer in cell membranes. Phospholipids are the main components of cell membranes. They form a lipid bilayer that shields the cell and controls the movement of substances in and out. This arrangement helps uphold the cell's structure and regulates the internal environment.

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Fatty acids

Lipids consist of repeating units called fatty acids. Fatty acids are organic compounds that have the general formula CH3(CH2)nCOOH, where n usually ranges from 2 to 28 and is always an even number. There are two types of fatty acids:

Saturated fatty acids

Unsaturated fatty acids

Saturated fatty acids have straight, tightly packed chains due to single-bonded carbon atoms, allowing them to store energy in a compact form. This is why they are solid at room temperature and are used by animals for energy storage.

Unsaturated fatty acids have double bonds in some carbon atoms, causing the chains to bend and remain liquid at room temperature. Plants use them to store energy.

Examples

• Fruits: Apples, bananas, oranges, grapes, berries.
• Dairy Products: Milk, yogurt.
• Honey: Natural sweetener containing glucose and fructose.

Sugars

• Whole Grains: Brown rice, quinoa, oats, whole wheat bread.
• Legumes: Beans, lentils, chickpeas, peas.
• Root Vegetables: Potatoes, sweet potatoes, yams.
• Cereals: Whole grain cereals such as bran flakes or oatmeal.

Starches

• Vegetables: Broccoli, carrots, leafy greens (spinach, kale).
• Fruits with Skin: Apples, pears, berries.
• Whole Grains: Brown rice, oatmeal, barley.
• Legumes: Lentils, beans.
• Nuts and Seeds: Almonds, chia seeds, flaxseeds.

Fiber

Progesterone

Progesterone is a steroid hormone primarily involved in the reproductive system. It is produced in the ovaries, the placenta (during pregnancy), and the adrenal glands. Progesterone plays a key role in the menstrual cycle and in maintaining pregnancy. It prepares the uterus for a fertilized egg and helps maintain a healthy pregnancy by regulating the uterine lining.

Triglycerides

Triglycerides are a type of fat, or lipid, that circulate in the blood and are a common part of the body's fat stores. They are found in many foods, especially fats, oils, and butter, and are also created by the body when it stores extra calories.

• A triglyceride is called a fat if it is a solid at 25°C. These are obtained from animal sources.
• A triglyceride is called an oil if it is a liquid at room temperature. These are commonly obtained from plants.

These differences in melting points reflect differences in the degree of unsaturation and number of carbon atoms in the constituent fatty acids. In the human body, triglycerides are stored primarily in specialized fat cells called adipocytes, which form adipose tissue.

Role of fats and oils

Classification

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Cholesterol

Cholesterol is a lipid molecule found in the cell membranes of animals. It is a type of steroid that is essential for maintaining the fluidity and stability of cell membranes. Cholesterol helps regulate membrane permeability, ensuring that the cell membrane remains flexible but not too fluid. It also serves as a precursor for the synthesis of other important steroids, including hormones like testosterone, progesterone, and cortisol.