Everyday Chemistry of Life (February 04, 2025)

Water is Life’s Essential Chemical

• Water is the most abundant molecule in living organisms.

  • Water makes up between 60 and 70 percent of total body weight.

  • Our bodies need water to carry out the basic functions of digestion, excretion, respiration, and circulation.

  • Without adequate water the body chemical reactions would fail, and our cells would cease to function.

Six Properties of water

1. Water is liquid at room temperature

   • The two atoms of hydrogen and one atom of oxygen form polar covalent bonds.

     • Making water molecules polar

   • Hydrogen bonds form between the slightly negative oxygen of one water molecule and the slightly positive hydrogen of another water molecules.

   • The hydrogen bonds between different water molecules continuously break and reform in the liquid water.

     

2. Water is able to dissolve many other substances and therefore and therefore is a good solvent.

   • Hydrophilic substances, such as NaCl(salt) carry a charge and are immediately separated in water.

   • Hydrophobic substances are not soluble in water.

     • Hydrophobic substances include large, uncharged particles like fats and oils.

3. Water is both cohesive and adhesive, allowing it to fill vessels.

   • These properties allow water to line membranes and provide lubrication.

   • Blood is 92 percent water, which allows it to stick to the sides of blood vessels and fills them completely.

     • Providing on excellent transport medium as blood flows through the blood vessels - carrying blood cells and other materials such as gasses and proteins.

4. Water has a high specific heat.

   • It takes a lot of energy to raise or lower its temperature.

   • It takes one calorie of energy to raise the temperature of one gram of water one degree Celsius.

   • This property helps to stabilize our body temperature as the water in our blood changes very slowly, thus keeping our body temperature relatively constant.

5. Water has a high heat of vaporization.

   • This is a measure of the amount of heat needed to vaporize the liquid.

   • A large amount of heat energy - 540 calories - is needed to convert 1 gram of water to vapor.

   • Sweating is a means by which heated body water evaporates from the surface of our skins, thus cooling our bodies.

6. Ice floats

   • As water cools, the molecules lose energy and move more slowly.

   • The hydrogen bonds that continuously break and re-form in liquid water stop breaking - and the water turns solid (forming ice)

   • The bonds hold a specific distance between the molecules.

     • Making solid water slightly less dense than liquid water.

     • The trapped air within ice may warm up, thus providing insulation and protection against the cold.

The pH scale measures the concentration of H⁺

• It ranges from 0 to 14.

• Lower pH readings indicate a higher H⁺ concentration and greater acidity (0-7)

• Pure water registers 7 on the pH scale.

  • It has equal numbers of H⁺ and OH^- ions.

• A higher pH reading indicates lower H+ concentrations and greater alkalinity (7-14)

The pH scale is logarithmic

• Each one unit represents a tenfold change in H⁺ concentration.

• A change from pH 3 to pH 8 would reduce the H⁺ concentration by a factor of 100,000

Hydrogen ion concentration affects chemical properties.

• One of the most important ions is the hydrogen ion, H+

  • Acidity matters to the human body because it affects the rate of most chemical reaction and the concentration of many chemicals.

• The pH of your blood must stay between 7.4 and 7.5 for your cells to function.

  • If you breathe too slowly, the carbon dioxide level in the blood will rise and the blood can become more acidic

  • Biological buffers stabilize pH by absorbing or releasing H⁺

  • The carbonic-bicarbonate buffering system in blood helps to maintain correct concentration of H⁺

Organic compounds

• Organic compounds contain carbon atoms.

  • With its four valence electrons a carbon atom can covalently bind with up to four other atoms.

    • Leading to an almost infinite set of carbon structures.

    • From simple methane (CH4) to complex ring and chain structures like simple sugars or complex starch molecules.

  • Attaching functional groups to the carbon structures helps to increase the solubility and reactivity of organic molecules in water - thus making them useful to biological systems.

• Four categories of organic compounds are important to living organisms.

  • Carbohydrates

  • Lipids

  • Proteins

  • Nucleic acids

Carbohydrates

• Carbohydrates are the most abundant organic molecules in organisms.

• A carbohydrate is composed of carbon, hydrogen, and oxygen atoms.

  • In a ratio of 1:2:1 - for example, C₆H₁₂O₆.

• Carbohydrates serve as energy source for the human body.

Many carbohydrates are saccharides (sugar)

• Monosaccharides

  • Single sugar molecules - simple carbohydrates

  • For example. glucose, fructose, ribose, etc…

• Disaccharides

  • Formed form the binding of two monosaccharides.

  • For example, sucrose (glucose and fructose); lactose (glucose and galactose)

• Oligosaccharides and polysaccharides

  • Longer chains (polymers) of monosaccharides (oligo = few, and poly = many)

  • Complex carbohydrates.

  • Glycogen is a polysaccharide that is stored in muscle and liver tissue.

    • It consists of long chains of glucose molecules - stored glucose in animals.

  • Starch and cellulose are polysaccharides that are found in plants.

    • They also are long chains of glucose molecules - but are organized differently than glycogen.

Lipids are long-chain organic compounds that are not soluble in water.

• Lipids are hydrophobic

  • Consisting of mostly carbon and hydrogen atoms.

  • Lipids are fats, oils, sterols, and waxes.

• Fatty acids

  • Energy-storing lipids.

  • Long chain of hydrogen and carbon atoms with a carboxyl functional group at one end.

  • The carboxyl group can bind to glycerol molecules to build fats.

    • Such as triglycerides (with three fatty acids)

    • And phospholipids (with two fatty acids)

Fatty acids

• Unsaturated fats have at least one double bond between adjacent carbons in their fatty acid chains - and bend in shape at each double bond.

  • Monounsaturated (1 double bond); polyunsaturated (2 or more double bonds).

  • Unsaturated fat tend to be liquid at room temperature - i.e., oils

• Saturated fats have no double bonds between the carbons in their fatty acid chains - and thus are straight in shape.

  • They are completely saturated with hydrogen atoms and cannot hold anymore.

  • Saturated fats are solid to semi-solid at room temperature - i.e., butter

  • A diet high in saturated fats may increase the risk of having a stroke or heart attack.

    

Phospholipids are both Hydrophilic and Hydrophobic

• Consist of a glycerol molecule, a polar head (containing a phosphate group), and 2 non-polar fatty acids.

• Their unique structure allows phospholipids to form bilayers when placed in water.

  • Polar heads face outwards - the non-polar fatty acid tails face inwards.

  • The cell membrane is one such bilayer.

  

Steroids are lipids with a common four-ring structure

• Steroids and sterols are important to normal growth and development.

  • Includes cholesterol, sex hormones, and metabolism regulators.

• Cholesterol is an integral part of cell membranes.

  • Allowing for membrane flexibility and growth.

• The sex hormones are steroids that are important to the reproductive systems.

  • Estrogen and testosterone.

• Anabolic steroids, which are related to testosterone, stimulate growth of the muscles.

  

Proteins

• All the different proteins found in the human body are formed from just 20 building blocks.

  • Called amino acids

• An amino acid is composed of

  • A central carbon atom with four groups attached to it.

    • A hydrogen atom

    • An amino group (-NH₂)

    • A carboxyl group (-COOH)

    • A radical group or side chain (R)

      • The R group determines the activity of the amino acid.

    

Individual Amino Acids Combine to Form Proteins

• Amino acids are gained by peptide bonds.

  • Peptide bonds form between the amino acids and the carboxyl group of the next amino acid.

  • The resulting two amino acid compound is called a dipeptide.

• As more amino join the growing chain, it becomes a polypeptide.

• Polypeptides are linear sequences (polymers) of amino acids.

  • Polypeptides normally cannot function as proteins.

  • Must first develop into a unique three-dimensional shape (conformation).

  • The shape depends on the specific sequence of amino acids.

  

Protein function emerges from its shape.

• That folding and interacting of adjacent amino acids within a polypeptide determine the final shape of a protein (it’s conformation).

• The final shape of a protein is either globular or fibrous.

  • Globular proteins are round and usually water-soluble.

  • Fibrous proteins are stringy, tough, and usually insoluble in water (provide the framework for supporting cells and tissues).

• The shape of a protein molecule determines its function, and the final shape is determined by its primary structure (amino acid sequence).

  • Changing even one amino acid can alter the folding pattern, with devastating effects on the protein’s function.

  • In sickle cell anemia, a change in only one amino acid leads to serious consequences.

Enzymes serve as catalysts for biochemical reactions

• Catalysts bring the reactants, or substrates, together, so that they can participate in a chemical reaction more quickly.

• Enzymes facilitate a specific chemical reaction without being altered during the chemical reactioin.

  • Unlike the substrates which may be altered during the chemical reaction.

• Enzymes rely on shape to function properly.

  • The active site of the protein is shaped to bind to one specific substrate.

  • After the substrate binds, the enzyme provides an environment for the specific chemical reaction to occur.

Enzyme function

Nucleic Acids Store and Process an Organisms Hereditary Information.

• There are two types of nucleic acids.

  • Deoxyribonucleic acid (DNA)

  • Ribonucleic acid (RNA)

• DNA exists in the nucleus of our cells.

  • It contains the hereditary (genetic) information of the cells.

    • To build proteins

    • To regulate physiological processes

    • To maintain homeostasis.

• RNA acts as a messenger molecule both inside and outside the nucleus.

  • RNA serves to regulate cellular metabolism. produce proteins, and govern developmental timing.

  

Life requires energy

• High energy compounds power cellular activity.

• Most often energy is available in spurt, rather than as a continuous stream all day long.

• Our energy storage system provides short- and long-term storage.

  • Long term energy storage includes

    • Glycogen in muscles and liver

    • Triglycerides packed into specialized storage cells called adipocytes (fat cells)

  • Short term energy storage uses high-energy system that is reversible and instantly available.

    • The most common storage system is ATP, or adenosine triphosphate.

    • ATP powers all cellular activity, forming proteins to contracting muscles.

Adenosine Triphosphate