Basic Cell Chemicals and Molecules

A solution that resists changes in pH when small amounts of acid or base are added. It's composed of a weak acid and its conjugate base.

A substance that can donate a proton (H+).

A substance that can accept a proton (H+).

A measure of the acidity or alkalinity of a solution. It ranges from 0 to 14, with 0 being the most acidic, 14 being the most alkaline, and 7 being neutral.

A state where the blood pH falls below 7.35. It can lead to various health problems.

The most abundant substance in most cells (10-20% of cell mass), responsible for structural support and carrying out various functions.

A type of protein that provides structural support within cells and helps form tissues like tendons and ligaments.

A type of protein that performs specific functions, like speeding up chemical reactions (enzymes), signaling messages (hormones), or fighting infections (antibodies).

The principal fluid medium of the cell, making up 70-85% of most cells, and plays a crucial role in dissolving and suspending cellular components.

Charged atoms or molecules that are essential for cellular reactions, transmitting electrochemical signals, and maintaining proper cell function.

A type of lipid, primarily composed of phospholipids and cholesterol, forming the cell membrane and separating cell compartments. It is insoluble in water.

A type of lipid primarily found in fat cells, serving as the body's main energy storage. It can be broken down to provide energy.

An important carbohydrate, mainly stored as a polymer of glucose, providing a readily accessible energy source in times of need.

A type of chemical bond where valence electrons are shared as pairs between two bonded atoms. Occurs between two nonmetal atoms of the same kind.

A type of chemical bond where valence electrons are shared unequally between two bonded atoms. Occurs between two different nonmetal atoms or a nonmetal and a metal.

A type of chemical bond where valence electrons are completely transferred from one atom to another. Occurs between metals and nonmetals with a large difference in electronegativity.

A type of attractive force between the hydrogen atom of one molecule and an electronegative atom of a different molecule. The electronegative atom is usually oxygen, nitrogen, or fluorine.

A compound that donates protons (H+) in a chemical reaction.

A compound that accepts protons (H+) in a chemical reaction.

A compound that produces hydrogen ions (H+) when dissolved in water.

A compound that produces hydroxide ions (OH-) when dissolved in water.

The ratio of the concentrations of the weak acid (HA) and its conjugate base (A-) in a buffer solution.

The equilibrium constant (Ka) for the dissociation of a weak acid (HA) in water.

The pH of a buffer solution is approximately equal to the pKa of the weak acid.

The amount of acid or base that can be added to a buffer solution before a significant change in pH occurs.

The range of pH values over which a buffer solution is most effective.

The principle that states that a system at equilibrium will shift to relieve stress.

The protein buffer system is a critical buffer in the human body and consists of proteins, which are large molecules composed of amino acids. One of these amino acids, histidine, acts as a weak base and can easily turn into its conjugate acid. Histidine's conjugate acid has a pKa of 6.0, but when incorporated into a protein, its pKa can rise to 7.0. Therefore, proteins containing histidine can effectively buffer around a pH of 7. This buffering capacity extends across a range of proteins and occurs both inside and outside cells. Protein buffers are particularly important inside cells, maintaining the pH of intracellular fluids at a constant level.

The phosphate buffer system is another significant buffer in the body. Phosphoric acid, with a pKa of 2.1, is not an effective buffer at the body's pH of 7. However, removing one proton from phosphoric acid creates H2PO4-, which has a pKa of 7.2. Therefore, a buffer containing both H2PO4- and HPO42- can effectively buffer around a pH of 7.2. This system operates in conjunction with the protein buffer to maintain the pH of intracellular fluid.

The carbonic acid buffer system is the most important extracellular buffer in the human body. This system relies on carbonic acid (H2CO3) and bicarbonate ions (HCO3-) to maintain the pH of blood plasma at a stable 7.4. However, carbonic acid's pKa at body temperature (37°C) is only 6.1, significantly lower than the plasma pH. To achieve the necessary pH, the concentration of HCO3- must be 20 times greater than that of H2CO3. High concentrations of HCO3- could disrupt osmotic balance, so the concentration of H2CO3 is kept very low.

The carbonic acid buffer system plays a crucial role in regulating blood pH. As you breathe faster, more CO2 is expelled from your body. This leads to a decrease in the concentration of carbonic acid (H2CO3) in the blood. Since this is a crucial component of the buffer system, the blood pH shifts slightly upward, becoming more alkaline or basic. This is why your blood pH goes up when you breathe too fast.

Buffers are vital for maintaining a stable pH in biological systems. They prevent large changes in pH when acids or bases are added. They do this by absorbing excess acid or base, minimizing the impact on the overall pH. Buffers are like tiny shock absorbers for pH. If an acid is added, the buffer will neutralize it. Conversely, if a base is added, the buffer will neutralize that as well.

The pKa value represents the acidity of a substance. It is the pH value at which a substance is half-ionized and half-unionized. A lower pKa value indicates a stronger acid, while a higher pKa indicates a weaker acid. The pKa value is crucial for determining the effectiveness of a substance as a buffer.

A buffer operates most effectively when its pKa value is close to the desired pH. This means the buffer is able to neutralize both acids and bases efficiently. Ideally, the pKa is within one pH unit of either side of the desired pH, making it a highly effective buffer in that pH range.

The most important buffer systems in the human body are the protein buffer system, the phosphate buffer system, and the carbonic acid buffer system. Each system plays a unique role in regulating pH in different body compartments, ensuring the proper functioning of various biological processes.