Water and the Molecular Composition of Cells PDF

WATER AND THE MOLECULAR COMPOSITION OF CELLS WATER Unique physical properties -the predominant -ability to solvate a chemical component wide range of organic of living organisms and inorganic molecules, derive...

WATER AND THE MOLECULAR COMPOSITION OF CELLS WATER Unique physical properties -the predominant -ability to solvate a chemical component wide range of organic of living organisms and inorganic molecules, derive from water’s dipolar structure and exceptional capacity for forming hydrogen excellent nucleophile Water is a reactant or product in Nephrogenic diabetes many metabolic reactions insipidus, which involves the inability to concentrate urine -In digestion, water is used to break or adjust to subtle changes in down complex molecules into simpler ones, a process known as hydrolysis. extracellular fluid osmolarity, results from the -regulation of water balance unresponsiveness of renal depends upon hypothalamic tubular osmoreceptors to mechanisms that control thirst, ADH on antidiuretic hormone (ADH),  - an inability to concentrate on retention or excretion of urine due to impaired renal water by the kidneys, and on tubule response to vasopressin (ADH), which leads to excretion evaporative loss of large amounts of dilute urine. WATER HAS A SLIGHT PROPENSITY TO DISSOCIATE INTO HYDROXIDE, IONS AND PROTOCOLS The concentration of protons, or acidity, of aqueous solutions is generally reported using the logarithmic pH scale. Bicarbonate and other buffers normally maintain the pH of extracellular fluid between 7.35 and 7.45 Suspected disturbances of acid-base balance are verified by measuring the pH of arterial blood and the CO2 content  WATER IS AN IDEAL BIOLOGIC SOLVENT Water Molecules Form Dipoles -water molecule is an irregular slightly skewed tetrahedron with oxygen at its center A Molecule with electrical - charge distributed asymmetrically about its structure is referred to as dipole -water’s strong dipole is responsible for its high dielectric constant enable water to dissolve large quantities of charged compounds such as salts  WATER MOLECULES FORM HYDROGEN BONDS A partially unshielded hydrogen nucleus covalently bound to an electron-withdrawing oxygen or nitrogen atom can interact with an unshared electron pair on another oxygen or nitrogen atom to form a hydrogen bond -since water molecules contain both of these features, hydrogen bonding favors the self-association of water molecules into ordered arrays -Hydrogen bonding profoundly influences the physical properties of water and accounts for its relatively high viscosity, surface tension, and boiling point -hydrogen bonding enables water to dissolve many organic biomolecules that contain functional groups which can participate in hydrogen bonding The oxygen atoms of aldehydes, ketones and amides, for example, provide lone pairs of electrons that can serve as hydrogen acceptors -alcohols, carboxylic acids and amines can serve both as hydrogen acceptors and as donors of unshielded hydrogen atoms for formation of INTERACTION WITH WATER INFLUENCES STRUCTURE OF BIOMOLECULES Covalent bond is the strongest force that holds molecules together -noncovalent forces, while of lesser magnitude, make significant contributions to the structure, stability and functional competence of macromolecules in living cells BIOMOLECULES FOLDED TO POSITION POLAR AND CHARGED GROUPS ON THEIR SURFACES Most biomolecules are Amino acids with charged or amphipathic, that is they polar amino side chains in the possess regions rich in charged interior (ex. Arginine, or polar functional groups as glutamate, serine) generally are well as regions with present on the surface in hydrophobic character contact with water -proteins tend to fold with the R- groups of amino acids with hydrophobic side chains in the interior MOLECULAR COMPOSITION OF CELLS -Cells are composed of water, inorganic The critical property of water in this ions, and carbon-containing (organic) respect is that it is a polar molecule, in molecules. which the hydrogen atoms have a slight positive charge and the oxygen has a -Water is the most abundant molecule in slight negative charge cells, accounting for 70% or more of total cell mass. -the interactions between water and the other constituents of cells are of central importance in biological chemistry -https://www.ncbi.nlm.nih.gov/ Because of their polar nature, water molecules can form hydrogen bonds with each other or with other polar molecules, as well as interacting with positively or negatively charged ions. nonpolar molecules, which cannot interact with water, are poorly soluble in an aqueous environment (hydrophobic) interactions of polar and nonpolar molecules with water and with each other play crucial roles in the formation of biological structures, such as cell membranes. The inorganic ions of the cell, including sodium (Na+), potassium (K+), magnesium (Mg2+), calcium (Ca2+), phosphate (HPO42-), chloride (Cl-), and bicarbonate (HCO3-), constitute 1% or less of the cell mass. These ions are involved in a number of aspects of cell metabolism, and thus play critical roles in cell function. the organic molecules that are the unique constituents of cells. Most of these organic compounds belong to one of four classes of molecules: carbohydrates, lipids, proteins, and nucleic acids. Proteins, nucleic acids, and most carbohydrates (the polysaccharides) are macromolecules formed by the joining (polymerization) of hundreds or thousands of low-molecular- weight precursors: amino acids, nucleotides, and simple sugars -Such macromolecules constitute 80 to 90% of the dry weight of most cells. PROTEINS large, complex molecules that play many important roles in the body. They are critical to most of the work done by cells and are required for the structure, function and regulation of the body's tissues and organs Swedish chemist Jöns Jacob Berzelius, who in 1838 coined the term protein, a word derived from the Greek prōteios, meaning “holding first place.” species-specific  -proteins of one species differ from those of another species. organ-specific  -for instance, within a single organism, muscle proteins differ from those of the brain and liver. ORGAN SPECIFIC PROTEINS A protein molecule is very large compared with molecules of sugar or salt and consists of many amino acids joined together to form long chains, much as beads are arranged on a string LIPIDS Lipids are fatty, waxy, or oily compounds that are soluble in organic solvents and insoluble in polar solvents such as water. Lipids include: Fats and oils (triglycerides) Phospholipids Waxes Steroids the triglycerides, is sequestered as fat in adipose cells, which serve as the energy-storage depot for organisms and also provide thermal insulation. Some lipids such as steroid hormones serve as chemical messengers between cells, tissues, and organs, and others communicate signals between biochemical systems within a single cell. The membranes of cells and organelles (structures within cells) are microscopically thin structures formed from two layers of phospholipid molecules.  CARBOHYDRATES -includesimple sugars as well as polysaccharides -These simple sugars, such as glucose, are the major nutrients of cells -their breakdown provides both a source of cellular energy and the starting material for the synthesis of other cell constituents. -Polysaccharides are storage forms of sugars and form structural components of the cell - polysaccharides and shorter polymers of sugars act as markers for a variety of cell recognition processes, including the adhesion of cells to their neighbors and the transport of proteins to appropriate intracellular destinations The structures of representative simple sugars (monosaccharides) are illustrated in The basic formula for these molecules is (CH2O)n, from which the name carbohydrate is derived (C= “carbo” and H2O= “hydrate”). The six-carbon (n= 6) sugar glucose (C6H12O6) is especially important in cells, since it provides the principal source of cellular energy STRUCTURE OF SIMPLE SUGARS -Monosaccharides can be joined together by dehydration reactions, in which H2O is removed and the sugars are linked by a glycosidic bond between two of their carbons -If only a few sugars are joined together, the resulting polymer is called an oligosaccharide. -If a large number (hundreds or thousands) of sugars are involved, the resulting polymers are macromolecules called polysaccharides. Two common polysaccharides— glycogen and starch—are the storage forms of carbohydrates in animal and plant cells, respectively -Both glycogen and starch are composed entirely of glucose molecules in the α configuration The structures of glycogen and starch are thus basically similar, as is their function: to store glucose. -Cellulose, has a quite distinct function as the principal structural component of the plant cell wall. -cellulose is also composed entirely of glucose molecules. The glucose residues in cellulose, however, are in the β rather than the α configuration, and cellulose is an unbranched polysaccharide -oligosaccharides and polysaccharides are important in a variety of cell signaling processes. For example, oligosaccharides are frequently linked to proteins, where they serve as markers to target proteins for transport to the cell surface or incorporation into different subcellular organelles.  Oligosaccharides and polysaccharides  serve as markers on the surface of cells,  playing important roles in cell recognition and the interactions between cells in tissues of multicellular organisms. NUCLEIC ACIDS large biomolecules that play essential roles in all cells and viruses. A major function of nucleic acids involves the storage and expression of genomic information. Deoxyribonucleic acid, or DNA, encodes the information cells need to make proteins