7.1.pdf

7.1 Most abundant elements in cells: Hydrogen (H), Carbon (C), Oxygen (O), Nitrogen (N), Phosphorus (P), and Sulfur (S). These are called macronutrients and make up about 99% of the cell's dry weight. Micronutrients (trace elements): Elements like Sodium (N...

7.1 Most abundant elements in cells: Hydrogen (H), Carbon (C), Oxygen (O), Nitrogen (N), Phosphorus (P), and Sulfur (S). These are called macronutrients and make up about 99% of the cell's dry weight. Micronutrients (trace elements): Elements like Sodium (Na), Potassium (K), Magnesium (Mg), Zinc (Zn), Iron (Fe), Calcium (Ca), Molybdenum (Mo), Copper (Cu), Cobalt (Co), Manganese (Mn), and Vanadium (V) are required in very small amounts. Role of elements: All these elements are essential for biochemical reactions necessary for life. Four most abundant elements in living matter: Carbon (C), Nitrogen (N), Oxygen (O), Hydrogen (H) have low atomic numbers, making them light and capable of forming strong bonds. Bonding characteristics: Carbon forms 4 bonds, Nitrogen forms 3, Oxygen forms 2, and Hydrogen forms 1. Lone pairs: Oxygen, sulfur, and nitrogen often have lone pairs of electrons, which affect a molecule’s properties. Diversity of molecules: These elements combine to create a wide variety of molecules, which are essential for forming the structures and enabling the functions of living organisms. Living organisms have both inorganic compounds (like water and salts) and organic molecules. Organic molecules contain carbon; inorganic compounds usually don't. Exceptions: Carbon oxides and carbonates have carbon but are still inorganic because they don't have hydrogen.Organic molecules are built around chains of carbon atoms. Inorganic compounds make up about 1%–1.5% of a cell’s dry weight. These inorganic compounds are small and simple but play important roles in cells, though they don't form cell structures. Carbon in organic molecules often comes from inorganic carbon sources, like carbon dioxide, through a process called carbon fixation by microorganisms. Organic Molecules and isomerism: Organic molecules are larger and more complex than inorganic molecules. They have carbon skeletons held together by covalent bonds. These molecules form the cells of organisms and perform chemical reactions needed for life. Organic molecules, also called biomolecules, contain carbon, which is essential for life. Carbon is special because it has four valence electrons, allowing it to form four covalent bonds with other atoms. Carbon can bond with atoms like oxygen, hydrogen, nitrogen, sulfur, phosphorous, and other carbon atoms. The simplest organic compound is methane, where carbon binds only to hydrogen. Carbon atoms can link together to form long chains called carbon skeletons, which can be straight, branched, or shaped like rings. These carbon skeletons allow for a huge variety of organic molecules with different sizes and shapes. No other element can form such a wide variety of molecules like carbon does. Isomers are molecules with the same atoms but arranged differently. Isomerism is important because the structure of a molecule affects how it works. Even small changes in the arrangement of atoms can cause big differences in properties. Structural formula shows how atoms are connected in a molecule. Structural isomers have the same molecular formula but different bonding arrangements.Example: Glucose, galactose, and fructose all have the formula but are arranged differently. Stereoisomers are molecules that differ in the arrangement of atoms in space. A special type of stereoisomer is called enantiomers. Louis Pasteur discovered enantiomers in 1848 while studying wine crystals under a microscope. Enantiomers are molecules that are nonsuperimposable mirror images of each other, a property called chirality. Chirality is important in many biological molecules, like glucose and alanine. Many organisms can only use one form of an enantiomer as nutrients or building blocks. Different enantiomers of the same molecule can have distinct tastes and smells. Example: L-aspartame (aspartame) tastes sweet, while D-aspartame is tasteless. Drug enantiomers can have different effects:  Example: Methorphan has two enantiomers: ○ Dextromethorphan is a cough suppressant. ○ Levomethorphan works like codeine (pain relief). Enantiomers (optical isomers) rotate polarized light. Clockwise rotation = d form (+) Counterclockwise rotation = l form (−) Labels "d" and "l" come from Latin words for "right" (dexter) and "left" (laevus). Biological significance: Different isomers have different biological properties. Certain species (e.g., molds, yeast, bacteria) can only use one type of isomer for nutrients. In drug treatment, only one isomer may be effective against specific microorganisms. Biologically Significant Functional Groups: Biomolecules contain functional groups (specific groups of atoms) besides carbon. Functional groups are categorized by their chemical structure and reactions, regardless of the molecule they are in. The symbol R represents the rest of the molecule, which can vary in size (e.g., a single hydrogen atom or many atoms). Some functional groups are simple (one or two atoms), while others are more complex, combining smaller groups. Example: ○ A carbonyl group (C=O) is made of a carbon atom double-bonded to oxygen. ○ Found in larger functional groups like ketones, aldehydes, carboxylic acids, and amides. ○ In ketones, the carbonyl group is inside the molecule. ○ In aldehydes, the carbonyl group is at the end of the molecule. Carbon Chains: Most organic molecules have carbon chains as their backbone. Functional Groups: These groups attach to carbon chains to form biomolecules. Macromolecules: These are large molecules made by linking smaller molecules called monomers. Monomers and Polymers: Monomers: The small building blocks. Polymers: The large macromolecules formed by connecting monomers. Four Main Types of Macromolecules in Cells: Polysaccharides Proteins Lipids Nucleic acids (covered in a later chapter). Dehydration Synthesis: A chemical reaction that links monomers to form polymers. During this process, water is produced as a byproduct.