Water Properties and Chemistry of Life

Water Properties

• Water molecules exhibit cohesion due to hydrogen bonding, causing them to stick together.
• Water has a high specific heat capacity, meaning it can absorb a large amount of heat before its temperature increases significantly.
• Water releases heat back into the environment as it cools, moderating temperature fluctuations.
• Water expands upon freezing, making ice less dense than liquid water, allowing freshwater organisms to survive winter.
• Water is a polar molecule, making it an excellent solvent for polar and charged substances, which are considered hydrophilic.
• Hydrophobic substances, like oils and lipids, do not dissolve in water.
• Buffers help maintain a stable pH, preventing drastic fluctuations.
• Blood is predominantly water and must maintain a pH between 7.35-7.45.

Chemistry of Life

• All living matter is composed of molecules subject to chemical and physical laws.
• Organic molecules contain carbon.
• Hydrocarbons are molecules consisting solely of carbon and hydrogen.
• Functional groups are chemical groups attached to carbon skeletons that influence the properties of organic molecules.
• Different functional groups lead to different chemical properties, impacting the function of molecules within cells.
• Steroid hormones are modified structures based on cholesterol.
• Biological molecules are complex organic compounds composed of subunits called monomers.
• Polymers are long chains of monomers.

Carbohydrates

• Carbohydrates are composed of carbon, hydrogen, and oxygen.
• They constitute 2-3% of the body's mass.
• Monosaccharides are simple sugars that serve as monomers.
• Dehydration synthesis joins monosaccharides together, forming glycosidic linkages to create disaccharides and polysaccharides.
• Glycogen, a branched chain of glucose monomers, is the primary storage polysaccharide in animals.
• Starches, linear chains of glucose monomers, are the primary storage polysaccharides in plants.
• Humans lack the enzyme to break down cellulose.

Lipids

• Lipids are hydrophobic molecules made of carbon, hydrogen, and a small proportion of oxygen.
• They represent 18-25% of human body mass.
• Types of lipids include: fatty acids, triglycerides, phospholipids, steroids, eicosanoids, and fat-soluble vitamins.
• Fatty acids consist of a hydrocarbon chain with a carboxyl group at one end, and can be saturated or unsaturated.
• Triglycerides are three fatty acids bonded to a glycerol backbone.
• Fats are solid triglycerides at room temperature, while oils are liquid triglycerides.
• Triglycerides are stored in fat cells called adipocytes.
• Saturated fats are rich in saturated fatty acids.
• Unsaturated fats are either monounsaturated or polyunsaturated.
• Phospholipids have a glycerol backbone attached to two fatty acids and a phosphate group.
• They have a hydrophilic phosphate head and hydrophobic fatty acid tails, making them amphipathic.
• Steroids are formed from four fused carbon rings.
• Cholesterol is the precursor to other steroids and helps maintain membrane fluidity.
• Sterols are steroids with at least one hydroxyl group.
• Eicosanoids are 20-carbon compounds, including prostaglandins and leukotrienes, involved in immune signaling.
• Fat-soluble vitamins (D, E, and K)are essential for human health.

Proteins

• Proteins are made of carbon, hydrogen, oxygen, and nitrogen.
• They constitute 12-18% of human body mass.
• Proteins determine the structure of body tissues.
• Amino acids are the monomers of proteins.
• Amino acids have a central carbon atom bonded to an amino group, a carboxyl group, and a unique side chain (R group) that dictates its properties.
• Dehydration synthesis forms peptide bonds between amino acids.
• Many amino acids linked together form a polypeptide.
• The difference between a peptide and a protein is that a protein can be made of multiple polypeptide chains.
• Protein structure is essential for its function.
• The primary structure of a protein is the sequence of amino acids.
• The secondary structure of a protein results from repeated folds stabilized by hydrogen bonds.
• Tertiary structure describes the three-dimensional shape determined by primary and secondary structures, plus interactions between peptide chains.
• Quaternary structure refers to the arrangement of multiple polypeptide chains in a multi-peptide protein.
• Fibrous proteins form long parallel bundles and are water-insoluble, such as keratin and actin.
• Globular proteins are rounded and water-soluble, such as antibodies and enzymes.
• Denaturation is the loss of protein structure, causing a loss of function.

Enzymes

• Enzymes are biological catalysts that accelerate chemical reactions without being consumed.
• Enzymes use nonprotein molecules called cofactors to assist in catalysis.
• Organic cofactors are known as coenzymes.
• Chemical reactions would proceed too slowly or not at all without enzymes.
• Enzymes are specific, efficient, and regulated.
• Substrates bind to the active site of an enzyme, forming an enzyme-substrate complex.
• The enzyme catalyzes the reaction, then releases the products.
• Enzymes are highly specific, with substrates fitting into their active sites via a lock-and-key mechanism.
• Enzymes lower activation energy, the energy required to break bonds, making reactions proceed faster.
• Cells regulate enzyme production and activity.
• Proenzymes are inactive forms of enzymes that must be processed to become active.

Nucleic Acids

• Nucleic acids are made of carbon, hydrogen, oxygen, nitrogen, and phosphorus.
• They are made up of DNA and RNA.
• Genes are segments of DNA that provide instructions for protein synthesis.
• DNA is transcribed into RNA.
• RNA is translated by ribosomes to produce proteins.
• Nucleotides are the monomers of nucleic acids, containing a nitrogenous base, pentose sugar, and phosphate group.
• DNA contains the bases adenine (A), guanine (G), cytosine (C), and thymine (T).
• RNA contains A, G, C, and uracil (U).
• Bases pair together, with purines (A and G) pairing with pyrimidines (T and C).
• DNA's pentose sugar is deoxyribose, while RNA's is ribose.
• The phosphate groups and pentose sugars form the backbone of the nucleic acid molecule.
• DNA forms a double helix, with bases forming the "rungs" of the helix.
• DNA replication produces a new copy of the double helix using one strand as a template.
• A change in the DNA sequence is called a mutation.
• RNA is single-stranded and has three major types: mRNA, rRNA, and tRNA.
• Adenosine triphosphate (ATP) is a biologically-important nucleotide that serves as the energy currency of cells.
• It consists of adenosine (adenine plus ribose) with three phosphate groups.
• ATP is produced by exergonic reactions and consumed by endergonic reactions to power cellular work.
• Hydrolysis of the terminal phosphate group of ATP releases energy.
• ATP synthesis is catalyzed by ATP synthase during aerobic cellular respiration.

Summary

• Biological molecules are diverse organic molecules with specific functions.
• There are four classes: carbohydrates, lipids, proteins, and nucleic acids.
• Lipids are the only group that is not made of polymers of monomers.
• The structure of these molecules is closely linked to their specific function.