뒤로Chapter 2: Chemistry Comes Alive – Chemical Bonds, Water, and Organic Molecules
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Chemistry Comes Alive
Molecules and Compounds
Atoms rarely exist alone; they combine to form molecules and compounds, which are essential for biological structure and function.
Molecule: A general term for two or more atoms bonded together (e.g., O2, H2).
Compound: A molecule that contains two or more different kinds of atoms bonded together (e.g., C6H12O6).
Example: C6H12O6 (glucose) is a compound; O2 is a molecule but not a compound.
Chemical Bonding
Chemical bonds are forces that hold atoms together in molecules and compounds. Electrons, especially those in the outermost shell (valence electrons), are responsible for bond formation.
Electrons determine whether a chemical reaction will occur and the type of bond formed.
Stability: Atoms are most stable when their outer electron shell is full (2 electrons in the first shell, 8 in subsequent shells).
Ionic Bonds
Ionic bonds form when electrons are transferred from one atom to another, resulting in charged particles called ions.
Formation: One atom donates electrons (becomes a cation, +), another accepts electrons (becomes an anion, -).
Result: Oppositely charged ions attract each other, forming an ionic bond.
Example: Sodium chloride (NaCl).
Covalent Bonds
Covalent bonds form when atoms share electrons to achieve stability.
Nonpolar Covalent Bonds: Equal sharing of electrons between atoms, resulting in nonpolar molecules (e.g., CO2).
Polar Covalent Bonds: Unequal sharing of electrons, resulting in polar molecules with partial charges (e.g., H2O).
Hydrogen Bonds
Hydrogen bonds are weak attractions between a hydrogen atom (already covalently bonded to an electronegative atom) and another electronegative atom.
Not a true bond: More of a weak magnetic attraction.
Common in water: Responsible for water's liquid state at room temperature.
Intramolecular role: Help maintain the three-dimensional shape of large molecules (e.g., proteins, DNA).
Importance of Water
Water is vital for life, making up 60-70% of total body weight. Its unique properties are essential for biological processes.
Hydrogen bonds between water molecules give water its special properties.
Key Properties of Water:
High heat capacity – absorbs and releases heat slowly.
High heat of vaporization – requires a lot of energy to change from liquid to gas.
Polar solvent properties – dissolves ionic and polar substances.
Reactivity – involved in many chemical reactions (e.g., hydrolysis, dehydration synthesis).
Cushioning – protects organs by forming a cushion (e.g., cerebrospinal fluid).
Cohesion and adhesion – allows water to move through vessels and tissues.
Hydrogen bonds occur between a hydrogen atom in a covalent bond and a negatively charged atom (often oxygen or nitrogen).
Making and Breaking Down Organic Molecules
Large organic molecules (macromolecules) are polymers, formed by joining smaller units called monomers.
Dehydration synthesis: Removal of water to link monomers into polymers.
Hydrolysis: Addition of water to break polymers into monomers.
Major Classes of Organic Molecules in Living Organisms
Four main types of organic molecules are found in living organisms, each with specific functions:
Type | Function |
|---|---|
Carbohydrates | Provide energy and structural support |
Lipids | Store energy, form cell membranes, act as hormones |
Proteins | Serve as enzymes, structural components, transporters, and more |
Nucleic Acids | Store and transmit genetic information (DNA, RNA) |
Enzymes and Enzyme Activity
Enzymes are biological catalysts that speed up chemical reactions in the body without being consumed.
Enzymes: Globular proteins that lower the activation energy required for reactions.
Specificity: Each enzyme acts on a specific substrate.
Effect: Increase the speed of reactions, making life-sustaining processes possible.
Adenosine Triphosphate (ATP)
ATP is the primary energy carrier in cells, a modified nucleotide that stores and releases energy as needed.
"Energy currency" of the cell: ATP provides energy for cellular work.
Formation: Breakdown of glucose and other nutrients leads to ATP production.
Structure: Consists of adenine, ribose, and three phosphate groups.
Equation for ATP hydrolysis:
Additional info: ATP hydrolysis releases energy used for muscle contraction, active transport, and biosynthesis.
