Biology Chapter: Basic Units of Life

Basic Units of Life

• Atoms are the smallest unit of matter, essential for chemical reactions, and cannot be divided without losing properties.
• Molecules are formed from multiple atoms bonded together.
• Cells are the smallest unit of life, numbering between 10 to 100 trillion in living organisms.
• Tissues consist of groups of similar cells performing a common function and may include an extracellular matrix (ECM).
• Organ systems are collections of organs working together for a specific function.

Hierarchical Organization

• The hierarchy of biological organization: Atoms → Molecules → Cells → Tissues → Organs → Organ systems → Organisms.

Chemical Elements and Ions

• Elements are pure substances that cannot be chemically broken down further.
• Atomic particles include protons (positive), neutrons (neutral), and electrons (negative), where the number of protons defines the element's identity.
• Cations are positively charged ions (more protons than electrons), while anions are negatively charged ions.

Electrolytes and pH

• Electrolytes are ionic substances that dissociate into ions in solution, crucial for nerve and muscle functions.
• The pH scale ranges from 0 (acidic) to 14 (basic), with 7 being neutral.
• Buffers are substances that resist pH changes, maintaining stable conditions for biological processes.

Bonds and Molecular Types

• Ionic bonds form through electron transfer, creating oppositely charged ions.
• Nonpolar covalent bonds share electrons equally, whereas polar covalent bonds share them unequally due to electronegativity.
• Electronegativity measures an atom's ability to attract electrons, with elements like fluorine, oxygen, and nitrogen being particularly electronegative.
• Hydrogen bonds are crucial for the properties of water and the structure of DNA.

Molecular Classification

• Molecules can be polar (asymmetric electron distribution) or non-polar (symmetric electron distribution).
• Inorganic substances include electrolytes and molecules without carbon-carbon bonds; organic substances contain carbon and hydrogen.

Properties of Water

• Water exhibits unique properties due to hydrogen bonding, such as cohesion, high specific heat, and lower density when frozen.
• Cohesion refers to water molecules attracting each other, vital for biological functions.
• High specific heat allows water to absorb/release heat with minimal temperature fluctuations, benefiting living organisms.
• Ice's lower density than liquid water enables it to float, insulating aquatic habitats.
• Water's polarity makes it an effective solvent, facilitating chemical reactions and nutrient transport.

Joints and Function of Water

• Water lubricates joints, allowing smooth movement and shock absorption.

Proteins

• Proteins are essential for tissue structure and cellular functions, composed of carbon, hydrogen, oxygen, and nitrogen.
• Amino acids are the monomer units of proteins, consisting of an amine group, a central carbon, and an acid group, with the side chain ('R group') determining the specific amino acid.
• Proteins have four structural levels: primary (amino acid sequence), secondary (alpha helix or beta-pleated sheet), tertiary (3D folding), and quaternary (multiple polypeptides).
• Protein denaturation disrupts secondary, tertiary, and quaternary structures, often due to extreme temperatures or pH shifts.
• Enzymes, a subset of proteins, accelerate chemical reactions without being consumed.

Lipids

• Lipids are hydrophobic, greasy, and lack true monomers and polymers, classified into four main types: triglycerides, phospholipids, steroids, and waxes.
• Triglycerides consist of a glycerol molecule attached to three fatty acids and function in energy storage, protection, and insulation.
• Saturated fatty acids contain only single bonds between carbon atoms, while unsaturated fatty acids have one or more double bonds.
• Phospholipids have a glycerol backbone, two nonpolar fatty acid tails, and a polar phosphate group, forming a lipid bilayer in cell membranes.