General Biology: Atomic Structure, Chemical Bonds, Water, Macromolecules, and Proteins

Atomic Structure and Elements

Atoms and Atomic Number

Atoms are the basic units of matter, composed of protons, neutrons, and electrons. The atomic number of an element is determined by the number of protons in its nucleus.

• Atomic Number: The number of protons in an atom; defines the element.

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Ions: Atoms with a charge due to loss or gain of electrons.

• Trace Elements: Elements required in small amounts for biological processes (e.g., fluorine for tooth decay prevention).

Example: Carbon has an atomic number of 6, meaning it has 6 protons. Equation: $\text{Atomic Mass} = \text{Number of Protons} + \text{Number of Neutrons}$

Chemical Bonds and Molecules

Types of Chemical Bonds

Atoms combine to form molecules through chemical bonds. The main types are:

• Covalent Bonds: Atoms share electrons; strongest type of bond in biology.

• Hydrogen Bonds: Weak attractions between polar molecules, important in water and DNA.

• Ionic Bonds: Transfer of electrons from one atom to another, forming charged ions.

• Polar Molecules: Molecules with uneven charge distribution (e.g., H2O).

Example: Water molecules are held together by hydrogen bonds.

Electron Shells and Valence

Electrons are arranged in shells around the nucleus. The outermost shell determines chemical reactivity.

• Maximum electrons in first shell: 2

• Valence shell: Outermost electron shell; atoms are most stable when it is full.

Properties of Water

Structure and States of Water

Water is essential for life and exists in three states: solid, liquid, and gas.

• States of Matter: Solid (ice), liquid (water), gas (vapor)

• Hydrogen Bonds: Cause water molecules to be spaced apart in ice, making ice less dense than liquid water.

• Buffer Systems: Minimize changes in pH in biological systems.

Example: Water's ability to act as a buffer helps maintain stable pH in cells.

Acids, Bases, and pH

Acids and bases affect the pH of solutions. pH is a measure of hydrogen ion concentration.

• Acidic: pH less than 7 (e.g., lemon juice)

• Basic: pH greater than 7 (e.g., household bleach)

• Neutral: pH of 7 (pure water)

Carbon Chemistry and Macromolecules

Carbon Bonds and Hydrocarbons

Carbon can form up to four covalent bonds, allowing for complex molecules.

• Hydrocarbons: Composed of carbon and hydrogen.

• Isomers: Molecules with the same formula but different structures.

Functional Groups

Functional groups are specific groups of atoms that confer particular properties to molecules.

• Phosphate Group: Contains phosphorus and oxygen; important in energy transfer.

• Hydroxyl, Carboxyl, Amino: Common functional groups in biological molecules.

• Hydrophobic Groups: Tend to repel water and increase solubility in nonpolar solvents.

Biological Macromolecules

Carbohydrates

Carbohydrates are energy sources and structural components.

• Monosaccharides: Simple sugars (e.g., glucose)

• Disaccharides: Two monosaccharides joined (e.g., lactose = glucose + galactose)

• Polysaccharides: Long chains of sugars (e.g., starch in plants, glycogen in animals, chitin in crustaceans)

Table: Types of Carbohydrates

Type	Example	Function
Monosaccharide	Glucose	Energy source
Disaccharide	Lactose	Energy source
Polysaccharide	Starch, Glycogen, Chitin	Energy storage, structure

Lipids

Lipids include fats, oils, and steroids. They are hydrophobic and serve as energy storage and structural components.

• Fats (Triglycerides): Composed of one glycerol and three fatty acids.

• Saturated Fats: No double bonds; solid at room temperature.

• Unsaturated Fats: Double bonds; liquid at room temperature.

• Phospholipids: Contain two fatty acids and a phosphate group; major component of cell membranes.

• Steroids: Lipids with a four-ring structure (e.g., cholesterol).

Table: Lipid Types and Functions

Lipid Type	Structure	Function
Fat (Triglyceride)	Glycerol + 3 fatty acids	Energy storage
Phospholipid	Glycerol + 2 fatty acids + phosphate group	Cell membrane structure
Steroid	Four fused rings	Hormones, membrane stability

Proteins

Structure and Function

Proteins are polymers of amino acids and perform a wide range of functions.

• Amino Acids: Building blocks of proteins; 20 different types.

• Peptide Bond: Linkage between amino acids.

• R Group: Side chain that determines chemical properties of each amino acid.

• Protein Functions: Catalyzing reactions (enzymes), providing strength and support (structural proteins), signaling (signal proteins), transporting molecules.

Levels of Protein Structure

Proteins have four levels of structure:

• Primary: Sequence of amino acids.

• Secondary: Local folding (alpha helix, beta sheet) stabilized by hydrogen bonds.

• Tertiary: Overall 3D shape of a single polypeptide.

• Quaternary: Association of multiple polypeptide chains.

Example: Hemoglobin has quaternary structure, composed of four subunits.

Nucleic Acids

DNA and RNA

Nucleic acids store and transmit genetic information.

• DNA: Double-stranded, contains thymine.

• RNA: Single-stranded, contains uracil instead of thymine.

Table: Nitrogenous Bases in DNA and RNA

Base	DNA	RNA
Adenine	Yes	Yes
Thymine	Yes	No
Uracil	No	Yes
Guanine	Yes	Yes
Cytosine	Yes	Yes

Additional info:

• Questions cover foundational topics in general biology, including atomic structure, chemical bonds, water properties, macromolecules, and protein structure.

• Tables and equations have been added for clarity and completeness.