General Biology: Biomolecules, Chemical Bonds, and Macromolecular Structure

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Scientific Method and Experimental Design

Variables in Experiments

Understanding variables is essential for designing and interpreting biological experiments.

Dependent Variable: The variable that is measured or observed in response to changes in the independent variable. Example: The amount of enzyme product formed in an enzyme assay.
Independent Variable: The variable that is deliberately changed or manipulated by the experimenter. Example: The amount of enzyme added to each assay.

Example: In an experiment testing the effect of enzyme concentration on reaction rate, the enzyme concentration is the independent variable, and the reaction rate (amount of product formed) is the dependent variable.

Elements and Chemical Bonds in Biology

Major Elements in Living Systems

Living organisms are primarily composed of a few key elements.

Most abundant elements: Hydrogen, carbon, oxygen, nitrogen, sulfur, and phosphorus.
Other important elements: Calcium, iron, sodium, potassium, magnesium, and chlorine.

Covalent Bonds and Polarity

Covalent bonds involve the sharing of electron pairs between atoms. The polarity of a covalent bond depends on the difference in electronegativity between the bonded atoms.

Polar Covalent Bond: Electrons are shared unequally, resulting in partial charges (e.g., O-H in water).
Nonpolar Covalent Bond: Electrons are shared equally (e.g., C-H bond).

Example: In water (H2O), the O-H bonds are polar; in methane (CH4), the C-H bonds are nonpolar.

Electronegativity

Electronegativity is a measure of an atom's ability to attract electrons in a chemical bond.

Higher electronegativity leads to stronger attraction for electrons.
Oxygen and nitrogen are highly electronegative, contributing to the polarity of biological molecules.

Water and Hydrogen Bonding

Hydrogen Bonds

Hydrogen bonds are weak attractions between a hydrogen atom covalently bonded to an electronegative atom (like O or N) and another electronegative atom.

Responsible for many of water's unique properties, such as high boiling point and surface tension.
Each water molecule can form up to four hydrogen bonds with neighboring water molecules.

Amphipathic Molecules

Amphipathic molecules contain both hydrophilic (water-loving) and hydrophobic (water-fearing) regions.

Example: Phospholipids, which form the basis of cell membranes.

Macromolecules: Structure and Function

Proteins

Proteins are polymers of amino acids linked by peptide bonds. They have several levels of structure:

Primary Structure: The sequence of amino acids in a polypeptide chain.
Secondary Structure: Local folding into alpha helices and beta sheets, stabilized by hydrogen bonds.
Tertiary Structure: The overall three-dimensional shape of a single polypeptide, stabilized by interactions such as hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide bridges.
Quaternary Structure: The arrangement of multiple polypeptide subunits in a protein.

Peptide Bond Formation: Peptide bonds are formed by dehydration synthesis (condensation reaction) between the amino group of one amino acid and the carboxyl group of another, releasing water.

Functional Groups: Amino acids contain amino, carboxyl, and variable R groups. Some also have hydroxyl or sulfhydryl groups.

Carbohydrates

Carbohydrates are composed of monosaccharides (simple sugars) and serve as energy sources and structural components.

Monosaccharides: Glucose, fructose, galactose.
Disaccharides: Sucrose, lactose, maltose.
Polysaccharides: Starch (energy storage in plants), glycogen (energy storage in animals), cellulose (structural component in plants).

Lipids

Lipids are hydrophobic molecules, including fats, oils, phospholipids, and steroids.

Triglycerides: Composed of glycerol and three fatty acids; primary energy storage in adipose tissue.
Phospholipids: Contain a hydrophilic head and two hydrophobic tails; form the bilayer of cell membranes.
Steroids: Four fused carbon rings; include cholesterol and hormones.

Fatty Acids: Saturated fatty acids have no double bonds (solid at room temperature); unsaturated fatty acids have one or more double bonds (liquid at room temperature).

Nucleic Acids

Nucleic acids (DNA and RNA) store and transmit genetic information.

DNA: Double-stranded helix; bases are adenine (A), thymine (T), cytosine (C), and guanine (G).
RNA: Single-stranded; bases are adenine (A), uracil (U), cytosine (C), and guanine (G).
Base Pairing: A pairs with T (or U in RNA), C pairs with G. G-C pairs have three hydrogen bonds, making them more stable than A-T pairs (which have two hydrogen bonds).

Example: The complementary strand to 5'-ATGCCGA-3' is 3'-TACGGCT-5'.

Immunology: Antibodies and Antigens

Antibodies

Antibodies are proteins produced by B cells that recognize and bind to specific antigens, marking them for destruction by the immune system.

Each B cell can produce a large variety of antibodies, each specific to a different antigen.

Antigens

Antigens are molecules (often proteins or polysaccharides) that are recognized by the immune system as foreign and elicit an immune response.

Immune Responses

Adaptive Immunity: Involves the production of antibodies and the activation of specific immune cells in response to pathogens.
Cellular Immunity: Helper T cells stimulate B cells and cytotoxic T cells to respond to antigens.

Tables and Comparisons

Table: Types of Chemical Bonds in Biology

Bond Type	Description	Example
Covalent	Sharing of electron pairs between atoms	Peptide bond in proteins
Hydrogen	Attraction between a hydrogen atom and an electronegative atom	Between water molecules
Ionic	Transfer of electrons from one atom to another	NaCl (table salt)
Hydrophobic interactions	Nonpolar molecules clustering to avoid water	Formation of cell membranes

Table: Macromolecule Classes and Examples

Macromolecule	Monomer	Bond Type	Example
Protein	Amino acid	Peptide bond	Hemoglobin
Carbohydrate	Monosaccharide	Glycosidic bond	Starch, cellulose
Lipid	Glycerol, fatty acids	Ester bond	Triglyceride, phospholipid
Nucleic acid	Nucleotide	Phosphodiester bond	DNA, RNA

Key Formulas and Equations

Dehydration Synthesis (Condensation Reaction):

Base Pairing in DNA:

Hydrogen Bonding in Water:

Each water molecule can form up to 4 hydrogen bonds.

Additional info:

Some diagrams and tables were inferred based on standard biology curriculum and the context of the questions.
All major macromolecule classes and their properties were included for completeness.