General Biology Study Guide: Water, Functional Groups, Macromolecules, and Protein Structure

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Chapter 3: Water and Its Properties

Structure and Function of Water

Water (H2O) is a polar molecule essential for life, serving as a universal solvent and participating in many biological processes.

Structure: Water consists of two hydrogen atoms covalently bonded to one oxygen atom, forming a bent molecular shape due to the oxygen's higher electronegativity.
Function: Water regulates temperature, transports substances, and facilitates chemical reactions in cells.
Example: Water dissolves ionic compounds like NaCl, enabling cellular transport.

Hydrogen Bonding in Water

Hydrogen bonds are weak attractions between the partially positive hydrogen atom of one water molecule and the partially negative oxygen atom of another.

Importance: Hydrogen bonding gives water its high cohesion, adhesion, surface tension, and specific heat capacity.
Example: Water's high heat capacity helps organisms maintain stable internal temperatures.

Polarity of Water

Water is a polar molecule due to the unequal sharing of electrons between oxygen and hydrogen atoms.

Polarity: Oxygen is more electronegative, creating a partial negative charge at the oxygen end and a partial positive charge at the hydrogen end.
Example: Water's polarity allows it to dissolve many substances, making it an effective solvent.

pH and Buffers in the Cell

The pH scale measures the concentration of hydrogen ions in a solution, affecting cellular processes. Buffers help maintain stable pH in cells.

pH: Defined as ; most cells function optimally at pH 7.2–7.4.
Buffers: Substances that minimize changes in pH by absorbing or releasing H+ ions.
Example: The bicarbonate buffer system in blood maintains pH homeostasis.

Chapter 4: Functional Groups and Isomerism

Seven Common Functional Groups

Functional groups are specific groups of atoms within molecules that confer distinct chemical properties.

Hydroxyl (-OH): Found in alcohols; increases solubility in water.
Carbonyl (C=O): Found in aldehydes and ketones; reactive in sugar chemistry.
Carboxyl (-COOH): Found in acids; acts as a proton donor.
Amino (-NH2): Found in amino acids; acts as a base.
Sulfhydryl (-SH): Found in thiols; forms disulfide bonds in proteins.
Phosphate (-PO4): Found in nucleotides; involved in energy transfer.
Methyl (-CH3): Nonpolar; affects gene expression when attached to DNA.

Types of Isomers

Isomers are molecules with the same molecular formula but different structures.

Structural Isomers: Differ in the covalent arrangement of atoms.
Cis-Trans (Geometric) Isomers: Differ in spatial arrangement around a double bond.
Enantiomers: Mirror-image isomers; important in pharmaceuticals.
Example: Glucose and fructose are structural isomers; cis and trans forms of fatty acids affect membrane fluidity.

Chapter 5: Macromolecules and Protein Structure

Structure and Function of Macromolecules

Macromolecules are large, complex molecules essential for life, including carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates: Provide energy and structural support; monomers are monosaccharides.
Lipids: Store energy, form membranes; include fats, phospholipids, steroids.
Proteins: Catalyze reactions, provide structure; monomers are amino acids.
Nucleic Acids: Store genetic information; monomers are nucleotides.

Common Atoms in Macromolecules

Carbohydrates: Carbon (C), Hydrogen (H), Oxygen (O)
Lipids: Carbon (C), Hydrogen (H), Oxygen (O) (sometimes Phosphorus (P))
Proteins: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), sometimes Sulfur (S)
Nucleic Acids: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P)

Synthesis and Hydrolysis

Macromolecules are built and broken down by specific chemical reactions.

Synthesis (Dehydration): Monomers join to form polymers, releasing water.
Hydrolysis: Polymers are broken into monomers by adding water.
Example: Formation and breakdown of starch in plants.

Monomer-Polymer Relationship

Monomers are small molecules that join to form polymers, which are large, chain-like molecules.

Example: Amino acids (monomers) form proteins (polymers).

DNA, Protein, and Enzyme Relationship

DNA encodes instructions for building proteins, which can function as enzymes to catalyze cellular reactions.

DNA: Contains genetic code.
Protein: Synthesized from DNA instructions via transcription and translation.
Enzyme: A type of protein that speeds up chemical reactions.

Mutation

A mutation is a change in the DNA sequence, which can affect protein structure and function.

Types: Point mutations, insertions, deletions.
Example: Sickle cell anemia is caused by a single nucleotide mutation in the hemoglobin gene.

Four Levels of Protein Structure

Proteins have four levels of structure that determine their shape and function.

Primary: Sequence of amino acids.
Secondary: Local folding (α-helix, β-sheet) stabilized by hydrogen bonds.
Tertiary: Overall 3D shape due to interactions among side chains.
Quaternary: Association of multiple polypeptide chains.

Protein Folding Rules

Protein folding is guided by chemical interactions and the sequence of amino acids.

Hydrophobic interactions: Nonpolar side chains fold inward.
Hydrogen bonds: Stabilize secondary and tertiary structures.
Disulfide bridges: Covalent bonds between cysteine residues.
Example: Incorrect folding can lead to diseases like Alzheimer's.

Structure and Classification of Amino Acids

Amino acids have a central carbon bonded to an amino group, carboxyl group, hydrogen atom, and variable R group.

Classification: Based on properties of R group: nonpolar, polar, acidic, basic.
Example: Glycine is nonpolar; glutamic acid is acidic.

Structure of DNA and RNA

DNA and RNA are nucleic acids with distinct structures and functions.

DNA: Double helix, deoxyribose sugar, bases A, T, C, G.
RNA: Single-stranded, ribose sugar, bases A, U, C, G.
Example: DNA stores genetic information; RNA helps synthesize proteins.

FRQ Preparation: Data Analysis and Protein Structure

Graphing Guidelines

Proper graphing is essential for visualizing biological data.

Axes: Label axes with units and variable names.
Title: Provide a descriptive title.
Legend: Include if multiple data sets are present.

Standard Error of the Mean (SEM) and Statistical Differences

SEM quantifies the precision of the sample mean; statistical tests determine if differences are significant.

SEM Formula: where is sample standard deviation and is sample size.
Statistical Significance: Determined by p-values; p < 0.05 is commonly considered significant.

Protein Structure and Function

Protein function is determined by its structure, which is encoded by the sequence of amino acids.

Enzyme Activity: Depends on the shape of the active site.
Denaturation: Loss of structure leads to loss of function.