General Biology: Core Concepts and Practice Questions

General Biology: Core Concepts and Practice Questions

Atomic Structure and Chemical Bonding

Understanding atomic structure and chemical bonding is fundamental to biology, as it underpins molecular interactions in living systems.

• Electronegativity: The tendency of an atom to attract electrons in a chemical bond. For example, nitrogen (N) is more electronegative than hydrogen (H), affecting the charge distribution in molecules like ammonia (NH3).

• Covalent Bonds: Formed when two atoms share a pair of valence electrons. Example: The bond between two hydrogen atoms.

• Ionic Bonds: Formed when electrons are transferred from one atom to another, resulting in oppositely charged ions. Example: The bond between sodium and chlorine in NaCl.

• Partial Charges: In polar molecules such as water (H2O), differences in electronegativity cause atoms to have partial positive or negative charges.

pH and Biological Systems

pH measures the concentration of hydrogen ions in a solution and affects many biological processes.

• pH Scale: Ranges from 0 (acidic) to 14 (basic). A decrease in pH indicates an increase in hydrogen ion concentration.

• Effect of pH Change: Shifting from pH 7 to pH 3 increases hydrogen ion concentration by 10,000 times. $[H^+]_{final} = [H^+]_{initial} imes 10^{(pH_{initial} - pH_{final})}$

Functional Groups in Organic Molecules

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

• Hydroxyl Group (-OH): Found in alcohols; makes molecules polar and can participate in hydrogen bonding.

• Carboxyl Group (-COOH): Found in acids like citric acid; acts as an acid by donating a proton (H+).

• Hydrocarbon: Nonpolar group consisting of hydrogen and carbon atoms.

Macromolecules: Carbohydrates and Nucleic Acids

Macromolecules are large, complex molecules essential for life.

• Monosaccharides: Simple sugars that link via covalent bonds (glycosidic linkages) to form polysaccharides.

• Polysaccharides: Long chains of monosaccharides; examples include starch and cellulose.

• Nucleic Acids: DNA and RNA are polymers of nucleotides, which consist of a nitrogenous base, a sugar, and phosphate groups.

Table: Components of a DNA Strand

Component	Description
Nitrogenous bases	Adenine, guanine, cytosine, thymine
Sugar	Deoxyribose
Phosphate group	Attached to 3' OH on pentose sugar

Cell Structure and Classification

Cells are the basic units of life and are classified as prokaryotic or eukaryotic.

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles. Examples: Bacteria and Archaea.

• Eukaryotic Cells: Have a nucleus and organelles such as mitochondria, chloroplasts, and endoplasmic reticulum.

• Cell Organelles:

  • Nucleus: Contains genetic material.

  • Mitochondria: Site of cellular respiration.

  • Chloroplast: Site of photosynthesis in plant cells.

  • Cell Wall: Provides structure in plant cells.

  • Lysosome: Involved in intracellular digestion.

Table: Comparison of Cell Structures

Structure	Prokaryotic Cell	Eukaryotic Cell
Nucleus	Absent	Present
Organelles	Absent	Present
Cell Wall	Present (most)	Present (plants, fungi)
Size	Smaller	Larger

Cell Membranes and Transport

Cell membranes regulate the movement of substances in and out of cells.

• Phospholipid Bilayer: Forms the basic structure of cell membranes.

• Transport Proteins: Facilitate movement of ions and polar molecules across membranes.

• Cholesterol: Modifies membrane fluidity.

Enzymes and Metabolism

Enzymes are biological catalysts that speed up chemical reactions in cells.

• Activation Energy: The energy required to start a reaction. Enzymes lower activation energy. $E_a$ (with enzyme) < $E_a$ (without enzyme)

• Specificity: Enzymes are highly specific for their substrates due to their active site structure.

• Competitive Inhibition: Occurs when a molecule competes with the substrate for the active site.

• Allosteric Inhibition: Occurs when a molecule binds to a site other than the active site, changing enzyme activity.

• ATP: Adenosine triphosphate; provides energy for cellular processes by transferring a phosphate group.

Thermodynamics in Biology

Thermodynamics governs energy changes in biological systems.

• Exergonic Reactions: Release energy; occur spontaneously.

• Endergonic Reactions: Require energy input.

• Entropy: A measure of disorder; reactions that increase entropy are favored.

• Gibbs Free Energy ($riangle G$): Determines whether a reaction is spontaneous. $riangle G = riangle H - T riangle S$ Where $riangle H$ is enthalpy, $T$ is temperature, and $riangle S$ is entropy.

Protein Structure

Proteins have four levels of structure that determine their function.

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Coils and folds, such as alpha-helices and beta-pleated sheets.

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

• Quaternary Structure: Association of multiple polypeptide chains.

Cellular Processes: Photosynthesis and Respiration

Cells convert energy through photosynthesis and respiration.

• Photosynthesis: Occurs in chloroplasts; converts light energy into chemical energy.

• Cellular Respiration: Occurs in mitochondria; breaks down glucose to produce ATP.

Classification of Life

Organisms are classified into three domains: Archaea, Bacteria, and Eukarya.

• Archaea: Prokaryotic, often found in extreme environments.

• Bacteria: Prokaryotic, diverse habitats.

• Eukarya: Eukaryotic, includes plants, animals, fungi, and protists.

Cell Cycle and Viral Life Cycles

Cells and viruses have distinct life cycles.

• Lytic Cycle: Virus replicates and lyses the host cell.

• Lysogenic Cycle: Viral DNA integrates into the host genome and replicates with it.

Practice Questions and Diagrams

The file contains multiple-choice questions and diagrams (e.g., cell structure, Euglena) to test understanding of the above concepts.

• Cell Diagrams: Used to compare prokaryotic and eukaryotic cells, and identify organelles.

• Functional Group Identification: Recognizing groups like hydroxyl and carboxyl in organic molecules.

• Enzyme Function: Understanding how enzymes lower activation energy and are affected by temperature and inhibitors.

Table: Cell Structure Comparison (from diagram)

Cell A	Cell B
Has cell wall, vacuole, chloroplast, nucleus, mitochondrion, lysosome, cell membrane, cytosol	Has cell membrane, nucleus, mitochondrion, lysosome, cytosol
Plant cell (eukaryotic)	Animal cell (eukaryotic)

Table: Euglena Structure

Structure	Function
Flagellum	Movement
Chloroplast	Photosynthesis
Nucleus	Genetic material storage
Reservoir	Storage
Eye spot	Light detection
Cell membrane	Boundary and transport

Additional info: Some explanations and tables have been expanded for clarity and completeness based on standard biology curriculum.