General Biology Study Guide: Biomolecules, Cell Structure, Membranes, Enzymes, and Cellular Respiration

Chapter 5: Biomolecules and Their Functions

Polysaccharides, Fats, and Proteins

Biomolecules such as polysaccharides, fats, and proteins are essential macromolecules in living organisms. Their synthesis and degradation are fundamental to cellular metabolism and structure.

• Polymers are large molecules made by joining smaller units called monomers through condensation reactions. Polysaccharides are polymers of monosaccharides (simple sugars), fats are composed of fatty acids and glycerol, and proteins are polymers of amino acids.

• Synthesis involves dehydration (removal of water), while degradation involves hydrolysis (addition of water).

• Monosaccharides are single sugar units (e.g., glucose), disaccharides are two sugars joined (e.g., sucrose), and polysaccharides are long chains (e.g., starch, cellulose).

Example: Starch is a polysaccharide used for energy storage in plants.

Types and Functions of Polysaccharides

• Starch: Energy storage in plants.

• Glycogen: Energy storage in animals.

• Cellulose: Structural component in plant cell walls.

• Chitin: Structural component in fungal cell walls and exoskeletons of arthropods.

Fats and Fatty Acids

• Triacylglycerol (Triglyceride): A fat molecule composed of three fatty acids linked to glycerol.

• Saturated fatty acids have no double bonds; unsaturated fatty acids have one or more double bonds, affecting fluidity and melting point.

• At room temperature, saturated fats are solid, while unsaturated fats are liquid.

Proteins and Amino Acids

• Proteins are made up of amino acids, which are linked by peptide bonds.

• There are 20 different amino acids, each with a unique side chain (R group).

• Primary structure: Sequence of amino acids.

• Secondary structure: Alpha helices and beta sheets formed by hydrogen bonding.

• Tertiary structure: Three-dimensional folding due to interactions among side chains.

• Quaternary structure: Association of multiple polypeptide chains.

• Protein shape can be disrupted by changes in pH, temperature, or ionic strength (denaturation).

Example: Hemoglobin is a protein with quaternary structure, responsible for oxygen transport in blood.

Phospholipids and Steroids

• Phospholipids are major components of cell membranes, consisting of two fatty acids, a phosphate group, and glycerol.

• Steroids are lipids with a four-ring structure; cholesterol is a common example.

Nucleic Acids: DNA and RNA

• DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are polymers of nucleotides.

• Nucleotides consist of a sugar, phosphate group, and nitrogenous base.

• DNA stores genetic information; RNA is involved in protein synthesis.

• DNA bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).

• RNA bases: Adenine (A), Uracil (U), Cytosine (C), Guanine (G).

• DNA is double-stranded; RNA is usually single-stranded.

Example: The structure of DNA is a double helix stabilized by hydrogen bonds between complementary bases.

Chapter 6: Cell Structure and Organelles

Prokaryotic vs. Eukaryotic Cells

Cells are classified as prokaryotic or eukaryotic based on their structure and organization.

• Prokaryotic cells lack a nucleus and membrane-bound organelles (e.g., bacteria).

• Eukaryotic cells have a nucleus and various organelles (e.g., plants, animals, fungi).

Major Organelles and Their Functions

• Nucleus: Contains genetic material (DNA).

• Mitochondria: Site of cellular respiration and ATP production.

• Chloroplasts: Site of photosynthesis in plant cells.

• Endoplasmic reticulum (ER): Protein and lipid synthesis.

• Golgi apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Digestion and waste removal.

• Ribosomes: Protein synthesis.

Cytoskeleton

• Microtubules, microfilaments, and intermediate filaments provide structural support and facilitate cell movement.

Chapter 7: Cell Membranes and Transport

Structure and Components of Cell Membranes

The cell membrane is a selectively permeable barrier composed of lipids, proteins, and carbohydrates.

• Phospholipid bilayer forms the basic structure.

• Peripheral proteins are attached to the membrane surface; integral proteins span the membrane.

• Carbohydrates are attached to proteins and lipids, functioning in cell recognition.

Membrane Transport Mechanisms

• Passive transport: Movement of substances down their concentration gradient without energy input (e.g., diffusion, osmosis).

• Active transport: Movement against the concentration gradient, requiring energy (ATP).

• Endocytosis: Uptake of large molecules via vesicles.

• Exocytosis: Release of substances from the cell via vesicles.

Types of Endocytosis

• Phagocytosis: "Cell eating"; uptake of large particles.

• Pinocytosis: "Cell drinking"; uptake of fluids and small molecules.

• Receptor-mediated endocytosis: Specific uptake of molecules via receptor proteins.

Osmosis and Diffusion

• Diffusion: Movement of molecules from high to low concentration.

• Osmosis: Diffusion of water across a selectively permeable membrane.

• In isotonic solutions, cells maintain normal shape; in hypertonic solutions, cells lose water; in hypotonic solutions, cells gain water.

Chapter 8: Enzymes and Metabolism

Enzyme Structure and Function

Enzymes are biological catalysts that speed up chemical reactions without being consumed.

• Active site: Region where substrate binds and reaction occurs.

• Substrate: The molecule upon which an enzyme acts.

• Enzyme-substrate complex: Temporary association during the reaction.

• Enzymes lower activation energy, increasing reaction rate.

Enzyme Regulation

• Competitive inhibitors bind to the active site, blocking substrate.

• Noncompetitive inhibitors bind elsewhere, changing enzyme shape.

• Allosteric regulation: Regulation by molecules binding to sites other than the active site.

• Feedback inhibition: End product inhibits an earlier step in the pathway.

• Enzyme activity is affected by pH and temperature; each enzyme has an optimum range.

Metabolic Pathways

• Catabolic pathways: Break down molecules to release energy.

• Anabolic pathways: Build complex molecules from simpler ones, requiring energy.

• Coupled reactions: Energy released from one reaction drives another.

Chapter 9: Cellular Respiration

Redox Reactions

Cellular respiration involves a series of redox reactions, where electrons are transferred between molecules.

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

Stages of Cellular Respiration

• Glycolysis: Occurs in the cytoplasm; breaks down glucose into pyruvate.

• Krebs cycle (Citric Acid Cycle): Occurs in mitochondria; processes pyruvate to produce electron carriers.

• Electron Transport Chain: Occurs in the inner mitochondrial membrane; uses electrons to produce ATP.

ATP Production

• ATP is produced during glycolysis, Krebs cycle, and mainly in the electron transport chain.

• Oxygen is the final electron acceptor in the electron transport chain.

• Maximum ATP production occurs during oxidative phosphorylation in the electron transport chain.

Key Equations

• General equation for cellular respiration: $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

• ATP yield from one glucose molecule: $\text{Up to 36-38 ATP}$

Summary Table: Comparison of Cell Types

Feature	Prokaryotic Cell	Eukaryotic Cell
Nucleus	Absent	Present
Membrane-bound Organelles	Absent	Present
Size	Small (1-10 μm)	Larger (10-100 μm)
Examples	Bacteria, Archaea	Plants, Animals, Fungi

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard General Biology curriculum.