Chapter 3: Protein Structure and Function

Amino Acid Structure

Proteins are polymers made from amino acid monomers, each with a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable R group.

• N & C Terminus: The amino (N) terminus is the start of a polypeptide, and the carboxyl (C) terminus is the end.

• Hydrophilic & Hydrophobic Amino Acids: Amino acids are classified based on the properties of their R groups; hydrophilic (polar/charged) side chains interact with water, while hydrophobic (nonpolar) side chains do not.

• Monomer, Polymer, Polymerization: Amino acids (monomers) join via dehydration synthesis to form polypeptides (polymers).

• Peptide Bonding: Amino acids are linked by peptide bonds formed between the carboxyl group of one and the amino group of another, releasing water.

Protein Structure (Primary, Secondary, Tertiary, Quaternary)

Proteins have four levels of structure that determine their function.

• Primary Structure: The sequence of amino acids in a polypeptide.

• Secondary Structure: Local folding patterns such as alpha helices and beta sheets, stabilized by hydrogen bonds.

• Tertiary Structure: The overall 3D shape of a polypeptide, determined by interactions among R groups.

• Quaternary Structure: The arrangement of multiple polypeptide chains into a functional protein complex.

Protein Folding

• Protein Folding: The process by which a protein assumes its functional shape, often assisted by chaperone proteins.

Enzymes

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy.

• Energy of Activation: The minimum energy required for a reaction to occur.

• Substrates and Active Sites: Substrates bind to the enzyme's active site, where the reaction occurs.

• Competitive & Non-Competitive Enzyme Inhibitors: Competitive inhibitors bind to the active site, blocking substrate binding; non-competitive inhibitors bind elsewhere, altering enzyme activity.

Example: The enzyme catalase breaks down hydrogen peroxide into water and oxygen.

Chapter 4: Nucleic Acids

Nucleotide Structure

Nucleic acids (DNA and RNA) are polymers of nucleotides, each consisting of a phosphate group, a five-carbon sugar, and a nitrogenous base.

• Ribose & Deoxyribose Nucleotides: RNA contains ribose; DNA contains deoxyribose.

• Purines and Pyrimidines: Purines (adenine, guanine) have two rings; pyrimidines (cytosine, thymine, uracil) have one ring.

• Complementary Base Pairing: In DNA, A pairs with T, and G pairs with C; in RNA, A pairs with U.

• Phosphodiester Bonding: Nucleotides are joined by phosphodiester bonds between the phosphate of one and the sugar of another.

Primary and Secondary Structure of Nucleic Acids

• Primary Structure: The sequence of nucleotides.

• Secondary Structure: DNA forms a double helix; RNA can form hairpins and other structures.

DNA and RNA Function

• DNA Function: Stores genetic information.

• RNA Structure and Function: Involved in protein synthesis and gene regulation.

Example: Messenger RNA (mRNA) carries genetic instructions from DNA to ribosomes.

Chapter 5: Carbohydrates

Structure and Function

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, serving as energy sources and structural components.

• Monosaccharide Monomers: Simple sugars like glucose, fructose, and galactose.

• Glycosidic Linkages: Covalent bonds that join monosaccharides to form disaccharides and polysaccharides.

Example: Starch (in plants) and glycogen (in animals) are polysaccharides used for energy storage.

Chapter 6: Lipids

Structure and Physical Properties of Lipids

Lipids are hydrophobic molecules including fats, phospholipids, and steroids, important for energy storage and membrane structure.

• Hydrocarbons: Chains or rings of carbon and hydrogen atoms.

• Saturated, Unsaturated, and Trans Fats: Saturated fats have no double bonds; unsaturated fats have one or more; trans fats are artificially altered unsaturated fats.

• Phospholipid Structure & Function: Phospholipids have a hydrophilic head and hydrophobic tails, forming bilayers in membranes.

• Amphipathic: Molecules with both hydrophilic and hydrophobic regions.

Membrane Structure and Permeability

• Selectively Permeable Membranes: Allow certain substances to pass while blocking others.

• Diffusion and Osmosis: Diffusion is the movement of molecules from high to low concentration; osmosis is the diffusion of water across a membrane.

• Passive and Active Transport: Passive transport does not require energy; active transport does.

• Tonicity: Refers to the relative concentration of solutes; isotonic (equal), hypertonic (higher outside), hypotonic (lower outside).

Example: Red blood cells in a hypertonic solution lose water and shrink.

Chapter 7: Inside the Cell

Features of All Cells

All cells share certain features, but prokaryotic and eukaryotic cells differ in complexity and organization.

• Prokaryotes vs. Eukaryotes: Prokaryotes lack a nucleus and membrane-bound organelles; eukaryotes have both.

• Cytoplasm & Organelles: The cytoplasm contains organelles that perform specific functions.

• DNA, Ribosomes, Smooth & Rough Endoplasmic Reticulum, Golgi Apparatus, Peroxisomes, Lysosomes, Mitochondria, Vacuoles, Chloroplasts, Cell Wall: Each organelle has a unique role in cell function.

• Compartmentalization: Eukaryotic cells use internal membranes to separate processes.

Example: Mitochondria generate ATP through cellular respiration.

Chapter 8: Energy and Enzymes

Enzymes and Activation Energy

Enzymes catalyze reactions by lowering the activation energy required.

• Activation Energy: The energy barrier that must be overcome for a reaction to proceed.

• Competitive vs. Allosteric Enzyme Regulation: Competitive inhibitors block the active site; allosteric regulators bind elsewhere, changing enzyme activity.

Example: Allosteric inhibition of phosphofructokinase regulates glycolysis.

Chapter 11: Cell Interactions

Extracellular Layers

Cells interact with their environment and each other through specialized structures.

• Cell Walls & Extracellular Matrix: Provide structural support and mediate cell signaling.

• Lamella: A layer that glues plant cells together.

Cell Junctions

• Tight Junctions: Seal cells together to prevent leakage.

• Desmosomes: Anchor cells together, providing mechanical strength.

• Plasmodesmata: Channels between plant cells for communication.

• Gap Junctions: Channels between animal cells for communication.

Example: Gap junctions allow ions to pass between heart muscle cells for coordinated contraction.

Table: Comparison of Cell Junctions

Key Equations

• Peptide Bond Formation:

• Phosphodiester Bond Formation:

• Diffusion Rate (Fick's Law):

• Enzyme Reaction Rate (Michaelis-Menten Equation):

Additional info: Some terminology and section headings were inferred and expanded for clarity and completeness. All major topics from the provided notes are included and explained in academic context.