Biol 203 Exam 1 Study Guide: Molecular and Cellular Foundations

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Chemical Bonds and Biological Molecules

Covalent vs. Non-Covalent Bonds

Chemical bonds are fundamental to the structure and function of biological molecules. Understanding the differences between covalent and non-covalent bonds is essential for grasping molecular interactions in biology.

Covalent Bonds: Formed when two atoms share one or more pairs of electrons. These bonds are strong and stable, commonly found in the backbone of biological macromolecules (e.g., DNA, proteins).
Non-Covalent Bonds: Include hydrogen bonds, ionic bonds, van der Waals interactions, and hydrophobic effects. These are weaker than covalent bonds but crucial for the dynamic interactions and 3D structure of biomolecules.
Example: Hydrogen bonds stabilize the double helix structure of DNA.

Role of Non-Covalent Bonding in Biological Reactions and 3D Structure

Non-covalent interactions allow molecules to recognize, bind, and respond to each other, enabling complex biological processes.

3D Structural Arrangements: Non-covalent bonds help proteins fold into their functional shapes and allow for reversible interactions.
Biological Reactions: Enzyme-substrate binding, antibody-antigen recognition, and membrane formation rely on non-covalent interactions.
Example: The hydrophobic effect drives the folding of proteins by causing nonpolar amino acids to cluster away from water.

Membrane Transport Mechanisms

Osmosis, Passive, and Active Transport

Cells regulate the movement of substances across membranes using various transport mechanisms.

Osmosis: The diffusion of water across a selectively permeable membrane from an area of low solute concentration to high solute concentration.
Passive Transport: Movement of molecules down their concentration gradient without energy input (e.g., simple diffusion, facilitated diffusion).
Active Transport: Movement of molecules against their concentration gradient, requiring energy (usually ATP).
Example: Sodium-potassium pump uses ATP to move Na+ out and K+ into the cell.

Electrochemical Gradient

An electrochemical gradient is the combined effect of a concentration gradient and an electrical potential across a membrane.

Definition: The difference in ion concentration and charge across a membrane.
Function: Drives the movement of ions (e.g., Na+, K+) and is essential for processes like nerve impulse transmission.
Example: The proton gradient across the mitochondrial membrane powers ATP synthesis.

Bioenergetics and Enzymes

Spontaneity of Reactions and ΔG

The spontaneity of a reaction is determined by the change in free energy (ΔG).

Spontaneous Reaction: Occurs without external energy input; ΔG is negative.
Nonspontaneous Reaction: Requires energy input; ΔG is positive.
Equation:

Where: ΔH = change in enthalpy, T = temperature (Kelvin), ΔS = change in entropy.
Example: Cellular respiration is spontaneous (ΔG < 0), while photosynthesis is nonspontaneous (ΔG > 0).

Roles of Enzymes and Activated Carriers

Enzymes and activated carriers are essential for facilitating and regulating biological reactions.

Enzymes: Biological catalysts that lower activation energy, increasing reaction rates without being consumed.
Activated Carriers: Molecules like ATP, NADH, and FADH2 that store and transfer energy or electrons.
Example: ATP hydrolysis provides energy for cellular processes.

Protein Structure and Function

Primary vs. Tertiary Structure

Protein structure is hierarchical, with each level influencing the next.

Primary Structure: The linear sequence of amino acids in a polypeptide.
Tertiary Structure: The overall 3D shape formed by folding and interactions among side chains.
Relationship: The primary structure determines how the protein folds, which in turn affects its function.
Example: A single amino acid change in hemoglobin can cause sickle cell disease.

Protein Binding Sites and Ligand Binding

Binding sites are regions on proteins where ligands (molecules) attach, often causing conformational changes.

Function: Enable proteins to interact with other molecules, regulate activity, and transmit signals.
Change Upon Binding: Ligand binding can alter protein shape, affecting function (e.g., allosteric regulation).
Example: Oxygen binding to hemoglobin changes its conformation, increasing affinity for more oxygen.

Cellular Structures and Processes

Junctional Complexes and the Extracellular Matrix (ECM)

Cells are organized and communicate through junctional complexes and the ECM.

Junctional Complexes: Structures like tight junctions, desmosomes, and gap junctions that connect cells and regulate passage of substances.
ECM: A network of proteins and polysaccharides outside cells that provides structural support and mediates cell signaling.
Example: Collagen in the ECM gives tissues strength and elasticity.

Endocytosis and Exocytosis Overview

Cells transport large molecules and particles via endocytosis and exocytosis.

Endocytosis: The process by which cells engulf external substances, forming vesicles.
Exocytosis: The process by which cells expel substances by merging vesicles with the plasma membrane.
Example: Neurotransmitter release at synapses occurs via exocytosis.

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