General Biology: Study Guide on Biomolecules and Cell Transport

Chapter 1: Introduction to Biology

Properties and Methods in Biology

This section introduces the fundamental properties of life and the scientific methods used in biological research.

• Properties of Life: Life is characterized by organization, metabolism, homeostasis, growth, reproduction, response to stimuli, and adaptation through evolution.

• Scientific Investigations: Biologists use observation, hypothesis formation, experimentation, and analysis to understand living systems. The scientific method involves ongoing cycles of these steps, with conclusions based on empirical evidence.

Chapter 2: The Chemistry of Life

Atomic Structure and Chemical Bonds

This section covers the structure of atoms, the types of chemical bonds, and their relevance to biological molecules.

• Structure of an Atom: Atoms consist of a nucleus (protons and neutrons) and electrons in orbitals.

• Elements and Compounds: Elements are pure substances of one type of atom; compounds are substances formed from two or more elements chemically bonded.

• Types of Chemical Bonds:

  • Ionic Bonds: Transfer of electrons between atoms (e.g., NaCl).

  • Covalent Bonds: Sharing of electrons between atoms (e.g., H2O).

  • Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., between water molecules).

• Supporting Properties of Water: Water's polarity, cohesion, adhesion, high specific heat, and solvent abilities are essential for life.

• Monomers and Polymers: Monomers are small building blocks (e.g., amino acids, monosaccharides) that join to form polymers (e.g., proteins, polysaccharides).

Chapter 3: Proteins and Their Structure

Amino Acids, Protein Structure, and Function

This section explores the structure of proteins, the properties of amino acids, and the relationship between protein structure and function.

• Water Solubility and Amino Acids: The solubility and interaction of amino acids depend on their side chains (R groups), which can be hydrophilic or hydrophobic.

• Levels of Protein Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Local folding (α-helix, β-sheet) stabilized by hydrogen bonds.

  • Tertiary: Overall 3D shape due to side chain interactions.

  • Quaternary: Association of multiple polypeptide chains.

• Protein Folding and Denaturation: Proper folding is essential for function; denaturation (by heat, pH, chemicals) leads to loss of function.

• Functions of Proteins: Proteins serve as enzymes, structural components, transporters, antibodies, and signaling molecules.

Chapter 5: Carbohydrates

Monosaccharides, Polysaccharides, and Their Functions

This section discusses the structure and function of carbohydrates, including simple sugars and complex polysaccharides.

• Structural Variations in Monosaccharides: Monosaccharides (e.g., glucose, fructose) differ in carbon number and arrangement.

• Storage Polysaccharides:

  • Starch: Storage form in plants.

  • Glycogen: Storage form in animals.

• Structural Polysaccharides:

  • Cellulose: Plant cell wall component.

  • Chitin: Fungal cell walls and exoskeletons of arthropods.

• Carbohydrate Structure and Function: The structure (branching, linkage type) determines digestibility and function (energy storage, structural support).

Chapter 6: Lipids and Membranes

Types of Lipids and Membrane Structure

This section covers the major types of lipids, their properties, and their roles in biological membranes.

• Major Types of Lipids:

  • Fats (Triglycerides): Energy storage, insulation.

  • Steroids: Hormones, membrane components (e.g., cholesterol).

  • Phospholipids: Main component of cell membranes.

• Phospholipid Behavior in Water: Phospholipids spontaneously form bilayers in aqueous environments due to their hydrophilic heads and hydrophobic tails.

• Properties of Substances and Membrane Permeability:

  • Polar molecules (e.g., H2O, ions) have low permeability.

  • Nonpolar molecules (e.g., O2, CO2) have high permeability.

  • Glucose and ions require transport proteins.

• Fatty Acid Structure:

  • Saturated: No double bonds, solid at room temperature.

  • Unsaturated: One or more double bonds, liquid at room temperature.

  • Cholesterol: Modulates membrane fluidity.

• Osmosis: Diffusion of water across a selectively permeable membrane from low to high solute concentration.

Membrane Transport

This section explains the mechanisms by which substances move across cell membranes.

• Passive Transport: Movement of substances down their concentration gradient without energy input. Includes:

  • Simple Diffusion: Direct movement through the membrane (e.g., O2, CO2).

  • Facilitated Diffusion: Movement via channel or carrier proteins (e.g., glucose transporters).

• Active Transport: Movement against the concentration gradient, requiring energy (usually ATP). Example: sodium-potassium pump.

• Sodium-Potassium Pump: Uses ATP to move 3 Na+ out and 2 K+ into the cell, establishing an electrochemical gradient.

Transport Type	Energy Required?	Direction	Example
Simple Diffusion	No	Down gradient	O2, CO2
Facilitated Diffusion	No	Down gradient	Glucose, ions via channels
Active Transport	Yes (ATP)	Against gradient	Sodium-potassium pump

Equation for Osmosis:

$\Psi = \Psi_s + \Psi_p$

Where $\Psi$ is water potential, $\Psi_s$ is solute potential, and $\Psi_p$ is pressure potential.

Example: The sodium-potassium pump is essential for nerve impulse transmission and muscle contraction.