General Biology: Core Concepts and Cellular Structures Study Guide

Macromolecules

Classes of Macromolecules

Macromolecules are large, complex molecules essential for life. Three of the four major classes are polymers, while the fourth is not.

• Carbohydrates: Polymers made of monosaccharide monomers (e.g., glucose).

• Proteins: Polymers composed of amino acid monomers.

• Nucleic Acids: Polymers of nucleotide monomers (e.g., DNA, RNA).

• Lipids: Not true polymers; composed of fatty acids and glycerol (e.g., fats, oils, phospholipids).

Example: Starch (a carbohydrate) is a polymer of glucose; DNA (a nucleic acid) is a polymer of nucleotides.

Aldoses and Ketoses

Monosaccharides (simple sugars) are classified based on the location of their carbonyl group:

• Aldose: Carbonyl group at the end of the carbon chain (e.g., glucose).

• Ketose: Carbonyl group within the carbon chain (e.g., fructose).

Example: Glucose is an aldose; fructose is a ketose.

Asymmetrical (Chiral) Carbon

An asymmetrical carbon (chiral carbon) is a carbon atom attached to four different groups. This property leads to isomerism (enantiomers).

• Chirality is important in biological molecules, affecting their function.

Example: The alpha carbon in amino acids is typically chiral (except in glycine).

Proteins and Amino Acids

Composition of an Amino Acid

Amino acids are the building blocks of proteins. Each amino acid contains:

• Amino group (-NH2)

• Carboxyl group (-COOH)

• Hydrogen atom

• R group (side chain, variable)

• All attached to a central (alpha) carbon

Example: Glycine has an R group of hydrogen; alanine has a methyl group (-CH3).

Composition of a Polypeptide

A polypeptide is a chain of amino acids linked by peptide bonds. The sequence of amino acids determines the protein's structure and function.

• Peptide bond: Covalent bond between the carboxyl group of one amino acid and the amino group of another.

• Polypeptides have an N-terminus (amino end) and a C-terminus (carboxyl end).

Determinants of Amino Acid Chemical Activity

• The R group (side chain) determines the chemical properties and reactivity of each amino acid.

• R groups can be nonpolar, polar, acidic, or basic.

Types of R Groups

• Nonpolar (hydrophobic): e.g., leucine, valine

• Polar (hydrophilic): e.g., serine, threonine

• Acidic (negatively charged): e.g., aspartic acid, glutamic acid

• Basic (positively charged): e.g., lysine, arginine

Nucleic Acids

DNA Base Pairing and Hydrogen Bonds

DNA is composed of two strands forming a double helix, held together by hydrogen bonds between complementary bases:

• Adenine (A) pairs with Thymine (T) via 2 hydrogen bonds.

• Guanine (G) pairs with Cytosine (C) via 3 hydrogen bonds.

Cell Structure and Function

Basic Features Shared by All Cells

• Plasma membrane

• Cytoplasm

• Genetic material (DNA)

• Ribosomes

• Metabolic machinery

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic cells: Lack a nucleus and membrane-bound organelles; DNA is in the nucleoid region (e.g., bacteria, archaea).

• Eukaryotic cells: Have a nucleus and membrane-bound organelles (e.g., plants, animals, fungi, protists).

Organelles: Functions and Identification

Each organelle has a specific function within the cell. Key organelles include:

• Nucleus: Stores genetic material; site of transcription.

• Mitochondria: Site of cellular respiration; produces ATP.

• Chloroplasts (plants/algae): Site of photosynthesis.

• Endoplasmic reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids.

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

• Lysosomes: Contain digestive enzymes; break down waste.

• Peroxisomes: Break down fatty acids and detoxify harmful substances.

• Ribosomes: Synthesize proteins.

• Vacuoles: Storage (large central vacuole in plants).

• Plasma membrane: Controls entry and exit of substances.

Additional info: Visual identification often relies on shape, size, and location within the cell.

Legendary Scientists and Evidence

• Famous scientists are associated with key discoveries (e.g., Watson and Crick for DNA structure, Hooke for cells).

Compartments of Mitochondria and Chloroplasts

• Mitochondria: Outer membrane, inner membrane, intermembrane space, matrix, cristae.

• Chloroplasts: Outer membrane, inner membrane, stroma, thylakoid membrane, grana.

Cytoskeleton and Motor Proteins

• Cytoskeleton: Network of protein fibers (microtubules, microfilaments, intermediate filaments) that provide structural support, shape, and movement.

• Motor proteins: Proteins (e.g., kinesin, dynein, myosin) that move along cytoskeletal fibers, transporting vesicles and organelles.

Extracellular Matrix (ECM)

• Composition: Network of proteins (collagen, elastin, fibronectin) and polysaccharides outside animal cells.

• Function: Provides structural support, regulates cell behavior, and facilitates cell communication.

Plasma Membrane Composition

• Phospholipid bilayer: Hydrophilic heads face outward; hydrophobic tails face inward.

• Proteins: Integral and peripheral proteins serve as channels, receptors, and enzymes.

• Carbohydrates: Attached to proteins/lipids, involved in cell recognition.

• Cholesterol: Modulates membrane fluidity (in animal cells).

Membrane Transport

Diffusion, Osmosis, and Tonicity

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

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

• Tonicity: The ability of a solution to cause a cell to gain or lose water.

Directional Water Flow:

• Hypotonic solution: Water enters the cell (cell may swell).

• Hypertonic solution: Water leaves the cell (cell may shrink).

• Isotonic solution: No net water movement.

Key Equations

• Osmosis can be described by the equation: $J = -P (C_2 - C_1)$ where $J$ is the flux, $P$ is the permeability, and $C_2 - C_1$ is the concentration difference.

Summary Table: Prokaryotic vs. Eukaryotic Cells

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