General Biology: Biomolecules, Cell Structure, and Membrane Transport Study Guide

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Biomolecules and Chemical Reactions

Dehydration vs. Hydrolysis Reactions

Biological systems use dehydration and hydrolysis reactions to build and break down macromolecules, which is essential for energy production and utilization, such as in ATP metabolism.

Dehydration Reaction: A chemical process that joins two molecules by removing a water molecule. Used to synthesize polymers from monomers.
Hydrolysis Reaction: A process that breaks down polymers into monomers by adding water. Critical for digestion and ATP utilization.
ATP Production: ATP is generated by dehydration reactions (e.g., during cellular respiration) and utilized via hydrolysis to release energy.
Example: Formation of maltose from two glucose molecules via dehydration; breakdown of ATP to ADP and Pi via hydrolysis.

Carbohydrates

Monosaccharides and Polysaccharides

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

Monosaccharides: Simple sugars (e.g., glucose, fructose) that are the building blocks of carbohydrates.
Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, cellulose).
Example: Glucose is a monosaccharide; starch is a polysaccharide made of glucose units.

Glucose

Glucose is a central molecule in metabolism, serving as a primary energy source for cells.

Structure: C6H12O6; a hexose sugar.
Function: Used in cellular respiration to produce ATP.
Isomers: Exists in alpha and beta forms, important in polysaccharide structure.
Example: Blood sugar regulation involves glucose uptake and storage.

Lipids and Proteins

Lipids

Lipids are hydrophobic molecules that include fats, oils, and steroids. They are important for energy storage and membrane structure.

Structure: Composed mainly of fatty acids and glycerol.
Function: Energy storage, insulation, and cell membrane formation.
Example: Phospholipids form the bilayer of cell membranes.

Proteins (3D Structure)

Proteins are polymers of amino acids that fold into specific three-dimensional shapes, determining their function.

Primary Structure: Sequence of amino acids.
Secondary Structure: Alpha helices and beta sheets formed by hydrogen bonding.
Tertiary Structure: Overall 3D shape due to interactions among R groups.
Quaternary Structure: Association of multiple polypeptide chains.
Example: Hemoglobin is a protein with quaternary structure.

Nucleic Acids and Nucleotides

Nucleic Acids

Nucleic acids store and transmit genetic information. The main types are DNA and RNA.

Bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C), Uracil (U).
DNA: Contains A, T, G, C; double-stranded.
RNA: Contains A, U, G, C; single-stranded.

Nucleotides and 5’–3’ Sequence

Nucleotides are the building blocks of nucleic acids, each consisting of a sugar, phosphate group, and nitrogenous base.

Structure: Phosphate group, pentose sugar (deoxyribose or ribose), nitrogenous base.
5’–3’ Direction: Nucleic acids are synthesized and read from the 5’ to 3’ end.
Example: DNA replication proceeds in the 5’ to 3’ direction.

Cell Structure and Function

Prokaryotic vs. Eukaryotic Cells

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

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	No	Yes
Organelles	Few (no membrane-bound)	Many (membrane-bound)
Examples	Bacteria, Archaea	Plants, Animals, Fungi

Cell Organelles: Names and Functions

Organelles are specialized structures within cells that perform distinct functions.

Organelle	Function	Plant/Animal
Nucleus	Stores genetic material	Both
Mitochondria	ATP production	Both
Chloroplast	Photosynthesis	Plant
Endoplasmic Reticulum	Protein/lipid synthesis	Both
Golgi Apparatus	Protein modification/sorting	Both
Lysosome	Digestion	Animal
Vacuole	Storage	Plant and animal

Endosymbiosis

The endosymbiotic theory explains the origin of mitochondria and chloroplasts as formerly free-living prokaryotes engulfed by ancestral eukaryotic cells.

Evidence: Double membranes, own DNA, ribosomes similar to prokaryotes.
Example: Mitochondria in animal cells, chloroplasts in plant cells.

Cell Membranes and Transport

Biological/Cell Membranes

Cell membranes are composed of a phospholipid bilayer with embedded proteins, providing selective permeability and structural support.

Phospholipid Bilayer: Hydrophilic heads face outward, hydrophobic tails inward.
Proteins: Serve as channels, receptors, and enzymes.
Example: Integral proteins facilitate transport across the membrane.

Diffusion and Facilitated Diffusion

Diffusion is the passive movement of molecules from high to low concentration. Facilitated diffusion uses membrane proteins to assist transport.

Passive Diffusion: No energy required; small, nonpolar molecules.
Facilitated Diffusion: Uses channel or carrier proteins for larger or polar molecules.
Active Transport: Requires energy (ATP) to move substances against their concentration gradient.
Example: Glucose transport via facilitated diffusion.

Osmosis

Osmosis is the movement of water across a semipermeable membrane from low to high solute concentration.

Water Only: Osmosis involves only water molecules.
Example: Water uptake by plant roots.

Solute and Solvent

Solutions are composed of solutes dissolved in solvents. Water is the universal solvent in biological systems.

Solute: Substance dissolved (e.g., NaCl).
Solvent: Substance doing the dissolving (e.g., water).
Example: Saltwater: NaCl is solute, water is solvent.

Hypertonic, Hypotonic, Isotonic Solutions

These terms describe the relative concentration of solutes in solutions compared to the cell's interior, affecting water movement and cell shape.

Solution Type	Effect on Animal Cells	Effect on Plant Cells
Hypertonic	Cell shrinks (crenation)	Plasmolysis
Hypotonic	Cell swells and may burst (lysis)	Turgid (normal)
Isotonic	No net change	Flaccid

Membrane Transport Mechanisms

Sodium-Potassium Pump

The sodium-potassium pump is an active transport protein found in animal cell membranes, maintaining electrochemical gradients.

Function: Pumps 3 Na+ out and 2 K+ in per ATP hydrolyzed.
Location: Plasma membrane of animal cells.
Equation:
Example: Essential for nerve impulse transmission.

Phagocytosis vs. Pinocytosis

Both are forms of endocytosis, allowing cells to internalize substances from their environment.

Process	Definition	Similarity	Difference
Phagocytosis	"Cell eating"; uptake of large particles	Both involve vesicle formation	Engulfs solids
Pinocytosis	"Cell drinking"; uptake of fluids	Both involve vesicle formation	Engulfs liquids

Additional info: Expanded explanations and tables were added for clarity and completeness.