General Biology Study Guide: Foundations, Chemistry of Life, Macromolecules, and Cell Membranes

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Biology and Life

What Does It Mean to Say That Something Is Alive?

Biology is the study of life, and scientists have identified five key traits shared by living things. Understanding these traits helps distinguish living organisms from non-living matter.

Key Traits of Life: Living things acquire and use energy, are made of cells, process information, replicate, and evolve.
Definition of Life: Scientists use these traits to define what it means to be alive.
Example: Viruses possess some but not all traits of life, leading to debate about their classification.

Life Is Cellular

The cell theory states that all living things are composed of cells. This foundational concept underpins much of biology.

Cell Theory: All organisms are made of cells, and all cells come from pre-existing cells.
Example: Pasteur's experiment with straight-necked vs. swan-necked flasks demonstrated that cells arise from other cells, not spontaneously.

Life Processes Information and Requires Energy

Genetic information is stored in DNA, which is the hereditary material of all living organisms. The flow of genetic information is described by the central dogma.

Central Dogma: DNA → RNA → Protein
Genes: Segments of DNA that code for proteins.
Energy Use: Organisms require energy to carry out cellular processes.

Life Evolves

Populations of organisms change over time through the process of evolution. Heritable changes occur in a population, leading to adaptation.

Evolution: Change in the genetic makeup of a population over generations.
Natural Selection: Mechanism by which evolution occurs.

The Tree of Life

All living organisms are related through common ancestry. The tree of life illustrates these relationships.

Phylogenetic Tree: Diagram showing evolutionary relationships among species.

Doing Biology

Biology is a science based on observation, measurement, and experimentation. Scientists use the scientific method to answer questions about the natural world.

Scientific Method: Involves forming hypotheses, conducting experiments, and analyzing data.
Example: "Why do giraffes have long necks?" is a question that can be investigated scientifically.

Atoms, Ions, and Molecules: The Building Blocks of Chemical Evolution

Atoms and Molecules

Atoms are the basic units of matter, and molecules are combinations of atoms. Chemical evolution describes how simple molecules formed complex molecules necessary for life.

Atomic Structure: Atoms consist of protons, neutrons, and electrons.
Electron Configuration: Determines chemical reactivity.
Valence Electrons: Electrons in the outermost shell, important for bonding.
Example: The number of protons defines the element; carbon has 6 protons.

Properties of Water and the Early Oceans

Water is essential for life due to its unique properties, which arise from its molecular structure.

Cohesion and Adhesion: Water molecules stick to each other and to other surfaces.
Acid-Base Chemistry: Water can ionize to form H+ and OH-.
Example: Water's high specific heat helps regulate temperature in organisms.

Chemical Reactions, Energy, and Chemical Evolution

Chemical reactions involve the making and breaking of chemical bonds. Energy changes accompany these reactions.

Balanced Chemical Equation: Shows the reactants and products of a reaction.
First Law of Thermodynamics: Energy cannot be created or destroyed.
Second Law of Thermodynamics: Entropy (disorder) tends to increase.
Spontaneous Reactions: Occur without input of energy if they increase entropy and release energy.
Example Equation:

Macromolecules: Proteins and Nucleic Acids

Amino Acids and Their Polymerization

Proteins are polymers made of amino acids. The sequence and properties of amino acids determine protein structure and function.

Amino Acid Structure: Central carbon, amino group, carboxyl group, R group.
Peptide Bond: Covalent bond linking amino acids in a protein.
Polymerization: Amino acids join via condensation reactions to form polypeptides.
Example: Hemoglobin is a protein that carries oxygen in blood.

Protein Structure and Function

Proteins have four levels of structure: primary, secondary, tertiary, and quaternary. Their structure determines their diverse functions.

Primary Structure: Sequence of amino acids.
Secondary Structure: Alpha helices and beta sheets formed by hydrogen bonding.
Tertiary Structure: Overall 3D shape of a polypeptide.
Quaternary Structure: Association of multiple polypeptides.
Enzymes: Proteins that catalyze biochemical reactions.

Nucleic Acids: DNA and RNA

Nucleic acids store and transmit genetic information. DNA and RNA are polymers of nucleotides.

Nucleotide Structure: Phosphate group, sugar (deoxyribose or ribose), nitrogenous base.
DNA: Double helix, complementary base pairing (A-T, G-C).
RNA: Single-stranded, can fold into complex shapes.
Central Dogma:

Carbohydrates

Sugars as Monomers

Carbohydrates are made of sugar monomers. They serve as energy sources and structural components.

Monosaccharides: Simple sugars like glucose.
Disaccharides: Two monosaccharides joined together (e.g., sucrose).
Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose).

The Structure of Polysaccharides

Polysaccharides differ in their structure and function. Small changes in structure can have major biological consequences.

Starch: Energy storage in plants.
Glycogen: Energy storage in animals.
Cellulose: Structural component in plant cell walls.
Chitin: Structural component in fungi and arthropods.

What Do Carbohydrates Do?

Carbohydrates provide energy and serve as building blocks for other biological molecules.

Energy Storage: Starch and glycogen store energy for later use.
Structural Roles: Cellulose and chitin provide support.

Lipids, Membranes, and the First Cells

Lipid Structure and Function

Lipids are hydrophobic molecules that include fats, oils, and phospholipids. They play key roles in energy storage and membrane structure.

Fatty Acids: Hydrocarbon chains with a carboxyl group.
Saturated vs. Unsaturated: Saturated fatty acids have no double bonds; unsaturated have one or more.
Phospholipids: Major component of cell membranes, with hydrophilic heads and hydrophobic tails.

Phospholipid Bilayers

Phospholipids form bilayers in water, creating the basic structure of cell membranes.

Amphipathic Nature: Hydrophilic heads face water; hydrophobic tails face inward.
Selective Permeability: Bilayers allow some substances to pass while blocking others.

How Substances Move Across Lipid Bilayers: Diffusion and Osmosis

Cells exchange materials with their environment through diffusion and osmosis.

Diffusion: Movement of molecules from high to low concentration.
Osmosis: Diffusion of water across a selectively permeable membrane.
Concentration Gradient: Difference in concentration across a space.

Proteins Alter Membrane Structure and Function

Membrane proteins facilitate the movement of substances across cell membranes and participate in cell signaling.

Transport Proteins: Channels and carriers for molecules.
Active vs. Passive Transport: Active transport requires energy; passive does not.

Macromolecule	Monomer	Function	Example
Protein	Amino acid	Catalysis, structure, transport	Enzyme, hemoglobin
Nucleic Acid	Nucleotide	Information storage, transmission	DNA, RNA
Carbohydrate	Monosaccharide	Energy, structure	Glucose, cellulose
Lipid	Fatty acid	Energy storage, membrane structure	Triglyceride, phospholipid

Additional info: Some details, such as the specific examples and expanded explanations, were inferred from standard biology curriculum to ensure completeness and clarity.