Biol 1610 Study Guide - Biology Fundamentals, Evolution, and Chemistry

Attributes of Life and Biological Levels of Organization

• Fundamental Attributes Defining Life:

  • Growth, Development, and Reproduction: Life forms must possess the intrinsic capacity to grow, develop, and replicate. If an organism cannot reproduce on its own, its other biological characteristics become functionally irrelevant to evolutionary persistence.
  • Cellular Organization: All living entities are composed of cells without exception. The cell represents the mandatory basic structural unit.
  • Energy Processing and Metabolism: Organisms must capture, transform, and utilize energy to power cellular work and maintain organization. Functionality is impossible without metabolic processes.
  • Response to Environmental Stimuli: Living systems perceive and react dynamically to changes in their external and internal environments as a cohesive whole.
  • Homeostasis: The active maintenance of internal physiological stability around a steady state. When regulation fails or falls outside normal parameters, homeostasis ceases to operate.
  • Genetic Material (DNA): Cells cannot exist or function without Deoxyribonucleic Acid ($DNA$). It contains the instructions necessary to express genes and synthesize functional proteins.
  • Emergent Properties: Novel properties that arise at each successive step in the hierarchy of biological complexity, which are not present in the individual components alone.
  • Adaptation and Evolution: Life adapts to environmental pressures through natural selection. Adaptation is the most critical driver of organismal persistence. Evolution does not act at an isolated individual level; it operates through dynamic interactions across populations over generations.
  • Criterion for Life: For any entity to be classified as biological life, every single one of these eight attributes must be demonstrated concurrently during observation.

• Hierarchical Levels of Biological Organization (Ordered from Smallest to Largest):

  1. Atom: The smallest and most fundamental unit of matter that retains all the specific chemical properties of an element. It consists of a dense atomic nucleus surrounded by an electron cloud.
  2. Molecule: A stable chemical structure consisting of at least two atoms held together by one or more chemical bonds.
  3. Macromolecule: A large, complex molecule typically formed by the polymerization of smaller subunits (monomers). Many biologically critical structures are macromolecules.
  4. Organelle: Specialized, membrane-bound or non-membrane-bound sub-cellular structures that perform specific functional tasks within a cell. Examples include:
     • Mitochondria: Cellular powerhouses that generate chemical energy to power metabolic functions.
     • Chloroplasts: Organelles in green plants and algae that capture solar energy from sunlight to synthesize sugars via photosynthesis.
  5. Cell: The smallest fundamental unit of structure, function, and organization in all living organisms. All life is composed of cells.
  6. Tissue: An aggregation of similar, interconnected cells that execute a joint, specific, or related physiological function.
  7. Organ: A discrete collection of distinct tissues combined structural-functionally to perform a shared primary task. Organs exist in both animals and plants (e.g., leaves, roots, heart, liver).
  8. Organ System: A higher-level functional organization consisting of multiple organs working in tandem. For example, the mammalian circulatory system utilizes the heart and blood vessels to transport blood throughout the body to and from the lungs.
  9. Organism: An individual, complete living entity. Examples include an individual tree in a forest, a human, or single-celled microorganisms (prokaryotes and single-celled eukaryotes).
  10. Population: A collective group of individuals belonging to the same species that reside within a defined geographical area simultaneously. For instance, all pine trees in a specific forest form a population. Multiple populations of different species (e.g., flowering plants, insects, microbes) inhabit the same area.
  11. Community: The sum total of all interacting biotic populations inhabiting a shared geographical area (e.g., all trees, plants, insects, fungi, and bacteria in a forest).
  12. Ecosystem: A comprehensive system consisting of all the living organisms (biotic community) in a particular region interacting with the non-living (abiotic) physical environment, such as soil nitrogen, water, sunlight, and atmospheric gases.
  13. Biosphere: The highest level of biological hierarchy, encompassing all ecosystems across the globe. It represents all zones of life on Earth, spanning land, aquatic environments, and lower atmospheric layers.

• Taxonomic Hierarchy and the Domains of Life:

  • Domain: The highest taxonomic rank in modern biological classification (introduced to supersede older systems). Life is categorized into three primary Domains:
    1. Bacteria (prokaryotic organisms lacking membrane-bound nuclei).
    2. Archaea (prokaryotic organisms with distinct biochemical/genomic traits, often inhabiting extreme environments).
    3. Eukaryotes / Eukarya (organisms containing complex cells with true membrane-bound nuclei and organelles).
  • Full Taxonomic Order (Highest to Lowest): Domain $\rightarrow$ Kingdom $\rightarrow$ Phylum $\rightarrow$ Class $\rightarrow$ Order $\rightarrow$ Family $\rightarrow$ Genus $\rightarrow$ Species.
  • Historical Note: Kingdom was the highest rank until the 1970s, but modern phylogenetics places Domain as the primary rank above Kingdom.

• Roles of Biomolecules in Life:

  • Biomolecules are organic molecules synthesized directly by living cells.
  • They are indispensable for sustaining life, providing structural integrity, energy storage, enzyme catalysis, and facilitating basic biological processes such as growth, development, sustainment, and reproduction.

• Four Universal Structural Features Shared by All Cells:

  1. Plasma / Cell Membrane: An outer protective boundary surrounding the cell that isolates the internal environment from the exterior world. It consists of a double layer of phospholipids (a phospholipid bilayer) structured with water-attracting (hydrophilic) polar heads facing outward and water-repelling (hydrophobic) nonpolar tails oriented inward. It is embedded with specialized membrane proteins that regulate the selective transport of molecules in and out of the cell.
  2. Cytoplasm and Cytosol: The cytoplasm is the entire contents within the cell membrane (excluding the nucleus in eukaryotes) that houses cellular organelles. It serves as the physical site for metabolic pathways, such as glycolysis (the conversion of glucose to energy). The fluid portion of the cytoplasm excluding organelles is the cytosol, a complex, aqueous mixture consisting of protein filaments, salts, and dissolved organic molecules.
  3. Ribosomes: Molecular machines constructed from ribosomal RNA ($rRNA$) complexes and proteins responsible for protein synthesis. Ribosomes translate messenger RNA ($mRNA$) sequences into protein chains with the aid of transfer RNA ($tRNA$). They function as cellular "factories" for protein manufacture:
     • In Eukaryotes: Ribosomes can be free-floating in the cytosol or attached to the rough endoplasmic reticulum ($RER$) adjacent to the nucleus.
     • In Prokaryotic Cells: Ribosomes float freely within the cytoplasm due to the absence of a membrane-bound nucleus.
  4. Double-Stranded DNA Genome: The universal genetic archive storing hereditary instructions. Located inside a membrane-bound nucleus in eukaryotes or within the nucleoid region in prokaryotes. DNA consists of a sugar-phosphate backbone (deoxyribose sugars linked to phosphoric acid) and nitrogenous base pairs:
     • Adenine ($A$)
     • Thymine ($T$)
     • Cytosine ($C$)
     • Guanine ($G$)
     • The sequential order of these bases forms the genetic code that determines the amino acid sequence of proteins.

• Distinguishing Prokaryotic vs. Eukaryotic Cells:

  • While both share a plasma membrane, cytoplasm, double-stranded DNA genome, and ribosomes, prokaryotes lack a membrane-bound nucleus and internal membrane-bound organelles. Eukaryotes feature a true nucleus housing their linear DNA, as well as membrane-bound compartments like mitochondria and chloroplasts.

• The Central Dogma of Molecular Biology:

  • A fundamental principle stating that genetic information flows strictly in a single direction:

$\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$

*   Alternatively, information can transfer directly from RNA to protein during translation.

The Scientific Method and Experimental Design

• The Scientific Method Defined:

  • A standardized, objective process of investigating the natural world through systematically observing phenomena, posing precise questions, formulating testable explanations, conducting empirical tests, and utilizing objective reasoning to draw evidence-based conclusions.

• Sequential Steps of the Scientific Process:

$\text{Observation} \rightarrow \text{Questioning} \rightarrow \text{Hypothesis Formation} \rightarrow \text{Experimentation} \rightarrow \text{Data Collection} \rightarrow \text{Conclusion}$

• Hypothesis Formulation and Requirements:

  • A hypothesis is a tentative, educated explanation proposed for an observed natural phenomenon.
  • Plausibility: Must align logically with existing scientific knowledge.
  • Testability: Must propose a mechanism that can be evaluated through direct observation or experimental trials.
  • Falsifiability: Must be structured such that empirical evidence could potentially disprove it if it is incorrect. Supernatural or metaphysical claims are neither testable nor falsifiable, placing them outside the realm of science.
  • Non-Absolute Proof: Science does not claim to definitively "prove" hypotheses in absolute terms; scientific understandings remain open to refinement, modification, or rejection upon discovery of new evidence. Openness to disproving ideas is the core feature distinguishing science from non-science.

• Experimentation and Controlled Experimental Design:

  • Experimentation provides a controlled approach to testing hypotheses.
  • Controlled Experiment: An experimental setup designed to isolate the effect of a single factor by comparing a control group against one or more experimental groups.
  • Control Group: Serves as the baseline for comparison. It retains every single environment and structural feature of the experimental group but does not receive the specific experimental treatment or variable manipulation being tested. The independent variable is held constant or omitted.
  • Experimental Group: Receives the precise treatment or variable manipulation whose effect is being investigated.
  • Placebo Considerations: A placebo (an inactive substance) is used in human trials to control for psychological expectations, but it is not a direct structural replacement for a standard negative control group.

• Types of Experimental Variables:

  • Variable: Any measurable feature, factor, or condition that can change or exist in differing amounts within an experiment.
  • Independent Variable (IV): The specific factor deliberately manipulated or varied by the researcher to test its effects.
  • Dependent Variable (DV): The factor measured or observed to assess the effect of the independent variable; the outcome of the experiment.
  • Control / Constant Variables: All extraneous conditions kept strictly identical between both control and experimental groups (e.g., temperature, light exposure, soil composition, subject age).

• Comprehensive Comparison: Hypothesis vs. Scientific Theory:

  • Scientific Hypothesis: A preliminary, unproven educated guess based on limited initial data; narrow in scope; tested to see if it holds true under specific conditions.
  • Scientific Theory: A broad, well-substantiated, highly reliable explanation of a natural phenomenon supported by extensive empirical data, repeated experiments, and unified scientific consensus. Theories possess immense predictive power and generate new, testable hypotheses. Examples include atomic theory, germ theory, and evolutionary theory.

• Communication of Science and Peer Review:

  • Scientific findings are disseminated to the global community via formal, peer-reviewed manuscripts published in scientific journals.
  • Peer Review Process: Qualified expert reviewers in the same field rigorously evaluate submitted papers prior to publication to verify that research methodologies are original, logically sound, ethically robust, thorough, and significant.

• Applied Example: Experimental Design, Hypothesis, Data Analysis, and Graphing:

  • Hypothesis: If a plant is exposed to increased levels of direct sunlight, then it will exhibit higher rates of vertical growth and enhanced photosynthesis efficiency.
  • Variables:
    • Independent Variable: Duration/Intensity of direct sunlight exposure.
    • Dependent Variables: Plant growth rate (measured in $\text{cm/week}$) and photosynthesis rate (measured via oxygen production and carbon dioxide uptake).
    • Control Variables: Soil volume and composition, watering frequency, ambient temperature, plant species.
  • Experimental Setup: Group A (Experimental) receives enhanced direct sunlight; Group B (Control) receives standard ambient indoor lighting.
  • Illustrative Results:
    • Treatment Group Growth: Average $2.5\,\text{cm/week}$.
    • Control Group Growth: Average $1.0\,\text{cm/week}$.
    • Treatment Group Photosynthesis: Substantially elevated oxygen release.
  • Graphical Representation: Plotting time on the X-axis and plant height on the Y-axis yields two distinct trendlines. The experimental group displays a steep positive slope ($2.5\,\text{cm/week}$), while the control group displays a flatter, gentler slope ($1.0\,\text{cm/week}$). The divergence confirms that sunlight significantly accelerates plant growth and metabolic rate.

Evolutionary Principles and Mechanisms

• Core Concepts in Evolutionary Biology:

  • Natural Selection: The primary mechanism of evolution characterized by the differential survival and prolific reproduction of individuals possessing favorable, heritable traits suited to their environment. This process leads to gradual evolutionary change in the population over time.
  • Level of Selection: Natural selection operates directly on individual organisms based on their physical traits (phenotype), but its evolutionary consequences change the genetic structure of populations over generations.
  • Evolutionary Fitness: A relative measure of an individual's reproductive success. Individuals that produce a higher number of surviving, viable offspring relative to others in the population possess higher evolutionary fitness.
  • Adaptation: A heritable, genetic trait that enhances an organism's capability to survive and reproduce within its specific environment.

• Mechanisms generating Genetic Diversity:

  • Genetic variation within a population arises primarily through two processes:
    1. Mutation: A random change in the nucleotide sequence of DNA. Mutation is the ultimate, original source of all new alleles and genetic novelty in any population.
    2. Sexual Reproduction: Shuffles pre-existing alleles during gamete formation (meiosis) and fertilization to create unique genetic combinations, producing distinct genotypes and phenotypes in every offspring.

• Modes of Natural Selection:

  • Stabilizing Selection: Occurs when natural selection favors the intermediate/average phenotype while selecting against extreme phenotypic variations. Decreases genetic variance and maintains the status quo.
  • Directional Selection: Occurs when an environmental change favors phenotypes at one extreme end of the existing variation spectrum. Causes a gradual shift in the population's trait distribution toward that extreme phenotype.
  • Diversifying / Disruptive Selection: Occurs when environmental conditions simultaneously favor two or more extreme phenotypes over intermediate phenotypes. Intermediate individuals are selected against, which can split a population into distinct phenotypic forms.

• Unity and Diversity of Life:

  • The Theory of Evolution reconciles both the unity and diversity of living things. Unity is demonstrated by shared ancestral traits, universal cellular structures, and a common genetic code ($DNA$). Diversity is driven by speciation and ongoing natural selection fitting populations to distinct ecological niches over millions of years.

• Five Major Lines of Evidence Supporting Biological Evolution:

  1. Anatomy: Structural similarities shared among distinct species due to common evolutionary ancestry (Homologous structures).
  2. Molecular Biology: The universal nature of the genetic code ($DNA$/$RNA$) and deep sequence similarities in shared genes/proteins reflect evolutionary relationships.
  3. Biogeography: The global spatial distribution of plants and animals, as well as unique island endemic species, aligned with tectonic geological history (continental drift).
  4. Fossil Record: Preserved remains documenting transitional forms of extinct organisms connecting ancestral traits to modern lineages.
  5. Direct Observation: Real-time empirical monitoring of microevolutionary changes in fast-reproducing organisms (e.g., pesticide resistance in insects, antibiotic resistance in bacteria).

• Anatomical Structures: Homologous vs. Analogous:

  • Homologous Structures: Anatomical features in different species that share a common underlying structural plan because they were inherited from a common ancestor, even if their current functions differ (e.g., Pentadactyl limbs shared by humans, cats, whales, and bats).
  • Analogous Structures: Anatomical features that perform similar functions but evolved independently through convergent evolution due to similar environmental selection pressures, rather than shared ancestral heritage (e.g., Streamlined body shapes and appendages in fish like sharks, birds like penguins, and mammals like dolphins).

Chemical Foundations of Life and Atomic Structure

• Elements and Biological Abundance:

  • Element: A fundamental substance with distinct chemical and physical properties that cannot be broken down into simpler substances by ordinary chemical reactions.
  • Four Primary Elements of Life: Oxygen ($O$), Carbon ($C$), Hydrogen ($H$), and Nitrogen ($N$) constitute approximately $96\%$ of living matter.
  • Secondary Essential Elements: Phosphorus ($P$) and Sulfur ($S$) are critically important for assembling biological macromolecules (nucleic acids, proteins, ATP, lipids).
  • Four Major Biological Macromolecules: Proteins, Nucleic Acids, Lipids, and Carbohydrates.

• Atomic Structure and Subatomic Particles:

  • Atom: The fundamental building block of matter that retains all unique chemical properties of its element.
  • An Atom consists of Two Primary Regions:
    1. Atomic Nucleus: The dense center containing positively charged Protons and uncharged/neutral Neutrons.
    2. Outer Cloud: Surrounding space occupied by negatively charged Electrons orbiting in discrete energy levels (electron shells).

• Electron Shells and the Bohr Model:

  • The Bohr model visualizes atoms with electrons orbiting the nucleus in concentric shells at specific energy distances.
  • Maximum Electron Capacity Per Shell:
    • Shell 1 (Innermost): Holds a maximum of $2$ electrons.
    • Shell 2: Holds a maximum of $8$ electrons.
    • Shell 3: Holds a maximum of $8$ electrons (for main group elements abiding by the octet rule).
  • Valence Electrons: The electrons present in an atom's outermost shell. The number of valence electrons determines an atom's chemical reactivity, valence state, and the maximum number of covalent bonds it can form.

• Predicting Chemical Reactivity:

  • Atoms gain, lose, or share electrons to satisfy the octet rule (achieving a full outer valence shell of $8$ electrons, or $2$ for hydrogen/helium).
  • Metals tend to lose electrons, forming positive cations.
  • Nonmetals tend to gain electrons (forming negative anions) or share electrons covalently.
  • Group 18 Noble Gases possess naturally full valence shells, making them chemically inert/unreactive.

• Types of Chemical Bonds:

  1. Covalent Bonds: Formed when two atoms share one or more pairs of valence electrons. These are the strongest, most dominant bonds in biological organisms:
     • Single Covalent Bond: Sharing $1$ pair of electrons ($2$ electrons total).
     • Double Covalent Bond: Sharing $2$ pairs of electrons ($4$ electrons total).
     • Triple Covalent Bond: Sharing $3$ pairs of electrons ($6$ electrons total). Bond strength increases with bond multiplicity, making triple bonds the strongest.
  2. Ionic Bonds: Formed when one or more electrons are completely transferred from one atom to another, generating oppositely charged ions (cations and anions) that attract electrostatically. Ionic interactions stabilize outer shells by complete transfer.
  3. Hydrogen Bonds: A weak electrostatic interaction occurring between a partially positive hydrogen atom ($\delta+$)—covalently bound to an electronegative atom like oxygen or nitrogen—and a neighboring electronegative atom possessing a partial negative charge ($\delta-$).
     • Biological Significance: Individually weak and easily broken, but collectively massive in numbers. They provide structural cohesion in water, stabilize protein folding, and hold together complementary base pairs in the $DNA$ double helix.

• Classifying Covalent Bonds via Electronegativity Differences ($\Delta EN$):

  • Nonpolar Covalent Bonds: Electronegativity difference is between $0.0$ and $0.4$. Electrons are shared equally between atoms (e.g., $O_2$, $N_2$, $H_2$, $CH_4$).
  • Polar Covalent Bonds: Electronegativity difference is between $0.4$ and $1.7$ (up to $2.1$). Electrons are shared unequally, being pulled closer to the more electronegative atom, creating partial negative ($\delta-$) and partial positive ($\delta+$) poles (e.g., $H_2O$, $HCl$, $NH_3$).
  • Ionic Bonds: Electronegativity difference is greater than $1.7$. Electron transfer occurs rather than sharing.

Water Chemistry and Biological pH Dynamics

• Biological Importance of Hydrogen Bonding:

  • In Water: Forms dynamic networks responsible for high cohesion, surface tension, high heat capacity, and universal solvent capabilities.
  • In Deoxyribonucleic Acid ($DNA$): Hydrogen bonds link adenine to thymine ($A=T$) and guanine to cytosine ($G \equiv C$) across opposite strands, maintaining the structural stability of the double helix while allowing easy unwinding for replication and transcription.
  • In Proteins: Dictates secondary structure folding (alpha-helices and beta-pleated sheets) and stabilizes overall tertiary shapes essential for enzymatic activity and immune recognition (antibody-antigen binding).

• Six Key Physical and Chemical Properties of Water:

  1. High Polarity and Solvent Power: Polar covalent $O-H$ bonds create permanent dipoles ($\delta-$ on Oxygen, $\delta+$ on Hydrogen). Water surrounds polar solutes and charged ions with hydration shells, making it an extraordinary solvent for biological reactions.
  2. Cohesion, Adhesion, and Surface Tension: Hydrogen bonding between adjacent water molecules produces cohesion (water sticking to water), while attraction to polar surfaces produces adhesion. Together, these enable capillary action (water movement up plant xylem) and high surface tension.
  3. High Specific Heat Capacity: Water absorbs or releases large amounts of thermal energy with minimal change in temperature, buffering organisms and aquatic ecosystems against sudden temperature spikes.
  4. High Heat of Vaporization: Requires substantial heat input to transition liquid water into water vapor, driving evaporative cooling mechanisms (e.g., sweating in mammals).
  5. Transparency to Light: Allows sunlight to penetrate through water columns, facilitating photosynthesis in aquatic plants and algae.
  6. Autoionization / Dissociation into Ions: Water naturally dissociates reversibly into hydrogen ions ($H^+$) and hydroxyl ions ($OH^-$):

$H_2O \rightleftharpoons H^+ + OH^-$

• Solute Behavior in Water:

  • Hydrophilic Substances: Polar molecules or charged ions that interact readily with water and dissolve via hydrogen bonding or electrostatic attraction (e.g., sugars, amino acids, salts).
  • Hydrophobic Substances: Nonpolar, uncharged molecules that do not form hydrogen bonds with water and repel it, aggregating together in aqueous environments (e.g., fats, oils, long hydrocarbon chains).
  • Amphipathic Molecules: Contain distinct hydrophilic (polar/charged) and hydrophobic (nonpolar) regions within the same structure (e.g., phospholipids, detergents).

• The pH Concept and Mathematical Scale:

  • pH Definition: A quantitative measure of the molar concentration of free hydrogen ions ($[H^+]$) in a solution.
  • Mathematical Formula:

$\text{pH} = -\log_{10}[H^+]$

*   **The pH Scale Ranges from $0$ to $14$:**
    *   *Neutral Solution:* $\text{pH} = 7.0$ ($[H^+] = [OH^-] = 10^{-7}\,mol\,dm^{-3}$).
    *   *Acidic Solution:* $\text{pH} < 7.0$ ($[H^+] > [OH^-]$). Higher concentration of free $H^+$ ions.
    *   *Basic / Alkaline Solution:* $\text{pH} > 7.0$ ($[H^+] < [OH^-]$). Lower concentration of free $H^+$ ions.
*   *Inverse Logarithmic Relationship:* Because the scale is logarithmic, every single $1$ unit decrease on the pH scale represents a $10$\text{-fold} increase in free $H^+$ ion concentration.

• Acids, Bases, and Physiological Homeostasis:

  • Acids: Proton donors; substances that release $H^+$ ions when dissolved in water, lowering solution pH.
  • Bases (Alkaline Substances): Proton acceptors; substances that bind free $H^+$ or release $OH^-$ ions, raising solution pH.
  • pH Homeostasis: Biological systems must maintain internal pH within strict tolerances (e.g., human blood pH must remain close to $7.4$). Deviations denature proteins and disrupt metabolic reactions.

• Buffer Systems and Mechanism of Action:

  • Buffer: A solution composed of a weak acid and its conjugate base (or a weak base and its conjugate acid) that resists drastic changes in pH.
  • Mechanism: When excess acid ($H^+$) is introduced, the conjugate base absorbs free $H^+$ ions. When excess base ($OH^-$) is introduced, the weak acid releases $H^+$ ions to neutralize it, preserving pH stability.

Carbon, Functional Groups, and Macromolecular Synthesis

• The Role of Carbon in Organic Biomolecules:

  • Carbon forms the structural backbone of biological macromolecules due to its tetravalent nature (4 valence electrons), enabling it to form four stable covalent bonds with diverse elements ($H, O, N, P, S, C$) in straight chains, branched structures, or rings.

• Seven Key Functional Groups in Biological Chemistry:

  1. Hydroxyl Group ($-OH$): Polar structure consisting of an oxygen atom bonded to a hydrogen atom. Increases water solubility; abundant in sugars and alcohols.
  2. Methyl Group ($-CH_3$): Nonpolar, hydrophobic group consisting of a carbon atom bound to three hydrogen atoms. Modulates gene expression and lipid characteristics.
  3. Carbonyl Group ($>C=O$): Polar group featuring a carbon atom double-bonded to an oxygen atom. Found in aldehydes, ketones, sugars, and proteins.
  4. Carboxyl Group ($-COOH$): Acidic functional group featuring a carbonyl group linked to a hydroxyl group. Ionizes in solution to release $H^+$ (forming $-COO^-$), making it acidic; found in amino acids and fatty acids.
  5. Amino Group ($-NH_2$): Basic functional group consisting of a nitrogen atom bound to two hydrogen atoms. Accepts $H^+$ from solution to form $-NH_3^+$; building block of amino acids.
  6. Phosphate Group ($-PO_4^{2-}$): Strongly acidic, negatively charged group consisting of a phosphorus atom bound to four oxygen atoms. Ionizes to release $H^+$; crucial in $DNA, RNA, ATP$, and phospholipids.
  7. Sulfhydryl Group ($-SH$): Polar group consisting of sulfur bound to hydrogen. Forms covalent disulfide bridges ($-S-S-$) that stabilize tertiary protein structures.

• Monomers, Polymers, and Biological Macromolecules:

  • Monomer: A small, repeating structural subunit that can bind covalently to other identical or similar subunits.
  • Polymer: A long macromolecule composed of many covalently linked monomers.
  • Monomer-Polymer Relationships Across Biomolecules:
    • Carbohydrates: Monosaccharides (e.g., glucose) link to form Polysaccharides (e.g., starch, glycogen, cellulose).
    • Proteins: Amino acids link via peptide bonds to form Polypeptides/Proteins.
    • Nucleic Acids: Nucleotides (sugar, phosphate, base) link to form $DNA$ and $RNA$ chains.
    • Lipids: Assembled from glycerol and fatty acids (not true repeating polymers, but classified as macromolecules).

• Anabolic vs. Catabolic Reactions in Macromolecules:

  • Dehydration Synthesis (Condensation Reaction): An anabolic reaction that links monomers together into polymers. A hydrogen ($-H$) is removed from one monomer and a hydroxyl group ($-OH$) is removed from the other, producing a covalent bond and releasing a water molecule ($H_2O$) as a byproduct. Requires energy input.
  • Hydrolysis Reaction: A catabolic reaction that breaks polymers down into constituent monomers. A water molecule ($H_2O$) is consumed and split ($-H$ and $-OH$) to cleave the covalent bond holding monomers together. Releases stored chemical energy.