Biol 101: Principles of Biology - Comprehensive Lecture Review

Comprehensive vocabulary flashcards covering introductory biology concepts from the nature of science and chemical foundations through molecular genetics, gene regulation, cellular division, and Mendelian inheritance.

Inductive Reasoning

A form of logical thinking common in descriptive science that uses multiple specific observations and data analysis to arrive at a general conclusion.

Deductive Reasoning

A form of logical thinking used in hypothesis-based science that applies a general premise or principle to predict specific experimental results.

IMRaD Format

The standard structural format used in scientific papers, consisting of Introduction, Materials and Methods, Results, and Discussion sections.

Miller-Urey Experiment

A 1953 experiment simulating prebiotic Earth conditions that tested the chemical evolution hypothesis by demonstrating the abiotic synthesis of small organic molecules, such as amino acids, from inorganic precursors.

Emergent Properties

Novel characteristics that emerge when matter is organized into chemical compounds that are absent in the individual isolated elements, such as table salt ($NaCl$) possessing properties distinct from metallic sodium and toxic chlorine gas.

Valence Electrons

Electrons residing in an atom's outermost electron shell that determine its chemical bonding capacity and reactivity.

Polar Covalent Bond

A covalent bond formed between atoms with differing electronegativities, causing electrons to be shared unequally and producing partial positive ($\delta^+$) and partial negative ($\delta^-$) charges.

Hydrogen Bond

A weak non-covalent attraction formed between the partial positive charge of a hydrogen atom in a polar molecule and the partial negative charge of an electronegative atom in another molecule.

Hydrocarbon

An organic molecule consisting entirely of carbon and hydrogen atoms, such as methane ($CH_4$).

Functional Groups

Specific polar clusters of atoms—including hydroxyl, carbonyl, carboxyl, amino, and phosphate groups—that confer hydrophilic properties and characteristic chemical reactivity to organic molecules.

Denaturation

A process in which environmental changes such as high heat, pH shifts, or altered salt concentrations cause a protein to unravel, lose its specific three-dimensional conformation, and forfeit its biological activity.

Primary Structure

The unique linear sequence of amino acids linked together by covalent peptide bonds in a polypeptide chain.

Secondary Structure

Localized, repetitive folding patterns within a polypeptide chain—primarily $\alpha$-helices and $\beta$-pleated sheets—stabilized by hydrogen bonds between backbone carbonyl oxygen and amide hydrogen atoms.

Tertiary Structure

The overall three-dimensional conformation of a single polypeptide chain, maintained by interactions among side-chain R groups, including ionic attractions, hydrogen bonds, disulfide bridges, and hydrophobic interactions.

Quaternary Structure

The structural level attained when two or more individual polypeptide subunits aggregate and interact via side-chain bonds to form a functional multi-subunit protein complex, such as hemoglobin.

Activation Energy ($E_a$)

The minimum energy barrier that must be overcome for a chemical reaction to occur; catalysts and enzymes accelerate reaction rates by lowering this barrier without altering overall free energy change ($\Delta G$).

Phospholipid Bilayer

A two-layer sheet of amphipathic lipid molecules whose hydrophilic heads contact external and internal aqueous solutions while nonpolar fatty acid tails face inward, establishing a fundamental selective barrier.

Fluid Mosaic Model

A structural model describing biological membranes as flexible, fluid phospholipid bilayers studded with a mosaic of freely moving proteins and cholesterol molecules.

Osmosis

The passive transport and net diffusion of water molecules across a selectively permeable membrane down their concentration gradient toward a higher solute concentration.

Facilitated Diffusion

The spontaneous passive movement of ions or polar molecules across a biological membrane down their concentration gradient via specific channel or carrier transport proteins, requiring no energy expenditure.

Active Transport

The energy-consuming process wherein a transport protein pumps a solute across a cellular membrane against its concentration gradient, directly coupled to ATP hydrolysis.

Bacterial Transformation

The process by which living bacteria take up foreign genetic material from their surroundings and express newly acquired traits, first discovered by Frederick Griffith and shown by Avery, MacLeod, and McCarty to be caused by DNA.

Phosphodiester Bond

The covalent linkage formed between the $3'\text{-OH}$ group of one nucleotide's sugar and the $5'\text{-phosphate}$ group of the adjacent nucleotide, creating the backbone of DNA and RNA.

Semiconservative Replication

The mode of DNA replication confirmed by Meselson and Stahl wherein each newly replicated double helix retains one intact parental template strand and one newly synthesized daughter strand.

DNA Helicase

The replication enzyme that unwinds the double helix at the replication fork by breaking hydrogen bonds between complementary base pairs.

Topoisomerase

An enzyme that prevents excessive supercoiling and torsional strain ahead of the replication fork by introducing temporary single- or double-strand breaks in DNA.

Okazaki Fragments

Short, discontinuously synthesized DNA segments generated on the lagging strand during DNA replication, which are subsequently sealed together by DNA ligase.

Central Dogma

Francis Crick's principle stating that genetic information flows unidirectionally from DNA to RNA via transcription, and from RNA to protein via translation.

Promoter

A non-coding DNA region located upstream ($5'$) of a gene—typically containing a conserved TATA box near $-25\,\text{bp}$—that directs RNA polymerase where to bind and initiate transcription.

RNA Splicing

A eukaryotic post-transcriptional modification in which non-protein-coding intron sequences are excised from pre-mRNA and coding exons are joined together.

Transfer RNA (tRNA)

A folded, cloverleaf-shaped RNA molecule bearing a specific amino acid at its $3'$ attachment site and a complementary three-nucleotide anticodon that pairs with mRNA codons during translation.

Frameshift Mutation

A genetic mutation caused by the insertion or deletion of nucleotides in numbers not divisible by three, shifting the triplet reading frame downstream and altering the entire resulting amino acid sequence.

Lysogenic Cycle

A bacteriophage infection pathway where viral DNA integrates into the host bacterial chromosome as an inactive prophage, replicating passively with the host without inducing cell lysis until triggered by stress.

Retrovirus

An RNA virus (such as HIV) that uses the viral enzyme reverse transcriptase to synthesize double-stranded DNA from its single-stranded RNA genome before integrating into the host cell's chromosomes.

Azidothymidine (AZT)

An anti-HIV reverse transcriptase inhibitor that mimics thymidine but carries an $-N_3$ group instead of a $3'\text{-OH}$ group, preventing phosphodiester bond formation and halting viral DNA elongation.

Operon

A functional genetic regulatory unit in prokaryotes comprising a cluster of related genes transcribed together under the control of a single promoter and an operator switch.

Nucleosome

The basic structural subunit of eukaryotic chromatin, consisting of approximately $140\,\text{bp}$ of DNA wrapped twice around a core octamer of basic histone proteins (H2A, H2B, H3, and H4).

Enhancer

A non-coding eukaryotic DNA sequence that binds activator proteins, bending the DNA molecule to recruit general transcription factors and RNA polymerase to the promoter.

Housekeeping Genes

Constitutively active genes (such as those encoding actin) that are expressed continuously across all cell types to perform essential physiological and structural functions.

X-Chromosome Inactivation

The epigenetic silencing and condensation of one of the two X chromosomes in female mammalian somatic cells, producing mosaic gene expression patterns such as the tortoiseshell coat in cats.

Binary Fission

The asexual mode of reproduction in prokaryotes where the single circular chromosome duplicates and moves to opposite poles as the cell elongates and splits in two.

Centromere

The constricted chromosomal region that tethers duplicated sister chromatids together and provides the assembly platform for kinetochores during cell division.

Cell Plate

A membranous disk that forms along the equatorial plane of a dividing plant cell during cytokinesis, formed by fusing Golgi vesicles that deposit cell wall material.

Density-Dependent Inhibition

The regulatory phenomenon in animal cell culture where physical contact between crowded cells inhibits further cell division.

Homologous Chromosomes

A pair of matched chromosomes in a diploid cell that possess the same length, centromere location, and gene loci, with one homolog inherited from each biological parent.

Crossing Over

The exchange of corresponding genetic segments between nonsister chromatids of homologous chromosomes during synapsis in prophase I of meiosis.

Nondisjunction

The failure of homologous chromosomes to separate during meiosis I, or sister chromatids to separate during meiosis II, yielding abnormal gametes with altered chromosome numbers ($n+1$ or $n-1$).

Trisomy 21

A human chromosomal condition resulting from nondisjunction, in which an individual inherits three copies of chromosome 21, resulting in Down syndrome.

Reciprocal Translocation

A chromosomal structural alteration where segments are exchanged between nonhomologous chromosomes, such as the translocation between chromosomes 9 and 22 associated with chronic myelogenous leukemia (CML).

Law of Segregation

Mendel's first law of inheritance stating that allele pairs separate during gamete production such that each gamete carries only one allele for each inherited character.

Law of Independent Assortment

Mendel's second law stating that the allele pairs of differing gene loci segregate independently into gametes during meiosis, yielding a classic $9:3:3:1$ phenotypic ratio in dihybrid crosses.

Testcross

The experimental mating between an individual showing a dominant phenotype of unknown genotype and a homozygous recessive individual to determine the unknown genotype.

Incomplete Dominance

A pattern of inheritance where the heterozygous phenotype is an intermediate blend between the homozygous parental phenotypes, as seen in pink snapdragons resulting from red ($RR$) and white ($rr$) crosses.

Codominance

An inheritance pattern where both alleles are simultaneously and fully expressed in heterozygous individuals, such as the simultaneous expression of both A and B glycoproteins in type AB human blood.

Pleiotropy

The phenomenon wherein a single gene influences multiple distinct, seemingly unrelated phenotypic traits, as exemplified by the sickle-cell hemoglobin allele causing anemia, organ damage, and malaria resistance.

Polygenic Inheritance

An additive genetic mechanism in which two or more separate genes collectively influence a single continuously variable phenotypic character, such as human skin color or height.

Pedigree

A standardized genealogical diagram charting the presence or absence of a phenotypic trait across family generations to deduce modes of inheritance and determine ancestral genotypes.