IB Biology Comprehensive Review: Biochemistry, Cellular Communication, Genetics, and Ecology

Comprehensive vocabulary review flashcards covering cell signaling pathways, stem cells, protein structure, transcription and RNA processing, population ecology, sampling methods, and water chemistry.

Adenylyl Cyclase

An enzyme embedded in the plasma membrane that is activated downstream of G-protein coupled receptor signaling to convert $ATP$ into the secondary messenger cyclic $AMP$ ($cAMP$).

Receptor Tyrosine Kinase (RTK)

A membrane receptor that, upon binding specific ligands such as insulin or epidermal growth factor (EGF), dimerizes and phosphorylates tyrosine residues on intracellular proteins to initiate signaling cascades.

Epidermal Growth Factor (EGF)

A signaling protein that binds to a tyrosine kinase receptor to activate an intracellular secondary signaling cascade, stimulating the synthesis of cyclin D and driving the cell from $G_1$ phase into $S$ phase.

GLUT Transport Protein

A carrier protein stored in intracellular vesicles that is translocated and embedded into the plasma membrane upon insulin-RTK signaling to facilitate the entry of glucose into the target cell.

G-Protein Coupled Receptor (GPCR)

A transmembrane receptor that, when bound by an extracellular ligand, activates an intracellular G-protein by causing its $\alpha$ subunit to release $GDP$ and bind $GTP$, prompting the separation of the $\beta$ and $\gamma$ subunits.

Hydrophobic Ligand

A nonpolar signaling molecule capable of passing directly through the lipid bilayer of the plasma membrane to bind to an intracellular receptor with a complementary binding site.

Hydrophilic Ligand

A polar or water-soluble signaling molecule that cannot cross the hydrophobic interior of the cell membrane and must bind to the extracellular domain of a transmembrane receptor.

Scientific Peer Review

The formal evaluation of research methodology, data integrity, and reproducibility by independent scientific experts before publication to detect flaws and prevent fraudulent claims, such as those in retracted stem cell studies by Haruko Obokata, Piero Anversa, Woo Suk Hwang, and Catherine Verfaillie.

Totipotent Stem Cell

An undifferentiated stem cell capable of forming every cell type in the body as well as extra-embryonic tissues like the placenta; an example is a zygote.

Pluripotent Stem Cell

A stem cell capable of differentiating into any body cell type except placental tissue; found in the inner cell mass of a blastocyst.

Multipotent Stem Cell

A partially differentiated adult stem cell capable of developing into a limited range of related specialized cell types within a specific tissue or organ.

Stem Cell Niche

A specialized microenvironment within adult tissues (such as bone marrow, hair follicles, brain, and heart) where stem cells reside and receive physical and chemical signals that maintain undifferentiation or trigger division.

Multicellularity

An emergent property evolved independently multiple times across eukaryotes, requiring the formation of cellular clusters from single cells followed by cellular differentiation for specialized functions.

Fibrous Protein

A structural protein characterized by long, narrow shapes, repetitive amino acid sequences, general insolubility in water, and resistance to changes in temperature and pH (e.g., collagen, myosin, fibrin, actin, keratin, and elastin).

Globular Protein

A functional protein characterized by a compact, rounded spherical shape, irregular amino acid sequence, general water solubility, and high sensitivity to heat and pH variations (e.g., catalase, hemoglobin, insulin, and immunoglobulin).

Primary Protein Structure

The unique linear sequence of amino acids forming a polypeptide backbone, covalently linked together by peptide bonds.

Secondary Protein Structure

Regular local folding patterns within a polypeptide backbone—specifically $\alpha$-helices and $\beta$-pleated sheets—stabilized by hydrogen bonds between amino and carboxyl groups of the peptide backbone.

Tertiary Protein Structure

The overall three-dimensional conformation of a single polypeptide chain produced by interactions between variable R groups, including ionic bonds, hydrogen bonds, hydrophobic interactions, and covalent disulfide bridges between cysteine residues.

Quaternary Protein Structure

The structural assembly formed when two or more distinct polypeptide subunits interact through non-covalent bonds or disulfide bridges to produce a functional multimeric protein complex.

Essential Amino Acids

Amino acids that cannot be manufactured from simpler molecules by animals and must be obtained pre-formed directly through the diet.

Exon

A protein-coding segment of eukaryotic pre-mRNA that is retained and spliced together with other coding sequences to form the mature mRNA transcript.

Intron

A non-protein-coding intervening nucleotide sequence in eukaryotic pre-mRNA that is removed during RNA modification in the nucleus.

Spliceosome

An enzymatic molecular complex composed of snRNPs that cuts out non-coding introns from newly transcribed pre-mRNA and joins remaining exons together in eukaryotic nuclei.

Alternative Splicing

A eukaryotic post-transcriptional process where different combinations of exons from the same primary RNA transcript are spliced together, enabling a single gene to encode multiple distinct proteins.

Promoter

A non-coding sequence of DNA located immediately upstream of a gene, often containing a TATAA box, where transcription factors and RNA polymerase bind to initiate RNA transcription.

Antisense Strand

The DNA template strand containing the informational sequence that is transcribed by RNA polymerase into complementary pre-mRNA; the non-transcribed strand is called the sense strand.

Terminator

A specific nucleotide sequence at the end of a gene signaling RNA polymerase to detach from the DNA template, releasing the newly synthesized pre-mRNA.

Fundamental Niche

The theoretical maximum range of physical, environmental, and dietary resources that a species could potentially occupy and exploit in the absence of interspecific competition or predation.

Realized Niche

The actual habitat conditions and portion of resources that a species utilizes in nature as restricted by biotic interactions such as competition and predation.

Lincoln Index

A mathematical formula used in mark-and-recapture sampling to estimate total population size: $\text{Population Estimate} = \frac{M \times N}{R}$, where $M$ is the initial marked individuals, $N$ is total recaptured individuals, and $R$ is marked recaptured individuals.

Intraspecific Competition

An interaction occurring between individuals of the same species and population competing for the same finite resources, such as food, space, territory, nesting sites, mates, or light.

Intraspecific Cooperation

Behaviors where individuals of the same species work together—such as group hunting, sentinel warning calls, or shared thermoregulation—to increase collective survival and reproductive success.

Carrying Capacity ($K$)

The maximum population size or density that an environment can sustainably support over time, represented by the plateau phase of a logistic (S) growth curve where natality and mortality equilibrate.

Density-Dependent Limiting Factor

A biotic environmental factor whose regulatory impact intensifies as population density increases (such as competition, predation, pathogens, and parasites), functioning as negative feedback to reduce population size.

Density-Independent Limiting Factor

An abiotic environmental factor that limits population growth or induces mortality irrespective of population density, such as rainfall, temperature, sunlight, and natural disasters.

Polar Covalent Bond

A chemical bond formed between two nonmetal atoms with different electronegativities, causing an unequal sharing of electron pairs and creating regions of partial positive ($\delta^+$) and partial negative ($\delta^-$) charge.

Hydrogen Bond

A weak intermolecular electrostatic attraction formed between a partially positive hydrogen atom of one polar covalent bond and an electronegative atom (such as oxygen or nitrogen) of another polar bond.

Raw Data

Unprocessed quantitative or qualitative values obtained directly from measurement instruments during an experiment without applying mathematical transformations or calculations.

Cohesion

The intermolecular attraction that causes water molecules to stick to one another primarily through continuous hydrogen bonding, contributing to high surface tension.

Adhesion

The property of water molecules to form hydrogen bonds and cling to other polar or electrically charged surfaces.

Goldilocks Zone

The circumstellar habitable zone around a star where orbital distance provides appropriate surface temperatures to allow water to exist continuously in a liquid state.