IB Biology: Water, Nucleic Acids, Carbohydrates, Lipids, Proteins, and Enzymes

Comprehensive vocabulary flashcards covering Topic A1.1 Water, Topic A1.2 Nucleic Acids, Topic B1.1 Carbohydrates and Lipids, Topic B1.2 Proteins, and Topic C1.1 Enzymes and Metabolism from the IB Biology syllabus.

Water as the Medium for Life

The liquid environment in which the first cells originated and where most chemical and metabolic processes of life continue to occur.

Polar Covalent Bonds in Water

Covalent bonds within a water molecule formed by the unequal sharing of electrons between oxygen and hydrogen, creating a partial negative charge ($\delta^-$) on oxygen and partial positive charges ($\delta^+$) on hydrogens.

Hydrogen Bond (in Water)

An intermolecular force of attraction formed between the partially negative oxygen atom of one water molecule and the partially positive hydrogen atom of another water molecule due to molecular polarity.

Cohesion

The attraction of water molecules to each other via hydrogen bonding, enabling water transport under tension in xylem vessels and generating surface tension.

Surface Tension

An effect caused by the cohesive hydrogen bonding between water molecules at the water-air interface that allows water surfaces to serve as biological habitats.

Adhesion

The intermolecular attraction of water molecules to other polar or charged materials, driving capillary action in soil and plant cell walls.

Capillary Action

The movement of water through narrow spaces in soil and through cellulose microfibrils in plant cell walls driven by the adhesive forces between water and polar surfaces.

Solvent Properties of Water

The capacity of water to dissolve a wide variety of hydrophilic substances, providing an aqueous medium for metabolic reactions catalyzed by enzymes and for fluid transport in plants and animals.

Buoyancy

The upward force exerted by a fluid on an immersed body; water provides much greater buoyant support than air, reducing the energetic cost of support for organisms like the ringed seal (Pusa hispida) compared to terrestrial organisms.

Viscosity

A fluid's internal resistance to flow; water has higher viscosity than air, requiring streamlined adaptations in aquatic swimmers such as the black-throated loon (Gavia arctica) and the ringed seal (Pusa hispida).

Thermal Conductivity

The rate at which heat passes through a material; water has a higher thermal conductivity than air, conducting heat away from organisms much faster.

Specific Heat Capacity

The amount of energy required to raise the temperature of a unit mass of a substance; water has a high specific heat capacity, creating thermally stable aquatic environments.

Asteroid Origin of Water

The hypothesis that Earth's water was delivered from extraplanetary sources via asteroid collisions over billions of years, retained by Earth's gravity and surface temperatures low enough to condense water vapor.

Goldilocks Zone

The habitable orbital region around a star where temperatures are just right to allow liquid water to condense and persist on a planet's surface, crucial for the search for extraterrestrial life.

Nucleotide

The monomer unit of nucleic acids, standardly diagrammed as a phosphate (circle), a pentose sugar (pentagon), and a nitrogenous base (rectangle).

Sugar-Phosphate Backbone

A continuous chain of covalently bonded atoms formed by sugar-phosphate linkages between adjacent nucleotides in DNA or RNA strands.

RNA (Ribonucleic Acid)

A single-stranded nucleic acid polymer formed by condensation reactions of nucleotide monomers containing ribose sugar and the nitrogenous bases adenine, cytosine, guanine, and uracil.

Antiparallel Strands (DNA)

The parallel orientation of the two complementary strands of nucleotides running in opposite directions, linked together across the center by hydrogen bonds between complementary base pairs.

Complementary Base Pairing

Specific hydrogen bonding between adenine (A) and thymine (T) / uracil (U), and between guanine (G) and cytosine (C), enabling precise replication and expression of genetic information.

$5'$ to $3'$ Linkages

Directional covalent linkages within the sugar-phosphate backbone linking the $5'$ carbon of one nucleotide's sugar to the $3'$ carbon of the next, determining orientation for replication, transcription, and translation.

Purine-to-Pyrimidine Bonding

Base pairing between a purine and a pyrimidine that produces equal lengths for A–T and C–G pairs, ensuring a uniform three-dimensional double helix diameter regardless of nucleotide sequence.

Nucleosome

A eukaryotic structural DNA unit consisting of a DNA molecule wrapped around an octamer core of eight histone proteins, held together by an additional histone protein attached to linker DNA.

Hershey–Chase Experiment

The landmark experiment utilizing radioactively labeled bacteriophages that provided definitive empirical evidence identifying DNA, rather than protein, as the genetic material.

Universal Common Ancestry (Genetic Code)

The conservation of the same genetic code across all forms of living organisms, serving as fundamental evidence that all life shares a single common evolutionary origin.

Covalent Properties of Carbon

The ability of a carbon atom to form up to four stable covalent single bonds, or combinations of single and double bonds, creating branched, unbranched chains, or rings with other carbon and non-metallic atoms.

Condensation Reaction

A chemical reaction that links monomer molecules together to produce macromolecules (polymers), releasing a water molecule in the process.

Digestion

The breakdown of large, insoluble biological polymers into small, soluble monomers via hydrolysis reactions so that they can be absorbed by an organism.

Hydrolysis Reaction

A cleavage reaction where polymers are digested into monomers by splitting water molecules to yield $-H$ and $-OH$ groups incorporated into the products.

Glucose

A hexose monosaccharide utilized as a primary metabolic substrate due to its high solubility, transportability, chemical stability, and high energy yield from oxidation.

Starch

A plant energy storage polysaccharide made of alpha-glucose monomers that is insoluble and compact due to coiling and branching during polymerization.

Glycogen

An animal energy storage polysaccharide formed from alpha-glucose monomers, characterized by high branching, compactness, insolubility, and ease of mobilization via hydrolysis.

Cellulose

A plant structural polysaccharide consisting of beta-glucose monomers joined in an alternating orientation, producing unbranched straight chains bundled and cross-linked by hydrogen bonds.

Glycoproteins

Proteins conjugated with carbohydrate chains that function as cell-surface markers for cell-cell recognition, exemplified by human ABO blood group antigens.

Lipids

A diverse group of biological compounds—including fats, oils, waxes, and steroids—that dissolve readily in non-polar solvents but are sparingly soluble in aqueous solvents.

Triglyceride

A lipid formed by condensation of one glycerol molecule with three fatty acid molecules, functioning as an efficient long-term energy storage compound and thermal insulator in adipose tissue.

Saturated Fatty Acid

A fatty acid having only single covalent bonds between carbon atoms (no $C=C$ double bonds), having a higher melting point and being predominant in endotherm fats.

Unsaturated Fatty Acid

A fatty acid containing one (monounsaturated) or more (polyunsaturated) carbon-carbon double bonds ($C=C$), reducing melting point and typically found in plant oils.

Amphipathic

Possessing both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions on the same molecule, which drives phospholipids to self-assemble into bilayers.

Steroids

Non-polar lipids composed of a characteristic four-ring carbon skeleton, such as oestradiol and testosterone, capable of freely diffusing across the hydrophobic core of the phospholipid bilayer.

Amino Acid Generalized Structure

A central alpha carbon bonded to four groups: an amine group ($-\text{NH}_2$), a carboxyl group ($-\text{COOH}$), a hydrogen atom ($-\text{H}$), and a variable R-group ($-\text{R}$).

Essential Amino Acids

Amino acids that cannot be synthesized internally by an animal and must be obtained pre-formed from dietary food sources.

Non-Essential Amino Acids

Amino acids that can be synthesized by an organism from other metabolic precursors or other amino acids.

R-Group Diversity

The chemical variations in amino acid side chains (which can be hydrophobic, hydrophilic, polar, charged, acidic, or basic) that determine the diverse conformations and functions of polypeptides.

Primary Structure

The linear sequence and precise position of amino acids within a polypeptide chain, which determines all subsequent levels of three-dimensional protein folding.

Secondary Structure

Regular local folding patterns within a polypeptide, specifically alpha helices and beta-pleated sheets, stabilized by hydrogen bonding between peptide backbone groups at regular positions.

Tertiary Structure

The overall three-dimensional conformation of a single polypeptide chain, stabilized by interactions among R-groups including hydrogen bonds, ionic bonds, hydrophobic interactions, and covalent disulfide bonds between cysteines.

Denaturation

A permanent structural alteration of a protein's conformation caused by extreme pH or high temperature that disrupts stabilizing interactions and destroys catalytic active sites.

Metabolism

The complex network of interdependent and interacting chemical reactions catalyzed by specific enzymes occurring within living organisms.

Anabolism

Metabolic reactions that construct complex macromolecules from simpler monomeric precursors via condensation reactions, including protein synthesis, glycogen formation, and photosynthesis.

Catabolism

Metabolic reactions that break down complex molecules into smaller units, such as the hydrolytic digestion of polymers and the oxidation of respiratory substrates.

Active Site

A specific catalytic pocket on a globular enzyme composed of a few precise amino acids, configured by the overall tertiary structure to bind specific substrates.

Induced-Fit Binding

The dynamic conformational adjustment occurring during enzyme-substrate interaction where both the substrate and the enzyme's active site change shape upon binding to achieve catalysis.