IB Biology: B1.1 Carbohydrates and Lipids

Flashcard practice set reviewing the structures, chemical bonding, condensation/hydrolysis pathways, and physiological functions of carbohydrates and lipids.

Covalent bond

The strongest type of chemical bond between atoms, formed by sharing a pair of electrons between two adjacent atoms whose positively charged nuclei attract the negatively charged shared electrons.

Tetrahedral shape of carbon bonds

The geometric arrangement that occurs because the four single covalent bonds formed by a carbon atom spread apart as far as possible, giving chains of covalently bonded carbon atoms a zig-zag configuration.

Cholesterol

A biological steroid molecule containing a core structure of four rings, all of which are composed entirely of carbon atoms.

Macromolecule

A molecule composed of a very large number of atoms with a relative molecular mass exceeding $10,000\,\text{atomic mass units}$, including polysaccharides, polypeptides, and nucleic acids.

Condensation reaction

A polymerization reaction requiring energy supplied by ATP that links two subunits together and releases a small molecule, which is always water ($H_2O$) during the synthesis of polysaccharides, polypeptides, and nucleic acids.

Glycosidic bond

A $C-O-C$ linkage formed between two monosaccharides by a condensation reaction involving their hydroxyl groups.

1-4 glycosidic bond

A covalent linkage formed between carbon 1 of a glucose unit and carbon 4 of the next glucose unit, creating an unbranched chain.

1-6 glycosidic bond

A covalent linkage formed between carbon 6 of a glucose unit already in a chain and carbon 1 of an added glucose unit, producing a side-branch.

Hydrolysis reaction

A chemical reaction that deconstructs polymers into monomers by splitting a water molecule to supply hydrogen and hydroxyl groups to replace the broken covalent bond.

Pentose

A five-carbon monosaccharide, such as ribose, that typically forms a ring structure containing four carbon atoms and one oxygen atom.

Fructose

A hexose monosaccharide widely used as a sweetener that has been associated with obesity and is preferentially taken up into ribose-producing pathways by pancreatic cancer cells.

Amylose

An unbranched plant storage starch molecule composed of $\alpha$-glucose units linked solely by $1\text{-}4$ glycosidic bonds, which coils into a helical shape due to its bond angles.

Amylopectin

A branched plant storage starch molecule containing over $100,000$ $\alpha$-glucose units linked by $1\text{-}4$ glycosidic bonds with $1\text{-}6$ branch points occurring roughly every $20$ subunits.

Glycogen

A compact animal energy storage polysaccharide found in liver and muscle cells composed of up to $60,000$ $\alpha$-glucose units linked by $1\text{-}4$ bonds, with $1\text{-}6$ branches occurring roughly every $10$ subunits.

Branching efficiency of amylopectin and glycogen

The property whereby the presence of multiple chain ends in branched polymers allows glucose molecules to be deposited or withdrawn more rapidly than in unbranched chains.

Cellulose

A structural polysaccharide found in plant cell walls composed of an unbranched chain of $10,000$ to $15,000$ or more $\beta$-glucose molecules linked by $1\text{-}4$ glycosidic bonds, reaching lengths over $10\,\mu\text{m}$.

Alternating inversion of beta-glucose

The structural requirement in cellulose where each added $\beta$-glucose unit is inverted relative to the previous one to align the upward-angled $-OH$ on $C_1$ with the downward-angled $-OH$ on $C_4$.

Osmotic advantage of storage polysaccharides

The low solubility of large macromolecules like starch and glycogen, which allows cells to store massive quantities of glucose without altering intracellular osmotic concentration or inducing excessive water uptake.

Lipids

A diverse group of hydrophobic organic compounds that are sparingly soluble in aqueous solvents but dissolve in non-polar solvents like ethanol, toluene, and propanone (acetone).

Oils

Lipids with a melting point below $20\,^\circ\text{C}$, causing them to remain liquid at room temperature and solidify only at low temperatures.

Fats

Lipids with a melting point between $20\,^\circ\text{C}$ and $37\,^\circ\text{C}$, making them solid at room temperature and liquid at normal animal body temperature.

Waxes

Lipids with a melting point above $37\,^\circ\text{C}$, remaining solid at body temperature and liquefying only at elevated temperatures.

Steroids

A class of lipids distinguished by a molecular structure containing four fused carbon rings.

Triglyceride

An entirely hydrophobic lipid molecule formed by combining three fatty acids with one glycerol molecule through three condensation reactions, releasing three water molecules.

Fatty acid

A molecule consisting of an unbranched hydrocarbon chain—usually between $14$ and $20$ carbon atoms long—with a carboxyl group ($-COOH$) at one end and a methyl group ($-CH_3$) at the other.

Saturated fatty acid

A fatty acid whose hydrocarbon chain contains only single covalent bonds between carbon atoms, holding the maximum possible number of hydrogen atoms.

Monounsaturated fatty acid

A fatty acid whose hydrocarbon chain contains exactly one double covalent bond between carbon atoms.

Polyunsaturated fatty acid

A fatty acid whose hydrocarbon chain contains two or more double covalent bonds between carbon atoms.

Adipose tissue

Specialized animal tissue located beneath the skin and around organs like the kidneys, which stores triglycerides to provide long-term energy storage, thermal insulation, and shock absorption.