Macromolecules: Proteins, Carbohydrates, Lipids and Nucleic Acids: every key term you need (+ practice quiz)
25 flashcard terms for General Biology I Topic 2, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 15-question quiz — free, no account needed.
The bond-forming step of polymer synthesis, in which two monomers are joined and a water molecule is released. Every peptide, glycosidic and phosphodiester bond in the cell is made this way.
Hydrolysis
The reverse of condensation: a water molecule is split across a bond to break a polymer into smaller units. Digestion, protein turnover and nucleic acid degradation all proceed by hydrolysis.
Amino acid
A monomer with an alpha carbon bearing an amino group, a carboxyl group, a hydrogen and a variable side chain. Twenty side chains are specified by the genetic code, and they alone determine a protein's chemistry.
Peptide bond
The amide linkage between the carboxyl carbon of one amino acid and the amino nitrogen of the next. Its partial double bond character makes it planar and rigid, restricting backbone rotation to two angles per residue.
Primary structure
The linear order of amino acids in a polypeptide, read from the amino terminus to the carboxyl terminus. Sequence alone, in the right environment, generally contains enough information to specify the folded shape.
Secondary structure
Local backbone folding stabilized by hydrogen bonds between backbone carbonyl oxygens and amide hydrogens, producing alpha helices and beta pleated sheets. Side chains are not directly involved.
Alpha helix
A right-handed coil with about 3.6 residues per turn, in which each backbone carbonyl hydrogen bonds to the amide hydrogen four residues ahead. Side chains project outward from the coil.
Beta pleated sheet
A secondary structure in which extended strands lie side by side, hydrogen bonded across the backbone. Strands may run parallel or antiparallel, and sheets often form the rigid core of a domain.
Tertiary structure
The overall three-dimensional shape of one polypeptide, driven by burial of hydrophobic side chains and stabilized by ionic bonds, hydrogen bonds, van der Waals contacts and disulfide bridges.
Quaternary structure
The assembly of two or more folded polypeptides into a functional complex. Hemoglobin's four subunits are the classic case, and their interaction produces cooperative oxygen binding.
Disulfide bridge
A covalent sulfur to sulfur bond between two cysteine side chains. It is the only covalent cross-link in ordinary tertiary structure and is common in secreted proteins facing oxidizing conditions.
Denaturation
Loss of folded structure caused by heat, extremes of pH, or agents such as urea, without breaking peptide bonds. Anfinsen showed that some denatured proteins refold spontaneously when conditions are restored.
Chaperone protein
A helper protein that shields exposed hydrophobic surfaces on a nascent or stressed polypeptide, giving it an isolated chamber or a binding cycle in which to reach its native fold without aggregating.
Monosaccharide
A simple sugar with the general formula of one carbon, two hydrogens and one oxygen per unit, existing as an open chain or a ring. Glucose, fructose and galactose all share the formula six-carbon sugar.
Glycosidic linkage
The covalent bond joining two sugars, formed by condensation between an anomeric carbon and a hydroxyl of the partner. Its geometry, alpha or beta, decides whether the polymer is digestible or structural.
Starch and glycogen
Storage polymers of glucose joined by alpha linkages, which coil into helices that enzymes readily hydrolyze. Glycogen is more highly branched than plant starch, giving faster mobilization in animals.
Cellulose
A glucose polymer with beta linkages that force alternating residues to flip, producing straight chains that hydrogen bond into microfibrils. Most animals lack the enzyme to cleave beta linkages.
Chitin
A structural polysaccharide of nitrogen-containing glucose units in beta linkage, forming arthropod exoskeletons and fungal cell walls. Its added amide groups allow extra hydrogen bonding between chains.
Triacylglycerol
Three fatty acids esterified to glycerol, the cell's densest fuel store because its carbons are highly reduced and it stores no associated water, unlike hydrated glycogen.
Saturated fatty acid
A fatty acid whose hydrocarbon tail contains no carbon double bonds, so the chain is straight and packs tightly. Such fats are solid at room temperature and stiffen membranes.
Unsaturated fatty acid
A fatty acid with one or more double bonds, usually in the cis configuration, which puts a kink in the tail. Kinks block tight packing, keeping oils liquid and membranes fluid.
Steroid
A lipid built on four fused carbon rings rather than fatty acid chains. Cholesterol is the animal precursor from which sex hormones and other signaling steroids are chemically derived.
Nucleotide
The nucleic acid monomer: a five-carbon sugar joined to a nitrogenous base and one or more phosphate groups. Beyond building polymers, nucleotides serve as energy carriers and signaling molecules.
Phosphodiester bond
The linkage joining the phosphate on one nucleotide's fifth carbon to the hydroxyl on the third carbon of the next, giving every nucleic acid strand a defined directionality.
Complementary base pairing
The specific hydrogen bonding of adenine with thymine or uracil and of guanine with cytosine. Because each strand specifies the other, the rule underlies replication, transcription and probe hybridization.