Large Biological Molecules: Structure and Function

Comprehensive vocabulary flashcards covering the structure, synthesis, and functions of carbohydrates, lipids, proteins, and nucleic acids.

Macromolecules

Giant molecules composed of thousands of covalently connected atoms, comprising three classes of large biological molecules: carbohydrates, proteins, and nucleic acids.

Polymer

A long molecule consisting of many similar or identical building blocks linked by covalent bonds.

Monomers

The repeating small building-block molecules that serve as the subunits of a polymer.

Dehydration Reaction

A reaction in which two monomers become covalently bonded to each other with the loss of a water molecule; also known as a condensation reaction.

Hydrolysis

A chemical reaction that breaks bonds between monomers in a polymer through the addition of a water molecule, functioning as the reverse of a dehydration reaction.

Enzymes

Macromolecules that act as catalysts to selectively speed up chemical reactions without being consumed by them.

Monosaccharides

The simplest carbohydrates, or single sugars, that generally have molecular formulas that are multiples of the unit $\text{CH}_2\text{O}$.

Aldose

A sugar classified by having a carbonyl group located at the end of the carbon skeleton (an aldehyde sugar), such as glucose and galactose.

Ketose

A sugar classified by having a carbonyl group located within the interior of the carbon skeleton (a ketone sugar), such as fructose and ribulose.

Disaccharide

A double sugar consisting of two monosaccharides joined by a covalent glycosidic linkage formed via a dehydration reaction.

Glycosidic Linkage

A covalent bond formed between two monosaccharides by a dehydration reaction.

Polysaccharides

Macromolecules formed from polymers of hundreds to thousands of monosaccharides joined by glycosidic linkages, functioning in energy storage or structural support.

Starch

A plant storage polysaccharide consisting entirely of glucose monomers connected by $\alpha$ 1–4 glycosidic linkages, stored as granules in plastids such as chloroplasts.

Glycogen

An extensively branched storage polysaccharide of glucose found in animals, primarily stored in liver and muscle cells.

Cellulose

A structural polysaccharide consisting of straight, unbranched chains of $\beta$ glucose monomers linked by $\beta$ 1–4 glycosidic linkages, serving as a primary component of plant cell walls.

Microfibrils

Cable-like units of parallel cellulose molecules held together by hydrogen bonds between hydroxyl groups, conferring high tensile strength to plant cell walls.

Chitin

A structural polysaccharide containing an amino sugar derivative, found in the exoskeletons of arthropods and in the cell walls of many fungi.

Lipids

A diverse class of large biological molecules that do not consist of polymers and are hydrophobic due to a high proportion of nonpolar hydrocarbon bonds.

Fat (Triacylglycerol)

A lipid composed of three fatty acid molecules linked to a three-carbon glycerol molecule by ester linkages; also called a triglyceride.

Fatty Acid

A molecule consisting of a long hydrocarbon skeleton with a carboxyl group at one end.

Saturated Fatty Acid

A fatty acid in which all carbons in the hydrocarbon chain are joined by single bonds, allowing the maximum number of hydrogen atoms to be bonded to the skeleton.

Unsaturated Fatty Acid

A fatty acid possessing one or more double bonds in the hydrocarbon chain, typically causing a kink or bend in the chain's shape due to a cis configuration.

Hydrogenation

The synthetic process of converting unsaturated fats into saturated fats by chemically adding hydrogen, which often generates trans fats as a byproduct.

Trans Fats

Unsaturated fats with trans double bonds produced during the industrial hydrogenation of vegetable oils, which can contribute to cardiovascular disease.

Phospholipid

An amphipathic lipid made of a glycerol molecule joined to two fatty acids and a phosphate group, forming hydrophobic tails and a hydrophilic head.

Steroids

A class of lipids characterized by a carbon skeleton composed of four fused carbon rings with attached functional groups.

Cholesterol

A steroid that forms an essential component of animal cell membranes and serves as the precursor for synthesize of other steroid molecules.

Polypeptides

Unbranched polymers built from amino acids linked by peptide bonds that make up the structural units of proteins.

Amino Acid

An organic monomer containing both an amino group ($-\text{NH}_2$) and a carboxyl group ($-\text{COOH}$), along with a variable side chain ($\text{R}$ group).

Peptide Bond

The covalent bond formed between the carboxyl group of one amino acid and the amino group of an adjacent amino acid via a dehydration reaction.

Primary Structure

The unique, genetically determined linear sequence of amino acids in a polypeptide chain.

Secondary Structure

The localized, repetitive coiling or folding of the polypeptide backbone, stabilized by hydrogen bonds between the constituents of the backbone.

$\alpha$ Helix

A delicate coil-shaped secondary protein structure held together by hydrogen bonds between every fourth amino acid in the polypeptide backbone.

$\beta$ Pleated Sheet

A secondary protein structure formed when two or more segments of a polypeptide chain lie parallel or antiparallel to each other, stabilized by hydrogen bonds between the backbones.

Tertiary Structure

The overall three-dimensional shape of a polypeptide resulting from interactions between the variable side chains ($\text{R}$ groups) of the amino acids.

Disulfide Bridges

Strong covalent linkages between the sulfur atoms of two cysteine side chains ($-\text{CH}_2-\text{S}-\text{S}-\text{CH}_2-$) that reinforce tertiary structure.

Quaternary Structure

The structural level resulting from the association and aggregation of two or more distinct polypeptide subunits into a single functional macromolecule.

Denaturation

The process where a protein unravels and loses its native native shape due to disruptions in hydrogen bonds, ionic bonds, or other interactions caused by extremes in pH, salt concentration, or temperature.

Chaperonins

Multi-protein complexes that assist in the proper folding of other proteins by sheltering them from damaging chemical environments in the cytoplasm.

X-ray Crystallography

A technique used to determine the three-dimensional atomic structure of biological molecules by analyzing the diffraction pattern of an X-ray beam passed through a crystal.

Gene

A discrete unit of inheritance that programs the amino acid sequence of a polypeptide, consisting of a specific segment of DNA.

Nucleic Acids

Polymers made of nucleotide monomers that serve as molecules for storing, transmitting, and expressing genetic hereditary information.

Nucleotide

The building-block monomer of a nucleic acid, consisting of a five-carbon sugar, a nitrogen-containing base, and one or more phosphate groups.

Nucleoside

The structural portion of a nucleotide that consists only of a nitrogenous base attached to a pentose sugar, lacking any phosphate group.

Pyrimidines

A family of nitrogenous bases characterized by a single six-membered ring of carbon and nitrogen atoms; includes cytosine (C), thymine (T), and uracil (U).

Purines

A family of nitrogenous bases characterized by a six-membered ring fused to a five-membered ring; includes adenine (A) and guanine (G).

Phosphodiester Linkage

The covalent bond that joins adjacent nucleotides along a polynucleotide chain, connecting the $-\text{OH}$ on the $3'$ carbon of one sugar to the phosphate attached to the $5'$ carbon of the next.

Antiparallel

The arrangement of the two sugar-phosphate backbones in a DNA double helix, running parallel to each other but oriented in opposite $5' \rightarrow 3'$ directions.

Macromolecules

Large molecules composed of thousands of covalently connected atoms, including carbohydrates, proteins, and nucleic acids.

Polymer

A long molecule consisting of many similar or identical building blocks linked by covalent bonds.

Monomer

Small building-block molecules that serve as the repeating units used to build polymers.

Dehydration Reaction

A reaction (also termed a condensation reaction) in which two monomers become covalently bonded together through the loss of a water molecule.

Hydrolysis

A chemical reaction that disassembles polymers into monomers, essentially reversing the dehydration reaction by adding a water molecule to break the covalent bond.

Enzyme

A macromolecule (typically a protein) that serves as a catalyst to selectively speed up chemical reactions without being consumed in the process.

Monosaccharides

The simplest carbohydrates, or single sugars, which possess molecular formulas that are generally multiples of $CH_2O$ and serve as major cellular fuel and building material.

Glycosidic Linkage

A covalent bond formed between two monosaccharides by a dehydration reaction.

Starch

A plant storage polysaccharide consisting entirely of glucose monomers linked together, stored as granules within chloroplasts and other plastids.

Glycogen

An extensively branched storage polysaccharide found in animals, stored predominantly in liver and muscle cells.

Cellulose

A major structural polysaccharide component of tough plant cell walls, consisting of straight, unbranched polymers of $\beta$ glucose monomers joined by $1-4$ glycosidic linkages.

Microfibrils

Parallel arrays of straight cellulose molecules held together by hydrogen bonds between hydroxyl groups and hydrogen atoms, forming strong structural units in plant cell walls.

Chitin

A structural polysaccharide found in the exoskeletons of arthropods and the cell walls of many fungi, also used to produce strong, flexible surgical thread.

Lipids

A diverse class of large biological molecules that do not form true polymers and share the unifying feature of being hydrophobic due to nonpolar hydrocarbon structures.

Triacylglycerol

A fat molecule constructed from one glycerol molecule joined to three fatty acid tails via ester linkages; also known as a triglyceride.

Saturated Fatty Acid

A fatty acid with a hydrocarbon chain containing no double bonds and having the maximum number of hydrogen atoms possible, typically solidifying at room temperature.

Unsaturated Fatty Acid

A fatty acid possessing one or more double bonds in the hydrocarbon chain (commonly cis double bonds causing kinks), typically remaining liquid at room temperature.

Hydrogenation

The industrial process of synthetically adding hydrogen to unsaturated fats to convert them into saturated fats, which often creates trans double bonds.

Trans Fats

Unsaturated fats containing trans double bonds formed during the hydrogenation of vegetable oils, which contribute heavily to cardiovascular disease.

Phospholipids

Lipids composed of a glycerol molecule joined to two hydrophobic fatty acid tails and a hydrophilic head containing a phosphate group and choline, assembling into cell membrane bilayers.

Phospholipid Bilayer

A double-layered arrangement formed when phospholipids are added to water, in which hydrophobic fatty acid tails shield themselves by facing inward while hydrophilic phosphate heads contact water.

Steroids

Lipids characterized by a carbon skeleton consisting of four fused rings with attached chemical functional groups.

Cholesterol

An essential steroid lipid found in animal cell membranes and used as a precursor for synthesizing other steroids, though high levels in the blood can contribute to cardiovascular disease.

Polypeptides

Unbranched polymers constructed from the 20 amino acid monomers, ranging in length from a few to more than a thousand units.

Amino Acids

Organic monomers consisting of an asymmetric alpha ($\alpha$) carbon bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group).

Peptide Bond

The covalent bond formed between the carboxyl group of one amino acid and the amino group of another through a dehydration reaction.

Primary Structure

The unique, genetically determined linear sequence of amino acids in a polypeptide chain.

Secondary Structure

Repetitive coils and folds within a polypeptide chain formed by hydrogen bonds between repeating constituents of the polypeptide backbone.

Alpha ($\alpha$) Helix

A delicate coiled secondary structure held together by hydrogen bonding between every fourth amino acid along the polypeptide backbone.

Beta ($\beta$) Pleated Sheet

A pleated secondary structure formed by parallel or antiparallel polypeptide backbone strands joined together by hydrogen bonds.

Tertiary Structure

The overall three-dimensional shape of a polypeptide determined by interactions among variable R groups, including hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals interactions.

Disulfide Bridges

Strong covalent bonds formed when the sulfhydryl groups ($-SH$) of two cysteine amino acids oxidize to link their sulfur atoms ($-S-S-$), reinforcing tertiary protein structure.

Quaternary Structure

The overall structural organization resulting from the association and assembly of two or more distinct polypeptide subunits into one functional protein complex.

Sickle-Cell Disease

An inherited blood disorder caused by a single amino acid substitution (valine substituted for glutamic acid at the 6th position) in the primary structure of hemoglobin, leading to fiber aggregation and deformed red blood cells.

Denaturation

The unraveling and structural breakdown of a protein caused by adverse changes in pH, salt concentration, temperature, or other environmental factors, resulting in a biologically inactive state.

Chaperonins

Multiprotein complexes with a hollow cylinder and cap that create a sheltered hydrophilic chamber to assist the proper folding of unfolded polypeptides.

X-ray Crystallography

An experimental method used to deduce the three-dimensional atomic structure of proteins and other macromolecules by recording the diffraction pattern of X-rays passed through a crystal.

Bioinformatics

The computational approach that employs computer programs to model and predict macromolecular structures and relationships based on amino acid or nucleotide sequences.

Gene

A discrete unit of inheritance made of DNA that programs the primary amino acid sequence of a polypeptide.

Nucleic Acids

Polymers (polynucleotides) composed of nucleotide monomers that store, transmit, and express hereditary genetic information, encompassing DNA and RNA.

Nucleotide

A monomer of a nucleic acid, consisting of a nitrogenous base, a five-carbon pentose sugar, and one or more phosphate groups.

Nucleoside

The portion of a nucleotide unit consisting solely of a nitrogenous base attached to a pentose sugar, without a phosphate group.

Pyrimidines

A family of nitrogenous bases characterized by a single six-membered ring; includes cytosine (C), thymine (T, in DNA), and uracil (U, in RNA).

Purines

A family of nitrogenous bases characterized by a six-membered ring fused to a five-membered ring; includes adenine (A) and guanine (G).

Deoxyribose and Ribose

The pentose sugars of nucleic acids; deoxyribose (present in DNA) lacks an oxygen atom on its $2'$ carbon atom, whereas ribose (present in RNA) possesses a hydroxyl group ($-OH$) on its $2'$ carbon.

Phosphodiester Linkage

The covalent bond that joins adjacent nucleotides in a polynucleotide, connecting the $-OH$ group on the $3'$ carbon of one sugar to the phosphate on the $5'$ carbon of the next.

Antiparallel

The structural arrangement of the two sugar-phosphate backbones in the DNA double helix, which run side by side in opposite $5' \rightarrow 3'$ directions.

Biological Macromolecule Linkages

The specific covalent bonds connecting biological monomers: glycosidic linkages for polysaccharides, ester linkages for triacylglycerols, peptide bonds for polypeptides, and phosphodiester linkages for polynucleotides.