Biochemistry: Carbohydrates, Amino Acids, Proteins, Water, and Lipids

Comprehensive practice vocabulary flashcards covering the structure, properties, reactions, and biological classifications of carbohydrates, amino acids, proteins, water/electrolytes/pH, and lipids.

Carbohydrate

A polyhydroxy aldehyde or ketone, or a substance that yields such compounds upon hydrolysis, often having the empirical formula $C_n(H_2O)_m$.

Photosynthesis Equation

The light- and chlorophyll-dependent process by which plants synthesize glucose from carbon dioxide and water: $6CO_2 + 6H_2O + \text{energy} \rightarrow C_6H_{12}O_6 + 6O_2$.

Aldose vs. Ketose

An aldose is a monosaccharide containing a carbonyl group at the end of the carbon chain (an aldehyde group, $\text{--CHO}$), whereas a ketose contains a carbonyl group ($C=O$) at an interior position.

Dextrose

An alternate name for D-glucose based on its ability to rotate plane-polarized light to the right (dextrorotatory).

Enantiomers (Carbohydrates)

Stereoisomers that are nonsuperimposable mirror images of each other, designated as D or L based on the spatial orientation of the $\text{--OH}$ group on the chiral center furthest from the carbonyl carbon relative to glyceraldehyde.

Epimers

Two sugars that differ in stereochemical configuration around only one specific chiral carbon atom (e.g., D-glucose and D-mannose at C-2, or D-glucose and D-galactose at C-4).

Hemiacetal / Hemiketal Formation

A reversible reaction where an alcohol adds to an aldehyde or ketone carbonyl group; an intramolecular reaction in pentoses and hexoses generates cyclic hemiacetals or hemiketals.

Anomers

Isomeric forms of monosaccharides that differ only in configuration about the newly formed chiral hemiacetal or hemiketal carbon atom (the anomeric carbon), designated as $\alpha$ and $\beta$.

Mutarotation

The gradual change in optical rotation accompanying the interconversion of $\alpha$ and $\beta$ anomers in aqueous solution via the open-chain intermediate until equilibrium is reached.

Glycosidic Bond

An acetal or ketal covalent bond formed between the anomeric carbon of a cyclic monosaccharide and an alcohol hydroxyl group (O-glycosidic) or an amine nitrogen (N-glycosidic).

Uronic Acid

A sugar acid formed by the enzyme-catalyzed oxidation of the terminal primary hydroxyl group ($\text{C-6}$ in hexoses) to a carboxylic acid ($\text{--COOH}$), such as D-glucuronic acid.

Aldonic Acid

A sugar acid produced when the aldehyde carbon ($\text{C-1}$) of an aldose is oxidized to a carboxylic acid or carboxylate under basic conditions, classifying the sugar as a reducing sugar.

Alditol

A polyhydroxy alcohol obtained by the reduction of the carbonyl group of a monosaccharide to a hydroxyl group, such as D-glucitol (D-sorbitol) from D-glucose.

Maltose

A reducing disaccharide formed by two D-glucose units joined by an $\alpha(1 \rightarrow 4)$ glycosidic bond ($\alpha\text{-D-glucopyranosyl-(1}\rightarrow\text{4)-}\alpha\text{-D-glucopyranose}$).

Lactose

A reducing disaccharide found in milk composed of D-galactose and D-glucose linked by a $\beta(1 \rightarrow 4)$ glycosidic bond ($\beta\text{-D-galactopyranosyl-(1}\rightarrow\text{4)-}\alpha\text{-D-glucopyranose}$).

Sucrose

A non-reducing disaccharide composed of D-glucose and D-fructose linked by an $\alpha(1 \rightarrow 2)\beta$ glycosidic bond between both anomeric carbons ($\alpha\text{-D-glucopyranosyl-(1}\rightarrow\text{2)-}\beta\text{-D-fructofuranose}$).

Invert Sugar

An equimolar mixture of glucose and fructose produced by the hydrolysis of sucrose, named because the strongly levorotatory nature of fructose inverts the initial dextrorotatory optical activity of sucrose.

Amylose

An unbranched, helical polysaccharide fraction of starch (constituting $13\%\text{--}20\%$) composed entirely of D-glucose residues joined by $\alpha(1 \rightarrow 4)$ glycosidic bonds.

Amylopectin

A highly branched polysaccharide fraction of starch (constituting $80\%\text{--}87\%$) composed of $\alpha(1 \rightarrow 4)$ linked D-glucose chains with $\alpha(1 \rightarrow 6)$ branch points occurring every 24 to 30 residues.

Glycogen

The primary glucose storage homopolysaccharide of animals, consisting of $\alpha(1 \rightarrow 4)$ linked chains with frequent $\alpha(1 \rightarrow 6)$ branches every 12 to 14 residues.

Cellulose

A fibrous, unbranched structural homopolysaccharide of plant cell walls composed of 10,000 to 15,000 D-glucose residues connected by $\beta(1 \rightarrow 4)$ glycosidic bonds that cannot be cleaved by mammalian digestive enzymes.

Chitin

A structural linear homopolysaccharide found in the exoskeletons of arthropods, crustaceans, and fungi, composed of repeating $N\text{-acetyl-D-glucosamine}$ units connected by $\beta(1 \rightarrow 4)$ glycosidic linkages.

Glycosaminoglycans (GAGs)

Unbranched, negatively charged heteropolysaccharides of the extracellular matrix consisting of repeating disaccharide units containing an amino sugar and typically a uronic acid.

Heparin

A highly sulfated glycosaminoglycan derived primarily from mast cells that acts as an anticoagulant by binding to and activating antithrombin to inhibit thrombin.

Proteoglycan

A macromolecule of the cell surface or extracellular matrix composed of a membrane or secreted core protein covalently joined to one or more sulfated glycosaminoglycan chains.

Lectins

Carbohydrate-binding proteins that recognize and bind with high specificity and affinity to the oligosaccharide portions of glycoproteins and glycosphingolipids.

Universal Blood Donor and Recipient

Type O negative is the universal donor because its red blood cells lack A, B, and Rh surface antigens; type AB positive is the universal recipient because its plasma lacks antibodies against these antigens.

Standard Amino Acids

The set of 20 primary $\alpha$-amino acids specified by the genetic code and utilized by ribosomes to build proteins, all possessing L-chirality at the $\alpha$-carbon (except achiral glycine).

Proline

A standard amino acid that contains a secondary cyclic imino group ($\text{--NH--}$) formed by the linkage of its aliphatic side chain to its $\alpha$-amino nitrogen.

Essential Amino Acids

The ten amino acids that cannot be synthesized endogenously by humans in sufficient amounts and must be supplied through the diet: Phe, Met, Val, His, Thr, Arg, Trp, Lys, Ile, and Leu.

Ketogenic Amino Acids

Amino acids whose catabolic carbon skeletons yield ketone bodies rather than glucose; leucine and lysine are exclusively ketogenic.

Zwitterion

A dipolar ion carrying both positive and negative charges simultaneously while maintaining an overall net electrical charge of zero at neutral or isoelectric pH.

Isoelectric Point (pI)

The characteristic pH at which a molecule carries no net electrical charge, exhibiting zero electrophoretic mobility and minimum aqueous solubility and buffering capacity.

Peptide Bond

A planar, rigid covalent amide bond formed with the loss of a water molecule between the $\alpha$-carboxyl group of one amino acid and the $\alpha$-amino group of another.

Primary Structure of Protein

The unique, genetically determined linear sequence of amino acid residues linked by peptide bonds, including the precise positions of any disulfide bonds.

$\alpha$-Helix

A secondary protein structure formed by a right-handed coiled polypeptide backbone stabilized by intramolecular hydrogen bonds between peptide $N\text{--}H$ and $C=O$ groups, having 3.6 residues and a pitch of $5.4\,\text{Å}$ per turn.

Tertiary Structure of Protein

The overall three-dimensional folding and arrangement of a single polypeptide chain into a compact, biologically active conformation stabilized by hydrophobic interactions, hydrogen bonds, ionic bonds, and disulfide bridges.

Quaternary Structure of Protein

The structural organization and spatial assembly of multiple polypeptide subunits into a multi-subunit protein complex held together by noncovalent interactions (e.g., hemoglobin).

Ion Product of Water ($K_w$)

The equilibrium constant for the autoionization of water, defined as $K_w = [H^+][OH^-] = 1.0 \times 10^{-14}\,\text{M}^2$ at $25\,^{\circ}\text{C}$.

pH

The negative logarithm of the hydrogen ion concentration: $pH = -\log[H^+]$.

Acidosis and Alkalosis

Clinical states where blood plasma pH deviates from the normal physiological range of 7.35 to 7.45; acidosis refers to pH values below 7.35, while alkalosis refers to pH values above 7.45.

Buffer Solution

An aqueous system consisting of a weak acid (proton donor) and its conjugate base (proton acceptor) that resists changes in pH when small amounts of acid or base are added.

Henderson-Hasselbalch Equation

An equation relating pH, $pK_a$, and the ratio of conjugate base to weak acid: $pH = pK_a + \log\left(\frac{[A^-]}{[HA]}\right)$.

Lipids

A heterogeneous group of organic compounds composed primarily of fatty acids and alcohols joined by ester linkages, characterized by being insoluble in water but soluble in non-polar organic solvents.

Saturated vs. Unsaturated Fatty Acids

Saturated fatty acids contain no double bonds along their hydrocarbon chain, whereas unsaturated fatty acids contain one (monounsaturated) or more (polyunsaturated) double bonds, typically in the cis configuration.

Omega-3 ($\omega\text{-}3$) Fatty Acids

Polyunsaturated fatty acids having their first carbon-carbon double bond located at the third carbon counting from the methyl ($\omega$) terminal end, such as $\alpha$-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).

Saponification

The alkaline hydrolysis of neutral fats (triacylglycerols) with sodium or potassium hydroxide to yield glycerol and the alkali metal salts of fatty acids (soaps).

Iodine Value

The number of grams of iodine absorbed by $100\,\text{g}$ of a fat or oil, serving as a quantitative measure of the degree of unsaturation.

Rancidity

The spoilage of natural fats and oils characterized by unpleasant odor and taste resulting from oxidation of unsaturated fatty acid double bonds and partial hydrolysis liberating free fatty acids.

Triacylglycerols (Triglycerides)

Neutral, hydrophobic storage lipids consisting of three fatty acids linked via ester bonds to the three hydroxyl groups of a single glycerol molecule.

Glycerophospholipid

A major membrane lipid composed of sn-glycerol 3-phosphate esterified with two fatty acid chains at C-1 and C-2 and a polar head group attached via a phosphodiester bond at C-3.

Ceramide

The structural parent molecule of all sphingolipids, formed when a long-chain fatty acid is joined in an amide linkage to the C-2 amino group of the amino alcohol sphingosine.

Sphingomyelin

A subclass of sphingolipids possessing a phosphocholine or phosphoethanolamine polar head group attached to ceramide, prominently localized in the myelin sheath of neurons.

Gangliosides

Complex glycosphingolipids containing an oligosaccharide head group with one or more terminal residues of sialic acid ($N\text{-acetylneuraminic}$ acid), which confers a net negative charge at pH 7.

Cholesterol

The principal sterol ($C_{27}H_{45}OH$) in animal tissues, possessing a fused cyclopentanoperhydrophenanthrene four-ring core, an $\text{--OH}$ group at C-3, a double bond at C-5/C-6, two methyl groups at C-10 and C-13, and an 8-carbon branched chain at C-17.

Eicosanoids

Potent 20-carbon paracrine signaling lipids derived enzymatically from membrane arachidonic acid ($20:4(\Delta^{5,8,11,14})$), categorized into prostaglandins, thromboxanes, and leukotrienes.

Thromboxanes

A class of eicosanoids produced by platelets that induce vasoconstriction and promote platelet aggregation during blood clotting, synthesized via cyclooxygenase ($\text{COX}$).

Leukotrienes

A class of eicosanoids first identified in leukocytes that mediate inflammatory and allergic responses, inducing potent contraction of airway smooth muscles during asthma and anaphylaxis.

Tocopherols (Vitamin E)

A group of fat-soluble isoprenoid lipids containing an aromatic ring that functions as a biological antioxidant by scavenging reactive free radicals and protecting membrane lipids from oxidation.

Dolichols

Long-chain isoprenoid alcohols that anchor and activate oligosaccharide precursors to biological membranes during the biosynthesis of glycoproteins and bacterial cell wall components.