Biochemistry: Fundamentals of Life, Water, Carbon, Carbohydrates, and Lipids

Comprehensive practice flashcards reviewing core biochemical principles from Unit 1: bioelements, chemical bonding, properties of water, buffer systems and pH regulation, carbon stereochemistry, and the structure and function of carbohydrates and lipids.

Primary Bioelements

The chemical elements ($C$, $H$, $O$, and $N$) that constitute roughly $96\%$ of the human body and form the structural basis of carbohydrates, lipids, proteins, and nucleic acids.

Secondary Bioelements

Essential mineral elements ($Ca$, $Na$, $K$, $Cl$, $Mg$, $P$, and $S$) responsible for osmotic regulation, nerve impulse conduction, bone composition, and teeth mineralization.

Trace Elements (Oligoelements)

Elements required in minute quantities (less than $1.0\%$ of body mass)—including $Fe$, $I$, $Cu$, $Zn$, $Mn$, $Co$, and $Mo$—whose deficiency causes malnutrition, anemia, and metabolic disorders.

Positron Emission Tomography (PET)

A diagnostic imaging technique that injects radioactive glucose to identify metabolically active tissues, revealing tumor sites as visible hot spots due to their high glucose consumption.

Valence Shell

The outermost electron shell of an atom that determines its chemical reactivity and propensity to form bonds.

Octet Rule

The chemical principle that atoms gain chemical stability when they share, gain, or lose electrons to attain a full outer valence shell of $8$ electrons.

Reduction

A chemical process characterized by the gain of electrons, gain of hydrogen atoms, loss of oxygen atoms, and an acquisition of energy.

Oxidation

A chemical process characterized by the loss of electrons, loss of hydrogen atoms, gain of oxygen atoms, and a release of energy.

Ionic Bond

A chemical bond formed by the electrostatic attraction between oppositely charged ions resulting from the transfer of electrons from a metal to a non-metal.

Polar Covalent Bond

A covalent bond formed between atoms with different electronegativities, leading to an unequal sharing of electrons and the creation of partial charges ($\delta^+$ and $\delta^-$).

Nonpolar Covalent Bond

A covalent linkage where electron pairs are shared equally between atoms of identical or very similar electronegativity, producing no permanent partial charges.

Hydrogen Bond

A weak intermolecular electrostatic attraction between an electropositive hydrogen atom ($\delta^+$) covalently bonded to an electronegative atom and an adjacent electronegative atom ($O$ or $N$).

High Specific Heat Capacity of Water

The property of water that requires a large amount of thermal energy to change its temperature by $1\,^\circ\text{C}$, helping living organisms maintain a stable internal temperature.

High Heat of Vaporization of Water

The property requiring substantial energy to break intermolecular hydrogen bonds and vaporize water, serving as a cooling mechanism via perspiration.

Capillary Action

The spontaneous movement of water upward inside a narrow tube, which occurs when the adhesive forces between water and the container wall overcome internal cohesive forces.

Dehydration Synthesis

A chemical reaction that links two monomers by removing an $-OH$ group from one and an $-H$ from the other to form a covalent bond while releasing a molecule of $H_2O$.

Hydrolysis

A cleavage reaction where the addition of an $H_2O$ molecule breaks a covalent bond between two subunits, restoring an $-OH$ to one and an $-H$ to the other.

Buffer System

A solution consisting of a weak acid and its conjugate base (or a weak base and its conjugate acid) that minimizes shifts in $pH$ upon the addition of acidic or basic substances.

Bicarbonate Buffer System

The primary extracellular buffer system in blood plasma operating via the equilibrium $H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$, physiologically integrated with the lungs and kidneys.

Acidosis

A clinical state where arterial blood $pH$ drops below $7.35$, classified as respiratory (caused by $CO_2$ retention from hypoventilation) or metabolic (caused by acid accumulation or bicarbonate loss).

Alkalosis

A clinical state where arterial blood $pH$ exceeds $7.45$, classified as respiratory (from excessive $CO_2$ loss during hyperventilation) or metabolic (from excess base or loss of gastric acid).

Diabetic Ketoacidosis (DKA)

A severe form of metabolic acidosis resulting from uncontrolled diabetes where cells metabolize fatty acids instead of glucose, producing acidic ketone bodies and prompting rapid Kussmaul respirations.

Osmosis

The movement of water across a semipermeable membrane from a region of lower solute concentration (hypotonic) toward a region of higher solute concentration (hypertonic).

Dialysis

The separation of small dissolved crystalloid solutes from large colloidal molecules across a selectively permeable membrane, medically modeled in hemodialysis.

Tetravalence of Carbon

The characteristic of carbon possessing four valence electrons that enables it to establish four stable covalent bonds in a three-dimensional tetrahedral geometry with angles of $109.5^\circ$.

Structural Isomers

Molecules that share the identical molecular formula but possess different covalent bonding arrangements and atom connections (e.g., butane and isobutane).

Geometric Isomers

Isomers whose atoms share the same connectivity but differ in spatial orientation around a rigid, non-rotating double bond, designated as cis (same side) or trans (opposite sides).

Enantiomers

Pairs of stereoisomeric molecules that are non-superimposable mirror images of one another around an asymmetric carbon, designated as D- and L-isomers.

Asymmetric Carbon

A carbon atom covalently bonded to four chemically distinct atoms or functional groups, creating chirality in an organic molecule.

Hydroxyl Group

A polar functional group consisting of $-OH$ that confers water solubility and characterizes alcohols and carbohydrates.

Carbonyl Group

A polar functional group with a carbon-oxygen double bond ($-C=O$), found as a terminal group in aldehydes and internally within ketones.

Carboxyl Group

An acidic functional group ($-COOH$) capable of releasing an $H^+$ ion into solution, characteristic of amino acids and fatty acids.

Amino Group

A basic nitrogen-containing functional group ($-NH_2$) capable of accepting an $H^+$ ion from solution, found in amino acids.

Phosphate Group

A negatively charged, polar functional group ($-PO_4^{2-}$) essential for energy transfer in $ATP$ and forming the structural backbone of nucleic acids.

Sulfhydryl Group

A functional group ($-SH$) found in the amino acid cysteine that forms covalent disulfide bridges to stabilize protein tertiary structures.

Anabolism

The metabolic pathway involving the synthesis of complex biomolecules from simpler precursors, requiring an input of energy in the form of $ATP$.

Catabolism

The metabolic pathway involving the breakdown of complex organic molecules into simpler compounds, yielding energy that is captured as $ATP$.

Adenosine Triphosphate (ATP)

The universal chemical energy currency of cells, composed of adenine, ribose, and three phosphate groups linked by high-energy phosphoanhydride bonds.

Monosaccharide

A simple sugar with the general formula $(CH_2O)_n$ containing $3$ to $7$ carbon atoms that cannot be hydrolyzed into smaller carbohydrate molecules.

Aldose

A monosaccharide featuring a carbonyl group located at the terminus of its carbon chain as an aldehyde (e.g., glyceraldehyde, ribose, glucose, and galactose).

Ketose

A monosaccharide containing an internal carbonyl group as a ketone (e.g., dihydroxyacetone, ribulose, and fructose).

Anomeric Carbon

The new asymmetric center created at the former carbonyl carbon when an open-chain monosaccharide undergoes cyclization to form a ring.

Mutarotation

The spontaneous interconversion between $\alpha$ and $\beta$ anomeric forms of a cyclic monosaccharide in aqueous solution until a dynamic equilibrium is reached.

Fehling's Test

A chemical assay used to identify reducing sugars, in which free carbonyl groups reduce blue cupric ions ($Cu^{2+}$) to form a brick-red precipitate of cuprous oxide ($Cu_2O$).

O-Glycosidic Bond

A covalent ether bond linking two monosaccharide units via a condensation reaction between an anomeric hydroxyl and another hydroxyl group.

Maltose

A reducing disaccharide formed by two glucose molecules joined via an $\alpha\text{-1,4-glycosidic}$ bond, produced during starch hydrolysis.

Sucrose

A non-reducing disaccharide composed of glucose and fructose joined by an $\alpha\text{-1,2-glycosidic}$ bond that locks both anomeric carbons.

Lactose

A reducing disaccharide found in milk composed of galactose and glucose joined by a $\beta\text{-1,4-glycosidic}$ bond, digested by the enzyme lactase.

Cellobiose

A disaccharide composed of two glucose molecules joined by a $\beta\text{-1,4-glycosidic}$ bond, produced by cellulose hydrolysis and indigestible by humans.

Starch

The primary storage polysaccharide in plant tissues, composed of a blend of unbranched helical amylose and branched amylopectin.

Amylose

The unbranched component of starch ($20\text{--}30\%$) consisting of $\alpha\text{-D-glucose}$ units connected exclusively by $\alpha\text{-1,4-glycosidic}$ bonds.

Amylopectin

The branched fraction of starch ($70\text{--}80\%$) composed of linear $\alpha\text{-1,4-glycosidic}$ chains with $\alpha\text{-1,6-glycosidic}$ branches occurring every $24\text{--}30$ glucose residues.

Glycogen

The major glucose storage homopolysaccharide in animals and fungi, structurally analogous to amylopectin but more extensively branched every $8\text{--}12$ residues.

Cellulose

An unbranched structural homopolysaccharide of plant cell walls composed of $\beta\text{-D-glucose}$ units joined by $\beta\text{-1,4-glycosidic}$ bonds that form rigid microfibrils.

Chitin

A structural nitrogenous polysaccharide consisting of $N\text{-acetyl-}\beta\text{-D-glucosamine}$ residues joined by $\beta\text{-1,4}$ linkages, forming arthropod exoskeletons and fungal cell walls.

Saponifiable Lipids

Lipids containing fatty acid residues linked by ester bonds (e.g., acylglycerols, phospholipids, and waxes) that undergo alkaline hydrolysis to form soaps.

Insaponifiable Lipids

Lipids lacking fatty acids in their molecular structure (e.g., steroids and isoprenoids) that do not undergo saponification.

Esterification

The condensation reaction between the carboxyl group ($-COOH$) of a fatty acid and a hydroxyl group ($-OH$) of an alcohol to produce an ester linkage and water.

Saponification

The alkaline hydrolysis of fat or oil esters with a strong base ($NaOH$ or $KOH$), producing free glycerol and fatty acid salts (soaps).

Saturated Fatty Acid

A hydrocarbon carboxylic acid lacking double bonds whose straight chains pack closely via Van der Waals interactions, resulting in a solid state at room temperature.

Unsaturated Fatty Acid

A fatty acid possessing one or more double bonds ($C=C$); cis configurations introduce bends that hinder molecular packing and lower the melting point.

Omega-3 Fatty Acids

Essential polyunsaturated fatty acids possessing their first double bond at the third carbon from the terminal methyl ($\omega$) group, known to lower blood pressure, reduce inflammation, and prevent cardiovascular disease.

Triacylglycerols (Triglycerides)

Neutral lipids composed of a glycerol molecule esterified to three fatty acids that serve as the main long-term metabolic energy reserve, releasing roughly $9.4\,\text{kcal/g}$.

Waxes (Ceres)

Saponifiable lipids formed by the esterification of a long-chain fatty acid with a high molecular weight monohydroxy alcohol, providing waterproofing on plants, animal fur, and insect cuticles.

Phospholipids

Amphipathic membrane lipids consisting of a glycerol molecule linked to two fatty acid tails and a phosphate headgroup, spontaneously forming the lipid bilayer of cellular membranes.

Sphingomyelin

A phosphosphingolipid composed of sphingosine, a fatty acid, a phosphate group, and choline, serving as a primary electrical insulator in the myelin sheaths produced by Schwann cells around neuronal axons.

Steroids

Insaponifiable lipids characterized by a core framework of four fused carbon rings known as cyclopentanoperhydrophenanthrene (sterane).

Cholesterol

The most abundant animal steroid, which modulates plasma membrane fluidity and serves as the precursor for steroid hormones, vitamin D, and bile salts.

Atherosclerosis

A progressive cardiovascular disease characterized by the buildup of cholesterol-rich plaques inside arterial walls, progressively narrowing the vascular lumen.

Low-Density Lipoprotein (LDL)

A lipoprotein carrier that transports cholesterol from the liver to peripheral tissues; high levels promote arterial plaque formation, giving it the designation bad cholesterol.

High-Density Lipoprotein (HDL)

A lipoprotein carrier that gathers excess cholesterol from peripheral tissues and arteries and transports it back to the liver for excretion, reducing cardiovascular risk.

Familial Hypercholesterolemia (FH)

An inherited genetic disorder affecting approximately $1$ in $250$ individuals, caused by mutations in the LDL receptor gene that impair hepatic LDL clearance and cause severe early-onset cardiovascular disease.

Calcitriol

The biologically active form of vitamin D ($1,25(OH)_2D$) synthesized in the kidneys, which stimulates calcium and phosphate absorption in the intestine and reabsorption in the kidneys.

Bile Acids

Steroid derivatives produced in the liver from cholesterol that act as biological detergents to emulsify dietary lipids in the small intestine, facilitating digestion by lipases.

Anabolic Steroids

Synthetic derivatives of testosterone that stimulate protein synthesis and muscle growth, whose non-medical abuse causes adverse effects such as liver damage, testicular atrophy, and elevated LDL levels.

Isoprenoids (Terpenes)

Insaponifiable lipids formed by polymerized 5-carbon isoprene units ($C_5H_8$), giving rise to essential plant oils, photosynthetic pigments (carotenoids), and fat-soluble vitamins (A, E, and K).