Biochemistry BM1

Water

What is the most abundant chemical component of the human body and the major solvent for biochemical reactions?

Hydrogen bonding

What type of noncovalent interaction accounts for many of water's unique physical properties?

Hydrophobic interactions

What force drives nonpolar molecules to aggregate in aqueous environments?

Hydrophilic substances

What substances interact readily with water and are generally polar or charged?

Amphipathic molecules

What molecules contain both hydrophilic and hydrophobic regions?

pH

What is the negative logarithm of the hydrogen ion concentration?

Henderson-Hasselbalch equation

What equation relates pH to pKa and the concentrations of a weak acid and its conjugate base?

pKa

What is the pH at which a weak acid is 50% dissociated?

Buffer

What system resists changes in pH when acid or base is added?

Bicarbonate buffer system

What is the principal extracellular buffer system in blood?

Phosphate buffer system

What buffer is particularly important in intracellular fluid and renal tubular fluid?

Histidine

Which amino acid residue is especially important in protein buffering because its side-chain pKa is near physiologic pH?

Metabolic acidosis

What acid-base disorder is characterized by decreased blood pH and decreased bicarbonate?

Metabolic alkalosis

What acid-base disorder is characterized by increased blood pH and increased bicarbonate?

Respiratory acidosis

What acid-base disorder results primarily from CO2 retention?

Respiratory alkalosis

What acid-base disorder results primarily from excessive CO2 loss?

Isoelectric point

What is the pH at which an amino acid or protein has no net electrical charge?

Amino acids

What compounds contain both amino and carboxyl groups and serve as the building blocks of proteins?

Zwitterion

What form of an amino acid contains both positively and negatively charged groups but has a net charge of zero?

Peptide bond

What covalent bond links amino acids together in proteins?

Essential amino acids

What amino acids cannot be synthesized adequately by humans and must be obtained from the diet?

Nonessential amino acids

What amino acids can generally be synthesized in sufficient amounts by the body?

Branched-chain amino acids

Which three essential amino acids are leucine, isoleucine, and valine?

Aromatic amino acids

Which amino acids contain aromatic rings and include phenylalanine, tyrosine, and tryptophan?

Sulfur-containing amino acids

Which amino acids contain sulfur and include cysteine and methionine?

Basic amino acids

Which amino acids have positively charged side chains at physiologic pH?

Acidic amino acids

Which amino acids have negatively charged side chains at physiologic pH?

Cysteine

Which amino acid forms disulfide bonds that stabilize many extracellular proteins?

Methionine

Which amino acid commonly serves as the initiating amino acid during protein synthesis?

Glycine

Which amino acid has the smallest side chain and provides exceptional conformational flexibility?

Proline

Which amino acid has a cyclic structure that restricts rotation around its peptide bond?

Phenylalanine hydroxylase deficiency

A child develops intellectual disability, seizures, eczema, and a musty body odor. What biochemical defect causes this disorder?

Phenylketonuria

What inherited disorder results from impaired conversion of phenylalanine to tyrosine?

Tyrosine

Which amino acid becomes conditionally essential in phenylketonuria?

Alkaptonuria

A patient develops dark urine on standing and ochronosis. Deficiency of which enzyme causes this disorder?

Homogentisate oxidase deficiency

What enzyme defect causes alkaptonuria?

Primary structure

What level of protein structure refers to the linear sequence of amino acids?

Secondary structure

What level of protein structure includes α-helices and β-sheets?

Tertiary structure

What level of protein structure describes the three-dimensional folding of a single polypeptide chain?

Quaternary structure

What level of protein structure describes the association of multiple polypeptide subunits?

Alpha helix

What protein secondary structure is stabilized primarily by hydrogen bonds between backbone peptide groups?

Beta sheet

What protein secondary structure consists of extended polypeptide strands stabilized by hydrogen bonding?

Disulfide bond

What covalent interaction between cysteine residues helps stabilize protein structure?

Hydrophobic interactions

What interactions between nonpolar side chains contribute strongly to protein folding?

Denaturation

What process disrupts a protein's higher-order structure without necessarily breaking its peptide bonds?

Chaperones

What proteins assist newly synthesized or damaged proteins in achieving proper folding?

Collagen

What structural protein is the major component of connective tissue and has a characteristic triple-helical structure?

Glycine-X-Y sequence

What repeating sequence is characteristic of collagen, with glycine occurring every third residue?

Proline hydroxylation

What posttranslational modification is important for stabilizing the collagen triple helix?

Vitamin C

Deficiency of which vitamin impairs hydroxylation of proline and lysine in collagen?

Scurvy

A patient has bleeding gums, poor wound healing, and petechiae. What deficiency is most likely responsible?

Keratin

What fibrous protein is a major structural component of hair, skin, and nails?

Sickle cell disease

A patient has chronic hemolytic anemia caused by a single amino acid substitution in the β-globin chain. What disorder is present?

Valine

Which amino acid replaces glutamate at position 6 of β-globin in sickle cell disease?

Hemoglobin S

What abnormal hemoglobin results from the β-globin Glu6Val mutation?

Myoglobin

What monomeric heme protein in muscle stores oxygen and has a higher oxygen affinity than hemoglobin?

Hemoglobin

What tetrameric protein transports oxygen from the lungs to peripheral tissues?

Heme

What prosthetic group allows hemoglobin and myoglobin to reversibly bind oxygen?

Cooperative binding

What property causes hemoglobin's oxygen-binding curve to be sigmoidal?

Bohr effect

What phenomenon describes decreased hemoglobin oxygen affinity caused by increased CO2 and H+ concentration?

2,3-Bisphosphoglycerate

What erythrocyte metabolite decreases hemoglobin's affinity for oxygen and facilitates oxygen delivery to tissues?

Fetal hemoglobin

What form of hemoglobin has greater oxygen affinity than adult hemoglobin?

Hemoglobin F

What hemoglobin predominates during fetal life and consists of α2γ2 subunits?

Methemoglobin

What form of hemoglobin contains Fe3+ and cannot effectively bind oxygen?

Methemoglobinemia

A patient develops cyanosis despite normal arterial oxygen tension after exposure to an oxidizing drug. What condition is likely?

Competitive inhibition

What type of enzyme inhibition increases apparent Km without changing Vmax?

Noncompetitive inhibition

What type of inhibition decreases Vmax without changing Km in the idealized pure form?

Uncompetitive inhibition

What type of inhibition decreases both Km and Vmax?

Michaelis-Menten equation

What equation describes the relationship between substrate concentration and reaction velocity for many enzymes?

Km

What kinetic constant corresponds to the substrate concentration at half Vmax?

Vmax

What is the maximum reaction velocity achieved when an enzyme is saturated with substrate?

Turnover number

What parameter represents the number of substrate molecules converted to product per enzyme molecule per unit time at saturation?

Allosteric enzyme

What enzyme changes activity when an effector binds at a site distinct from the active site?

Isoenzyme

What is an enzyme variant that catalyzes the same reaction but differs in molecular or tissue properties?

Lactate dehydrogenase

Which enzyme exists as five isoenzymes formed from combinations of H and M subunits?

Enzyme-linked immunosorbent assay

What technique uses enzyme-linked antibodies to detect and quantify specific molecules?

Iron

Which transition metal is essential for hemoglobin, myoglobin, and many electron-transfer proteins?

Copper

Which transition metal is required for cytochrome c oxidase and several enzymes involved in connective tissue formation?

Zinc

Which transition metal serves as a catalytic or structural component of many enzymes, including carbonic anhydrase?

Selenium

Which trace element is incorporated into selenocysteine and is important for glutathione peroxidase?

Manganese

Which transition metal serves as a cofactor for mitochondrial superoxide dismutase?

Wilson disease

A young patient has liver disease, neurologic symptoms, and Kayser-Fleischer rings. What disorder causes abnormal copper accumulation?

ATP

What high-energy nucleotide serves as the major immediate energy currency of cells?

Phosphoanhydride bonds

What bonds in ATP are commonly described as high-energy because their hydrolysis has a large negative free-energy change?

Free energy

What thermodynamic quantity determines whether a biochemical reaction is energetically favorable?

Oxidation-reduction reaction

What type of reaction involves transfer of electrons between molecules?

NAD+

What major electron carrier accepts a hydride ion during many oxidation reactions?

FAD

What flavin coenzyme can accept two hydrogen atoms during oxidation-reduction reactions?

Carbohydrates

What class of biomolecules includes glucose, fructose, galactose, and glycogen?

Monosaccharide

What is the simplest carbohydrate unit that cannot be hydrolyzed into smaller carbohydrates?

Glucose

What six-carbon monosaccharide is the major circulating blood sugar and a central metabolic fuel?

Fructose

What ketohexose is found in fruits, honey, and sucrose?

Galactose

What hexose combines with glucose to form lactose?

Ribose

What five-carbon sugar is present in RNA and many nucleotides?

Deoxyribose

What five-carbon sugar is present in DNA?

Disaccharide

What carbohydrate consists of two monosaccharides linked by a glycosidic bond?

Sucrose

What disaccharide consists of glucose and fructose?

Lactose

What disaccharide consists of glucose and galactose?

Maltose

What disaccharide consists of two glucose molecules linked by an α(1→4) bond?

Glycogen

What highly branched glucose polymer serves as the major storage carbohydrate in animals?