Biochem 1 Midterm Logan University

What does biochemistry primarily study?

The chemistry of living organisms. Biochemistry explains life through molecular structures, reactions, and energy transformations.:

What are valence electrons?

Electrons in the outermost occupied shell. Valence electrons largely determine an atom's bonding behavior.:

What best defines electronegativity?

An atom's attraction for shared electrons. Unequal attraction for shared electrons produces bond polarity.:

Which description best represents the formation of NaCl?

Electron transfer followed by attraction between opposite ions. Sodium loses an electron and chlorine gains one; the resulting ions attract electrostatically.:

Why is an O to H bond in water polar covalent?

Oxygen attracts the shared electrons more strongly. Oxygen is partially negative and hydrogen is partially positive.:

What interaction holds separate water molecules together?

Hydrogen bonds. Hydrogen bonds occur between molecules; covalent O to H bonds occur within a water molecule.:

Why does water dissolve many salts effectively?

It forms hydration shells around ions through ion dipole interactions. Water's partial charges orient around cations and anions and stabilize them in solution.:

Which example best illustrates cohesion?

Water molecules attracting other water molecules. Cohesion is attraction among molecules of the same substance.:

Which example best illustrates adhesion?

Water attracting a glass surface. Adhesion is attraction between different substances and contributes to capillary action.:

What mainly explains water's high surface tension?

Cohesive hydrogen bonding at its surface. Surface water molecules experience cohesive forces that resist surface disruption.:

Why does water help stabilize body temperature?

Its high specific heat limits temperature changes during heat transfer. Hydrogen bonding contributes to water's high specific heat.:

Why does evaporating sweat cool the body?

Evaporation absorbs substantial heat from the skin. Water's high heat of vaporization makes evaporation an effective cooling mechanism.:

Why do nonpolar molecules tend to cluster in water?

Clustering reduces nonpolar surface exposed to water. The hydrophobic effect contributes to membrane formation and protein folding.:

Which force can occur between all atoms and molecules?

London dispersion forces. Transient fluctuations in electron distribution produce dispersion attractions.:

What happens during dehydration synthesis?

Building blocks join while water is released. Dehydration reactions build larger molecules from smaller units.:

What happens during hydrolysis?

Water is used to break a covalent linkage. Digestive hydrolysis helps break macromolecules into absorbable components.:

Which pairing is correct for carbohydrates?

Monosaccharides joined by glycosidic bonds. Carbohydrates include glucose, glycogen, starch, and cellulose.:

Which pairing is correct for proteins?

Amino acids joined by peptide bonds. Protein sequence and folding support catalysis, transport, signaling, and structure.:

What are the three components of a nucleotide?

A pentose sugar, a phosphate group, and a nitrogenous base. Nucleotides form nucleic acids and also participate in energy transfer and signaling.:

Which bonds link adjacent nucleotides within a DNA strand?

Phosphodiester bonds. Hydrogen bonds connect complementary bases across the two strands.:

What is a triglyceride composed of?

Glycerol and three fatty acids linked by ester bonds. Triglycerides serve as concentrated long term energy stores.:

Why do phospholipids form bilayers in water?

They have hydrophilic heads and hydrophobic tails. Amphipathic structure allows membranes to separate aqueous compartments.:

Which pair consists of major human energy stores?

Glycogen and triglycerides. Glycogen stores carbohydrate, whereas triglycerides store large amounts of energy in fat.:

What distinguishes structural isomers from stereoisomers?

Structural isomers differ in connectivity; stereoisomers differ in spatial arrangement. Isomers share a molecular formula but differ in connectivity or arrangement.:

What makes a tetrahedral carbon chiral?

It is attached to four different groups. A chiral center can generate stereoisomers that differ in biological interactions.:

Why is D glycine not a valid stereochemical designation?

Glycine is achiral because its alpha carbon has two hydrogen atoms. D and L configurations cannot be assigned to achiral glycine.:

Which stereochemical statement is most accurate?

Proteins predominantly contain L amino acids; many common metabolic sugars are D sugars. D/L describe configuration relative to glyceraldehyde, not the sign of optical rotation.:

What determines an amino acid's side chain classification?

The chemical properties of its R group. The R group determines polarity, charge, and many folding interactions.:

Which group contains the acidic amino acids?

Aspartate and glutamate. Their side chains are usually negatively charged near physiological pH.:

Which group contains the basic amino acids?

Lysine, arginine, and histidine. Histidine is often mostly uncharged near physiological pH but can readily accept or donate protons.:

Which amino acid is aromatic and usually classified as nonpolar?

Tryptophan. Tryptophan has an aromatic side chain and is generally grouped with nonpolar amino acids.:

Which amino acid forms disulfide bonds?

Cysteine. Oxidation of two cysteine thiol groups can form a covalent disulfide bond.:

Why does proline often disrupt an alpha helix?

Its rigid ring restricts the backbone and its internal peptide nitrogen lacks an H donor. Proline is conformationally restricted and commonly occurs in turns.:

Which statement best defines an essential amino acid?

The body cannot synthesize enough to meet needs, so dietary intake is required. Nonessential amino acids can normally be synthesized adequately; some become conditionally essential.:

What is the predominant form of a nonpolar amino acid at its isoelectric point?

A zwitterion with zero net charge. The amino group is positively charged and the carboxylate is negatively charged; the charges balance.:

What defines protein primary structure?

The amino acid sequence. Peptide bonds connect the amino acids in a specific sequence.:

What mainly stabilizes alpha helices and beta sheets?

Hydrogen bonds between backbone groups. Secondary structure relies on hydrogen bonding involving backbone C=O and N H groups.:

What defines protein tertiary structure?

The overall three dimensional structure of one polypeptide. Side chain interactions and the hydrophobic effect help stabilize the fold.:

Which protein has quaternary structure?

A protein composed of multiple interacting polypeptide subunits. Quaternary structure describes the arrangement of multiple polypeptide chains.:

Which change usually occurs during protein denaturation?

Loss of native higher order structure and often function. Heat or extreme pH can disrupt folding without usually changing the primary sequence.:

What is a major function of molecular chaperones?

Helping proteins fold and limiting inappropriate aggregation. Chaperones assist folding but do not replace the information encoded in primary sequence.:

Which statement correctly expresses the first law of thermodynamics?

Energy is conserved but can be transferred or transformed. Cells transform chemical energy rather than creating or destroying energy.:

Which statement correctly expresses the second law of thermodynamics?

A spontaneous process increases the total entropy of the system plus surroundings. Local biological order can increase while the total entropy of the universe increases.:

Which equation defines Gibbs free energy change at constant temperature?

Delta G = Delta H minus T Delta S. Temperature must be in kelvin and energy units must be consistent.:

What does a negative Delta G indicate?

The forward reaction is thermodynamically favorable under the stated conditions. Spontaneity predicts thermodynamic direction, not reaction speed.:

Which sign combination favors a reaction at all positive temperatures?

Negative Delta H and positive Delta S. Both terms make Delta G negative when Delta H is negative and Delta S is positive.:

For Delta H = +20 kJ/mol and Delta S = +0.10 kJ/(mol K), what is Delta G at 300 K?

negative 10 kJ/mol. Delta G = 20 minus (300 x 0.10) = negative 10 kJ/mol.:

A forward reaction has Delta H = +420 kJ/mol. What is Delta H for the reverse reaction?

negative 420 kJ/mol. Reversing a reaction reverses the sign of its enthalpy change.:

What changes when an enzyme catalyzes a reaction?

The activation energy decreases. Catalysts speed approach to equilibrium without changing Delta G or the equilibrium constant.:

Which statement correctly describes oxidation?

Loss of electrons. LEO means loss of electrons is oxidation; GER means gain of electrons is reduction.:

In A + B becoming oxidized A + reduced B, what is A's role?

Electron donor and reducing agent. The electron donor is oxidized and reduces the electron acceptor.:

What happens when NAD+ becomes NADH?

NAD+ is reduced. NAD+ accepts a hydride equivalent and carries reducing equivalents as NADH.:

What is ATP composed of?

Adenine, ribose, and three phosphate groups. ATP is a nucleotide used for energy transfer and phosphate transfer.:

Why can ATP hydrolysis drive an endergonic process?

Coupling can make the total Delta G negative. ATP hydrolysis is favorable overall because its products are more stabilized; bond breaking itself requires energy.:

A process has Delta G = +12 kJ/mol and a coupled process has Delta G = negative 30 kJ/mol. What is the total Delta G?

negative 18 kJ/mol. For coupled reactions, free energy changes add; +12 + (negative 30) = negative 18.:

What is the pH of a solution with hydrogen ion concentration 1 x 10^(negative 5) M?

5. pH = minus log10[H+], so minus log10(10^(negative 5)) = 5.:

How does hydrogen ion concentration change when pH falls from 7 to 5?

It increases 100 fold. Each decrease of one pH unit corresponds to a tenfold rise in hydrogen ion concentration.:

What distinguishes a weak acid from a strong acid in water?

A weak acid ionizes partially; a strong acid ionizes essentially completely. Acid strength describes extent of ionization, not the amount of acid present.:

What is the main action of a biological buffer?

Accepting or donating H+ to resist pH changes. Buffers have finite capacity and work best near their pKa.:

For a weak acid buffer, what is true when pH equals pKa?

The concentrations of HA and A (negative charge) are equal. Henderson Hasselbalch gives pH = pKa + log10([A (negative charge)]/[HA]).:

If pKa = 6.1 and [A (negative charge)]/[HA] = 10, what is pH?

7.1. pH = 6.1 + log10(10) = 7.1.:

Which buffer pair is central to blood acid base regulation?

Carbonic acid and bicarbonate. CO2, carbonic acid, and bicarbonate participate in a system regulated by lungs and kidneys.:

Why can extreme pH reduce enzyme activity?

It changes group ionization and can disrupt the active site and protein folding. Enzyme catalysis depends on suitable protonation states and a functional three dimensional structure.:

What is a holoenzyme?

An apoenzyme together with its required cofactor. An apoenzyme is the protein component; a coenzyme is an organic type of cofactor.:

For a Michaelis Menten enzyme, what is Km?

The substrate concentration at half Vmax. Km is a kinetic parameter; lower Km often suggests greater apparent substrate affinity under comparable conditions.:

If Vmax = 100 units and [S] = Km, what is reaction velocity?

50 units. v = Vmax[S]/(Km + [S]); when [S] = Km, v = Vmax/2.:

At fixed enzyme concentration, what happens as substrate concentration becomes very high?

Velocity approaches Vmax. Substrate saturation raises velocity toward a fixed Vmax, not the value of Vmax itself.:

Which kinetic pattern indicates competitive inhibition?

Increased apparent Km with unchanged Vmax. Competitive inhibitors compete at the active site and can be overcome by sufficiently high substrate concentration.:

Which kinetic pattern indicates pure noncompetitive inhibition?

Unchanged Km with decreased Vmax. Pure noncompetitive inhibition is a special case of mixed inhibition with equal inhibitor affinity for E and ES.:

What characterizes uncompetitive inhibition?

Binding only ES and decreasing both apparent Km and Vmax. An uncompetitive inhibitor binds the enzyme substrate complex; Km and Vmax decrease by the same factor in the simple model.:

What is specific heat?

The heat required to raise the temperature of a unit mass by one degree.:

What is heat of vaporization?

The heat required to convert a unit amount of liquid into vapor.:

Why is ice less dense than liquid water?

Its hydrogen bonded lattice holds water molecules farther apart, allowing ice to float and insulate water below.:

Why is water not literally a universal solvent?

It dissolves many ionic and polar solutes well but dissolves many nonpolar substances poorly.:

How does water support enzyme activity?

It provides a solvent for substrates and ions, supports folding and molecular movement, and can participate directly in reactions.:

How does water support cellular homeostasis?

It supports transport, temperature control, osmotic balance, and the aqueous conditions required for biochemical reactions.:

How are water's properties used in biotechnology?

Aqueous buffers provide controlled pH and dissolved reactants for enzyme assays and DNA amplification.:

What is a covalent bond?

A bond formed when atoms share electron pairs.:

What is a nonpolar covalent bond?

A bond in which electrons are shared approximately equally.:

What is a dipole dipole interaction?

An attraction between permanent partial charges on polar molecules.:

How do covalent bonds compare with individual hydrogen bonds?

Covalent bonds are generally much stronger; many weak noncovalent interactions together can strongly stabilize a biological structure.:

Are all ionic compounds soluble in water?

No; solubility depends on the balance of lattice stabilization and hydration, among other factors.:

What elements are common in carbohydrates?

Carbon, hydrogen, and oxygen; many simple sugars approximately follow the formula (CH2O)n.:

What elements are common in proteins?

Carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.:

What elements are common in nucleic acids?

Carbon, hydrogen, oxygen, nitrogen, and phosphorus.:

What elements are common in lipids?

Mainly carbon, hydrogen, and oxygen; some also contain phosphorus or nitrogen.:

Are lipids true polymers of one repeating monomer?

Generally no; lipids are a diverse class that includes triglycerides, phospholipids, and steroids.:

What is the major storage carbohydrate in humans?

Glycogen, especially in liver and skeletal muscle.:

What is a structural carbohydrate example?

Cellulose provides structural support in plant cell walls.:

How do saturated and unsaturated fatty acids differ?

Saturated fatty acids lack carbon to carbon double bonds; unsaturated fatty acids contain one or more.:

How do cis double bonds influence membrane fluidity?

They kink fatty acid chains and reduce tight packing, generally increasing fluidity at the same temperature.:

What are steroids structurally characterized by?

Four fused carbon rings; cholesterol is an example and a precursor of steroid hormones.:

How do DNA and RNA sugars differ?

DNA contains deoxyribose; RNA contains ribose with a hydroxyl group at the 2 prime carbon.:

What base pairing occurs in DNA?

Adenine pairs with thymine through two hydrogen bonds; guanine pairs with cytosine through three.:

What distinguishes a nucleoside from a nucleotide?

A nucleoside contains a sugar and base; a nucleotide also contains phosphate.:

What are enantiomers?

Nonsuperimposable mirror image stereoisomers.:

Do D and L labels specify optical rotation direction?

No; they specify relative configuration, not whether rotation is clockwise or counterclockwise.:

Can L glucose exist?

Yes; it is a possible stereoisomer, although D glucose is the predominant form used in human metabolism.:

What four groups attach to the alpha carbon of a typical amino acid?

An amino group, a carboxyl group, a hydrogen atom, and an R group.:

Which amino acids are usually classified as nonpolar?

Glycine, alanine, valine, leucine, isoleucine, methionine, proline, phenylalanine, and tryptophan.: