Biochem Exam 1 Review

How does the chemical structure of water explain its unique properties?

Water has two O–H bonds and two lone pairs on oxygen, giving it a bent shape with a bond angle of about 104.5°. Oxygen is more electronegative than hydrogen, so oxygen has a partial negative charge and the hydrogens have partial positive charges. This makes water polar and allows water molecules to form hydrogen bonds with each other. These hydrogen bonds contribute to properties such as water’s high boiling point, high melting point, high heat of vaporization, and cohesive behavior.

What is hydrogen bonding, and how can you identify hydrogen-bond donors and acceptors in biomolecules?

A hydrogen bond forms between a hydrogen-bond donor and a hydrogen-bond acceptor. A donor usually contains a hydrogen covalently bonded to an electronegative atom, such as O–H or N–H. An acceptor is usually an electronegative atom, such as oxygen or nitrogen, that has an available lone pair. The strength of a hydrogen bond also depends on the positioning of the atoms and the surrounding environment.

Why is water called the “solvent of life,” and how do polar, nonpolar, and amphipathic molecules interact differently with water?

Water is called the solvent of life because biological molecules and cellular processes operate mainly in an aqueous environment. Polar and charged molecules are hydrophilic and can interact favorably with water through hydrogen bonding or ionic-dipole interactions. Nonpolar molecules are hydrophobic and cannot form favorable interactions with water. Amphipathic molecules contain both polar and nonpolar regions, so their polar regions interact with water while their nonpolar regions tend to group together away from water. This behavior is important for the organization of proteins, membranes, and lipids.

What are the major weak interactions in biological systems, and how do their relative strengths contribute to biological organization?

Important noncovalent interactions include ionic interactions, hydrogen bonds, and van der Waals interactions. These interactions are much weaker individually than covalent bonds, but many weak interactions acting together can strongly stabilize biological structures. Ionic interactions involve charged groups, hydrogen bonds involve donors and acceptors, and van der Waals interactions result from temporary or induced dipoles between nearby atoms. Weak interactions are important because they provide both stability and flexibility to biomolecules.

What is the hydrophobic effect, and why do hydrophobic molecules self-segregate in water?

Hydrophobic molecules cannot interact favorably with water through hydrogen bonding. Water molecules therefore become more ordered around exposed hydrophobic surfaces, forming cage-like arrangements called clathrate. This ordering decreases the entropy of water. When hydrophobic molecules cluster together, less nonpolar surface is exposed to water, fewer water molecules need to remain highly ordered, and the entropy of the surrounding water increases. This tendency of hydrophobic molecules to associate and minimize contact with water is called the hydrophobic effect.

What acid-base concepts are important for understanding weak-acid dissociation?

An acid donates a proton, while a base accepts a proton. A weak acid can be represented as HA ⇌ H⁺ + A⁻, where HA is the acid and A⁻ is its conjugate base. Weak acids only partially dissociate in water. Ka describes the tendency of an acid to dissociate, while pKa is related to acid strength. A lower pKa means a stronger acid and a greater tendency to release H⁺. pH reflects the concentration of hydrogen ions in solution, and changes in pH affect the protonation state of biological molecules.

pH > pKa: more base

pH < pKa: more acid

What is the Henderson-Hasselbalch equation, and how is it used in buffer problems?

The Henderson-Hasselbalch equation relates pH, pKa, and the concentrations of a weak acid and its conjugate base:

pH = pKa + log([A⁻]/[HA])

is pH > pKa, the ratio should be greater than 1 which means there is more conjugate base

It can be used to determine the ratio or concentrations of acid and conjugate base needed for a desired pH. Once the required concentrations are found, the amount of each substance can be calculated using molarity, volume, and molecular weight.

What is buffering, and how is the buffering range related to pKa?

A buffer resists large changes in pH when small amounts of acid or base are added. Effective buffering generally occurs within pKa ± 1 because both the protonated and deprotonated forms are present in useful amounts within this range. At pH = pKa, the concentrations of the acid and conjugate base are equal. Buffering is especially important in biological systems because amino acids and proteins contain ionizable groups whose charges depend on pH.

How can you determine the protonation state and charge of a molecule using its pH and pKa values?

Compare the pH of the solution to the pKa of each ionizable group. When pH < pKa, the group tends to remain protonated. When pH > pKa, the group tends to be deprotonated. When pH = pKa, the protonated and deprotonated forms are present in equal amounts. For molecules with several ionizable groups, consider each group separately and follow deprotonation from the lowest pKa to the highest pKa. This allows you to determine the molecule’s predominant form and overall charge at a given pH.

How are amino acids and proteins affected by pH, pKa, and buffering?

Amino acids and proteins contain ionizable functional groups, so their protonation states and charges change as pH changes. Each ionizable group has its own pKa and becomes deprotonated as the pH rises above that pKa. These changes in charge can affect interactions within proteins and between proteins and other molecules. The pH at which a molecule has an overall net charge of zero is called its isoelectric point, or pI.

What are the major ideas that connect water, weak interactions, and biological organization?

Water’s polarity and ability to form hydrogen bonds strongly influence how biomolecules behave. Polar and charged groups interact favorably with water, while nonpolar groups tend to avoid water through the hydrophobic effect. Hydrogen bonds, ionic interactions, van der Waals interactions, and hydrophobic effects work together to organize proteins, lipids, and other biomolecules. Acid-base chemistry also affects biological organization because changes in pH alter the protonation and charge of biomolecules.

What is hierarchical assembly, and how does it relate to biochemistry?

Hierarchical assembly describes how biological systems are built from the bottom up. Small chemical building blocks combine to form macromolecules, macromolecules form supramolecular structures, and these larger structures contribute to subcellular and cellular compartments. The main idea is that the nature of the building blocks determines structure, and structure determines function.

Chemical building blocks -> macromolecules -> supramolecular structures -> subcellular compartments -> cells

What is the relationship between molecular structure and biological function?

The chemical structure of a biomolecule influences its 3-D shape and interactions, and that structure determines what the molecule can do in the cell.

What are the general properties of alcohols, amines, and thiols?

Alcohols are weak acids and can participate in hydrogen bonding. Amines are generally weak bases and good nucleophiles. Thiols are weak acids and can act as nucleophiles.

What are the general properties of carbonyl-containing groups such as aldehydes and ketones?

Their carbonyl carbon is electron-poor, so aldehydes and ketones generally act as electrophiles.

What are the general properties of carboxylic acids and their derivatives?

Carboxylic acids are weak acids. Esters and amides are less reactive derivatives, while thioesters are generally more reactive electrophiles.

Why are functional groups important in biochemistry?

Functional groups control how biomolecules react, what kinds of bonds they form, whether they carry charge, and how they interact with water and other molecules.

Why are weak interactions so important in biochemistry?

Even though each interaction is weak, many weak interactions acting together can strongly stabilize biomolecules and help control folding, binding, recognition, and molecular organization

Why is it important to understand the different energies of chemical bonds and interactions?

Biomolecules depend on a balance between strong and weak interactions. Strong bonds maintain the molecule itself, while weaker interactions allow molecules to fold, associate, separate, and interact in a controlled way.

What is the overall connection between hierarchical assembly, functional groups, chemical bonding, and biological function?

Chemical building blocks contain specific functional groups and form different types of bonds and interactions. These interactions determine how biomolecules assemble and what structure they take, and that structure ultimately determines their biological function

Gibbs free energy

Delta G = Delta H - T Delta S

• ΔG < 0 → reaction is spontaneous/favorable

• ΔG > 0 → reaction is nonspontaneous/unfavorable

• ΔG = 0 → reaction is at equilibrium

ATP hydrolysis releases a lot of free energy because:

The main reasons are:

• Bond Strian elimination : ATP has several negatively charged phosphate groups packed close together. Hydrolysis separates them and reduces that repulsion.

• Resonance stabilization: The products, especially inorganic phosphate can spread their negative charge over several atoms more effectively.

• Better hydration: ADP and Pi interact more favorably with water than ATP does.

• Greater disorder : Hydrolysis produces more separate particles, which generally increases entropy.

• Stabilixation by ionization

All of these reasons lead to a more stable product than ATP

concentration gradients exploited as sources of energy?

Concentration gradients store potential energy because molecules naturally tend to move from high concentration to low concentration.

Cells exploit this by allowing ions or molecules to move down their concentration gradient and coupling that favorable movement to useful work.

For example:

• H⁺ gradient in mitochondria: H⁺ flows back across the inner mitochondrial membrane through ATP synthase, and that energy is used to make ATP.

Oxidation- reduction reaction exploited as sources of energy?

Oxidation-reduction, or redox, reactions involve the transfer of electrons.

• Oxidation = loss of electrons

• Reduction = gain of electrons

• The molecule that loses electrons is the electron donor

• The molecule that gains electrons is the electron acceptor

A useful memory aid is OIL RIG: Oxidation Is Loss, Reduction Is Gain.

Redox reactions can provide energy because electrons tend to move from molecules with lower electron affinity to molecules with higher electron affinity. The difference in their tendency to accept electrons creates an electromotive force (EMF), also called a redox potential difference.

Electron in biological system are transferred by

electron carriers during oxidation-reduction reactions.

Common carriers include NAD⁺/NADH, FAD/FADH₂,

Electrons are often transferred along an electron transport chain, moving from one carrier to another. As they move toward molecules with a greater tendency to accept electrons, energy is released.

That energy can then be used to do cellular work, such as pumping H⁺ across a membrane to create a proton gradient for ATP production.