Chemistry: Biomolecules and Chemical Bonds

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Which of the following is a key structural difference between amylose and amylopectin?

Amylopectin is a simpler form of starch with 1--4 linkages, while amylose has 1--6 linkages.
Amylose contains fructose monomers, while amylopectin contains only glucose monomers.
Amylopectin is a branched polymer with 1--6 linkages, while amylose is unbranched. (correct)
Amylose is found in animals, while amylopectin is found in plants.

What is the primary function of polysaccharides like starch and glycogen?

To store genetic information within cells.
To serve as storage material, providing sugar for cells when hydrolyzed. (correct)
To catalyze biochemical reactions.
To provide structural support in plant cell walls.

How does sucrose contribute to plant physiology?

It is the primary form in which plants transport carbohydrates from leaves to nonphotosynthetic organs. (correct)
It directly provides energy for muscle contraction in plants.
It serves as a building material for cell walls.
It facilitates the storage of glucose within plastids.

Which process allows humans to utilize the glucose stored in plant starch?

Hydrolysis (A) Signup and view all the answers

In what way does glycogen differ from amylopectin?

Glycogen is more extensively branched than amylopectin. (C) Signup and view all the answers

What type of bond is formed when two monosaccharides join to form a disaccharide?

Glycosidic linkage (B) Signup and view all the answers

If a person is lactose intolerant, they have difficulty digesting lactose. What monosaccharides are produced when lactose is broken down during digestion?

Glucose and Galactose (B) Signup and view all the answers

Which of the following lists contain ONLY polysaccharides?

Starch, Glycogen, Cellulose (A) Signup and view all the answers

Which of the following electronegativity differences between two atoms would likely result in a polar covalent bond?

0.6 (C) Signup and view all the answers

What is the primary distinction between a polar covalent bond and an ionic bond?

Polar covalent bonds involve the unequal sharing of electrons, while ionic bonds involve the transfer of electrons. (A) Signup and view all the answers

Why is water considered an excellent solvent, especially for ionic compounds?

Water's polarity allows it to effectively disrupt the electrostatic interactions holding ions together. (B) Signup and view all the answers

What is the significance of water existing in three phases (solid, liquid, gas) on Earth?

The interchange of phases significantly impacts life due to water's role as a solvent and its effects on environments. (A) Signup and view all the answers

Hydrogen bonds in water are described as constantly forming, breaking, and reforming. What is the significance of this dynamic behavior?

It allows for the continuous reorganization of water molecules, facilitating various biological processes and reactions. (C) Signup and view all the answers

What is the role of hydrogen bonding in the cohesive properties of water?

Hydrogen bonds link water molecules, making water structured than other liquids (A) Signup and view all the answers

Cohesion and adhesion are properties of water that are important for plant life. Which of the following statements best describes how these properties contribute to water transport in plants?

Cohesion allows water molecules to stick to each other, while adhesion allows water molecules to stick to the plant cell walls, helping to pull water up the xylem. (B) Signup and view all the answers

Considering the properties of water, which of the following is the most likely reason life on Earth originated in water?

Water is a versatile solvent that supports a wide range of chemical reactions necessary for life. (A) Signup and view all the answers

What primarily stabilizes the α-helix secondary structure in proteins?

Hydrogen bonds between every fourth amino acid. (B) Signup and view all the answers

In β-pleated sheets, what type of interaction connects the parallel polypeptide backbones?

Hydrogen bonds. (B) Signup and view all the answers

Which amino acids are commonly found in turns, facilitating sharp bends in the polypeptide backbone?

Glycine and proline. (A) Signup and view all the answers

What is the primary structural difference between cellulose and starch molecules?

Cellulose contains $\beta$ glucose monomers, while starch contains $\alpha$ glucose monomers. (D) Signup and view all the answers

What distinguishes loops from turns in the context of protein structure?

Turns are shorter and exhibit just a few well-defined structures, while loops can be formed in many different ways. (D) Signup and view all the answers

Why can't humans digest cellulose?

Humans do not produce the enzyme necessary to hydrolyze the $\beta$ linkages of cellulose. (B) Signup and view all the answers

How do hydrophobic interactions contribute to the tertiary structure of a protein?

By repelling water molecules and causing nonpolar amino acids to cluster at the protein's core. (A) Signup and view all the answers

If a polypeptide contains 50 amino acid residues, how would it be generally classified?

As a polypeptide. (C) Signup and view all the answers

How does cellulose contribute to a healthy human diet, despite not being a nutrient?

It abrades the digestive tract, stimulating mucus secretion and aiding the passage of food. (C) Signup and view all the answers

What structural level are hydrogen bonds between repeating constituents of the polypeptide backbone primarily associated with?

Secondary structure. (C) Signup and view all the answers

Which characteristic of cellulose contributes to its strength and its role as a structural component in plant cell walls?

The ability of its hydroxyl groups to form hydrogen bonds with neighboring cellulose molecules. (C) Signup and view all the answers

What property of cellulose is primarily responsible for its classification as 'insoluble fiber' in food packaging?

Its $\beta$ linkages prevent it from dissolving in water. (B) Signup and view all the answers

What is the general distinction between a polypeptide and a protein?

A protein has a well-defined three-dimensional structure, while a polypeptide is a chain of amino acids without a specific structure. (B) Signup and view all the answers

How do cows benefit from microorganisms in their digestive system?

The microorganisms break down cellulose into glucose monomers that the cow can absorb. (A) Signup and view all the answers

Considering the structural properties of cellulose, what makes it suitable for manufacturing paper and cotton products?

Its strong microfibrils provide strength and flexibility. (C) Signup and view all the answers

If an organism can digest starch but not cellulose, what can be inferred about the enzymes it produces?

It produces enzymes that hydrolyze $\alpha$ glycosidic linkages but not $\beta$ glycosidic linkages. (C) Signup and view all the answers

Which statement accurately describes the role of enzymes in biochemical reactions?

Enzymes accelerate the rate of reaction without changing the overall G. (C) Signup and view all the answers

In coupled reactions, what key property must be true for the overall reaction to proceed spontaneously?

The sum of the individual G values must be negative. (C) Signup and view all the answers

In the context of indirect coupling, which of the following best explains how an unfavorable reaction (X Y) can proceed?

By rapidly converting Y to Z, maintaining a low concentration of Y and high concentration of X. (B) Signup and view all the answers

In the series of reactions V W X Y Z, if the reaction X Y has a positive G, and Y Z has a very negative G, what is the key factor that allows the formation of some Y?

A very high concentration difference between X and Y due to high concentration of X. (C) Signup and view all the answers

Which of the following is NOT true regarding the first one billion years after the existence of life?

Organisms could efficiently use oxidative phosphorylation. (D) Signup and view all the answers

ATP hydrolysis to ADP and inorganic phosphate (Pi) has a G of -7.3 kcal/mol. How is this reaction typically used in cells to drive energetically unfavorable reactions?

By direct coupling, where the energy released is used to power the unfavorable reaction. (C) Signup and view all the answers

Consider a reaction A B with G1 > 0 coupled to C D with G2 < 0. If the overall reaction A + C B + D proceeds spontaneously, what must be true regarding the magnitudes of G1 and G2?

|G<del>2</del>| must be greater than |G<del>1</del>|. (C) Signup and view all the answers

The equation G = G^o^' + RT ln Q relates the change in Gibbs free energy (G) to the standard free energy change (G^o^') and the reaction quotient (Q). Which of the following describes how a cell might use this relationship to drive an unfavorable reaction forward?

Maintain a low ratio of products to reactants to decrease Q. (C) Signup and view all the answers

Which of the following best describes what occurs when a strong base, such as NaOH, is added to water?

It dissolves and ionizes completely, releasing OH$^-$ and Na$^+$ ions, leading to an increase in OH$^-$ concentration. (B) Signup and view all the answers

What distinguishes a reversible acid-base reaction from an irreversible one?

Reversible reactions proceed in both directions depending on reactant/product concentrations, while irreversible reactions proceed predominantly in one direction. (D) Signup and view all the answers

In the context of acid-base chemistry, what is the significance of water's ionization?

It establishes the baseline concentrations of H$^+$ and OH$^-$ ions, influencing the pH of aqueous systems. (A) Signup and view all the answers

Which of the following is the correct representation of the reaction between an amine group (--NH2) and a proton (H$^+$)?

--NH2 + H$^+$ → --NH3$^+$ (D) Signup and view all the answers

Acetic acid (CH3COOH) dissolving in water exhibits reversible behavior. Which statement accurately describes the equilibrium state of this reaction?

At equilibrium, the rate of CH3COOH ionization equals the rate of CH3COO$^-$ and H$^+$ recombination. (A) Signup and view all the answers

How does the hydronium ion (H3O$^+$) concentration relate to the hydrogen ion (H$^+$) concentration in biochemical contexts?

For simplicity, biochemists often use H$^+$ to represent H3O$^+$, as it represents a hydrogen ion bound to a water molecule. (C) Signup and view all the answers

Given that pure water has an H$^+$ concentration of 10^-7 M, what is the relationship between the H$^+$ and OH$^-$ concentrations in pure water at standard conditions?

The H$^+$ and OH$^-$ concentrations are equal in pure water. (A) Signup and view all the answers

Which of the following solutions would be considered the most acidic, based on the information provided?

A 1 M HCl solution, with an H$^+$ concentration of 1 M. (B) Signup and view all the answers

Trioses

Three-carbon sugars

Pentoses

Five-carbon sugars.