Chapter 2 Chemical components of cells Flashcards by Scott Longmaid

Which of the following statements is true regarding the structure of an atom?

A) The number of neutrons in an atom determines its atomic number.
B) The atomic weight of an atom is equal to the number of protons only.
C) Electrons are the heaviest subatomic particles and make up most of the atom’s mass.
D) The atomic number of an atom is determined by the number of protons.

D) The atomic number of an atom is determined by the number of protons.

Explanation:
The atomic number corresponds to the number of protons in the nucleus of an atom, which is fundamental in determining the identity of the element. Electrons have negligible mass compared to protons and neutrons, so they do not contribute significantly to the atomic weight. The atomic weight is the sum of protons and neutrons, not just protons.

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Which of the following statements correctly distinguishes between a covalent bond and an ionic bond?

A) A covalent bond involves the transfer of electrons, while an ionic bond involves sharing of electrons.
B) In a covalent bond, electrons are shared, whereas in an ionic bond, electrons are transferred between atoms.
C) A covalent bond always results in the formation of ions, while an ionic bond does not.
D) Covalent bonds are weaker than ionic bonds and do not form molecules.

B) In a covalent bond, electrons are shared, whereas in an ionic bond, electrons are transferred between atoms.

Explanation: A covalent bond is formed when two atoms share electrons to fill their outer electron shells, while an ionic bond forms when one atom transfers an electron to another, creating positive and negative ions that are attracted to each other.

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Which of the following statements is true regarding the reactivity of elements?

A) Elements with completely filled outermost electron shells are highly reactive in chemical reactions.
B) Elements with incomplete outer electron shells can interact with other atoms, which makes them more reactive.
C) The reactivity of an element is determined solely by the number of protons in the nucleus.
D) Inert gases, like helium and neon, have incomplete outermost shells and are chemically reactive.

B) Elements with incomplete outer electron shells can interact with other atoms, which makes them more reactive.

Explanation: The reactivity of an element depends on the completeness of its outer electron shell. Elements with incomplete outer shells (such as oxygen, nitrogen, and carbon) can form bonds with other atoms to fill their outer shells, making them more chemically reactive. In contrast, inert gases like helium and neon have completely filled outer shells, making them chemically unreactive.

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In a polar covalent bond, such as in H₂O, what causes the unequal sharing of electrons?

A) The oxygen and hydrogen atoms have the same electronegativity.
B) Electrons are shared equally between oxygen and hydrogen atoms.
C) Oxygen has a higher electronegativity than hydrogen, which attracts electrons more strongly.
D) The oxygen atom has a neutral charge, while the hydrogen atom is positively charged.

Answer:

C) Oxygen has a higher electronegativity than hydrogen, which attracts electrons more strongly.

Explanation: In polar covalent bonds, the atom with higher electronegativity, such as oxygen in water, attracts electrons more strongly, resulting in a partial negative charge on oxygen and a partial positive charge on hydrogen.

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What defines the bond length of a covalent bond between two hydrogen atoms?

A) It is the distance at which the two hydrogen atoms are closest together without repelling each other.
B) It is the distance at which the shared electrons between the two atoms are most likely to be found.
C) It is the distance where the shared electrons are repelled by the nuclei.
D) It is the distance at which the atoms are so far apart that no electrons are shared.

B) It is the distance at which the shared electrons between the two atoms are most likely to be found.

Explanation: The bond length is the defined distance between the two nuclei where the shared electrons are in their most stable orbit, resulting in the strongest bond between the atoms.

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What happens if two hydrogen atoms are brought closer together than the defined bond length of 0.074 nm?

A) The electrons will be shared more equally between the atoms.
B) The positive charges of the nuclei will repel each other, weakening the bond.
C) The bond will become stronger as the distance decreases.
D) The atoms will stop sharing electrons, and the bond will break.

B) The positive charges of the nuclei will repel each other, weakening the bond.

Explanation: When atoms are too close, the positively charged nuclei repel each other, which reduces the effectiveness of the shared electron interaction, weakening the bond.

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Which of the following molecules has a specific three-dimensional shape defined by bond angles and bond lengths?

A) Propane (CH₃-CH₂-CH₃) forms a linear structure with equal bond angles between its atoms.
B) Water (H₂O) forms a “V” shape with a bond angle of approximately 109°.
C) Carbon dioxide (CO₂) forms a square shape with 90° bond angles.
D) A hydrogen molecule (H₂) has a linear structure with no specific bond angle.

Answer:

B) Water (H₂O) forms a “V” shape with a bond angle of approximately 109°.

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What is the primary factor that defines the three-dimensional geometry of molecules?

A) The type of bonds between atoms (ionic or covalent)
B) The atomic mass of the constituent elements
C) The bond angles and bond lengths of covalent bonds
D) The polarity of the bonds between atoms

Answer:

C) The bond angles and bond lengths of covalent bonds

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What is the main difference between the single bond in ethane (C₂H₆) and the double bond in ethene (C₂H₄)?

A) The single bond in ethane allows for the rotation of the CH₃ groups, while the double bond in ethene restricts rotation.
B) The double bond in ethene allows for the rotation of the CH₂ groups, while the single bond in ethane does not.
C) The single bond in ethane is shorter and more rigid than the double bond in ethene.
D) The double bond in ethene allows for more flexibility in the geometry of the molecule than the single bond in ethane.

A) The single bond in ethane allows for the rotation of the CH₃ groups, while the double bond in ethene restricts rotation.

Explanation: In ethane (C₂H₆), the single covalent bond between carbon atoms allows for the free rotation of the CH₃ groups. However, in ethene (C₂H₄), the double bond restricts rotation and keeps the atoms in a fixed planar geometry.

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Which of the following is true about the geometry of the carbon atoms in ethene (ethylene)?

A) The carbon atoms form a tetrahedral arrangement with bond angles of 109° around each atom.
B) The double bond between the two carbon atoms forces the atoms to be in the same plane.
C) The single bond between the two carbon atoms causes them to form a linear arrangement.
D) The geometry of the carbon atoms in ethene allows for free rotation around the bond axis.

B) The double bond between the two carbon atoms forces the atoms to be in the same plane.

Explanation: In ethene (C₂H₄), the double bond causes the two carbon atoms and the associated hydrogen atoms to lie in the same plane. This rigidity prevents rotation around the carbon-carbon bond.

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Why is sodium chloride (NaCl) soluble in water?

A) Water molecules are hydrophobic and dissolve NaCl by forming covalent bonds.
B) Water molecules are polar and interact favorably with Na⁺ and Cl⁻ ions, causing dissociation.
C) Sodium chloride forms a stable nonpolar covalent bond that dissolves in water.
D) Sodium chloride is soluble in water because it forms hydrogen bonds with water molecules.

B) Water molecules are polar and interact favorably with Na⁺ and Cl⁻ ions, causing dissociation.

Explanation: The polar nature of water molecules allows them to interact with the oppositely charged Na⁺ and Cl⁻ ions, effectively separating them and causing NaCl to dissolve in water. This process is due to electrostatic interactions between water and the ions.

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How do ionic bonds form between sodium (Na) and chlorine (Cl)?

A) Sodium shares an electron with chlorine to form a stable molecule.
B) Sodium loses an electron to chlorine, resulting in two oppositely charged ions.
C) Chlorine shares electrons with sodium to create a neutral molecule.
D) Sodium and chlorine form a covalent bond by equally sharing their electrons.

B) Sodium loses an electron to chlorine, resulting in two oppositely charged ions.

Explanation: Sodium (Na) loses an electron to chlorine (Cl), resulting in Na⁺ and Cl⁻ ions. These oppositely charged ions are attracted to each other and form an ionic bond, creating sodium chloride (NaCl).

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Why is sodium chloride (NaCl) considered a salt rather than a molecule?

A) The atoms in NaCl are held together by covalent bonds.
B) The Na⁺ and Cl⁻ ions are held together by ionic bonds, forming a crystal structure.
C) NaCl is formed by the sharing of electrons between sodium and chlorine.
D) Sodium chloride forms hydrogen bonds between its molecules.

B) The Na⁺ and Cl⁻ ions are held together by ionic bonds, forming a crystal structure.

Explanation: Sodium chloride (NaCl) is held together by ionic bonds between Na⁺ and Cl⁻ ions. These ions are packed into a precise, three-dimensional crystal structure, making NaCl a salt, rather than a molecular compound.

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What is the primary reason that water molecules form extensive networks of hydrogen bonds?

A) The oxygen atom in water is highly electronegative, attracting electrons from neighboring hydrogen atoms.
B) Water molecules are nonpolar and do not interact with each other.
C) The hydrogen atoms in water have a negative charge that attracts positive charges from neighboring water molecules.
D) The covalent bonds between oxygen and hydrogen in water are easily broken, allowing for easy interaction between molecules.

A) The oxygen atom in water is highly electronegative, attracting electrons from neighboring hydrogen atoms.

Explanation: Water is a polar molecule, meaning that the oxygen atom is more electronegative than hydrogen, creating partial positive and negative charges. This polarity causes water molecules to form hydrogen bonds, where the negatively charged oxygen atom of one molecule is attracted to the positively charged hydrogen atom of another.

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Which of the following statements is true about hydrogen bonds in water?

A) Hydrogen bonds are stronger than covalent bonds and play a major role in the structure of water.
B) Hydrogen bonds form between the oxygen of one water molecule and the hydrogen of another due to the attraction between partial positive and partial negative charges.
C) Hydrogen bonds are about 10 times stronger than covalent bonds, making water a stable molecule.
D) Hydrogen bonds cause water molecules to repel each other, preventing any molecular interaction.

B) Hydrogen bonds form between the oxygen of one water molecule and the hydrogen of another due to the attraction between partial positive and partial negative charges.

Explanation: In water, hydrogen bonds form between the partially negative oxygen atom of one molecule and the partially positive hydrogen atom of another molecule. These bonds are weaker than covalent bonds but are crucial for water’s unique properties, such as its high boiling point and ability to dissolve many substances.

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Which of the following is true regarding hydrogen bonds in biological systems?

A) Hydrogen bonds only form between hydrogen and carbon atoms.
B) The atom bearing the hydrogen is called the H-bond acceptor, while the atom interacting with the hydrogen is called the H-bond donor.
C) Hydrogen bonds commonly form between molecules containing oxygen or nitrogen.
D) Nonpolar substances are more likely to form hydrogen bonds with water than polar substances.

C) Hydrogen bonds commonly form between molecules containing oxygen or nitrogen.

Explanation: Hydrogen bonds typically form between molecules that contain electronegative atoms like oxygen or nitrogen. The hydrogen atom is attracted to the partial negative charge of these atoms, resulting in hydrogen bonds.

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Which of the following molecules is most likely to be hydrophilic?

A) Lipids
B) Sugars
C) Proteins in cell membranes
D) Fatty acids

B) Sugars

Explanation: Hydrophilic molecules, such as sugars, organic acids, some amino acids, and nucleotides, have an affinity for water due to their ability to form hydrogen bonds. These molecules dissolve easily in water.

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What is the primary characteristic of hydrophobic interactions?

A) Hydrophobic molecules can easily dissolve in water and form hydrogen bonds.
B) Hydrophobic interactions involve the attraction of water molecules to nonpolar groups.
C) Hydrophobic molecules tend to cluster together to minimize their exposure to water.
D) Hydrophobic interactions are stronger than covalent bonds.

C) Hydrophobic molecules tend to cluster together to minimize their exposure to water.

Explanation: Hydrophobic interactions occur when nonpolar molecules or nonpolar groups associate with each other to reduce their contact with water. These interactions are often seen in proteins or lipids embedded in the nonpolar interior of membranes.

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What role do ionic bonds play in protein structure and interactions?

A) Ionic bonds only form between different proteins and do not affect the structure of the protein.
B) Ionic bonds contribute to the folding of a protein by linking distant parts of the same protein and influencing its structure.
C) Ionic bonds only occur between proteins and water molecules, not between proteins themselves.
D) Ionic bonds are not important for protein function, as they are weak and do not stabilize proteins.

B) Ionic bonds contribute to the folding of a protein by linking distant parts of the same protein and influencing its structure.

Explanation: Ionic bonds between functional groups within the same protein help stabilize its structure

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How do weak interactions in an aqueous environment influence the binding of proteins?

A) Weak interactions cause proteins to denature and lose their function.
B) Weak interactions help proteins recognize each other and form tight complexes.
C) Weak interactions prevent proteins from binding to other macromolecules.
D) Weak interactions alter the covalent bonding between proteins, causing them to become unstable.

B) Weak interactions help proteins recognize each other and form tight complexes.

Explanation: In the aqueous environment of a cell, many individual weak interactions between proteins can lead to the specific recognition of one protein by another, facilitating the formation of tight and stable protein complexes. These interactions are crucial for biological processes.

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What is the primary force that drives hydrophobic interactions in biological systems?

A) Attractive forces between hydrophobic molecules and water molecules.
B) Water molecules forming hydrogen bonds with hydrophobic groups.
C) Hydrophobic groups being forced together to minimize their disruptive effects on the water network.
D) Covalent bonds forming between hydrophobic molecules in water.

C) Hydrophobic groups being forced together to minimize their disruptive effects on the water network.

Explanation: Hydrophobic interactions occur because water molecules are attracted to hydrophobic groups, forcing them together to reduce their disruption of the hydrogen-bonded water network.

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What happens when acetic acid dissolves in water?

A) It reacts to form acetate ions and hydronium ions.
B) It forms hydroxyl ions and water molecules.
C) It dissociates into acetate ions and hydroxide ions.
D) It forms a stable molecule that does not participate in ion exchange.

A) It reacts to form acetate ions and hydronium ions.

Explanation: When acetic acid dissolves in water, it donates a proton (H⁺) to water molecules, forming acetate ions (CH₃COO⁻) and hydronium ions (H₃O⁺).

Which of the following statements is true regarding acids and bases in aqueous solutions?

A) Acids are molecules that accept protons in water.
B) Bases donate protons to water to form hydronium ions.
C) Acids release protons when dissolved in water.
D) Bases release hydroxide ions when dissolved in water.

C) Acids release protons when dissolved in water.

Explanation: Acids are substances that release protons (H⁺) when dissolved in water, while bases accept protons. The hydronium ion (H₃O⁺) forms when a proton is transferred from an acid to a water molecule.

Which of the following is true about the general formula for sugars?

A) The formula (CH₂O)n is only applicable to pentoses (five-carbon sugars).
B) The formula (CH₂O)n is common for sugars and leads to the general term carbohydrate.
C) Sugars with more than six carbons are classified as hexoses.
D) Sugars can only have three or four carbons.

B) The formula (CH₂O)n is common for sugars and leads to the general term carbohydrate.

Explanation: The formula (CH₂O)n is a general formula for sugars, and it led to the term “carbohydrate.” Sugars typically have between three and six carbons and are classified as triose, tetrose, pentose, or hexose based on the number of carbons.

What is the most common monosaccharide? A) D-glucose (C₆H₁₂O₆) B) D-fructose (C₆H₁₂O₆) C) Ribose (C₅H₁₀O₅) D) Galactose (C₆H₁₂O₆)

A) D-glucose (C₆H₁₂O₆) Explanation: D-glucose (C₆H₁₂O₆) is the most common monosaccharide and is a six-carbon sugar, known as a hexose.

Which of the following is true about monosaccharides? A) They are only composed of six carbon atoms. B) They always contain a ketone group. C) They contain either an aldehyde group or a ketone group. D) They cannot form rings in aqueous solutions.

C) They contain either an aldehyde group or a ketone group. Explanation: Monosaccharides are simple sugars that contain either an aldehyde group (as in aldoses) or a ketone group (as in ketoses). They usually have the general formula (CH₂O)n.

What is the main structural difference between glucose and galactose? A) Glucose contains a ketone group, while galactose contains an aldehyde group. B) The hydroxyl groups in glucose and galactose are arranged differently around two carbon atoms. C) Galactose is a pentose, while glucose is a hexose. D) Glucose is a disaccharide, while galactose is a monosaccharide.

B) The hydroxyl groups in glucose and galactose are arranged differently around two carbon atoms. Explanation: Glucose and galactose are isomers with the same molecular formula (C₆H₁₂O₆), but the hydroxyl groups are arranged differently around carbon atoms, giving them distinct chemical properties.

What type of bond forms when two monosaccharides are linked together to form a disaccharide? A) Ionic bond B) Hydrogen bond C) Glycosidic bond D) Peptide bond

C) Glycosidic bond Explanation: A glycosidic bond is formed when two monosaccharides undergo a condensation reaction, linking them together to form a disaccharide.

Which of the following best describes the difference between a disaccharide and an oligosaccharide? A) A disaccharide is composed of two sugar units, while an oligosaccharide is composed of many sugar units. B) A disaccharide consists of many sugar units, while an oligosaccharide is composed of only two sugar units. C) Disaccharides contain a single monosaccharide, while oligosaccharides contain multiple monosaccharides. D) Disaccharides form as a result of hydrolysis, while oligosaccharides are formed by condensation.

A) A disaccharide is composed of two sugar units, while an oligosaccharide is composed of many sugar units. Explanation: Disaccharides are composed of two monosaccharides, while oligosaccharides consist of several (more than two) monosaccharide units.

What is a common feature of complex oligosaccharides? A) They contain no repeating sugar subunits. B) They form by linking amino acids to form a long peptide chain. C) They often involve sugar sequences that are non-repetitive and can be linked to proteins or lipids. D) They are formed from a single type of monosaccharide.

C) They often involve sugar sequences that are non-repetitive and can be linked to proteins or lipids. Explanation: Complex oligosaccharides are formed from repeating sugar subunits but can have non-repetitive sequences and often form part of larger molecules, including proteins or lipids, contributing to cell surface recognition.

What is the main role of hydrophobic interactions in the formation of cell membranes? A) Hydrophobic interactions cause the hydrophilic groups of phospholipids to face inward, creating a water-soluble membrane. B) Hydrophobic interactions cause hydrophobic groups to be isolated from water, promoting the formation of the lipid bilayer. C) Hydrophobic interactions form covalent bonds between lipid molecules, stabilizing the membrane. D) Hydrophobic interactions allow for easy rotation of phospholipid molecules within the membrane.

B) Hydrophobic interactions cause hydrophobic groups to be isolated from water, promoting the formation of the lipid bilayer. Explanation: The hydrophobic tails of phospholipids interact with each other to minimize exposure to water, which leads to the formation of the lipid bilayer that forms the structural basis of cell membranes.

Which of the following is true about the difference between saturated and unsaturated fatty acids? A) Saturated fatty acids contain one or more double bonds, while unsaturated fatty acids contain no double bonds. B) Saturated fatty acids have no double bonds between carbon atoms, making them solid at room temperature, while unsaturated fatty acids contain double bonds, creating kinks that make them liquid at room temperature. C) Unsaturated fatty acids have no double bonds, while saturated fatty acids contain multiple double bonds. D) Saturated and unsaturated fatty acids both have similar structures and behave the same in biological systems.

B) Saturated fatty acids have no double bonds between carbon atoms, making them solid at room temperature, while unsaturated fatty acids contain double bonds, creating kinks that make them liquid at room temperature. Explanation: Saturated fatty acids have no double bonds and are typically solid at room temperature, while unsaturated fatty acids contain one or more double bonds that cause kinks in the hydrocarbon chain, making them liquid at room temperature.

What is the characteristic feature of unsaturated fatty acids? A) They have no double bonds in their hydrocarbon chain. B) They have one or more double bonds in their hydrocarbon tail, creating a kink in the chain. C) They are typically solid at room temperature. D) They contain a carboxyl group but do not form lipid aggregates.

B) They have one or more double bonds in their hydrocarbon tail, creating a kink in the chain. Explanation: Unsaturated fatty acids have one or more double bonds in their hydrocarbon tail, which creates a rigid structure and causes a kink in the chain.

What is the role of triacylglycerols in cells? A) They serve as a structural component of cell membranes. B) They are primarily used as an energy reserve in cells. C) They form the hydrophilic head in phospholipids. D) They are responsible for forming the steroid backbone.

B) They are primarily used as an energy reserve in cells. Explanation: Triacylglycerols (fats and oils) are used as energy reserves in cells and are stored in the form of fat droplets.

Which of the following best describes phospholipids? A) Phospholipids have two fatty acid tails, one hydrophilic head, and are the major components of cell membranes. B) Phospholipids have one fatty acid tail, a hydrophobic head, and are not important for cell membrane structure. C) Phospholipids are found only in plants and not in animal cells. D) Phospholipids consist of a hydrophobic tail and are responsible for energy storage in cells.

A) Phospholipids have two fatty acid tails, one hydrophilic head, and are the major components of cell membranes. Explanation: Phospholipids, which have two fatty acid tails and a hydrophilic head, form the lipid bilayer that is the structural basis of all cell membranes.

Which of the following is true about steroids? A) Steroids are a type of lipid with a multiple-ring structure and are involved in cell signaling. B) Steroids contain a single hydrocarbon chain and are part of the cell membrane. C) Steroids are water-soluble molecules that serve as energy storage molecules in cells. D) Steroids are only found in animal cells and not in plants.

A) Steroids are a type of lipid with a multiple-ring structure and are involved in cell signaling. Explanation: Steroids, such as cholesterol and testosterone, have a common multiple-ring structure and are involved in various biological functions, including cell signaling and membrane structure.

Which of the following is true about amino acids? A) Amino acids contain an amino group, a carboxyl group, and a side chain (R) attached to the α-carbon. B) The side chain (R) is always an amino group. C) All amino acids have the same side chain (R) structure. D) Amino acids do not contain carboxyl groups in their structure.

A) Amino acids contain an amino group, a carboxyl group, and a side chain (R) attached to the α-carbon. Explanation: Amino acids are the building blocks of proteins, and they all have an amino group, a carboxyl group, and a side chain (R) attached to the α-carbon atom. The structure of the side chain differs between each amino acid.

At a pH close to 7, in what form do free amino acids exist? A) Non-ionized form B) Ionized form, with both the amino and carboxyl groups charged C) Ionized form, with no charges on the amino and carboxyl groups D) In a polymerized form, without charges

B) Ionized form, with both the amino and carboxyl groups charged Explanation: At physiological pH (close to 7), free amino acids exist in their ionized form, with the amino group (–NH₃⁺) and the carboxyl group (–COO⁻) carrying charges. However, when amino acids are incorporated into polypeptides, these charges are lost.

What is the function of a peptide bond in proteins? A) It forms a rigid planar unit between two amino acids and allows rotation around the C-N bond. B) It links two amino acids together by transferring an electron from one to the other. C) It forms a flexible bond that connects nucleotides in nucleic acids. D) It joins amino acids with carbohydrates to form glycoproteins.

A) It forms a rigid planar unit between two amino acids and allows rotation around the C-N bond. Explanation: Peptide bonds form between amino acids and create a rigid planar structure, which prevents rotation around the C-N bond. This structure is crucial for the stability and shape of the protein.

Which of the following is true about the structure of peptides? A) Peptides are always more than 100 amino acids long. B) Peptides are shorter polymers, usually fewer than 50 amino acids in length. C) Peptides are always written with the C-terminus on the left. D) Peptides contain multiple peptide bonds but do not include any N-terminus.

B) Peptides are shorter polymers, usually fewer than 50 amino acids in length. Explanation: Peptides are shorter than proteins and typically consist of fewer than 50 amino acids. They are written with the N-terminus on the left and the C-terminus on the right.

What is the primary function of adenosine triphosphate (ATP) in cells? A) ATP is used as a storage molecule for genetic information. B) ATP is synthesized from ADP and inorganic phosphate to store energy. C) ATP participates in energy transfer by releasing energy during hydrolysis to drive biochemical reactions. D) ATP is broken down into glucose to provide energy for cellular processes.

C) ATP participates in energy transfer by releasing energy during hydrolysis to drive biochemical reactions. Explanation: ATP serves as a short-term energy carrier in cells. Its hydrolysis releases energy that is used to drive biochemical reactions, such as biosynthesis and intracellular work.

What happens when ATP is hydrolyzed? A) Energy is stored in the phosphate bonds, which are transferred to other molecules. B) It releases energy that is used for intracellular work and chemical synthesis. C) The phosphate group is added to ADP, creating a high-energy molecule. D) It is converted back into glucose to fuel cellular activities.

B) It releases energy that is used for intracellular work and chemical synthesis. Explanation: Hydrolysis of ATP releases energy by breaking the high-energy phosphoanhydride bonds, which is used by the cell to perform various tasks such as chemical synthesis and intracellular work.

Which of the following nitrogenous bases are classified as purines? A) Cytosine and uracil B) Thymine and cytosine C) Adenine and guanine D) Thymine and uracil

C) Adenine and guanine Explanation: Adenine (A) and guanine (G) are purines, which have a two-ring structure. Cytosine (C), thymine (T), and uracil (U) are pyrimidines, which have a single-ring structure.

What is the main difference between nucleosides and nucleotides? A) Nucleosides are composed of a base, sugar, and phosphate group, while nucleotides only contain a base and sugar. B) Nucleotides contain a phosphate group, while nucleosides only consist of a base and sugar. C) Nucleosides are larger molecules than nucleotides. D) Nucleotides contain a base and phosphate group but no sugar.

B) Nucleotides contain a phosphate group, while nucleosides only consist of a base and sugar. Explanation: Nucleotides are composed of a nitrogenous base, a five-carbon sugar, and one or more phosphate groups. Nucleosides, on the other hand, consist of only a base and sugar.

Which of the following molecules is formed by a phosphoanhydride bond and carries chemical energy? A) Coenzyme A (CoA) B) ATP C) DNA D) RNA

B) ATP Explanation: ATP (adenosine triphosphate) contains phosphoanhydride bonds that release energy when hydrolyzed, which is used for cellular work.

What does the term “5' end” refer to in the context of nucleic acids? A) The carbon atom that carries the phosphate group. B) The end of the molecule that contains the base group. C) The end of the molecule where the sugar is attached to the base. D) The end of the molecule where the phosphate group is linked to the 5' carbon of the sugar.

D) The end of the molecule where the phosphate group is linked to the 5' carbon of the sugar. Explanation: The 5' end of a nucleic acid refers to the phosphate group attached to the 5' carbon of the sugar, marking the beginning of the chain.

What experimental technique helped confirm that proteins are macromolecules? A) Gel electrophoresis B) Ultrafast chromatography C) Ultracentrifugation D) PCR (Polymerase Chain Reaction)

C) Ultracentrifugation Explanation: Ultracentrifugation was used by Theodor Svedberg to study the size and behavior of proteins. This technique showed that proteins, like hemoglobin, are large macromolecules by observing the sharp band formed when the sample was centrifuged, rather than a diffuse smear, which would indicate smaller, heterogeneous molecules.

Which of the following is true about the early scientific skepticism regarding macromolecules? A) Chemists thought that large biological molecules like proteins were simple aggregates of small molecules held together by weak forces. B) The idea of macromolecules was universally accepted in the early 20th century. C) Proteins and polysaccharides were believed to be small, non-repetitive molecules. D) Researchers in the early 20th century thought that proteins were made from a single type of amino acid.

A) Chemists thought that large biological molecules like proteins were simple aggregates of small molecules held together by weak forces. Explanation: In the early 20th century, many scientists were skeptical about the existence of large macromolecules. They believed that proteins and other large biological molecules were simply aggregates of smaller molecules, held together by weak forces, rather than being composed of repeating units linked by covalent bonds.

What restricts the flexibility and shape of most biological macromolecules despite their potential for high flexibility? A) Strong covalent bonds B) The random thermal energy of the molecules C) Noncovalent interactions like hydrogen bonds, electrostatic attractions, and van der Waals forces D) The inability of the polymer chain to rotate

C) Noncovalent interactions like hydrogen bonds, electrostatic attractions, and van der Waals forces Explanation: Although the polymer chain of a macromolecule has flexibility, noncovalent interactions such as hydrogen bonds, electrostatic attractions, and van der Waals forces constrain its shape by causing the polymer to adopt a specific conformation based on the sequence of monomers.

How do the unique conformations of macromolecules, such as proteins and RNA, influence their function? A) They determine their ability to form hydrogen bonds. B) They dictate the chemical activity and interactions with other biological molecules. C) They prevent the macromolecule from interacting with any other molecules. D) They allow them to rotate freely in solution, resulting in a lack of defined function.

B) They dictate the chemical activity and interactions with other biological molecules. Explanation: The unique three-dimensional conformation of macromolecules, formed by noncovalent interactions, is crucial for determining their function, including how they interact with other molecules. The structure allows them to carry out specific biochemical roles, like catalyzing reactions or binding to substrates.

How do multiple weak noncovalent bonds contribute to the specificity of molecular interactions? A) They enable molecules to bind randomly to any partner in the cell. B) They form irreversible covalent linkages upon contact. C) They allow many low-affinity contacts to add up, creating a strong, highly specific interaction that only occurs when molecular surfaces match closely. D) They are too weak individually and do not contribute to binding specificity.

C) They allow many low-affinity contacts to add up, creating a strong, highly specific interaction that only occurs when molecular surfaces match closely. Explanation: Although individual noncovalent bonds are weak, when many such interactions occur simultaneously—as when two molecules fit together like a hand in a glove—they produce a strong and highly specific binding. This multipoint contact mechanism ensures that only a molecule with a complementary surface and charge distribution will bind effectively.

Question 1: Which statement best describes how large macromolecular assemblies like ribosomes form? A) They are built by covalently linking small subunits into macromolecules, which are then assembled via noncovalent interactions. B) They form solely through hydrogen bonds among monomers. C) They arise exclusively from ionic bonds between nucleotides and amino acids. D) They do not require any bonding.

Answer: A Explanation: Small subunits (e.g., amino acids, nucleotides) are first joined by covalent bonds to form macromolecules. These macromolecules then assemble into large complexes like ribosomes through weaker, noncovalent interactions.