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Exam 2: Chemical Components of Cells

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Question 31

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Indicate whether the statements below are TRUE or FALSE.If a statement is false, explain why it is false.

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Any covalently bonded H atom can participate in a hydrogen bond if it comes in close proximity with an oxygen atom that forms part of a water molecule.

True

Protons are constantly moving between water molecules, which means there is an overall equilibrium between hydroxyl ions and hydronium ions in aqueous solutions.

False

Electrons are always shared equally between covalently bonded atoms.

A strong base is defined as a molecule that can readily remove protons from water.

Premises

Any covalently bonded H atom can participate in a hydrogen bond if it comes in close proximity with an oxygen atom that forms part of a water molecule.

Protons are constantly moving between water molecules, which means there is an overall equilibrium between hydroxyl ions and hydronium ions in aqueous solutions.

Electrons are always shared equally between covalently bonded atoms.

A strong base is defined as a molecule that can readily remove protons from water.

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True

False

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Correct Answer

Premises

Responses

Any covalently bonded H atom can participate in a hydrogen bond if it comes in close proximity with an oxygen atom that forms part of a water molecule.

Protons are constantly moving between water molecules, which means there is an overall equilibrium between hydroxyl ions and hydronium ions in aqueous solutions.

Electrons are always shared equally between covalently bonded atoms.

A strong base is defined as a molecule that can readily remove protons from water.

Premises

Any covalently bonded H atom can participate in a hydrogen bond if it comes in close proximity with an oxygen atom that forms part of a water molecule.

Protons are constantly moving between water molecules, which means there is an overall equilibrium between hydroxyl ions and hydronium ions in aqueous solutions.

Electrons are always shared equally between covalently bonded atoms.

A strong base is defined as a molecule that can readily remove protons from water.

Responses

Question 32

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A protein chain folds into its stable and unique three-dimensional structure, or conformation, by making many noncovalent bonds between different parts of the chain.Such noncovalent bonds are also critical for interactions with other proteins and cellular molecules.From the list provided, choose the class or classes of amino acids that are most important for the interactions detailed below. A.forming ionic bonds with negatively charged DNA B.forming hydrogen bonds to aid solubility in water C.binding to another water-soluble protein D.localizing an "integral membrane" protein that spans a lipid bilayer E.tightly packing the hydrophobic interior core of a globular protein acidic nonpolar basic uncharged polar

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A.basic
B.uncharged ...

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Question 33

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Carbon atoms can form double bonds with other carbon atoms, nitrogen atoms, and oxygen atoms.Double bonds can have important consequences for biological molecules because they are __________ compared to single covalent bonds.

Select the answer that BEST completes the following statement: Chemical reactions in living systems occur in an __________ environment, within a narrow range of temperatures.

Carbon 14 is an unstable isotope of carbon that decays very slowly.Compared to the common, stable carbon 12 isotope, carbon 14 has two additional

Selenium (Se) is an element required in the human body in trace amounts.Selenium is obtained through the diet and levels of selenium found in food depend greatly on the soil where it is grown.Once ingested and absorbed as selenate, it can become incorporated into a small number of polypeptides.These selenoproteins are formed when selenium replaces an element that is found in 2 of the 20 "standard" amino acids.Using your knowledge of atomic structure, the periodic table in Figure 2-7, and the structure of amino acids found in Panel 2-5, deduce which two amino acids may be converted to "seleno" amino acids and used to make selenoproteins.

You are trying to make a synthetic copy of a particular protein but accidentally join the amino acids together in exactly the reverse order.One of your classmates says the two proteins must be identical, and bets you $20 that your synthetic protein will have exactly the same biological activity as the original.After having read this chapter, you have no hesitation in staking your $20 that it will not.What particular feature of a polypeptide chain makes you sure your $20 is safe and that the project must be restarted?

There are 20¹⁰⁰ different possible sequence combinations for a protein chain with 100 amino acids.In addition to the amino acid sequence of the protein, what other factors INCREASE the potential for diversity in these macromolecules?

Both DNA and RNA are synthesized by covalently linking a nucleoside triphosphate to the previous nucleotide, constantly adding to a growing chain.In the case of DNA, the new strand becomes part of a stable helix.The two strands are complementary in sequence and antiparallel in directionality.What is the principal force that holds these two strands together?

The amino acids glutamine and glutamic acid are shown in Figure 2-38.They differ only in the structure of part of their side chains (circled) .At pH₇, what type of interactions are possible for glutamic acid but not for glutamine? Figure 2-38

Cells require one particular monosaccharide as a starting material to synthesize nucleotide building blocks.Which of the monosaccharides below fills this important role?

Double covalent bonds are both shorter and stronger than single covalent bonds, but they also limit the geometry of the molecule because they

The variety and arrangement of chemical groups on monomer subunits contribute to the conformation, reactivity, and surface of the macromolecule into which they become incorporated.What type of chemical group is circled on the nucleotide shown in Figure 2-41? Figure 2-41

A.Sketch three different ways in which three water molecules could be held together by hydrogen-bonding. B.On a sketch of a single water molecule, indicate the distribution of positive and negative charge (using the symbols δ⁺ and δ⁻). C.How many hydrogen bonds can a hydrogen atom in a water molecule form? How many hydrogen bonds can the oxygen atom in a water molecule form?

Macromolecules in the cell can often interact transiently as a result of noncovalent interactions.These weak interactions also produce stable, highly specific interactions between molecules.Which of the factors below is the most significant in determining whether the interaction will be transient or stable?

A.In which scientific unit is the strength of a chemical bond usually expressed? B.If 0.5 kilocalories of energy are required to break 6 × 10²³ bonds of a particular type, what is the strength of this bond?

Figure 2-26 -Larger molecules have hydrogen-bonding networks that contribute to specific, high-affinity binding.Smaller molecules such as urea can also form these networks.How many hydrogen bonds can urea (Figure 2-26) form if dissolved in water?

Indicate whether the statements below are TRUE or FALSE.If a statement is false, explain why it is false.

Table 2-14 -Table 2-14 indicates the number and arrangement of electrons in the first four atomic electron shells for selected elements.On the basis of the information in the chart and what you know about atomic structure, which elements will form ions with a net charge of +2 in solution?

A covalent bond between two atoms is formed as a result of the