Book cover for Chemistry The Science in Context

Chemistry The Science in Context

Thomas R. Gilbert

ISBN #9780393615142

5th Edition

2,675 Questions

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191,124 Students Helped

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

Chapter 20 delves into the intricate world of organic and biological molecules, emphasizing how a limited number of building blocks can create immense molecular diversity. The chapter highlights the importance of molecular structure, including functional groups, isomerism, and chirality, in determining the biological roles of proteins, carbohydrates, lipids, and nucleic acids. A clear understanding of noncovalent interactions further illustrates how biomolecules assemble and function within living cells, linking chemical properties to life processes.

Learning Objectives

1

Describe the basic molecular structures of organic and biological molecules including proteins, carbohydrates, lipids, and nucleic acids.

2

Explain how functional groups, isomerism, and chirality influence chemical behavior and biological function.

3

Analyze the role of noncovalent interactions in the formation, stabilization, and function of biomolecules.

4

Evaluate the processes of biomolecule synthesis and degradation in living cells.

5

Discuss the relationship between molecular structure and the diverse functions of life.

Key Concepts

CONCEPT

DEFINITION

Organic Molecules

Compounds primarily made of carbon atoms combined with other elements, forming the basis of life.

Functional Groups

Specific groups of atoms within molecules that determine their chemical reactivity and properties.

Isomerism

The existence of molecules with the same molecular formula but different structural arrangements, influencing their reactivity and function.

Chirality

A property where a molecule cannot be superimposed on its mirror image, often crucial for biological activity.

Noncovalent Interactions

Weak bonds such as hydrogen bonds, ionic interactions, and van der Waals forces that facilitate molecular recognition and assembly.

Proteins

Complex biomolecules composed of amino acids that perform diverse functions including catalysis, structure, and regulation.

Carbohydrates

Organic molecules made of sugar units that are essential for energy storage and structural integrity in cells.

Lipids

Hydrophobic molecules including fats and oils, vital for energy storage, insulation, and forming cellular membranes.

Nucleotides

The building blocks of nucleic acids, consisting of a sugar, a phosphate group, and a nitrogenous base.

Nucleic Acids

Macromolecules such as DNA and RNA that store and transmit genetic information.

Example Problems

Example 1

The nucleotides in DNA contain the bases with the structures shown in Figure P20.1. Identify the basic functional groups in the structures. (FIGURE CAN'T COPY)

Example 2

Bentiromide (Figure $\mathrm{P} 20.2$ ) is a peptide that was once evaluated as an agent to monitor the function of the pancreas during therapy. Draw the structures of the amino acids that form bentiromide, and indicate whether they are $\alpha$ -amino acids. (FIGURE CAN'T COPY)

Example 3

Olive oil contains triglycerides such as those shown in Figure P20.3. Which of the fatty acids in these triglycerides is/are saturated? (FIGURE CAN'T COPY)

Example 4

The major component of the antibiotic ointment bacitracin is a cyclic polypeptide called bacitracin A. It was first isolated in 1943 from a knee scrape from a girl named Margaret Tracy, after whom it is named. Bacitracin is effective topically and is used to treat skin, eye, and wound infections. Figure $\mathrm{P} 20.4$ shows the structure of bacitracin A. Identify the amino acids found in human proteins that are also part of the structure of bacitracin A. (FIGURE CAN'T COPY)

Example 5

The human brain produces polypeptides called endorpbins that help in controlling pain. The pentapeptide in Figure $\mathrm{P} 20.5$ is called enkephalin. Identify the five amino acids that make up enkephalin. (FIGURE CAN'T COPY)

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Step-by-Step Explanations

QUESTION

How does isomerism influence the function of a biomolecule?

STEP-BY-STEP ANSWER:

Step 1: Identify the molecular formula of the biomolecule which dictates the types of atoms present.
Step 2: Consider the different structural arrangements (isomers) that can be formed using the same formula.
Step 3: Analyze how each isomer's structure leads to variations in reactivity and binding properties with other molecules.
Step 4: Understand that these structural differences can significantly affect biological roles, such as enzyme specificity and hormone activity.
Final Answer: Isomerism results in distinct molecules with unique chemical and biological functions, impacting the activity and interaction of biomolecules.

Isomerism

QUESTION

How does chirality affect the biochemical properties of a molecule?

STEP-BY-STEP ANSWER:

Step 1: Define chirality as the non-superimposable nature of a molecule and its mirror image.
Step 2: Recognize that chiral molecules have enantiomers which may interact differently with biological systems.
Step 3: Evaluate how the three-dimensional arrangement of atoms in a chiral molecule influences its binding with enzymes and receptors.
Step 4: Understand that only one enantiomer might be biologically active or beneficial, while the other could be inactive or harmful.
Final Answer: Chirality is critical because it determines the specific interactions and biological activity of molecules in living organisms.

Chirality

QUESTION

Why are noncovalent interactions essential for biomolecular function?

STEP-BY-STEP ANSWER:

Step 1: Identify the types of noncovalent interactions such as hydrogen bonds, ionic bonds, and van der Waals forces.
Step 2: Explain that these interactions are weaker than covalent bonds but essential for flexible molecular assembly.
Step 3: Discuss how noncovalent interactions enable the formation of complex structures like protein folds and double helixes in nucleic acids.
Step 4: Highlight how these interactions play a role in molecular recognition, signal transduction, and enzymatic activity.
Final Answer: Noncovalent interactions are vital because they allow biomolecules to form complex, dynamic structures necessary for cellular functions.

Noncovalent Interactions

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Common Mistakes

  • Confusing isomerism with chirality; while both relate to structural variation, they have distinct effects on molecular behavior.
  • Overlooking the significance of noncovalent interactions, which are crucial for maintaining the structure and function of biomolecules despite being weaker than covalent bonds.
  • Assuming that all molecules with the same formula behave identically without considering the impact of different spatial arrangements.
  • Neglecting the interdependence between molecular structure and biological function, leading to misunderstandings about how changes in structure can affect overall cellular processes.