Biochemistry Chapter 2: Water

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Questions and Answers

What percentage of water typically makes up organisms?

70–90% (correct)

50–60%

90–100%

60–70%

Which property of water is primarily responsible for its biological significance?

Low pH levels

High molecular weight

Ability to form hydrogen bonds (correct)

Presence of nonpolar molecules

What is the geometry of a water molecule?

Planar triangle

Linear

Distorted tetrahedron (correct)

Cubic

What concept describes the interactions of lipids in an aqueous environment?

Micelles Signup and view all the answers

Which property of water contributes to its high heat capacity?

Extensive hydrogen bonding Signup and view all the answers

What are the two types of electron pairs present in a water molecule?

Bonding pairs and nonbonding pairs Signup and view all the answers

How does the dipole moment of water affect its behavior in biological systems?

Acts as a hydrogen bond donor and acceptor Signup and view all the answers

What is the significance of the ionization of water?

It affects pH and solute interactions. Signup and view all the answers

Which type of molecules do not easily interact with water?

Nonpolar molecules Signup and view all the answers

Why is water considered a critical determinant of biological molecules?

It is a universal solvent. Signup and view all the answers

What is a key feature of hydrogen bonds?

They involve a covalently bound hydrogen and a lone pair of electrons. Signup and view all the answers

Which property of water is primarily due to hydrogen bonding?

High specific heat Signup and view all the answers

Why are nonpolar molecules poorly soluble in water?

They disrupt hydrogen bonding. Signup and view all the answers

Hydrogen bonds play a critical role in the structure of which of the following?

Soluble proteins Signup and view all the answers

What is the primary reason water is a good solvent for polar substances?

It forms hydrogen bonds with them. Signup and view all the answers

Which of the following statements is true regarding the solubility of polar and nonpolar solutes in water?

Polar solutes readily mix due to similar interactions with water. Signup and view all the answers

Which type of molecules would likely show low solubility in water?

Nonpolar gases Signup and view all the answers

What is the consequence of low entropy surrounding hydrophobic solutes in water?

Thermodynamic unfavorable conditions Signup and view all the answers

Which molecule is generally considered more polar than the others?

H2O Signup and view all the answers

What is the primary function of the CFTR protein in the membrane?

Conducts chloride ions across epithelial membranes Signup and view all the answers

Which of the following describes the ionization of water?

Ionic product of water relates hydrogen and hydroxide ion concentrations Signup and view all the answers

What does the equilibrium constant $K_{eq}$ for water ionization represent?

The relationship between concentrations of products and reactants Signup and view all the answers

How does the polarity of water influence its interactions with biological molecules?

Polarity allows water to form hydrogen bonds with charged solutes Signup and view all the answers

What is the role of amphipathic molecules in biological membranes?

They stabilize the lipid bilayer structure by interacting with water Signup and view all the answers

Which of the following accurately describes micelles?

They contain a hydrophobic core surrounded by polar heads Signup and view all the answers

What is commonly observed in cystic fibrosis due to CFTR mutations?

Increased levels of respiratory infections Signup and view all the answers

What is the significance of the lipid bilayer in cell membranes?

It is a dynamic structure allowing fluid movements and interactions Signup and view all the answers

Study Notes

Water Properties and Biological Relevance

Water's polarity and hydrogen-bonding capability are essential for life, influencing the structure and function of biological molecules.
Organisms contain 70-90% water, making it crucial for biochemical reactions, which predominantly occur in an aqueous environment.

Structure of the Water Molecule

Water follows the octet rule, with oxygen atom covalently bonded to two hydrogen atoms and possessing two nonbonding lone pairs.
The water molecule exhibits a distorted tetrahedral geometry, resulting in a net dipole moment due to the electronegativity of oxygen, facilitating hydrogen bonding.

Hydrogen Bonds

Hydrogen bonds are strong interactions between a hydrogen atom and electronegative atoms like oxygen or nitrogen, significant for the unique properties of water.
These bonds contribute to the structural and functional properties of proteins, DNA, polysaccharides, enzyme-substrate binding, and mRNA-tRNA matching.

Solvent Properties of Water

Water effectively dissolves charged and polar solutes such as amino acids, small alcohols, and carbohydrates.
Nonpolar substances like nonpolar gases and aromatic compounds show poor solubility in water due to lower entropy, as water molecules form a structured shell around them.

Fluid Mosaic Model and Membranes

The lipid bilayer forms the basis of cell membranes, incorporating proteins like CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) which is linked to cystic fibrosis, a condition affecting multiple organs.

Ionization of Water

Water ionizes to H⁺ and OH⁻, with the equilibrium constant (Keq) represented by [H+][OH-]/[H2O].
At 25°C, Keq is 1.8 x 10⁻¹⁶ M, and the ionic product of water (Kw) is 1 x 10⁻¹⁴ M².

Important Concepts

The matching of mRNA and tRNA is essential for protein synthesis.
Understanding the different types of molecular interactions (hydrogen bonds, ionic, hydrophobic, van der Waals) is critical in biochemistry.
Nonpolar and amphipathic molecules behave distinctly in water, influencing interactions and solubility.
Micelles, membranes, and lipid bilayer models illustrate important structural and functional aspects of cellular components.
The CFTR protein mutations can lead to cystic fibrosis, diagnosed typically with sweat tests.

Key Questions for Review

Differentiate between hydrogen bonds and ionic, hydrophobic, and van der Waals interactions.
Explain water's polarity and its ability to hydrogen bond with itself and other biological molecules.
Describe the characteristics of nonpolar and amphipathic molecules in aqueous solutions.
Analyze solubility trends relative to polarity and water.
Detail the structure and function of the CFTR molecule and its association with cystic fibrosis.
Examine the ionization of water and the relationship between Keq and Kw.

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Description

This quiz covers Chapter 2 from Lehninger Principles of Biochemistry, focusing on the relationships between water, pH, solutes, and biological molecules. Test your understanding through interpreting tables and graphs related to this essential topic in biochemistry.