Water: The Solvent for Biochemical Reactions - Lecture Slides | CHEM 3550, Study notes of Biochemistry

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Mary K. Campbell Shawn O. Farrell http://academic.cengage.com/chemistry/campbell Chapter Two Water: The Solvent for Biochemical Reactions Dr. Joe Davis Spring 2011

Chapter 2 Homework

25, 27, 29, 32, 39, and 45.

****You think you know about water??**

1. Water [H 2 O]: vital for all life forms. 2. Principle component of most living cells. - (^) Makes up ~70 - 85% of intracellular weight of typical cells (animals).

• (^) See Table 2.
  • (^) Extracellular body fluids (blood, CSF, saliva, urine, tears) are all water-based (aqueous) solutions. 3. Simple substance with Extraordinary physical, chemical and biological properties!

**Some Specific Biological Roles of Water - 2

2. Water: a critical buffer;** It helps regulate both Temperature and pH. A. Has high specific heat capacity.

• (^) Helps maintain the body’s temperatures. B. Dissolves solutes/biomolecules that regulate the cell’s hydrogen ion concentration [pH].
• (^) Biological buffers react with / in water to help regulate cellular fluid pH.
• (^) Key concept: All Biological molecules require a “constant” pH environment to function properly (More Later!!).

**Some Specific Biological Roles of Water - 3

3. Water: a critical, direct participant in several Biochemical Reactions.** Example (Plants): Photosynthesis

• (^) 6 CO 2 + 6 H 2 O  C 6 H 12 O 6 + 6 O 2
• (^) Water: a reducing agent (electron source) to reduce CO 2 forming glucose. Examples (Animals):
• (^) Water: often a direct reactant in biochemical hydrolysis reactions (cleavage of bonds with water).
• (^) Includes: initial steps of digestion of proteins, carbohydrates, and degradation of nucleic acids, etc.

Why is WATER such a polar Molecule? Recall: Polarity results from differences in electronegativity of atoms involved in bonds.

• (^) Electrons are unequally shared; the more negative charges localize closer to one atom.
• (^) Water : a nonlinear molecule ( bent geometry) with a H—O—H bond angle of ~ 104.3 o.
• (^) Due to large electronegativity difference between O and H [∆E ~ 1.4], electrons cannot be shared equally.
• (^) See next slide.

Water’s Unique Structure CO 2 : nonpolar molecule b/c it has a linear, sym- metrical structure. Water

• Ion-dipole and dipole-dipole interactions help ionic and polar compounds dissolve in water Ion-dipole and Dipole-dipole Interactions

***Hydration Shells Surrounding Ions in Water

Some Examples of Hydrophobic and Hydrophilic Biological Substances

Solvent Properties of H

2

O - 3

3) Amphipathic molecules : Possess both polar and nonpolar character.

• (^) Electrostatic interactions between water and the polar region of molecules allows specialized interactions in water. See next slide.

Summary of 4 important NONCOVALENT INTERACTIONS of BIOMOLECULES important in Biochemistry

• (^) Four main types of noncovalent inter-

actions include (See Table 2.3):

**1) Ionic bonds

2. Vander waals forces
3. Hydrophobic interactions, and
4. Hydrogen bonds (H – bonding).**

• (^) All are weak, intermolecular interactions, vitally important to biochemistry.
• (^) Students: be familiar with these forces NONCOVALENT INTERACTIONS of BIOMOLECULES*