Enzymes, Nucleic Acids, and Biochemical Properties: Study Notes for Anatomy & Physiology

Enzymes and Enzyme Activity

Definition and Function of Enzymes

Enzymes are globular proteins that act as biological catalysts, speeding up chemical reactions in the body without being consumed in the process.

• Catalysts regulate and increase the speed of chemical reactions.

• Enzymes lower the activation energy needed to initiate a chemical reaction.

• They allow for millions of reactions to occur rapidly and efficiently.

Characteristics of Enzymes

• Most functional enzymes are called holoenzymes, which consist of two parts:

  • Apoenzyme: the protein portion

  • Cofactor (often an ion) or coenzyme (organic molecule)

• Enzymes are specific—each enzyme acts on only one substrate or a group of closely related substrates.

• Enzymes are usually named for the reaction they catalyze, often ending in -ase (e.g., hydrolase, oxidase).

Enzyme Action: How Enzymes Work

Enzymes function by binding to their specific substrate(s) and facilitating the chemical reaction.

1. Substrate binds to the enzyme's active site, forming an enzyme-substrate complex.

2. Enzyme-substrate complex undergoes rearrangement of substrate, resulting in the product(s).

3. Product is released from the enzyme, which is then free to catalyze another reaction.

Activation Energy and Reaction Rates

Every chemical reaction requires an initial input of energy, called activation energy, to get started. Enzymes lower this energy barrier, allowing reactions to proceed quickly at normal body temperatures.

• Without enzymes, reactions would require excessive heat that could denature proteins and damage cells.

Nucleic Acids

Structure and Function

Nucleic acids are large biomolecules composed of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and phosphorus (P). They are the largest molecules in the body and store and transmit genetic information.

• Nucleic acids are polymers made up of monomers called nucleotides.

• Each nucleotide consists of:

  • A nitrogenous base

  • A pentose sugar

  • A phosphate group

• Two main classes:

  • DNA (deoxyribonucleic acid)

  • RNA (ribonucleic acid)

Water and Biochemical Properties

Polar Solvent Properties

Water is a polar molecule and an excellent solvent, meaning it can dissolve many substances, especially ionic compounds and other polar molecules.

• Water's polarity allows it to form hydration layers around charged molecules, facilitating their transport and chemical reactions in the body.

• It is the body's main transport medium.

Salts

Salts are ionic compounds that dissociate into ions in water. They are vital for many physiological processes.

• When dissolved, salts separate into cations (positively charged ions) and anions (negatively charged ions).

• Common physiological salts include sodium chloride (NaCl), potassium chloride (KCl), and calcium phosphate (Ca3(PO4)2).

• Salts help maintain electrolyte balance and are essential for nerve impulse transmission and muscle contraction.

Acids and Bases

Acids and bases are substances that, when dissolved in water, affect the concentration of hydrogen ions (H+) in solution.

• Acids are proton donors; they release H+ ions in solution (e.g., HCl → H+ + Cl-).

• Bases are proton acceptors; they take up H+ ions or release hydroxide ions (OH-) in solution (e.g., NaOH → Na+ + OH-).

• Acids and bases are important for maintaining the body's pH balance.

pH: Acid-Base Concentration

The pH scale measures the concentration of hydrogen ions in a solution, indicating its acidity or alkalinity.

• The pH scale ranges from 0 to 14:

  • pH < 7: Acidic solution (higher H+ concentration)

  • pH = 7: Neutral solution

  • pH > 7: Basic (alkaline) solution (lower H+ concentration)

• Each unit change in pH represents a tenfold difference in H+ concentration.

Formula:

$\text{pH} = -\log_{10}[\text{H}^+]$

• Buffers help maintain stable pH in the body by releasing or binding H+ ions as needed.

Summary Table: Properties of Water, Salts, Acids, and Bases

Substance	Main Properties	Physiological Role
Water	Polar, excellent solvent, high heat capacity	Transport, temperature regulation, chemical reactions
Salts	Ionic, dissociate into cations and anions	Electrolyte balance, nerve and muscle function
Acids	Release H+ ions (proton donors)	pH regulation, digestion (e.g., gastric acid)
Bases	Accept H+ ions or release OH-	pH regulation, neutralize acids

Additional info:

• Enzyme activity can be affected by temperature, pH, and the presence of inhibitors or activators.

• DNA stores genetic information, while RNA is involved in protein synthesis.

• Buffers in the blood include the bicarbonate and phosphate buffer systems.