Biochemistry Chapter 1: Enzymes

Enzymes Overview

• Enzymes are primarily proteins that act as biological catalysts, accelerating biochemical reactions in living cells without changing themselves.
• They increase reaction rates by a factor of 10^2 to 10^8.
• Enzymes are involved in numerous metabolic processes, such as glycolysis, where glucose transforms into pyruvate.
• Enzymes are essential for reading genetic information from DNA and synthesizing non-protein cell components.
• Roughly 2,000 enzymes exist in bacterial cells (e.g., Escherichia coli) and about 10,000 in eukaryotic animal cells.
• Enzymes have diverse applications in healthcare, food production, and various industries due to their specificity.

Structure of Enzymes

• Enzymes are constituted either solely of proteins or in conjunction with non-protein molecules or metal ions.
• The protein component is termed apoenzyme, and the non-protein part is a cofactor, which can be inorganic (metal ion) or organic (coenzyme).
• A complete and active enzyme system is referred to as a holoenzyme, derived from the combination of an apoenzyme and its cofactor.

Protein Structure and Function

• Most enzymes are proteins, necessitating an understanding of protein structure for enzyme comprehension.
• Proteins are large macromolecules with molecular weights exceeding several thousand Daltons, constituting more than half the dry weight of cells.
• Two main protein types exist:
  • Fibrous Proteins: Insoluble in water; provide structural support (e.g., α-keratin in hair, collagen in skin).
  • Globular Proteins: Generally soluble and compact, playing functional roles (most enzymes fall into this category).
• Each protein has a specific function tied to its structure and shape, differentiating them from polysaccharides and lipids which primarily serve energy storage.
• Proteins can be degraded for energy or building materials as needed.

Protein Structure Levels

• Primary Structure: Sequential arrangement of amino acids connected by peptide bonds, including disulfide bonds.
• Secondary Structure: Polypeptides can form structures like α-helices, contributing to overall protein functionality.

Enzymes Overview

• Enzymes are primarily proteins that act as biological catalysts, accelerating biochemical reactions in living cells.
• They significantly increase reaction rates, often by 10^2 to 10^8 times.
• Enzymes are crucial for metabolic processes, such as glycolysis, which converts glucose to pyruvate.
• Over 2000 enzymes can be found in bacteria, while eukaryotic animal cells contain around 10,000 different enzymes.
• Enzymes are utilized in various applications, including hospital diagnostics, food manufacturing, and meat tenderization.

Enzyme Structure

• Enzymes are categorized as either proteins alone or as proteins combined with cofactors (organic or inorganic).
• The protein portion is called an apoenzyme, while the complete enzyme structure with cofactors is termed a holoenzyme.
• Simple enzymes consist solely of proteins, while conjugated enzymes require additional molecules for activity.

Protein Structure

• Proteins are macromolecules with molecular weights typically over several thousand Daltons, constituting over 50% of cellular dry weight.
• Types include fibrous proteins (e.g., keratin, collagen) and globular proteins, the latter being more prevalent among enzymes.
• Proteins serve specific functions based on their structure but can also provide energy or raw materials when necessary.

Levels of Protein Structure

• Primary structure involves the sequence of amino acids linked by peptide bonds.
• Secondary structures include formations like α-helices and β-sheets arising from hydrogen bonding.
• Tertiary structure represents the 3D folding of a single polypeptide, affecting functionality.
• Quaternary structure involves multiple polypeptide chains (subunits) and can form complex functional assemblies.

Types of Enzymes

• Monomeric enzymes consist of a single polypeptide chain, found predominantly in hydrolytic reactions (e.g., trypsin, chymotrypsin).
• Oligomeric enzymes contain two or more polypeptide chains (subunits), can be dimers or tetramers, and generally possess a higher molecular weight than monomeric enzymes.
• Oligomeric enzymes often demonstrate cooperative properties, which are absent in isolated units, and are regulated by feedback inhibition.

Cofactors

• Cofactors are necessary small molecules or ions that assist enzyme function.
• Metal ions play crucial roles, leading to classifications such as metalloenzymes (tightly bound metal) and metal-activated enzymes (looser binding).

Active Site Features

• The active site is the enzyme region that binds substrates and contains catalytic amino acids, typically around 12.
• Enzymes are large compared to substrates; only a small portion is directly involved in catalysis.
• Active sites form intricate 3D pockets designed for substrate interaction.
• Weak interactions (e.g., electrostatic, hydrogen bonds) facilitate substrate binding within the active site, compared to the strength of covalent bonds.

Sites Within Enzymes

• Two key functional sites in enzymes are identified:
  • Catalytic site: Involved in the catalytic process.
  • Regulatory site: Modulates enzyme activity and interaction (not detailed in the text provided).

This quiz covers Chapter 1 on the structure and function of enzymes. It explores the role of enzymes as biological catalysts that significantly increase the rate of biochemical reactions. Test your understanding of enzymes and their importance in cellular processes.