BCT Macromolecules_of_the_cell-Fall_2024__3_

Welcome to Biology of Cells and Tissues (BASC-5101)

Parker College Rules of Life

  • Each class will cover one or more principles of Dr. Parker’s rules of life or Principles of Success.

    • Rule #1: Image plus action equals feelings.

Macromolecules

Objectives

  • Understand the chemical nature of monomers involved in the biosynthesis of macromolecules.

  • Describe the synthesis and properties of macromolecules of cells.

Types of Macromolecules

  • Proteins: Polymers of amino acids.

  • Polysaccharides: Polymers of sugars.

  • Nucleic Acids: Polymers of nucleotides.

  • Lipids: Composed of a variety of different molecules.

    • Note: Except for lipids, these macromolecules are also called polymers.

Function of Macromolecules

  • Macromolecules are crucial as they are responsible for most of the form and order of living systems.

  • Generated through the polymerization of small organic molecules.

    • Monomers: The repeating units (e.g., glucose in sugar/starch, amino acids in proteins, nucleotides in nucleic acids).

Macromolecules

Chemical Structures

  • Carbohydrates: Chemical structure represented as CH₂OH, with examples illustrated.

  • Proteins: Visualized as a polypeptide backbone.

    • Amino Group: N-C-C, forming peptide bonds.

  • Lipids: Structural depiction including nonpolar and polar regions.

Visual Representation of Elements in Macromolecules

  • Macromolecules consist of various elements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Sulfur (S), and Phosphorus (P) with their respective atomic weights.

Macromolecule Synthesis

Overview

  1. **Monomer Activation:

    • Activation of monomers using energy from ATP.

    • Activated monomers couple to carrier molecules.

  2. **Monomer Condensation:

    • Condensation of two activated monomers releases carrier molecules.

  3. **Polymerization:

    • Addition of next activated monomer to an existing polymer chain.

Process Details

  • Synthesis from smaller molecules:

    • Stepwise addition releases H₂O, termed condensation or dehydration synthesis.

    • Reactive hydrogen and hydroxyl groups on molecules are necessary.

    • Energy is required, with components attached to carrier molecules.

Carrier Molecules

  • Different carrier molecules are utilized based on the polymer being synthesized:

    • Protein Synthesis: Amino acids linked to transfer RNA (tRNA).

    • Polysaccharides: Sugars activated by ADP or UDP.

    • Nucleotides: ATP and GTP act as high-energy molecules in nucleic acid synthesis.

Biologically Important Macromolecules (Table 2-1)

General Function

Examples

Type of Monomer

Number of Different Monomers

Polysaccharides

Structural (Cellulose, Chitin)

Monosaccharides

One or a few

Proteins

Informational (Enzymes, hormones)

Amino acids

20

Nucleic Acids

Storage (DNA, RNA)

Nucleotides

One or a few

Proteins

  • Composed of a nonrandom series of amino acids.

    • The amino acid sequence determines the three-dimensional structure and function of the protein.

    • With 20 different amino acids, infinity of sequences can be formed.

Functions of Proteins

  • Comprise 20–30% of cell mass.

  • Have varied functions including:

    • Structural: e.g., Collagen in connective tissues.

    • Enzymatic: Protein enzymes catalyze biochemical reactions.

    • Transport: Hemoglobin transports oxygen in blood.

    • Contractile: Actin and myosin facilitate muscle contractions.

    • Communication: Proteins act as messengers (e.g., insulin).

    • Defensive: Antibodies protect against disease (e.g., bacterial infections).

Amino Acids

Structure

  • Composed of:

    • Carbon atom (chiral center) bonded to:

    • Hydrogen atom

    • Amine group

    • Variable side chain (R)

  • Peptide bonds link amino acids.

Peptide Bonds

  • Formed between the amine group of one amino acid and the carboxyl group of another.

Polypeptides

  • Chains of amino acids joined by peptide bonds.

Types of Proteins

  • Monomeric Proteins: Single polypeptides.

  • Multimeric Proteins: Two or more polypeptides (e.g., hemoglobin: tetramer).

Structural Levels of Proteins

Protein Structure Types

  • Primary Structure: Linear sequence of amino acids.

  • Secondary Structure: Hydrogen bonding creates α-helices and β-pleated sheets.

  • Tertiary Structure: Three-dimensional folding due to R group interactions.

  • Quaternary Structure: Interaction of multiple polypeptides to form a functional protein.

Bonds in Protein Folding

  • Disulfide bonds: Between cysteine residues.

  • Hydrogen bonds: Facilitate interactions between R groups.

  • Ionic bonds: Form between charged R groups.

  • Van der Waals interactions: Occur in nonpolar regions.

Quaternary Structure

  • Level of organization involving subunit interactions in multimeric proteins.

  • Example: Hemoglobin with multiple subunits (2α and 2β).

Sickle Cell Anemia

  • Inherited disorder affecting red blood cells.

  • Normal cells are round and deliver oxygen; affected cells are sickle-shaped, leading to clogs and pain.

Fibrous and Globular Proteins

Shapes of Proteins

  • Fibrous Proteins: Strand-like, structural; e.g., collagen.

  • Globular Proteins: Compact, functional; e.g., enzymes, antibodies.

Lipids

Overview

  • Biochemically diverse, hydrophobic, stable in nonpolar solvents.

  • Composed primarily of hydrocarbons; some lipid classes have polar regions (amphipathic).

Classes of Lipids

  1. Fatty Acids (Saturated vs. Unsaturated)

  2. Triglycerides (Storage form of fats, composed of glycerol and fatty acids).

  3. Phospholipids (Key component of cell membranes).

  4. Glycolipids (Carbohydrates attached).

  5. Steroids (Hormones such as cholesterol).

  6. Terpenes (Derived from isoprene).

Fatty Acids

  • Long amphipathic chains with a carboxyl group.

Triacylglycerols

  • Structure: Glycerol with three fatty acids.

  • Formation: Linked via ester bonds through water removal.

Role of Phospholipids

  • Phospholipids are fundamental in forming cell membranes due to their amphipathic nature.

Steroids

  • Composed of four linked carbon rings; components of membrane stability and signaling, e.g., cholesterol.

Terpenes

  • Primary constituents of essential oils; contribute to plant fragrances and some medicines.

Polysaccharides (Carbohydrates)

Overview

  • Long-chain polymers of sugars, not informational molecules; consists of repeating monosaccharide units.

Energy Storage Polysaccharides

  • Starch: Storage in plants.

  • Glycogen: Storage in animals and bacteria.

Structural Polysaccharides

  • Cellulose: Main component of plant cell walls; indigestible by most mammals without microbiome assistance.

Nucleic Acids

Overview

  • Nucleic acids are the largest molecules in the body, consisting of nucleotides.

  • Composed of:

    • Nitrogen base (purines: A, G; pyrimidines: C, T, U)

    • Pentose sugar (ribose for RNA, deoxyribose for DNA)

    • Phosphate group.

Functions in the Cell

  • Storage of genetic information (DNA).

  • Expression of genetic information (RNA).

  • Protein synthesis (RNA).

Base Pairing

  • A:T (or U) via 2 hydrogen bonds; C:G via 3 hydrogen bonds.

Hierarchy of Cellular Components

  • Level 1: Small organic molecules (e.g., amino acids).

  • Level 2: Macromolecules (e.g., proteins, polysaccharides).

  • Level 3: Supramolecular structures (e.g., cell membranes, ribosomes).

  • Level 4: Organelles (e.g., mitochondria, nucleus).

  • Level 5: The cell itself (the complete biological unit).