ch 3

Chapter 3: Molecules of Life

Study Objectives

  1. Y

Table 3.1: Macromolecules Overview

  • Macromolecules are large molecules assembled from smaller building blocks known as monomers:

    • Amino Acids:

    • Monomer: Amino acid

    • Polymer: Protein

    • Example: Structure of alanine.

    • Nucleotides:

    • Monomer: Nucleotide

    • Polymer: Nucleic acid (DNA)

    • Example: Structure of nucleic acid built from nucleotide monomers.

    • Monosaccharides:

    • Monomer: Monosaccharide (e.g., glucose)

    • Polymer: Carbohydrate (e.g., starch)

    • Fatty Acids:

    • Monomer: Fatty acid

    • Polymer: Lipid (fat molecule)

Note:

  • Macro = large: Macromolecules consist of many similar small components (monomers).

Dehydration Synthesis and Hydrolysis

  • Dehydration Synthesis:

    • Involves covalent bonding between two subunits (monomers) through the removal of a hydroxyl group (OH) from one and a hydrogen (H) from another, resulting in the formation of water (H2O).

  • Hydrolysis:

    • Disassembles polymers into monomers by adding a water molecule to break the covalent bond between them.

    • Definitions:

    • Hydro = water, lysis = breaking or digestion.

Study Objectives 2

  1. Describe the structure of an amino acid and the four general groups of amino acids.

    • Structure: Central carbon atom, an amino group (NH2), a carboxyl group (COOH), a hydrogen atom, and an R group (side chain).

    • Types of amino acids: Based on R groups (nonpolar, polar, acidic, basic).

  2. Describe the chemical structure of proteins and their importance.

    • Proteins are complex polymers of amino acids that perform various functions in organisms.

  3. Illustrate the formation of a peptide bond between two amino acids.

    • Formed by the dehydration synthesis between the amino group of one amino acid and the carboxyl group of another, releasing water.

  4. Distinguish among the 4 levels of protein structure:

    • Primary: Sequence of amino acids.

    • Secondary: Local folds (alpha helix & beta sheet).

    • Tertiary: Overall 3D shape determined by interactions among R groups.

    • Quaternary: Assembly of multiple polypeptide chains.

  5. Explain how the polar nature of water influences protein folding.

    • Water’s polarity affects the interactions between amino acids in a protein, leading to specific folding patterns.

  6. Differentiate between the structure and function of enzymes and structural proteins.

    • Enzymes: Globular proteins facilitating biochemical reactions. Structural proteins: Long, cable-like shapes providing support, e.g., collagen.

  7. Explain how a chaperone protein works.

    • Assists in the proper folding of proteins, preventing misfolding or aggregation.

  8. Define prion.

    • An infectious agent composed of protein that can cause abnormal folding of normal cellular proteins, leading to diseases.

Biological Macromolecules

  • Proteins: Major biological macromolecules providing structure and function to cells.

    • Composed of 20 different types of amino acids, each with unique functional groups.

Amino Acid Structure

  • An amino acid consists of:

    • A carbon atom with:

    • Amino group (-NH2)

    • Carboxyl group (-COOH)

    • Functional group (R) that varies among different amino acids.

    • Formation of peptide bond responsible for linking amino acids into polypeptides.

Levels of Protein Structure

  1. Primary Protein Structure:

    • Consists of an assembled amino acid polymer called a polypeptide.

    • The order and type of amino acids critically influence protein folding.

  2. Secondary Protein Structure:

    • Consists of local structures (e.g., alpha helices, beta pleated sheets) stabilized by hydrogen bonds between backbone atoms.

  3. Tertiary Protein Structure:

    • Overall 3D shape determined by diverse interactions (hydrophobic, ionic, hydrogen bonds) among R groups.

  4. Quaternary Protein Structure:

    • Formed when two or more polypeptides join together to form a functional protein.

Peptide Bonds and Secondary Structures

  • Peptide Bonds:

    • Covalent bonds connecting amino acids.

  • Secondary Structures:

    • Alpha Helix: Spiral structure maintained by hydrogen bonds.

    • Beta Pleated Sheet: Sheets formed by hydrogen bonds between parts of a polypeptide chain.

Scientist Spotlight: Dr. H. R. Branson

  • Importance:

    • Known for his significant contributions in identifying the protein's alpha-helix structure but did not receive the Nobel Prize due to various reasons including racial bias.

Protein Denaturation

  • Definition:

    • Changes to the environment (e.g., temperature, pH) can cause proteins to unfold and lose activity (denatured protein becomes inactive).

Function of Proteins

  • Proteins perform numerous dynamic functions in the body, serving roles such as:

    • Enzymes, transport proteins, antibodies, hormones, receptors, muscle movers, structural components (collagen), and storage molecules.

  • Structural proteins are often elongated and cable-like, while enzymes are globular and have specific 3D shapes that fit to facilitate a chemical reaction (e.g., catalase decomposing hydrogen peroxide into oxygen and water).

Study Objectives 3

  1. Name the three parts of a nucleotide:

    • Nitrogenous base, sugar (ribose or deoxyribose), phosphate group.

  2. Describe the chemical structure of nucleic acids and explain how they relate to inheritance:

    • Chain of nucleotides forming DNA and RNA, responsible for storing and transmitting genetic information.

  3. State the two major chemical differences between DNA and RNA:

    • DNA contains thymine, while RNA has uracil; DNA typically is double-stranded, while RNA is usually single-stranded.

Nucleotide Structure

  • Composed of:

    • Five different types of nucleotides, which encode information through sequences.

RNA vs. DNA

  • RNA:

    • Uses uracil instead of thymine.

    • Single-stranded.

    • Sugar backbone is ribose.

The DNA Double Helix

  • Structure:

    • Base pairing occurs: Adenine (A) pairs with Thymine (T) and Cytosine (C) pairs with Guanine (G).

    • Base pairs connected by hydrogen bonds, which are broken when DNA unzips for replication.

Study Objectives 4

  1. Define monosaccharides, disaccharides, and polysaccharides:

    • Monosaccharides: Single sugar molecules (e.g., glucose).

    • Disaccharides: Two monosaccharides linked together (e.g., sucrose, maltose).

    • Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose).

  2. Illustrate how a disaccharide forms:

    • Formed through dehydration synthesis (removal of water) between monosaccharides.

  3. Explain why you cannot digest cellulose but a termite can:

    • Humans lack the enzyme to break down cellulose, while termites harbor bacteria capable of digesting cellulose.

Carbohydrates and Energy

  • Function:

    • Carbohydrates primarily provide energy for the body and are composed of carbon (C), hydrogen (H), and oxygen (O) in a 1:2:1 ratio.

  • Glucose:

    • Monosaccharide used as a primary energy source.

  • Disaccharides:

    • Examples include sucrose (glucose + fructose).

Polysaccharides: Structure and Function

  • Starch:

    • Polymer of glucose; energy storage in plants (found in potatoes).

  • Glycogen:

    • Energy storage in animals; more branched than starch.

  • Cellulose:

    • Structural polysaccharide in plant cell walls; resistant to enzymatic breakdown.

  • Chitin:

    • Structural polysaccharide found in invertebrate exoskeletons and fungi.

Complex Carbohydrates

  • Long polymer chains rich in C-H bonds lead to high stored energy.

Study Objectives, Part 5

  1. Define lipids, phospholipids, and steroids:

    • Lipids: Diverse group of hydrophobic molecules, important for energy storage and cellular function (e.g., triglycerides).

    • Phospholipids: Major constituents of cell membranes, comprising hydrophobic and hydrophilic regions.

    • Steroids: Function as hormones and structural components (e.g., cholesterol).

  2. Distinguish between saturated and unsaturated fats:

    • Saturated: Maximum hydrogen atoms; solid at room temperature (e.g., butter).

    • Unsaturated: Less than maximum hydrogens due to double bonds; liquid at room temperature (e.g., oils).

  3. Explain how trans fats are formed in food:

    • Result from hydrogenation processes; artificially created to solidify oils.

  4. Explain why phospholipids are polar while triglycerides are not:

    • Phospholipids have a hydrophilic head and hydrophobic tails, whereas triglycerides are entirely hydrophobic.

  5. Describe evidence suggesting trans fats are more unhealthy than saturated fats:

    • Associated with increased LDL cholesterol and heart disease risk.

  6. Explain how lactose tolerance has evolved in humans:

    • Evolutionary adaptation allowing adults to digest lactose due to a genetic mutation that prolongs lactase production.

Lipids

  • Function:

    • Store energy, provide insulation, and serve structural roles in cell membranes.

  • Composition:

    • Comprised of fatty acids as building blocks.

Types of Lipids

  • Fats:

    • Long-term energy storage, composed of glycerol and fatty acids.

  • Phospholipids:

    • Key components of cell membranes with hydrophilic heads and hydrophobic tails.

  • Steroids:

    • Include cholesterol, vital in cellular membranes and serving as precursors for hormones.

Importance of Cholesterol

  • Cholesterol is embedded in animal cell membranes and serves as a precursor for the synthesis of steroid hormones.