Biological Macromolecules

Chapter 3: Biological Macromolecules

Learning Objectives

  • Define and describe organic molecules

  • List and describe the four categories of macromolecules in organisms

Characteristics of Organic Molecules

  • Organic molecules consist of:

    • Carbon (C) and Hydrogen (H) atoms.

    • Characterized by covalent bonds.

    • Often large in size.

    • Frequently associated with living organisms.

Backbone of Organic Molecules

  • Carbon (C) provides the backbone for organic molecules.

  • Carbon possesses 4 electrons in its valence shell:

    • Enables it to share with up to 4 other elements.

    • Forms stable C-C bonds, facilitating the creation of long chains, branches, double bonds, and rings.

Functional Groups

  • Functional groups are responsible for the reactivity of a macromolecule.

    • Hydroxyl Group (–OH):

    • Hydrophilic, makes hydrocarbons turn into alcohols.

    • Carboxyl Group (–COOH):

    • Hydrophilic.

    • Amino Group (–NH2):

    • Hydrophilic.

    • Carbonyl Group:

    • Hydrophilic

    • Aldehyde Group (–CHO) and Ketone Group (–CO).

    • Isomers: Molecules with the same molecular formula (e.g., C₆H₁₂O₆) but different spatial arrangements (e.g., glucose vs. fructose).

Synthesis and Breakdown Reactions

  • Synthesis reaction:

    • A polymer is synthesized from subunits (monomers) through a dehydration reaction.

  • Breakdown reaction:

    • A polymer breaks down into its subunits through a hydrolysis reaction.

Check Understanding

  • Complete the following:

    • All organic molecules contain both C and H atoms.

    • A chain of C atoms forms the backbone of a macromolecule.

    • Attaching a hydroxyl group onto a hydrocarbon converts it into an alcohol.

    • Molecules with the same molecular formula but different arrangements are called isomers.

    • Hydrolysis reaction is:

    • A) synthesis reaction

    • B) a reaction that consumes water

    • C) a reaction that links monomers into a polymer

    • D) all of the above

  • The correct answer: B.

Carbohydrates

General Characteristics

  • Contain Carbon (C), Hydrogen (H), and Oxygen (O).

  • Most have a ratio of C:H:O = 1:2:1.

  • The number of carbon atoms can range from 3 to hundreds.

Major Functions

  • Energy source: e.g., glucose leading to ATP production.

  • Cell surface marking: MHC (Major Histocompatibility Complex).

  • Structural materials:

    • Cellulose: forms the cell wall of plants.

    • Chitin: exoskeleton of crabs and cell walls of fungi.

    • Peptidoglycan: cell wall of bacteria.

Classification of Carbohydrates

  • Monosaccharides:

    • Contain a single sugar molecule (simple sugar).

    • Have polar functional group (–OH), making them soluble in water.

    • Pentose sugar (C₅H₁₀O₅): contains 5 carbons.

    • Hexose sugars (C₆H₁₂O₆): contains 6 carbons.

  • Disaccharides: composed of 2 monosaccharides.

    • Examples:

    • Maltose: glucose + glucose.

    • Sucrose: glucose + fructose.

    • Lactose: glucose + galactose.

    • All three are isomers derived from the formula (2imesC6H12O6−H2O=C12H22O11)(2 imes C₆H₁₂O₆ - H₂O = C₁₂H₂₂O_{11}).

  • Polysaccharides: contain many subunits.

    • Starch: polymer of glucose.

    • Glycogen: energy storage in animals (mainly in the liver and muscles), structured with heavy branches.

    • Cellulose: most abundant organic molecule on earth; contributes to plant cell walls.

    • Dietary fiber; only some microorganisms can digest cellulose.

Check Understanding

  • Glycogen is a B) carbohydrate.

  • A) Ribose is a monosaccharide.

  • Animals store carbohydrate energy as B) glycogen.

  • Typical ratio of C:H:O in monosaccharides is 1:2:1.

  • D) Glucose and glycogen are isomers.

Lipids

General Characteristics

  • Mainly consist of C and H.

  • Characterized by large nonpolar regions.

  • They are hydrophobic, meaning they do not dissolve in water.

  • Major groups include:

    • Triglycerides

    • Phospholipids

    • Steroids

Triglycerides (Oils and Fats)

  • Composed of 3 fatty acids bonded to 1 glycerol (an alcohol) via dehydration synthesis.

  • Energy storage: triglycerides provide more energy than glycogen due to the energy in C-H bonds.

Types of Fatty Acids

  • Saturated fatty acids:

    • Found in animal fat (e.g., butter), consist of single bonds between C atoms, where each C bonds to 2 H atoms.

  • Unsaturated fatty acids:

    • Found in plant oils, they have one or more double bonds between C atoms, leading to less H bonding.

  • Trans fatty acids:

    • Increase LDL (bad cholesterol) and decrease HDL (good cholesterol), raising the risk for cardiovascular diseases.

Phospholipids

  • Comprised of one glycerol, two fatty acids, and a phosphate group.

  • Exhibit a polar "head" and a nonpolar "tail".

  • Major component of cell membranes.

Steroids

  • Characterized by 4 fused carbon rings.

  • Examples include cholesterol, vitamin D, steroid hormones, and bile salts.

  • Vary by functional groups present;

  • Phytoestrogens: nonsteroidal compounds found in flax seeds and soybeans (e.g., coumestan, isoflavones).

Check Understanding

  • A triglyceride is made up of 3 fatty acids and 1 glycerol.

  • Triglycerides are False for hydrophilic.

  • Unsaturated fatty acids contain double bonds.

  • Phospholipids have 2 fatty acid chains.

  • The phosphate group makes part of phospholipids hydrophilic.

  • All steroids contain 4 fused rings.

  • C) Isoflavone is not a steroid.

Proteins

Structure

  • Proteins are polymers made from 20 types of amino acids connected by peptide bonds.

    • Peptide: a chain of 2 or more amino acids.

    • Polypeptide: many amino acids joined together.

    • Protein: consists of one or more polypeptide chains.

Amino Acids

  • Basic structure includes an amino group, carboxyl group, and a side chain.

  • Among the amino acids, 8 are essential for human adults:

    • Leucine (Leu)

    • Isoleucine (Ile)

    • Valine (Val)

    • Methionine (Met)

    • Threonine (Thr)

    • Tryptophan (Trp)

    • Lysine (Lys)

    • Phenylalanine (Phe)

  • Side chains determine the properties of amino acids:

    • Nonpolar side chains: less soluble in water.

    • Polar side chains: hydrophilic.

    • Charged side chains: hydrophilic, categorized into:

    • Acidic: dissociate carboxyl group gives side chains a negative charge.

    • Basic: additional proton on amino group gives side chains a net positive charge.

Structural Levels of Proteins

  • Primary structure: the specific sequence of amino acids.

  • Secondary structure: constitutes alpha helix and beta sheet formations, stabilized by hydrogen bonds (e.g., fibrous proteins).

  • Tertiary structure:

    • Further folds into a globular 3-D shape, where nonpolar amino acids gather in the center, and polar/charged amino acids interact with water externally.

  • Quaternary structure:

    • Involves the joining of 2 or more polypeptide chains.

Folding and Chaperones

  • Chaperone proteins facilitate the proper folding of peptide chains and can correct misfoldings to prevent aggregation into nonfunctional structures.

Functions of Proteins

  • Support: structural proteins (e.g., silk, keratin, collagen).

  • Metabolism: enzymes that catalyze chemical reactions.

  • Transport: through channel proteins and hemoglobin.

  • Defense: function of antibodies.

  • Regulation: involves protein hormones such as insulin and growth hormone.

  • Motion: comprises muscle proteins like actin and myosin.

Protein Denaturation

  • Refers to the disruption of the protein’s natural shape (active sites).

  • Causes include:

    • Strong acids/bases, high salt concentrations, organic solvents, high temperatures, and radiation.

  • Most denaturations are reversible; however, irreversible changes occur if the damage is beyond repair.

Nucleic Acids

Overview

  • Largest molecules in the body, they are polymers composed of nucleotides that contain:

    • Nitrogenous base

    • Pentose sugar

    • Phosphate group

DNA (Deoxyribonucleic Acid)

  • Serves as the blueprint for protein synthesis.

  • Contains the pentose sugar deoxyribose and the bases: adenine (A), guanine (G), cytosine (C), thymine (T).

  • Structured as a double helix, stabilized by base pairing through hydrogen bonds.

RNA (Ribonucleic Acid)

  • Functions in executing the instructions from DNA during protein synthesis (i.e., DNA → mRNA → protein).

  • Contains the pentose sugar ribose and the bases: adenine (A), guanine (G), cytosine (C), uracil (U).

  • Generally exists in a single strand.

  • Three principal varieties:

    • Messenger RNA (mRNA)

    • Transfer RNA (tRNA)

    • Ribosomal RNA (rRNA)

Comparison between DNA and RNA Structure

Feature

DNA

RNA

Sugar

Deoxyribose

Ribose

Bases

Adenine, Guanine, Thymine, Cytosine

Adenine, Guanine, Uracil, Cytosine

Strands

Double stranded with base pairing

Single stranded

Helix

Yes

No

ATP (Adenosine Triphosphate)

  • A special nucleotide, essential for cellular energy.

  • Composed of:

    • Pentose sugar: ribose

    • Base: adenine

    • Phosphate group: three

  • Functions as the primary energy carrier in cells.

Check Understanding

  • Protein is a polymer of amino acids.

  • Nucleic acid is a polymer of nucleotides.

  • C) The R group determines the properties of an amino acid.

  • Secondary structures encompass alpha helices and beta sheets.

  • A protein becomes denatured when its active sites are disrupted and its native shape is altered.

  • A nucleotide consists of A) base, B) pentose sugar, C) phosphate (D) all 3.

  • In DNA, T pairs with A.

  • ATP is a/an C) nucleotide.

Chapter Summary

  • Characteristics of organic molecules include C, H, covalent bonds, large size, and a C atom backbone.

  • Functional groups play key roles in reactivity.

  • Synthesis occurs via dehydration, breakdown through hydrolysis.

  • Main macromolecule categories in organisms: Carbohydrates, Lipids, Proteins, Nucleic Acids.

Study Guide

  • Discuss the general characteristics of organic molecules.

  • List the four classes of organic molecules in living organisms.

  • Identify the types of carbohydrates: ribose, glucose, starch, galactose, fructose, lactose, sucrose, and maltose.

  • Explain the functions of starch, glycogen, and cellulose and their building blocks.

  • Compare the structure of triglycerides and phospholipids and their polarity.

  • Define saturated and unsaturated fatty acids.

  • Determine how the property of a specific amino acid is defined.

  • State the kinds of amino acids found in living organisms and how many are essential for human adults.

  • Describe base pairing in DNA and the stabilizing factors for complementary bases.

  • Contrast the structures of DNA and RNA.

  • Detail the structural components of ATP and its significance to cells.

  • Define isomers and identify major functional groups.

  • Explain protein denaturation and its causes.

  • Discuss the four levels of protein structures.

  • Identify the protein that facilitates proper folding.

  • Classify DNA and RNA as organic compounds and their building blocks.

  • Enumerate the components of a nucleotide.

  • Define the basic structure of steroids and the building blocks for proteins.

  • Explain the importance of carbon in organic molecules.

  • Define dehydration and hydrolysis reactions.