Biological Macromolecules
Biological Macromolecules
Introduction
Biological macromolecules are large molecules essential for life, constructed from smaller organic molecules.
There are four major classes of biological macromolecules:
Carbohydrates
Lipids
Proteins
Nucleic Acids
These molecules are organic, meaning they contain carbon and may include hydrogen, oxygen, nitrogen, and other minor elements.
Dehydration Synthesis
Macromolecules (polymers) are formed from monomers through a covalent bond.
Monomers (from Greek 'mono' meaning one) are subunits or building blocks of larger molecules.
Polymers (from Greek 'poly' meaning many) consist of multiple monomers covalently bonded.
Dehydration Synthesis: This is the process of bonding two or more monomers together, releasing water as a byproduct.
Hydrolysis
Hydrolysis: The process by which polymers break down into monomers.
The terms are derived from:
Hydro: meaning water
Lysis: meaning to break apart.
Both dehydration synthesis and hydrolysis reactions are catalyzed by specific enzymes.
Dehydration synthesis requires energy to bond monomers, while hydrolysis releases energy when breaking down polymers.
Carbohydrates
Defining Carbohydrates
Carbohydrates are organic molecules that can be represented by the formula (1:2:1 ratio of carbon to hydrogen to oxygen).
Monosaccharides
Monosaccharides are simple sugars, with glucose being the most common example.
The term monosaccharide (from Greek 'mono' meaning one and 'sacchar' meaning sugar) refers to the simplest form of carbohydrates.
Common characteristics:
Carbons range from 3 to 7.
They can exist in linear forms or ring-shaped molecules.
Important examples include Glucose, Galactose, and Fructose, which are isomeric monosaccharides with the formula .
Example of a function: Glucose is used to produce ATP, the energy currency of cells.
Disaccharides
Disaccharides are formed when two monosaccharides undergo a dehydration reaction to form a covalent bond.
The term 'disaccharide' derives from 'di' meaning two and 'sacchar' meaning sugar.
Glycosidic Bond: This is the covalent bond that forms between a carbohydrate molecule and another molecule.
Common disaccharides include:
Lactose (milk sugar)
Maltose (grain sugar)
Sucrose (table sugar).
Polysaccharides
Polysaccharides: Long chains of monosaccharides linked by glycosidic bonds.
The term 'polysaccharide' comes from 'poly' meaning many and 'sacchar' meaning sweet.
They can be branched or unbranched and composed of different types of monosaccharides.
Common polysaccharides include:
Starch: Storage form of sugar in plants.
Glycogen: The storage form of glucose in humans and other vertebrates, primarily composed of glucose monomers.
Cellulose: A structural component of the plant cell wall.
Chitin: A nitrogen-containing polysaccharide.
Benefits of Carbohydrates
Essential for a balanced diet.
Energy content: 1 gram of carbohydrates provides approximately 4.3 kilocalories.
Fiber: Promotes regular bowel movements and regulates blood glucose levels. It removes excess cholesterol, preventing its entry into the bloodstream and may reduce the occurrence of colon cancer.
Glucose serves as an immediate energy source, particularly for cellular processes such as ATP production.
Lipids
Defining Lipids
Lipids are a diverse group of compounds characterized primarily by their hydrophobic nature; they are mostly nonpolar in composition.
They include hydrocarbons predominantly consisting of carbon-carbon or carbon-hydrogen bonds.
Key characteristics:
Nonpolar Molecules: Hydrophobic, unable to mix with water.
Functions include storing long-term energy, providing insulation, serving as building blocks for hormones, and forming cellular membranes.
Main categories of lipids:
Fats
Oils
Waxes
Phospholipids
Steroids.
Fats and Oils
A fat molecule consists of:
Glycerol: An organic compound with three carbons, five hydrogens, and three hydroxyl (OH) groups.
Fatty Acids: Long chains of hydrocarbons with a carboxyl group attached; lengths ranging from 4 to 36 carbons.
Saturated and Unsaturated Fatty Acids
Saturated Fatty Acids: Characterized by single bonds between neighboring carbons in the fatty acid chains, resulting in a solid state at room temperature.
Examples: Stearic acid, palmitic acid, butyric acid, and animal fats.
Unsaturated Fatty Acids: Contain at least one double bond within the hydrocarbon chains and typically remain liquid at room temperature (oils).
Plant-derived, they assist in lowering blood cholesterol levels.
Identified as either cis (hydrogens on the same side) or trans (hydrogens on opposite sides).
Examples: Oleic acid, olive oil, corn oil, and cod liver oil.
Trans Fats
Trans Fats: Created by artificially hydrogenating oils to transform them into a semi-solid state.
High trans fat intake can elevate low-density lipoproteins (LDL - bad cholesterol), posing cardiovascular risks.
Food labeling is required when trans fats are present. Common examples include margarine and certain peanut butter types.
Omega Fatty Acids
Omega Fatty Acids: Essential fatty acids that must be obtained through the diet since the body cannot synthesize them.
Health benefits include reducing heart attack risks, lowering triglyceride levels, and decreasing blood pressure.
Examples: Omega-3 fatty acids include alpha-linoleic acid (ALA), eicosatetraenoic acid (EPA), and docosahexaenoic acid (DHA) found in fatty fish like salmon, trout, and tuna.
Waxes and Phospholipids
Waxes: Lipids comprising long-chain fatty acids esterified to long-chain alcohols, serving protective functions on surfaces like leaves and animal fur.
Phospholipids: Major components of plasma membranes, comprised of fatty acid chains linked to a glycerol backbone, characterized as amphipathic (having both hydrophobic and hydrophilic parts).
Steroids
Steroids: Comprise fused ring structures, are hydrophobic and insoluble in water. Many, such as cholesterol, possess –OH functional groups, classifying them as sterols.
Proteins
Defining Proteins
Proteins are among the most abundant organic molecules in living systems and showcase the widest variety of functions of any macromolecule.
Functions may include:
Structural roles
Regulatory roles
Protective functions
Involvement in transport, storage, toxin creation, or enzymatic activity.
Each cell may contain thousands of types of proteins, which are polymers of amino acids arranged in specific linear sequences.
Types and Functions of Proteins
Enzymes: Catalysts for biochemical reactions, often complex or conjugated proteins, specialized for substrates.
Example: Digestive enzymes like amylase, lipase, pepsin, and trypsin facilitate nutrient breakdown into monomeric units.
Hormones: Chemical-signaling molecules, often small proteins or steroids, secreted by endocrine cells to regulate physiological processes, including growth and metabolism.
Additional protein types include:
Transport: Hemoglobin and albumin carrying substances in blood or lymph.
Structural: Includes actin, tubulin, keratin for constructing structural components like the cytoskeleton.
Defense: Immunoglobulins for protecting against pathogens.
Contractile: Actin and myosin for muscle contraction.
Storage: Legume storage proteins and egg white (albumin) providing nourishment during early development stages.
Amino Acids
Proteins are formed from monomers called amino acids, with 20 common amino acids.
Among these, 9 are essential amino acids that humans must obtain from dietary sources.
Amino acids are linked by peptide bonds, which form through dehydration reactions and create polypeptides (polymers of amino acids with free amino groups).
Protein Structure
Primary Structure: Linear sequence of amino acids constituting a protein.
Secondary Structure: Regular structures formed through hydrogen bonds between amino acids, including:
α-Helix: A helical structure stabilized by hydrogen bonds.
β-Pleated Leaflet: A structure with hydrogen bonding creating 'pleats'.
Tertiary Structure: The overall three-dimensional conformation resulting from interactions between secondary structural elements and amino acid side chains.
Quaternary Structure: The assembly of discrete polypeptide subunits within a protein.
Denaturation and Protein Folding
Denaturation: The loss of structural integrity in a protein due to environmental factors (e.g., temperature, pH, chemicals), which can be reversible or irreversible.
Protein Folding: Critical for protein function, often assisted by chaperones that help the protein achieve its proper configuration before dissociating after folding completion.
Nucleic Acids
Defining Nucleic Acids
Nucleic Acids are biological macromolecules that carry the genetic blueprint for cells and instruct cell functioning.
Two primary types exist:
DNA (Deoxyribonucleic Acid)
RNA (Ribonucleic Acid).
Both nucleic acids are made of monomers called nucleotides, which consist of:
A nitrogenous base
A pentose (five-carbon) sugar
A phosphate group.
DNA Structure
Double Helix Structure: Formed by two strands of nucleotides coiling around each other.
The sugar and phosphate groups form the backbone of the helices, while nitrogenous bases (A, T, G, C) stack in the center like steps on a staircase.
Hydrogen bonds connect the base pairs.
Strands exhibit antiparallel orientation (running in opposite directions).
Base Pairing in DNA and RNA
In base pairing, the following relationships hold:
Cytosine pairs with Guanine
Adenine pairs with Thymine in DNA and Uracil in RNA.
Purines include Adenine and Guanine; Pyrimidines include Cytosine, Thymine, and Uracil.
RNA Structure and Types
RNA is involved in protein synthesis, typically single-stranded, comprising ribonucleotides linked by phosphodiester bonds.
Contains ribose as the sugar and has bases A, U, G, and C.
Four types of RNA:
Messenger RNA (mRNA): Carries genetic information from DNA to ribosomes during protein synthesis.
Ribosomal RNA (rRNA): Helps align mRNA and tRNA during translation and catalyzes peptide bond formation.
Transfer RNA (tRNA): Transports activated amino acids to the ribosome during protein synthesis.
MicroRNA (miRNA): Involved in regulating gene expression and suppressing mRNA messages.
Central Dogma of Molecular Biology
The Central Dogma of Life describes the flow of genetic information in organisms as:
From DNA to RNA to Protein.
The processes:
Transcription: The synthesis of mRNA from DNA.
Translation: The synthesis of proteins based on mRNA structure.
Exceptions occur in specific viral processes that do not conform to this flow.