BIOLOGY 2e Chapter 3 BIOLOGICAL MACROMOLECULES Lecture PowerPoint Slides

Biological Macromolecules

Chapter 3 Overview

This chapter covers the four major classes of biological macromolecules: carbohydrates, lipids, proteins, and nucleic acids.

3.1 Synthesis of Biological Macromolecules

Learning Objectives

• Understand macromolecule synthesis.

• Explain dehydration (condensation) and hydrolysis reactions.

Macromolecules and Monomers

• Macromolecules are made of individual subunits called monomers.

• Two monomers can link via a covalent bond to form a dimer.

• Multiple monomers join to form a polymer.

Dehydration Synthesis (Condensation)

• Forms bonds between monomers by removing a water molecule.

• Example: two glucose molecules link to form maltose, a disaccharide, with the release of water.

Hydrolysis

• Breaks polymers into individual monomers by adding water.

• Water acts as a reactant; one monomer receives a H+, and the other receives an OH-.

• It is the reverse of dehydration synthesis.

Enzymes in Macromolecule Reactions

• Enzymes catalyze (speed up) hydrolysis and dehydration reactions.

• Dehydration reactions require energy to form new bonds.

• Hydrolysis reactions release energy by breaking bonds.

• Specific enzymes exist for each macromolecule class:

  • Carbohydrates: amylase, sucrase, lactase, maltase.

  • Lipids: lipases.

  • Proteins: pepsin and peptidase.

3.2 Carbohydrates

Learning Objectives

• Discuss the role of carbohydrates in cells and extracellular materials.

• Explain carbohydrate classifications.

• List common monosaccharides, disaccharides, and polysaccharides.

Carbohydrates

• Found in grains, fruits, and vegetables.

• Provide energy in the form of glucose.

• General formula: (CH2O)n

• Carbon:Hydrogen:Oxygen ratio is 1:2:1.

Classes of Carbohydrates

1. Monosaccharides

2. Disaccharides

3. Polysaccharides

Monosaccharides

• Usually have 3-7 carbons bound to a hydroxyl group.

• Names end with the suffix '-ose'.

• Contain a carbonyl group (C=O).

Examples of Monosaccharides

• Aldoses: Carbonyl group at the end of the carbon chain.

• Ketoses: Carbonyl group in the middle of the carbon chain.

• Trioses: three carbons.

• Pentoses: five carbons.

• Hexoses: six carbons.

Structural Isomers of Hexose Monosaccharides

• Formula (C6H{12}O_6)

  1. Glucose: important energy source.

  2. Galactose: part of lactose (milk sugar).

  3. Fructose: part of sucrose (fruit sugar).

Monosaccharide Structure

• Exist as linear chains or ring-shaped molecules in aqueous solutions.

• Five- and six-carbon monosaccharides exist in equilibrium between linear and ring forms.

• Ring forms are locked into α or β positions.

• Fructose and ribose also form rings.

Disaccharide Formation

• Formed when two monosaccharides are linked via dehydration.

• Example: Glucose + Fructose = Sucrose.

• Monosaccharides are joined by a glycosidic bond (glycosidic linkage).

• Water is released.

• Carbon atoms in a monosaccharide are numbered from the carbon closest to the carbonyl group.

• A 1,2 glycosidic linkage forms between carbon 1 in glucose and carbon 2 in fructose.

Common Disaccharides

• Maltose (grain sugar).

• Lactose (milk sugar).

• Sucrose (table sugar).

• All created by covalent glycosidic linkages.

Polysaccharides

• Long chain of monosaccharides joined by glycosidic linkages.

• May be branched or unbranched.

• May consist of multiple types of monosaccharides.

• Molecular mass > 10,000 amu.

• Examples with glucose monomers:

  • Starch: energy storage in plants.

  • Cellulose: cell walls of plants.

  • Chitin: cell walls of fungi and arthropod exoskeletons.

  • Glycogen: energy storage in animals.

Starch

• Composed of amylose and amylopectin.

• Joined by two linkage types:

  1. α 1-4 glycosidic bonds.

  2. α 1-6 glycosidic bonds.

• Amylose: unbranched glucose monomers in α 1-4 glycosidic bonds.

• Amylopectin: branched glucose monomers in α 1-4 and α 1-6 glycosidic bonds.

Cellulose

• Glucose monomers linked in unbranched chains by β 1-4 glycosidic linkages.

• Every glucose monomer is flipped relative to the next, forming a linear, fibrous structure.

• Found in plant cell walls and is the major component of wood and paper.

• Most animals lack enzymes to digest cellulose.

Chitin

• The hard exoskeleton of arthropods and cell walls of fungi.

• Contains nitrogen.

3.3 Lipids

Learning Objectives

• Describe the four major types of lipids.

• Explain the role of fats in storing energy.

• Differentiate between saturated and unsaturated fatty acids.

• Describe phospholipids and their role in cells.

• Define the basic structure of a steroid and some steroid functions.

Lipids

• Diverse group of non-polar hydrocarbons.

• Hydrophobic (water-hating).

Functions of Lipids

• Long-term energy stores.

• Insulation for plants and animals.

• Building blocks for some hormones.

• Important component of cellular membranes.

Types of Lipids

1. Fats & Oils

2. Waxes

3. Phospholipids

4. Steroids

Fats and Oils

• Contain two main components:

  1. Glycerol

  2. Fatty Acids

• Triacylglycerol: formed by joining three fatty acids to a glycerol backbone via ester linkages.

• Three molecules of water are released in this reaction.

Saturated Fatty Acids

• Contain no carbon-carbon double bonds.

• Pack tightly and are solid at room temperature (butter, fat in meats).

• May be associated with cardiovascular disease; should be limited in the diet.

Unsaturated Fatty Acids

• Contain at least one carbon-carbon double bond.

• Monounsaturated fat: one double bond.

• Polyunsaturated fat: more than one double bond.

• Most are liquids at room temperature (oils).

Trans-Fats

• Each double bond of an unsaturated fat can be in cis or trans configuration.

• Cis: hydrogens on the same side of the chain, causing a kink; liquid at room temperature.

• Trans: hydrogens on opposite sides; no kink, can be created through processing.

• Trans fats increase LDL cholesterol (bad for the heart).

Essential Fatty Acids

• Required but not synthesized by the body; must be part of the diet.

• Example: omega-3 fatty acids (salmon, trout, tuna); heart-healthy.

• Reduce the risk of heart attack, reduce triglycerides, lower blood pressure.

• Alpha-linolenic acid is an example of an omega-3 fatty acid.

Waxes

• Hydrophobic; prevent water from sticking to surfaces.

• Found on feathers of aquatic birds and on the surface of leaves.

Phospholipids

• Molecule with two fatty acids and a modified phosphate group attached to a glycerol backbone.

• Amphipathic: has a hydrophobic portion (fatty acid tails) and a hydrophilic portion (phosphate group head).

Phospholipids and Plasma Membrane

• Hydrophilic heads face the aqueous solution.

• Hydrophobic tails sequester in the middle of the bilayer.

• Contribute to the dynamic nature of the plasma membrane.

Steroids

• Have a closed ring structure (four linked carbon rings).

• Hydrophobic and insoluble in water.

• Cholesterol is the most common steroid, synthesized in the liver.

• Precursor to other hormones like testosterone and estradiol and to vitamin D.

3.4 Proteins

Learning Objectives

• Describe the functions proteins perform in cells and tissues.

• Discuss the relationship between amino acids and proteins.

• Explain the four levels of protein organization.

• Describe the ways in which protein shape and function are linked.

Protein

• Most abundant organic molecules.

• Diverse functions: regulatory, structural, protective, transport, catalytic (enzymes).

Enzymes

• Catalysts in biochemical reactions.

• Specific enzyme for a specific substrate.

• Most enzyme names end in '-ase'.

• Types: catabolic (break down) and anabolic (build complex molecules).

Protein Types and Functions

• Digestive Enzymes: Amylase, lipase, pepsin, trypsin. Help in digestion by catabolizing nutrients into monomeric units.

• Transport: Hemoglobin, albumin. Carry substances in the blood or lymph throughout the body.

• Structural: Actin, tubulin, keratin. Construct different structures, like the cytoskeleton.

• Hormones: Insulin, thyroxine. Coordinate the activity of different body systems.

• Defense: Immunoglobulins. Protect the body from foreign pathogens.

• Contractile: Actin, myosin. Muscle contraction.

• Storage: Legume storage proteins, egg white (albumin). Provide nourishment in early development.

Amino Acids

• Monomers that make up proteins.

• Fundamental structure:

  • Central carbon atom (α-carbon).

  • Amino group (−NH_2).

  • Carboxyl group (−COOH).

  • Hydrogen.

  • Side chain (R-group).

• R-groups determine the chemical nature of each amino acid.

Amino Acid Properties

• 20 common amino acids.

• Each has a different R group (side chain).

• Categories: nonpolar aliphatic, polar, positively charged, negatively charged, nonpolar aromatic.

• Amino acids are represented by a single upper-case letter or a standard three-letter symbol (e.g., Valine = V or Val).

Essential Amino Acids

• Must be supplied in the diet for humans:

  • isoleucine

  • leucine

  • cysteine

• The sequence and number of amino acids determine protein shape, size, and function.

Peptide Bond Formation

• Amino acid monomers are linked by peptide bonds (dehydration synthesis).

• The carboxyl group of one amino acid links to the amino group of the next.

• A molecule of water is released.

Polypeptides and Proteins

• Polypeptide: a chain of amino acids joined together in peptide linkages.

• Protein: a polypeptide or multiple polypeptides with a biological function, often combined with non-peptide groups; has a unique structure and function.

Protein Structure

• Based on four levels:

  1. Primary structure

  2. Secondary structure

  3. Tertiary structure

  4. Quaternary structure

• Protein shape is crucial to function.

Primary Structure

• The unique sequence of amino acids in a polypeptide.

• Protein function is compromised if the order is changed.

• Amino acid sequence is based on the gene encoding that protein.

• A change in nucleotide sequence of DNA could lead to a change in amino acid, affecting protein structure and function.

Sickle Cell Anemia

• Demonstrates how one amino acid change can impact health. In sickle cell hemoglobin, glutamic acid is replaced by valine at position seven.

Secondary Structure

• Local folding of the polypeptide due to hydrogen bonding in the polypeptide backbone.

• Two types:

  1. α-helix

  2. β-pleated sheet

Tertiary Structure

• The unique three-dimensional structure of a polypeptide due to chemical interactions between R-groups.

• R-groups with like charges repel; hydrophobic R-groups cluster in the interior; cysteine side chains form disulfide bridges.

• Determined by hydrophobic interactions, ionic bonding, hydrogen bonding, and disulfide linkages.

Quaternary Structure

• Interactions between several polypeptides that make up a protein.

Denaturation

• Protein structure and shape can change if chemical interactions are broken due to changes in pH or temperature.

• Denaturation: changes in protein structure that lead to changes in function.

3.5 Nucleic Acids

Learning Objectives

• Describe nucleic acid structure and define the two types of nucleic acids.

• Explain DNA structure and role.

• Explain RNA structure and roles.

Nucleic acid

• Nucleic acids: polymers of different nucleotides in a specific sequence.

• Two types:

  • Deoxyribonucleic acid (DNA).

  • Ribonucleic acid (RNA).

DNA

• Genetic material inherited from the previous generation and replicated whenever a cell divides.

• Contains instructions for synthesizing specific proteins and RNAs.

RNA

• Involved in protein synthesis.

• The nucleotide sequence is made from a DNA template.

DNA and the Genome

• DNA codes for the genome of the cell (entire genetic content).

• Chromatin: a complex of DNA and histone proteins.

• Chromosomes: threadlike structures containing tightly wound and packed chromatin.

• DNA codes for thousands of genes, which contain instructions for producing proteins or RNAs.

Nucleotides

• Monomers of nucleic acids.

• Consist of three parts:

  1. Nitrogenous base

  2. Pentose sugar

  3. One or more phosphate groups

• Joined by phosphodiester linkages (covalent bonds).

Components of Nucleic Acids

• Nitrogenous bases:

  • Pyrimidines (single ring): cytosine, thymine (DNA), uracil (RNA).

  • Purines (double ring): adenine, guanine.

• Pentose sugars:

  • Deoxyribose (DNA).

  • Ribose (RNA).

DNA Structure

• Double helix structure.

• Sugar and phosphate lie on the outside; nitrogenous bases are stacked in the interior.

• Strands run in opposite directions (antiparallel).

• Each base from one strand interacts by hydrogen bonding with a base from the opposite strand.

Polymerization of Nucleotides

• 5' and 3' refer to the numbered carbon atoms in the pentose sugar.

• Phosphodiester bonds form between the phosphate (bound to the 5' carbon) of one nucleotide and the 3' carbon of the other.

Base-Pairing in DNA

• Strands run antiparallel (one 5' to 3', the other 3' to 5').

• Adenine (A) pairs with thymine (T).

• Guanine (G) pairs with cytosine (C).

DNA Replication

• The process by which DNA is copied.

RNA Roles

• Primarily involved in protein synthesis.

• Types:

  1. Messenger RNA (mRNA): carries information for protein synthesis.

  2. Transfer RNA (tRNA): serves as a bridge between nucleotides and amino acids.

  3. Ribosomal RNA (rRNA): component of ribosomes; functions in protein synthesis.

Protein Synthesis Overview

• Instructions are coded in DNA nucleotide sequences.

• An RNA copy (mRNA) is synthesized via transcription.

• The mRNA is then used to synthesize the protein via translation.

Central Dogma of Molecular Biology

• DNA can make copies of itself (replication).

• DNA is transcribed into RNA.

• RNA is translated to protein.

Transcription

• DNA expresses a particular gene by synthesizing mRNA.

• The RNA base sequence is complementary to the DNA sequence, but uracil is used in place of thymine.

RNA and Protein Production

• Ribosomes are made of proteins and rRNA; the mRNA transcript binds with ribosomes, and the rRNA has catalytic activity.

• mRNA bases are read in sets of three (codons).

• tRNA base pairs with the codon and delivers the correct amino acid.

• Peptide linkages are made at the ribosome to grow the polypeptide.

DNA vs. RNA

Biological Polymers Summary