Monomers, Polymers, and Macromolecules

• This study reviews the biology of molecules, also known as molecular biology.
• The study of biological molecules involves the composition, structure, and interactions of cellular molecules, such as nucleic acids and proteins that carry out essential biological processes.
• Four elements are the most common in living organisms: hydrogen, carbon, oxygen, and nitrogen.
• The coursework marks total 40%, and the final examination is worth 60%.

Key Terms

• Monomers: Relatively simple molecules used as basic building blocks for the synthesis of polymers.
• Polymer: A giant molecule made from many similar repeating subunits joined together in a chain.
• Macromolecule: Large biological molecule such as a protein, polysaccharide, or nucleic acid.

Learning Outcomes

• Define and explain the terms monomer, polymers, and macromolecule.
• Describe and explain the function and roles of carbohydrates, protein, lipids, and nucleic acids.
• Describe and draw molecular structures of monomers and polymers of carbohydrates, protein, lipids, and nucleic acids.
• Describe and explain the synthesis and breakdown of polymers via condensation and hydrolysis with reference to glycosidic bonds, ester bonds, peptide bonds, and phosphodiester bonds.
• Describe and draw the arrangement and formations of polymers like carbohydrates, protein, lipids, based on molecular structure.
• Polymers should consider hydrogen bonding, Van der Waals forces, ionic and covalent bondings.
• Explain the effects of polymer arrangement on organisms.
• Explain how hydrogen bonding occurs between water molecules and the properties of water and its roles in living organisms.

Carbohydrates

• Carbohydrates contain carbon (C), hydrogen (H), and oxygen (O).
• Carbohydrates are essential as the primary source of energy.
• Hydrogen and oxygen atoms within carbs are typically present in a 2:1 ratio like water (hydrate).
• Carbohydrates have three main groups: monosaccharides, disaccharides, and polysaccharides.

Monosaccharides

• Simplest carbohydrates (simple sugars).
• They can exist in linear or in ring form.
• Examples are glucose, fructose, and galactose.
• Characteristics: colorless, water-soluble, sweet-tasting, and crystalline solids.
• They can be classified by the number of carbon atoms such as; Trioses (3C), Pentoses (5C) which includes Ribose and deoxyribose, and Hexoses (6C) such Glucose, fructose and galactose

Ring Structure of Glucose

• Alpha (α)-glucose OH group on the first carbon (C1) projects below the plane of the ring.
• Beta (β)-glucose OH group on the first carbon (C1) projects upward the plane of the ring.
• Easy way to memorize the position of OH & H at each carbon (C) of α-glucose & β-glucose.
• Alpha(α)-glucose C1-C4 = BBAB, Beta (β)-glucose C1-C4 = ABAB, *A= above; B= below .
• OH group at C1 is at the below for α-glucose while at the above for β-glucose.
• OH group & H are in the same position at C2-C6 for both glucose.

Disaccharides

• Two monosaccharides join via a glycosidic linkage via condensation to form a disaccharide.
• Glycosidic linkages can be broken via hydrolysis by adding water to the bond.
• Characteristics : water soluble, sweet taste, crystallized
• Three common examples:
  • Maltose (glucose + glucose)
  • Sucrose (glucose + fructose)
  • Lactose (glucose + galactose)

Example Formation and Breakdown of Maltose

• Formation is a condensation or dehydration process that forms a glycosidic bond with the loss of a water molecule.
• Breakdown is a hydrolysis process when a water molecule is added and breaks a glycosidic bond.

Polysaccharides

• Polymers of hundreds to thousands of monosaccharides joined by glycosidic linkages
• Chains may be variable in length, can be branched or unbranched, or straight or coiled.
• Characteristics include being tasteless, insoluble in water, and cannot be crystallized
• Examples are starch, glycogen, and cellulose.

Starch

• Polysaccharide formed from a-glucose.
• It is a major storage form of carbohydrate in plants.
• Due to being insoluble in water can be stored in large amounts with little effect on the water potential
• It is made up of Amylose and Amylopectin:

Amylose

• Made from α-glucose molecules, forms a linear, unbranched polymer chain.
• The linear chain is joined by α-1,4 glycosidic bonds.
• The chains coil into the helix held by hydrogen bond formed between hydroxyl group.

Amylopectin

• Also made from α-glucose molecules, forms branched chains of up to 1500 units
• Linear chain is joined by α-1,4 glycosidic bond between.
• Branches occur every 30 units between neughbouring C1 and C6 atoms.
• Each branch is joined by α-1,6 glycosidic bond.

Glycogen

• Primarily found in the liver and muscle cells where metabolic activities are high.
• Is similar in structure to amylopectin.
• This is major storage form of carbohydrates in animals.
• Consist of 1,4 linked a-glucose with 1,6 linkages.
• have more branches than amylopectin and clump together to form granules which visible and form an energy reserve

Cellulose

• Essential structural material in plants.
• Consisting of long chains of b-glucose which are held together by b-1,4- glycosidic linkages.
• It a straight chain polymer
• Parallel strands of cellulose are linked by hydrogen bonds which forms a very stable structure of cell walls.

Comparison between Starch, Glycogen & Cellulose:

• Starch is made of a-glucose, is branched (amylopectin) and unbranched (amylose), is helical, and stores glucose in plants.
• Glycogen is made of a-glucos is highly branched, and stores glucose in vertebrates, specifically in liver and muscle cells.
• Cellulose is made of β-glucose, is unbranched, consists of straight molecules, and provides building material for a plant's cell wall.

Comparison Between Monosaccharide, Disaccharide & Polysaccharide:

• Monosaccharides have a general formula of [CH2O]n, are simple sugars, have 1 basic monomer unit, are a subunit for di- and polysaccharides, are water-soluble, can crystallize, taste sweet, and have a small molecule and Examples are Glyceraldehyde (3C) and Glucose (6C)
• Disaccharides have a general formula of C12H22O11, are made from double sugars, consist of a combination of two monosaccharides, are water-soluble, can crystallize, taste sweet, are reducing and non-reducing agents and examples are Maltose and Sucrose
• Polysaccharides have a general formula of [C6H10O5]n, are made of complex sugars, and polymers of long chains of repeating units of monosaccharides, are water-insoluble, and cannot crystallize or taste sweet, form colloids and have large molecules; Examples are Starch and Glycogen.

Nucleic Acids

• DNA and RNA molecules are nucleic acids.
• DNA contains information essential for almost all cell activities, including cell division.
• RNA stores and transfers information essential for the manufacturing proteins
• Nucleic acids are polymers made up of monomers called nucleotides.
• Nucleotides are made up of three smaller components which are: a nitrogen-containing base, a pentose sugar (5C) and a phosphate group

Nucleotide Composition

• Pentose sugar: Ribose is found RNA nucleotides.
• Deoxyribose is found in DNA nucleotides.
• Deoxyribose lacks an oxygen atom on carbon number two that ribose has.
• Nitrogenous base: Consists of Rings of carbon and nitrogen.
• Two types : purines & pyrimidines

Pyrimidines

• Contains a single ring
• Three nitrogenous bases: Cytosine (C), Thymine (T), and Uracil (U).

Purines

• Contains double rings
• Two nitrogenous bases: Adenine (A) and Guanine (G).

Differences Between DNA and RNA Nucleotides

• DNA consists of Deoxyribonucleotide, 5 carbon Deoxyribose, and the nitrogenous bases A, C, G, T
• RNA consists of Ribonucleotide, 5 carbon Ribose, and the nitrogenous bases A, C, G, U

Nucleic Acids: DNA and RNA bonding

• Condensation occurs between sugar and the phosphate group of different nucleotides, forming a phosphodiester bond to link nucleotides into a long chain.
• The covalent sugar-phosphate bonds link the 5-carbon of one sugar molecule and the 3-carbon of the next.
• Polynucleotide sequences are referenced in the 5' to 3' direction

Nucleic Acids: DNA

• Two polynucleotides running in opposite directions
• Held together by hydrogen bonds between the bases
• Complementary base pairing: A links with T by two hydrogen bonds; C links with G by three hydrogen bonds.
• Uracil (U) replaces Thymine (T) in RNA

Nucleic Acids: RNA

• Is a molecule with a single strand of RNA
• Contains the sugar ribose
• Uses 4 different nucleotide bases of A, G, C and U
• Three types: mRNA, rRNA, and tRNA
  • Messenger RNA (mRNA) transcribes the DNA and directs the translation of protein.
  • Ribosomal RNA (rRNA) is involved in the translation of proteins.
  • Transfer RNA (tRNA) delivers amino acids to the ribosomes during translation

Differences between DNA and RNA

• DNA contains Deoxyribonucleotide building blocks, the pentose sugar Deoxyribose, the nitrogenous bases Adenine, Guanine, Cytosine, Thymine arranged in a Double-stranded structure, is a Large molecule and its location is in the nucleus.
• RNA contains Ribonucleotide building blocks, the pentose sugar Ribose, the nitrogenous bases, Adenine, Guanine, Cytosine, Uracil arranged in a Single-stranded structure, is a Relatively small molecule and its location is in the nucleus and cytoplasm.

Lipids

• Water insoluble organic molecules that are soluble in organic solvents such as alcohol, ether, and chloroform
• Contains C, H and O
• Lipid functions cell membrane components, energy storage, and insulation
• Familiar examples are; fats and oils
• Animal origin fats (butter) are solid at room temperature and plant origin oils (corn oil) are often liquid at room temperature
• Consist of fatty acids are the building block

Fatty Acids in Lipids

• Series of acids found in fats (lipids)
• Contain an acidic group -COOH, known as a carboxyl group.
• Consist of larger molecules that have long hydrocarbon tails attached to an acid 'head'.

Triglycerides

• They are common lipids, and consist of 1 glycerol and 3 fatty acids.
• The molecules are joined together by ester linkage formed via condensation or esterification.
• Occurs between a hydroxyl group of glycerol and a carboxyl group of fatty acids.
• A water molecule is removed in each reaction with a total loss of 3 water molecules per triglyceride

Phospholipids

• 2 fatty acids are attached to glycerol and a phosphate group
• Example are cell membrane structures
• They self assemble into aggregates with the hydrophobic tails pointing toward the center and the hydrophilic heads on the outside when they reacts with water.

Test your understanding of monomers, polymers, and macromolecules. Explore bonding, synthesis, and properties. Review the role of water and key elements.