Biological Molecules

Polymers are large molecules made by bonding together many smaller, repeating units called monomers. Think of it like a train (polymer) made up of individual train cars (monomers).

• Polymer: A large molecule composed of repeating subunits.

• Monomer: A small, basic unit that makes up a polymer.

There are four major types of polymers:

1. Polysaccharides: Made from many glucose molecules.

2. Lipids: (fats or oils) Made from fatty acids and glycerol.

3. Proteins: Made from amino acids.

4. DNA: (deoxyribonucleic acid) Made from nucleotides.

Types of Bonds in Biological Molecules

Different types of bonds hold monomers together to form polymers:

• Glycosidic bonds: Link monosaccharides in polysaccharides.

• Ester bonds: Link fatty acids and glycerol in lipids.

• Peptide bonds: Link amino acids in proteins.

• Hydrogen bonds: Link nucleotides in DNA.

Summary: Polymers and Monomers

Polymers are large molecules built from repeating monomer units. The four major types of polymers are polysaccharides, lipids, proteins, and DNA, each formed from specific monomers linked by particular bonds.

Think About It: Can you think of other examples of polymers in everyday life?

Carbohydrates

Introduction to Carbohydrates

Carbohydrates are organic molecules containing carbon, hydrogen, and oxygen. They are composed of sugar molecule units called saccharides.

Examples: glucose, sucrose, lactose, starch, glycogen, and cellulose.

Types of Carbohydrates

Carbohydrates are classified into three main types based on the number of sugar units:

1. Monosaccharides: Simple sugars consisting of one molecule.

2. Disaccharides: Carbohydrates made of two monosaccharides joined together.

3. Polysaccharides: Large, complex carbohydrates made up of many monosaccharides.

Monosaccharides

Monosaccharides are simple sugars with the general formula C6H12O6C6​H12​O6​.

Example: Glucose.

Disaccharides

Disaccharides are formed when two monosaccharides bond together through a glycosidic bond.

Polysaccharides

Polysaccharides are large, insoluble carbohydrates formed by the polymerization of many monosaccharides.

Summary: Carbohydrates

Carbohydrates are essential organic molecules made of carbon, hydrogen, and oxygen. They are classified as monosaccharides, disaccharides, or polysaccharides based on their complexity, with glycosidic bonds linking the sugar units.

Think About It: How do the structures of monosaccharides, disaccharides, and polysaccharides relate to their functions?

Proteins

Introduction to Proteins

Proteins are complex molecules containing carbon, hydrogen, oxygen, and nitrogen, and sometimes sulfur. They are made up of amino acids.

• Amino acids: The building blocks of proteins, with about 20 different naturally occurring types.

Protein Structure

One protein molecule consists of many amino acids linked together by peptide bonds.

Summary: Proteins

Proteins are vital molecules composed of amino acids linked by peptide bonds. They contain carbon, hydrogen, oxygen, and nitrogen, and sometimes sulfur.

Think About It: Why are proteins so diverse in their functions?

Lipids

Introduction to Lipids

Lipids (fats or oils) are composed of hydrogen, carbon, and oxygen. A lipid molecule consists of glycerol and three fatty acids linked by ester bonds.

Properties of Lipids

• Fats do not dissolve in water.

• Animal fats: Made up of saturated fatty acids and are usually solid at room temperature.

• Plant fats: Composed of unsaturated fatty acids and are usually liquid at room temperature.

Summary: Lipids

Lipids are essential molecules made of glycerol and fatty acids, joined by ester bonds. They are insoluble in water and can be either saturated (animal fats, solid at room temperature) or unsaturated (plant fats, liquid at room temperature).

Think About It: What makes lipids hydrophobic (water-repelling)?

Roles of Carbohydrates, Proteins, and Lipids

Roles of Carbohydrates

• Glucose: Broken down during respiration to release energy.

• Sucrose: A transport form of carbohydrates in plants.

• Glycogen: A storage form of carbohydrates in animals.

• Starch: A storage form of carbohydrates in plants.

• Cellulose: Used in the formation of cell walls.

Roles of Proteins

• Responsible for growth.

• Help repair damaged tissues.

• Provide energy in the absence of carbohydrates and fats.

• Enzymes: Act as biological catalysts in chemical reactions.

• Collagen: Needed in cartilage, tendons, and ligaments.

• Some hormones, like insulin, are proteins.

• Part of the immune system as antibodies help fight against infections.

Roles of Lipids (Fats or Oils)

• Major source of energy.

• Act as an insulating layer against heat loss.

• Help form the waterproof cuticle in leaves to reduce water loss.

• Part of the structure of a cell membrane.

Summary: Biological Molecule Roles

Carbohydrates, proteins, and lipids each play vital roles in living organisms, from energy storage and transport to structural support and catalysis.

Think About It: How do the different roles of carbohydrates, proteins, and lipids contribute to the overall function of a living organism?

Role of Water as a Solvent

Water as a Solvent

Water dissolves solutes to make solutions and dissolves more substances than any other liquid. It acts as a transport medium for many blood molecules.

Importance of Water

• Water is part of blood plasma, in which soluble nutrients dissolve after digestion to be transported to other parts.

• Aids in the removal of metabolic waste as the wastes dissolve in blood plasma to be transported to excretory organs.

• Dissolves plant nutrients in the soil, allowing them to be absorbed by root hair cells.

Summary: Water as a Solvent

Water's role as a solvent is critical for transporting nutrients, removing waste, and facilitating absorption in both plants and animals.

Think About It: Why is water such a good solvent?

Amino Acid Sequences and Protein Shape

Amino Acid Sequences

There are 20 types of amino acids in protein structures. Long chains of amino acids linked together through peptide bonds make up protein molecules.

Protein Shape and Function

Each protein chain has its own particular amino acid sequence. These sequences cause a folding of the chain to give proteins different shapes and functions. The sequence of amino acids in a protein is determined by the sequence of nucleotide bases in the DNA.

Summary: Protein Structure

The specific sequence of amino acids in a protein determines its unique shape and, consequently, its specific function. This sequence is dictated by the DNA.

Think About It: How does a change in the amino acid sequence affect a protein's function?

DNA Structure

Introduction to DNA

Deoxyribonucleic acid (DNA) is the heredity material in organisms as it carries genetic instructions. DNA is located in the chromosomes in the nucleus of cells. DNA is a long molecule in the form of a double helix.

DNA Structure Details

Two strands go together to form a double helix. Each strand contains chemicals called bases.

• Bases always pair up in the same way: adenine (A) with thymine (T), and cytosine (C) with guanine (G).

Nucleotides

The DNA molecule is made up of subunits called nucleotides. Each nucleotide is made up of three chemical groups:

1. A sugar molecule called deoxyribose sugar.

2. A nitrogenous base.

3. A phosphate group.

Nitrogenous Bases

There are four nitrogenous bases: adenine, thymine, guanine, and cytosine. The nitrogenous bases have complementary pairing: adenine combines with thymine, while guanine combines with cytosine.

• Between the complementary base pairs are weak hydrogen bonds. There are two hydrogen bonds between A and T, while there are three hydrogen bonds between G and C.

• Adenine and guanine are called purines (large bases), while cytosine and thymine are called pyrimidines (small bases).

• DNA is made up of many nucleotides joined together; hence, it is a polynucleotide.

Summary: DNA Structure

DNA is a double helix composed of nucleotides, each containing a deoxyribose sugar, a phosphate group, and a nitrogenous base (adenine, thymine, guanine, or cytosine). Bases pair complementarily (A with T, and C with G) via hydrogen bonds.

Think About It: How does the structure of DNA enable it to store and transmit genetic information?

Chemical Tests

Benedict's Test (Reducing Sugars)

Benedict's solution is used to test for reducing sugars, like glucose and maltose.

• Benedict's solution is a clear blue solution. In the presence of simple sugars, the blue solution changes color to green, yellow, or red, depending on the amount of sugar.

Procedure:

1. Place 5 cm³ of Benedict's solution in a test tube.

2. Shake the test tube gently to obtain a clear blue color.

3. Crush the food sample to be tested and add it to the test solution.

4. Shake the mixture thoroughly and heat the tube in a water bath over a Bunsen burner.

Result Interpretation:

| Color | Interpretation | | ---------------- | ------------------------------ | | Orange to Red | Large amount of sugar present | | Greenish Yellow | Small amount of glucose present | | Remains Blue | No reducing sugar present |

Iodine Test (Starch)

Iodine solution is used to test for the presence of starch in food samples.

• Iodine solution is a brown solution that turns blue to black in the presence of starch.

Procedure:

1. Crush the food to be tested into small pieces.

2. Spread the crushed food on a white tile.

3. Use a dropper or syringe to add a few drops of iodine solution to the food.

Result Interpretation:

| Color Change | Interpretation | | ------------------- | ---------------- | | Brown to Black/Blue | Starch is present | | Remains Brown | No starch is present |

Biuret Test (Proteins)

The Biuret test detects the presence of protein in food.

• Biuret reagent is blue and consists of potassium hydroxide or sodium hydroxide and copper sulfate. It detects peptide bonds in proteins.

Procedure:

1. Crush the food sample (if necessary) and place it in a test tube.

2. Add equal amounts (e.g., 5 cm³) of Biuret reagent A (copper sulfate) and Biuret reagent B (potassium hydroxide or sodium hydroxide) to the test tube containing the food sample.

3. Add distilled water to the mixture and shake it gently.

4. Allow the mixture to settle for a few minutes and observe color changes.

Result Interpretation:

| Color Change | Interpretation | | ----------------- | -------------- | | Remains Blue | No protein present | | Changes to Purple | Protein is present |

🧪 Tests for Nutrients in Foods

Ethanol Test for Fats

The ethanol test identifies the presence of fats in a food sample.

Procedure:

1. Take a food sample and add ethanol (alcohol), about 2 centimeters cubic.

2. Shake the mixture thoroughly.

3. Allow it to settle for 10 minutes to let the food dissolve in the ethanol.

4. Pour the clear liquid into another test tube.

5. Add 2 centimeters cubic of distilled water.

6. Observe the results.

Interpretation of the Ethanol Test

• If the sample contains fat, tiny globules will float in the water.

• A milky or white suspension indicates the presence of a lipid.

• If it stays clear, there is no fat present in the sample.

DCPIP Test for Vitamin C (Ascorbic Acid)

The DCPIP test is used to detect the presence of vitamin C (ascorbic acid) in food. The DCPIP solution is initially blue in color.

Procedure:

1. Place 5 centimeters cubic of blue DCPIP solution in a test tube.

2. Use a dropper or graduated pipette to add the sample drop by drop to the DCPIP test tube.

3. Shake the tube gently after adding each drop.

4. Record the number of food sample drops that are added to the DCPIP.

Interpretation of the DCPIP Test

• The fewer the drops taken to change the blue DCPIP to clear, the more vitamin C the sample contains.

• If the DCPIP remains blue, there is no vitamin C present.

Summary: Chemical Tests

Various chemical tests are used to identify the presence of specific biological molecules in food samples. These tests rely on color changes to indicate the presence or absence of the target molecule.

Think About It: Why is it important to use controls when performing chemical tests?

🍎 Investigating the Distribution of Carbohydrates, Fats, and Proteins in Seeds and Fruits

Materials Needed

• Fruits (e.g., camel thorn pods, bananas, apples)

• Seeds (e.g., sunflower seeds, watermelon seeds)

• Benedict's solution

• Biuret solution

• Iodine solution

• Ethanol

• Distilled water

• Mortar and pestle

• Test tubes

Procedure

1. Follow the procedures for each test as described above.

2. Test various food sources for starch, reducing sugar, fats, and protein content separately.

3. Draw a well-labeled table and record your observations for each test.

4. Make conclusions by comparing the various results for each test.

Summary: Investigating Food Content

By performing the chemical tests described, you can investigate the distribution of carbohydrates, fats, and proteins in different seeds and fruits.

Think About It: How can this investigation help you understand the nutritional value of different foods?

Comprehensive Review

• Polymers are large molecules made of repeating monomer units.

• The four major types of polymers are polysaccharides, lipids, proteins, and DNA.

• Carbohydrates are organic molecules made of carbon, hydrogen, and oxygen, classified as monosaccharides, disaccharides, and polysaccharides.

• Proteins are made of amino acids linked by peptide bonds.

• Lipids are made of glycerol and fatty acids linked by ester bonds.

• Water is an essential solvent that facilitates transport and absorption.

• DNA is a double helix made of nucleotides with complementary base pairing (A with T, C with G) linked by hydrogen bonds.

• Chemical tests like Benedict's, iodine, Biuret, ethanol, and DCPIP tests are used to identify the presence of specific biological molecules