CH 4 : Biological Molecules

Biological Molecules

• Key biological molecules include carbohydrates, fats, and proteins
• Large molecules are made from smaller molecules
• Starch and glycogen are made from glucose
• Cellulose is made from glucose
• Proteins are made from amino acids
• Fats are made from fatty acids and glycerol

Testing for Biological Molecules

• Iodine solution tests for starch (blue-black colour change is positive)
• Benedict's solution tests for reducing sugars (orange-red precipitate is positive)
• Biuret test tests for proteins (purple-mauve colour change is positive)
• DCPIP test tests for vitamin C (colour change from blue to colourless shows a positive test)
• Ethanol test tests for fats (cloudiness in ethanol solution and the forming of a clear solution after adding water confirms fats are present)

Carbohydrates

• Carbohydrates are a source of energy for respiration
• In plants, carbohydrates are stored as starch
• In animals, carbohydrates are stored as glycogen
• Cellulose is found in plant cell walls
• Polysaccharides are insoluble so they don't create an osmotic effect

Proteins

• Proteins are essential for growth and tissue repair
• Proteins form enzymes and hormones
• Proteins are used for protection against diseases (e.g., antibodies and white blood cells)
• Proteins form the cell membrane
• Amino acids are water soluble
• Some proteins are water insoluble (e.g., keratin in hair and nails)
• Excess amino acids are deaminated and excreted in humans
• Proteins are made up long chains of amino acids joined together

Fats

• Fats are an even larger source of energy than carbohydrates
• Fats form a part of the cell membrane (often cholesterol)
• Fats are stored in the body as a food reserve
• Fats insulate the body
• Fats form a waterproof layer for skin, fur, feathers
• Fats are solid at room temperature (e.g., butter)
• Fats are liquid at room temperature (e.g., oils)

Importance of Water

• Water is essential for metabolic reactions
• It transports digested food
• It transports excretory products
• It dissolves enzymes and hormones
• It's crucial for regulating body temperature (through sweating)
• Water is the main component of cytoplasm

Classification of Carbohydrates

• Monosaccharides: basic units of carbohydrates like glucose (C₆H₁₂O₆), fructose, galactose
• Disaccharides: made from two monosaccharides linked together like maltose, lactose, sucrose (C₁₂H₂₂O₁₁)
• Polysaccharides: long chains of monosaccharides like starch, cellulose, glycogen (C₁₂H₂₂O₁₁)_n

Vitamins (Vitamin C)

• Found in citrus fruits, tomatoes and vegetables
• Important in collagen formation (protein in skin, bones, and blood vessels)
• Maintains healthy gums and blood vessels
• Sensitive to heat and air, so refrigeration is important
• Water-soluble vitamin, so it cannot be stored in the body

Vitamins (Vitamin D)

• Found in butter, egg yolks, fish liver oil, and sunlight.
• Helps in the absorption of calcium and phosphorus for bone and tooth formation
• Essential for bone development and maintenance
• Fat-soluble vitamin, so it can be stored in the body (liver)
• Exposure to sunlight aids in vitamin D production

Minerals (Iron)

• Important for haemoglobin production
• Haemoglobin carries oxygen throughout the body
• Deficiency causes anaemia (fatigue and shortness of breath)
• Sources include red meat, spinach, and liver

Minerals (Calcium)

• Necessary for strong bones and teeth
• Important for blood clotting
• Important for muscle contraction
• Deficiency causes weak bones, brittle teeth, and poor blood clotting
• Sources include milk, dairy products, and bread

Fibers

• Stimulates peristalsis (movement of food in the gut) to prevent constipation
• Sources include cereals, grains, bread, and vegetables

DNA

• DNA is a double helix made of nucleotides
• Nucleotides: composed of a base, sugar, and phosphate group- There are four bases: Adenine (A), Cytosine (C), Guanine (G), and Thymine (T)
• The sequence of bases in DNA determines the sequence of amino acids in proteins
• DNA carries genetic information that determines traits

How traits are formed

• Genes carry codes for proteins' synthesis
• Each code word (codon) is made up of 3 bases
• Each codon corresponds to a specific amino acid
• The order of codons determines the protein's structure and function
• Traits are determined by the order of bases in genes which codes for proteins