Atoms, Molecules, and Chemical Compounds

• An atom represents the smallest unit of an element involved in a chemical reaction
• A molecule comprises two or more atoms bound by chemical bonds and constitutes the simplest unit of a chemical compound
• A compound denotes a molecule containing two or more different elements held together by chemical bonds

Chemical Compounds

• Chemical compounds are classified as either organic or inorganic
• Inorganic compounds lack carbon or a carbon chain, examples being water and mineral salts
• Organic compounds contain carbon and hydrogen, originate from plants, and include carbohydrates, lipids(fats and oils), and proteins
• Carbon dioxide (CO2) is not an organic molecule although it contains carbon
• All organic compounds have a carbon skeleton combined with various atoms
• Carbon possesses a valency of 4, enabling it to form four bonds with atoms like hydrogen, oxygen, nitrogen, sulfur, or phosphorus
• Carbon atoms can bond with each other, creating chains or rings, and can form single or double bonds

Carbohydrates

• Carbohydrates consist of carbon, hydrogen, and oxygen
• Carbohydrates have a hydrogen to oxygen ratio of 2:1
• Sugars constitute the most abundant carbohydrates where the number and arrangement of atoms results in diverse compounds, including starches and cellulose
• Carbohydrates are classified into three primary groups: monosaccharides, disaccharides, and polysaccharides

Monosaccharides

• Monosaccharides serve as simple sugars and the building blocks (monomers) for more complex carbohydrates
• Glucose is a six-carbon sugar with a six-sided structure (C6H12O6)
• Fructose is a six-carbon sugar with a five-sided structure (C6H12O6)

Disaccharides

• Disaccharides form through the combination of two monosaccharides
• Glycosidic bonds connect the monosaccharides
• Sucrose (cane sugar) is made from one glucose and one fructose molecule and is the most abundant sugar in plants
• Glucose plus fructose equates to sucrose
• Maltose (malt sugar) is abundant in germinating seeds and is formed by the combination of two glucose molecules
• Glucose plus glucose equates to maltose

Polysaccharides

• Polysaccharides form when numerous glucose molecules bond together
• Starch, cellulose, glycogen, chitin, and lignin are examples of polysaccharides

Carbohydrate Properties

• Monosaccharides and disaccharides present as white, crystalline substances, soluble in water, and sweet to taste
• Polysaccharides don't exhibit a crystalline structure, lack a sweet taste, and remain insoluble in water

Biological Importance

• Monosaccharides provide an immediate energy source
• Polysaccharides serve as food storage, such as starch in plant cells and glycogen in liver/muscle cells of animals
• Structural strengthening is provided by the cellulose & lignin in plant cell walls, chitin in arthropod exoskeletons
• Transport of food is important since monosaccharides & disaccharides are soluble
• Ribose sugar can be found in DNA and RNA

Glucose Test

• To test for glucose, prepare a hot water bath
• Label two test tubes 1 and 2
• Place a glucose solution in test tube 1, and water into test tube 2
• Add 10 ml of Benedict’s solution to each test tube, and put both test tubes in the hot water bath for 5 minutes, then note color changes
• With a positive control (glucose), the solution turns orange/yellow after heating
• With a negative control (water), the colour turns blue after heating

Starch Test

• To test for starch, label two test tubes 1 and 2, then place a starch solution onto test tube 1 and water into test tube 2
• Add some iodine solution to each test tube, and then note the colour changes
• Starch: Colour changes to blue-black after the addition of iodine solution
• Water: Colour changes to yellow-brown after the addition of iodine solution

Lipids

• Lipids contain carbon, hydrogen, and oxygen elements
• The hydrogen to oxygen ratio of lipids exceeds 2:1 and fats contain very little oxygen relative to hydrogen
• A glycerol molecule (alcohol) and three fatty acid molecules constitute the monomers (building blocks) of lipid molecules
• Ester links are the bonds that link the fatty acids to the glycerol
• Saturated fats are generally solid at room temperature, such as animal fat, butter, and beeswax
• Unsaturated fats (oils) are generally liquid at room temperature and most plant oils and fish fats are unsaturated, such as olive oil (plant oil) and cod-liver oil (a fish oil).

Lipid Properties

• Lipids are insoluble in water and repel water (hydrophobic)
• Lipids are soluble in other lipids (lipophilic)

Biological Importance

• Fats and oils represent a rich source of stored energy
• Lipids form an important part of the protoplasm and cell membrane
• Plants store food as oils, e.g., peanut, olive, palm, and castor oil
• Fat stores in animals form heat-insulating layers under the skin
• Waxy cuticle over leaves limits water loss
• Waxy cuticle over insect exoskeletons limits water loss
• Lipids release water during respiration
• Absorption of fat-soluble vitamins A and D is enabled by lipids
• Lipids protect organs such as the heart and kidneys

Heart Disease

• The real enemy is sugar
• The western diet is associated with increased rates of obesity, diabetes, heart disease, hypertension, and cancer
• Trans fats increase LDL (bad cholesterol) and decrease HDL (good cholesterol)
• The combination of trans fats and sugar is particularly detrimental which leads to inflammation, then leads to heart disease and diabetes
• Dietary fats are essential to life and good health. Better fats to choose, are those found in nature e.g.: duck fat, avocado and olive oil

Lipid Tests

• Label test tubes 1 and 2
• Place alcohol into both test tubes
• Place a drop of oil into test tube 1, and some water in test tube 2
• Add water to both test tubes and shake
• With a positive control (oil), a milky emulsion results
• With a negative control (water), the solution remains clear

Translucent Stain Test

• Place ether into test tubes 1 and 2
• Place some oil into test tube 1, and some water in test tube 2
• Shake both test tubes
• Pour the contents of test tube 1 onto a piece of filter paper, and allow to dry
• Pour the contents of test tube 2 onto another piece of filter paper, and allow to dry
• For the positive test (oil), a translucent stain is present on filter paper, after adding ether mixture
• Note any marks on the filter paper.
• For the negative test (water), no stain is present on filter paper, after adding ether mixture

Proteins

• Proteins contain the elements carbon, hydrogen, oxygen, and nitrogen and sometimes contain sulphur, phosphorous and iron
• Amino acids, containing an amino group and a carboxyl group, serve as the monomers (building blocks) of proteins
• Twenty amino are used.
• If there are 50 or more amino acids present, they are called a protein
• If there are less than 50 amino acids present, they are called a polypeptide
• Amino acids are connected with peptide bonds
• Examples of proteins include legumin in peas, myosin in muscles, albumin in egg whites, gluten in wheat and fibrin in blood

Protein Properties

• Proteins are insoluble in water
• Proteins are sensitive to heat and pH
• Proteins are denatured by high temperatures and changes in pH

Biological Properties

• As components of cell membranes and much of the protoplasm of the cell, proteins form important functions
• Proteins are enzymes that catalyse (speed up) cellular reactions
• Haemoglobin transports oxygen and CO2 in the blood
• Antibodies fight infections in the body
• Part of chromosomes store hereditary information
• They give support as keratin in nails / hooves / scales and collagen in connective tissue and muscle
• Proteins act as a reserve "last resort" source when carbohydrates and lipids aren't available