Year of discovery Vitamin Food source

1913 Vitamin A (Retinol) Cod liver oil

1910 Vitamin B1 (Thiamine) Rice bran

1920 Vitamin C (Ascorbic acid) Citrus, most fresh foods

1920 Vitamin D (Calciferol) Cod liver oil

1920 Vitamin B2 (Riboflavin) Meat, dairy products, eggs

1922 (Vitamin E) (Tocopherol) Wheat germ oil, unrefined vegetable oils

1926 Vitamin B12 (Cobalamins) Liver, eggs, animal products

1929 Vitamin K1 (Phylloquinone) Leafy green vegetables

1931 Vitamin B5 (Pantothenic acid) Meat, whole grains, in many foods

1931 Vitamin B7 (Biotin) Meat, dairy products, eggs

1934 Vitamin B6 (Pyridoxine) Meat, dairy products

1936 Vitamin B3 (Niacin) Meat, grains

1941 Vitamin B9 (Folic acid) Leafy green vegetables

36)Alkaloids are a group of naturally occurring chemical compounds, that contain mostly basic nitrogen atoms. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of similar structure are also attributed to alkaloids. In addition to carbon, hydrogen and nitrogen, alkaloids may also contain oxygen, sulfur and more rarely other elements such as chlorine, bromine, and phosphorus.

Alkaloid-containing plants have been used by humans since ancient times for therapeutic and recreational purposes. For example, medicinal plants have been known in the Mesopotamia at least around 2000 BC. A Chinese book on houseplants written in 1st–3rd centuries BC mentioned a medical use of Ephedra and opium poppies. Also, coca leaves have been used by South American Indians since ancient times. Extracts from plants containing toxic alkaloids, such as aconitine and tubocurarine, were used since antiquity for poisoning arrows.

Alkaloids are highly reactive substances with biological activity in low doses.

DEFINITION

1. Contains nitrogen - usually derived from an amino acid.
2. Bitter tasting, generally white solids (exception - nicotine is a brown liquid).
3. They give a precipitate with heavy metal iodides.
• Most alkaloids are precipitated from neutral or slightly acidic solution by Mayer's reagent (potassiomercuric iodide solution). Cream coloured precipitate.
• Dragendorff's reagent (solution of potassium bismuth iodide) gives orange coloured precipitate with alkaloids.
• Caffeine, a purine derivative, does not precipitate like most alkaloids.
4. Alkaloids are basic - they form water soluble salts. Most alkaloids are well-defined crystalline substances which unite with acids to form salts. In plants, they may exist
• in the free state,
• as salts or
• as N-oxides.
5. Occur in a limited number of plants. Nucleic acid exists in all plants, whereas, morphine exists in only one plant species.

Alkaloids can be classified;

• in terms of their BIOLOGICAL activity,
• CHEMICAL structure (nucleus containing nitrogen),
• BIOSYNTHETIC pathway (the way they are produced in the plant).

Alkaloids are often divided into the following major groups:

1. " True alkaloids", which contain nitrogen in the heterocycle and originate from amino acids. Their characteristic examples are atropine, nicotine, and morphine. This group also includes some alkaloids that besides nitrogen heterocycle contain terpene (e.g., evonine) or peptide fragments (e.g. ergotamine). This group also includes piperidine alkaloids coniine and coniceine although they do not originate from amino acids.
2. " Protoalkaloids", which contain nitrogen and also originate from amino acids. Examples include mescaline, adrenaline and ephedrine.
3. Polyamine alkaloids – derivatives of putrescine, spermidine, and spermine.
4. Peptide and cyclopeptide alkaloids.

5. Pseudalkaloids – alkaloid-like compounds that do not originate from amino acids. This group includes, terpene-like and steroid-like alkaloids, as well as purine-like alkaloids such as caffeine, theobromine, theacrine and theophylline. Some authors classify as pseudoalkaloids such compounds such as ephedrine and cathinone. Those originate from the amino acid phenylalanine, but acquire their nitrogen atom not from the amino acid but through transamination.

Some alkaloids do not have the carbon skeleton characteristic of their group. So, galantamine and homoaporphines do not contain isoquinoline fragment, but are, in general, attributed to isoquinoline alkaloids.

HORMONES A hormone is a class of regulatory biochemicals produced in particular parts of organisms by specific cells, glands, and/or tissues and then transported by the bloodstream to other parts of the body, with the intent of influencing a variety of physiological and behavioral activities, such as the processes of digestion, metabolism, growth, reproduction, and mood control. Generally, only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one cell to another. All multicellular organisms produce hormones; plant hormones are also called phytohormones. Hormones in animals are often transported in the blood. Cells respond to a hormone when they express a specific receptor for that hormone. The hormone binds to the receptor protein, resulting in the activation of a signal transduction mechanism that ultimately leads to cell type-specific responses.

Hormonal signaling involves the following:

1. Biosynthesis of a particular hormone in a particular tissue
2. Storage and secretion of the hormone
3. Transport of the hormone to the target cell(s)
4. Recognition of the hormone by an associated cell membrane or intracellular receptor protein
5. Relay and amplification of the received hormonal signal via a signal transduction process: This then leads to a cellular response. The reaction of the target cells may then be recognized by the original hormone-producing cells, leading to a down-regulation in hormone production. This is an example of a homeostatic negative feedback loop.
6. Degradation of the hormone.

Hormones have the

• sexual arousal

A hormone may also regulate the production and release of other hormones. Hormone signals control the internal environment of the body through homeostasis.