1.2.6 Vitamins

the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.

2. Ribonucleic acid (RNA)

Ribonucleic acid (RNA) functions in converting genetic information from genes into the amino acid sequences of proteins. The three universal types of RNA include transfer RNA (tRNA), messenger RNA (mRNA), and ribosomal RNA (rRNA).  Messenger RNA acts to carry genetic sequence information between DNA and ribosomes, directing protein synthesis.  Ribosomal RNA is a major component of the ribosome, and catalyses peptide bond formation.  Transfer RNA serves as the carrier molecule for amino acids to be used in protein synthesis, and is responsible for decoding the mRNA. In addition, many other classes of RNA are now known.

Base Pairing and Double Stranded Nucleic Acids

Most DNA exists in the famous form of a double helix, in which two linear strands of DNA are wound around one another. The major force promoting formation of this helix is complementary base pairing: A's form hydrogen bonds with T's (or U's in RNA), and G's form hydrogen bonds with C's. If we mix two ATGC's together, the following duplex will form

1.2.6 Vitamins

Vitamins are substances that your body needs to grow and develop normally. There are 13 vitamins your body needs. They are vitamins A, C, D, E, K and the B vitamins (thiamine, riboflavin, niacin, pantothenic acid, biotin, vitamin B-6, vitamin B-12 and folate). You can usually get all your vitamins from the foods you eat. Your body can also make vitamins D and K. People who eat a vegetarian diet may need to take a vitamin B12 supplement. Each vitamin has specific jobs. If you have low levels of certain vitamins, you may develop a deficiency disease. For example, if you don't get enough vitamin D, you could develop rickets. Some vitamins may help prevent medical problems. Vitamin A prevents night blindness.

 Vitamins are essential for the normal growth and development of a multicellular organism. Using the genetic blueprint inherited from its parents, a foetus begins to develop, at the moment of conception, from the nutrients it absorbs.  It requires certain vitamins and minerals to be present at certain times. These nutrients facilitate the chemical reactions that produce among other things, skin, bone, and muscle. If there is serious deficiency in one or more of these nutrients, a child may develop a deficiency disease. Even minor deficiencies may cause permanent damage  For the most part, vitamins are obtained with food, but a few are obtained by other means. For example, microorganisms in the intestine — commonly known as "gut flora" — produce vitamin K and biotin, while one form of vitamin D is synthesized in the skin with the help of the natural ultraviolet wavelength of sunlight. Humans can produce some vitamins from precursors they consume.

Examples include vitamin A, produced from beta carotene, and niacin, from the amino acid tryptophan  Once growth and development are completed, vitamins remain essential nutrients for the healthy maintenance of the cells, tissues, and organs that make up a multicellular organism; they also enable a multicellular life form to efficiently use chemical energy provided by food it eats, and to help process the proteins, carbohydrates, and fats required for respiration

Deficiencies

Humans must consume vitamins periodically but with differing schedules, to avoid deficiency.

 The human body's stores vitamins A, D, and B12 in significant amounts in the human body, mainly in the liver  An adult human's diet may be deficient in vitamins A and D for many months and B12 in some cases for years, before developing a deficiency condition.  Vitamin B3 (niacin and niacinamide) is not stored in the human body in significant amounts

 For vitamin C, the first Table 1.7 Nomenclature of reclassified vitamins symptoms of scurvy in experimental studies of Previous name Chemical name complete vitamin C deprivation in humans have varied widely, Vitamin B4 Adenine from a month to more than six months, depending on previous Vitamin B8 Adenylic acid dietary history that determined body stores. Vitamin F Essential fatty acids  Deficiencies of vitamins are Vitamin G Riboflavin classified as either primary or secondary. Vitamin H Biotin  A primary deficiency occurs when an organism does not get Vitamin J Catechol, Flavin enough of the vitamin in its food. A secondary deficiency Vitamin L1 Anthranilic acid may be due to an underlying Vitamin L2 Adenylthiomethylpentose disorder that prevents or limits the absorption or use of the Vitamin M Folic acid vitamin, due to a "lifestyle Vitamin O Carnitine factor", such as smoking, excessive alcohol Vitamin P Flavonoids consumption, or the use of Vitamin PP Niacin medications that interfere with the absorption or use of the Vitamin S Salicylic acid vitamin. People who eat a varied diet are unlikely to Vitamin U S-Methylmethionine develop a severe primary vitamin deficiency. In contrast, restrictive diets have the potential to cause prolonged vitamin deficits, which may result in often painful and potentially deadly diseases

Vitamin A

Vitamin B1 Vitamin B2 Vitamin B3 Vitamin B5

Vitamin B12 Vitamin B9

Vitamin C Vitamin B7

Vitamin K Vitamin D

Figure 1.22 Vitamins and their structures Vitamin B6

Vitamin E

 Well-known human vitamin deficiencies involve thiamine (beriberi), niacin (pellagra), vitamin C (scurvy), and vitamin D (rickets). In much of the developed world, such deficiencies are rare due to (1) an adequate supply of food and (2) the addition of vitamins and minerals to common foods, often called fortification.

Vitamin generic descriptor name

Vitamerche mical name(s) (list not complete) Solubil ity Recommended dietary allowances (male, age 19–70) Deficiency disease

Vitamin A Retinol, retin al, and four caroten oids including bet a carotene Table 1.6 Vitamins and all necessary info Upper Intake Level (UL/day)

Overdose disease Food sources

Fat 900 µg Nightblindness,Hyperkerat osis, andKeratomalacia 3,000 µg Hypervitaminosis A Orange, ripe yellow fruits, leafy vegetables, carrots, pumpkin, squash, spinach, liver, soy milk, milk

Vitamin B1 Thiamine Water 1.2 mg Beriberi, WernickeKorsakoff syndrome N/D

Vitamin B2 Riboflavin Water 1.3 mg Ariboflavinosis N/D

Vitamin B3 Niacin, namide niaci Water 16.0 mg Pellagra 35.0 mg Drowsiness or muscle relaxation with large doses.

Liver damage (doses > 2g/day)and other problems Pork, oatmeal, brown rice, vegetables, potatoes, liver, eggs Dairy products, bananas, popcorn, green beans, asparagus Meat, fish, eggs, many vegetables, mushrooms, tree nuts

Vitamin B5 Pantothenic acid Water 5.0 mg Paresthesia N/D Diarrhea; possibly nausea and heartburn. Meat, broccoli, avocados

Vitamin B6 Pyridoxine,p yridoxamine, pyridoxal Water 1.3–1.7 mg Anemia peripheral neuropathy. 100 mg

Vitamin B7 Biotin Water 30.0 µg Dermatitis, enteritis N/D

Vitamin B9

Vitamin B12 Folic acid, folinic acid

Cyanocobala min,hydroxy cobalamin,m ethylcobala min Water 400 µg Megaloblast and Deficiency during pregnancy is associated with birth defects, such asneural tube defects 1,000 µg

Water 2.4 µg Megaloblastic anemia N/D Impairment of proprioception, nerve damage (doses > 100 mg/day)

May mask symptoms of vitamin B12 deficiency; other effects. Meat, vegetables, tree nuts, bananas

Raw egg yolk, liver, peanuts, certain vegetables

Leafy vegetables, pasta, bread, cereal, liver

Acne-like rash [causality is not conclusively established]. Meat and other animal products

Vitamin C Ascorbic acid Water 90.0 mg Scurvy Vitamin D Cholecalcifer

ol Fat 10 µg Rickets and Osteoma lacia

Vitamin E Tocopherols tocotrienols , Fat 15.0 mg Deficiency is very rare; mild hemolytic anemia in newborn infants 2,000 mg Vitamin C megadosage Many fruits and vegetables, liver 50 µg Hypervitaminosis D Fish, eggs, liver, mushrooms

1,000 mg Increased congestive heart failure seen in one large randomized study. Many fruits and vegetables, nuts and seeds

Vitamin K phylloquinon e,menaquino nes Fat 120 µg Bleeding diathesis N/D Increases coagulation in patients taking warfarin Leafy green vegetables such as spinach, egg yolks, liver

Critical thinking Questions 1. Why is glycine a highly conserved amino acid residue in the evolution of proteins? 2. The gene encoding a protein with a single disulphide bond undergoes a mutation that changes a serine residue into a cysteine residue. Propose a direct method to find out whether the disulphide pairing in this mutant is the same as in the original protein. 3. The atmosphere of the primitive earth before the emergence of life contained N2, NH3,

H2, HCN, CO and H2O. Which of these compounds is the most likely precursor of most of the atoms in adenine? Why? 4. Are organic solvents like benzene and ether polar or non-polar substances?