CBSE Class 12, Unit-10: Biomolecules Notes
Vitamins
Vitamins are organic compounds required in the diet in small amounts to perform specific biological functions for normal maintenance of optimum growth. Human's body cannot synthesize most vitamins in sufficient quantities, so they must be obtained from dietary sources or supplements.
Types of Vitamins
Vitamins are of two types based on their solubility:
Fat-Soluble Vitamins:
Fat soluble vitamins are soluble in fats and are stored in fatty tissues of the body. The main fat-soluble vitamins are-
Vitamin A: Important for vision and immune function.
Vitamin D: Essential for calcium absorption and bone health; synthesized by the body when exposed to sunlight.
Vitamin E: Acts as an antioxidant, protecting cells from damage.
Vitamin K: Necessary for blood clotting and bone metabolism.
Water-Soluble Vitamins:
Water soluble vitamins are soluble in water and are not stored in the body. Excess amounts of these vitamins are excreted through urine. Water-soluble vitamins are-
Vitamin C (Ascorbic Acid): Important for immune function, collagen synthesis, and antioxidant protection.
B Vitamins: This group includes several vitamins that play vital roles in energy metabolism and red blood cell formation:
B1 (Thiamine)
B2 (Riboflavin)
B3 (Niacin)
B5 (Pantothenic Acid)
B6 (Pyridoxine)
B7 (Biotin)
B9 (Folate)
B12 (Cyanocobalamin)
Functions of Vitamins:
Each vitamin has specific roles and function for maintaining the good health:
Vitamin A supports vision and skin health.
Vitamin C aids in wound healing and acts as an antioxidant.
Vitamin D help to absorb calcium.
B Vitamins helps in energy production and the formation of red blood cells.
Sources of Vitamins:
Vitamins are found in a number of foods:
Fruits and Vegetables: Good sources of vitamins C and A, as well as various B vitamins.
Dairy Products: Good sources of vitamins D, A, and B2.
Meat and Fish: Provide B vitamins, especially B12, which is primarily found in animal products.
Nuts and Seeds: Contain vitamin E and various B vitamins.
Functions, Deficiency Disease and Sources of Vitamins
| Vitamins | Functions | Deficiency Diseases | Foods |
|---|---|---|---|
| Vitamin A (retinol) |
Essential for good eye health | Night blindness and keratomalacia (a condition that involves drying and clouding of the cornea) | carrots, milk, liver (of lamb/beef/chicken), broccoli, spinach, and pumpkin |
| Vitamin B1 (thiamine) |
Essential for producing enzymes that break down blood sugar | Beriberi (symptoms include loss of appetite, weakness) and Wernicke-Korsakoff syndrome (a disorder that affects the memory system in the brain) | Yeast, pork, sunflower seeds, brown rice |
| Vitamin B2 (riboflavin) |
Growth and development of body cells | A deficiency of Vitamin B2 can cause inflammation of lips and fissures in the mouth | Milk, yoghurt, meat, fish, eggs, cottage cheese, bananas |
| Vitamin B3 (niacinamide) |
Growth and proper functioning of body cells | Pellagra (marked by dementia, diarrhoea, and dermatitis) | Milk, eggs, leafy vegetables, carrots, tofu, lentils |
| Vitamin B5 (pantothenic acid) |
Provides energy to the body | Symptoms include paresthesia (or pins and needles) | Milk, broccoli, avocados, yoghurt |
| Vitamin B6 (pyridoxine) |
Formation of red blood cells | Anaemia or peripheral neuropathy (weakness, numbness, and pain due to nerve damage) | Chickpeas, liver (of lamb/beef/chicken), bananas, nuts |
| Vitamin B7 (biotin) |
Contributes to the formation of keratin and metabolises carbohydrates, protein, and fats | dermatitis, inflammation of intestines | egg yolk, liver (of lamb/beef/chicken), broccoli |
| Vitamin B9 (folic acid) |
Essential for making DNA and RNA | This form of vitamin B is advised to be taken before or during pregnancy as a deficiency can affect the foetus' nervous system | Leafy vegetables, fruits, legumes, liver (of lamb/beef/chicken) |
| Vitamin B12 (cyanocobalamin) |
Contribute towards a healthy nervous system | Neurological problems and some forms of anaemia | Milk and dairy products, fish, meat, eggs |
| Vitamin C (ascorbic acid) |
The function of Vitamin C includes collagen production, wound healing, bone formation, strengthening the immune system, and absorbing iron | Scurvy (a condition that causes bleeding gums and swollen mouth). A deficiency of vitamin C can also result in a decreased resistance to diseases. | Citrus fruits like lemons, mosambi (or sweet lemon), oranges |
| Vitamin D (ergocalciferol) |
The function of vitamin D include healthy mineralisation of bones | Rickets in children, softening of bones | Liver (of lamb/beef/chicken), eggs. However, the most absorbable form of vitamin D is produced by our own body when it comes in contact with sunlight. |
| Vitamin E (tocopherol) |
Vitamin E Helps prevent oxidative stress | May cause haemolytic anaemia in newborns | Wheat germs, almonds, eggs, leafy greens, kiwis |
| Vitamin K (phylloquinone) |
Necessary for blood clotting | Unusual susception to bleeding | Natto, green vegetables, pumpkins |
Nucleic Acids
Nucleic acids are macromolecules that are found in every living cell, either alone or in conjunction with other substances. It has been observed that nucleus of a living cell is responsible for the transmission of genetic characters (heredity) from parents to their offspring. The particles in nucleus of the cell responsible for heredity, are called chromosomes which are made up of proteins and another type of biomolecules called nucleic acids. These are mainly of two types, the deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Since nucleic acids are long chain polymers of nucleotides, so they are also called polynucleotides.
Properties of Nucleic Acid
Followings are the main properties of nucleic acid-
1. Nucleotides are the building blocks of nucleic acid.
2. These make up all living things' genetic material.
3. In a live cell, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are two forms of nucleic acids. In 1969, Friedrich Miescher discovered both DNA and RNA.
4. A nucleotide is made up of three chemically different components. A heterocyclic base, or nitrogenous base, a monosaccharide pentose sugar and phosphoric acid, or phosphate group.
5. The nitrogenous bases are made up of one or two heterocyclic rings that include nitrogen atoms. Adenine (A), guanine (G), uracil (U), cytosine (C), and thymine (T) (5-methyl uracil) are the five bases.
6. Adenine and guanine are substituted purines with two heterocyclic rings, whereas uracil, cytosine, and thymine are substituted pyrimidines with three heterocyclic rings (1 heterocyclic ring).
7. DNA has the nitrogenous bases A, T, G, and C, whereas RNA has the nitrogenous bases A, U, G, and C.
8. Polynucleotides either include beta-ribose sugar (in RNA) or beta 2′ deoxyribose sugar (in DNA) (in DNA).
9. Nucleosides: Sugar + Base.
10. Nucleotides are made up of three parts: base, sugar, and phosphate.
11. The backbone of DNA strands is made up of phosphodiester linkages, which are sugar and phosphate residues.
12. Due to the presence of phosphate groups, they are acidic and negatively charged.
Chemical Composition of Nucleic Acid
Complete hydrolysis of DNA (or RNA) yields a pentose sugar, phosphoric acid and nitrogen containing heterocyclic compounds (called bases). In DNA molecules, the sugar moiety is β-D-2-deoxyribose whereas in RNA molecule, it is β-D-ribose.
DNA contains four bases viz. adenine (A), guanine (G), cytosine (C) and thymine (T). RNA also contains four bases, the first three bases are same as in DNA but the fourth one is uracil (U).
Structure of Nucleic Acids
Nucleic acids have two types of structures – primary structure and secondary structure. Primary structure gives the sequence of nucleotides in a nucleic acid chain. The secondary structure of DNA was given by James Watson and Francis Crick.
Watson and Crick's double-stranded double-helical model is the most widely accepted structural model of DNA (1953).
Double Helical Structure of DNA
The structure of DNA, according to the model, is as follows:
☛ A right-handed helical spiral is formed by each chain of DNA, and two chains coil around each other to form a double helix.
☛ The phosphodiester bond is the link between the sugar and phosphate molecules, and the bases project inside.
☛ The chains run in antiparallel directions, with one strand coming from the 5’→3′ direction and the other coming from the 3’→5′ direction.
Credit: Microbenotes
☛ The nitrogenous bases on one strand form hydrogen bonds with the bases on the other strand. Adenine forms two H -bonds with thymine (A=T), and guanine forms three H -bonds with cytosine (G≡C). The helical structure is stabilised by this coupling.
☛ The chains are complementary because, for every adenine in one chain, there will be thymine in the other; for every guanine in one chain, there will be cytosine in the other, and so on.
☛ DNA has a 2nm consistent thickness.
☛ The pitch of the helix is 3.4nm for each round of the double helix.
☛ Each turn comprises around 10 base pairs. The distance between two neighbouring base pairs is about 0.34 nanometers.
☛ The helix's backbone is made up of sugar and phosphate, with bases aligned along the axis.
James Watson, Francis Crick, and Maurice Wilkins won the Nobel Prize in 1962 for the double helical model of DNA.
Differences between DNA and RNA
| Comparison | DNA | RNA |
|---|---|---|
| Full Name | Deoxyribonucleic Acid | Ribonucleic Acid |
| Function | DNA replicates and stores genetic information. It is a blueprint for all genetic information contained within an organism. | RNA converts the genetic information contained within DNA to a format used to build proteins, and then moves it to ribosomal protein factories. |
| Structure | DNA consists of two strands, arranged in a double helix. These strands are made up of subunits called nucleotides. Each nucleotide contains a phosphate, a 5-carbon sugar molecule and a nitrogenous base. | RNA only has one strand, but like DNA, is made up of nucleotides. RNA strands are shorter than DNA strands. RNA sometimes forms a secondary double helix structure, but only intermittently. |
| Length | DNA is a much longer polymer than RNA. A chromosome, for example, is a single, long DNA molecule, which would be several centimetres in length when unraveled. | RNA molecules are variable in length, but much shorter than long DNA polymers. A large RNA molecule might only be a few thousand base pairs long. |
| Sugar | DNA contains deoxyribose sugar having one less hydroxyl group than RNA's ribose. | RNA contains ribose sugar molecules, without the hydroxyl modifications of deoxyribose. |
| Bases | Adenine (A), Thymine (T), Guanine (G) and Cytosine (C) | Adenine (A), Guanine (G), Cytosine (C) and Uracil (U) |
| Base Pairs | Adenine and Thymine pair (A-T) Cytosine and Guanine pair (C-G) |
Adenine and Uracil pair (A-U) Cytosine and Guanine pair (C-G) |
| Location | DNA is found in the nucleus, with a small amount of DNA also present in mitochondria. | RNA forms in the nucleolus, and then moves to specialized regions of the cytoplasm depending on the type of RNA formed. |
| Reactivity | Due to its deoxyribose sugar, which contains one less oxygen-containing hydroxyl group, DNA is a more stable molecule than RNA, which is useful for a molecule which has the task of keeping genetic information safe. | RNA, containing a ribose sugar, is more reactive than DNA and is not stable in alkaline conditions. RNA's larger helical grooves mean it is more easily subject to attack by enzymes. |
| Ultraviolet (UV) Sensitivity | DNA is vulnerable to damage by ultraviolet light. | RNA is more resistant to damage from UV light than DNA. |
Credit: Technology Networks
Biological functions of nucleic acids
DNA is the chemical basis of heredity and may be regarded as the reserve of genetic information. DNA is exclusively responsible for maintaining the identity of different species of organisms over millions of years. A DNA molecule is capable of self duplication during cell division and identical DNA strands are transferred to daughter cells. Another important function of nucleic acids is the protein synthesis in the cell. Actually, the proteins are synthesised by various RNA molecules in the cell but the message for the synthesis of a particular protein is present in DNA.
Functions of DNA
DNA is a genetic material which carries all the hereditary information from one generation to other.
DNA controls all the biological activities of cells as it synthesizes proteins, enzymes and biochemical.
DNA synthesize RNA through the process transcription.
DNA guides the process of protein synthesis in the cell.
DNA helps in recombination during meiosis by crossing over.
