Molecules of the Cell

MOLECULES OF THE CELL PROTOPLASM 1. Living matter in the animal cells was termed as sarcode by Dujardin in1835. 2. Living matter in plant cells was named protoplasm by Purkinje and von Mohl. 3. The term protoplasm was first coined by Purkinje. 4. Protoplasm was called as the physical basis of life' by Huxley in 1868. 5. Five theories regarding the physical appearance of protoplasm are (i) Granular Theory - Altmann. (ii) Alveolar Theory - Butschlii (iii) Fibrillar Theory - Flemming (iv) Reticular Theory - Klein and Comoy (v) Colloidal Theory - Fisher 6. The colloidal theory of protoplasm has been given by Fischer. Protoplasm is a colloidal system. 7. Cell organelles are embedded in protoplasm. 8. The largest amount of substance in protoplasm in water. 9. Water forms about 80% of protoplasm. 10. Three most important (abundant) elements in protoplasm are. Carbon Hydrogen and Oxygen 11. Four elements making 99% of the living system are Carbon, Hydrogen, Oxygen, and Nitrogen. 12. The largest constituent element of protoplasm is oxygen by weight (63%). 13. All the protoplasm of a cell except the nucleus (karyoplasm) is termed as cytoplasm. 14. The term cytoplasm was first introduced by Strasburger in 1882. 15. Cytoplasm contains many cytoplasmic organelles like plastids, mitochondria, ribosomes, lysosomes, centrioles, Golgi bodies, etc. 16. The term hyaloplasm was first introduced by Pfeffer in 1877. 17. The ribosome-containing components of groundplasmis are called ergastoplasm, a term introduced by Garnier in 1897. 18. The 'Protoplasm theory' was formulated by Max Schult 19. According to protoplasm theory there is a similarity between the protoplasm of plants and animals. CARBOHYDRATES 1. Carbohydrates are nature's most abundant organic substance. 2. The principal source of energy for the body is carbohydrates 3. Our food mainly contains carbohydrates. 4. Carbohydrates make up 75 percent of the dry weight of the plant world, upon which animal life primarily depends. 5. Carbohydrates contain carbon combined with hydrogen and oxygen often in the same ratio as in water ( 10:2H:10). 6. Carbohydrates are usually divided into the following three classes: (1) monosaccharides or simple sugar. (2) oligosaccharides (contain up to 10 monosaccharides) and (3) polysaccharides (a polymer of more than 10 monosaccharide units). MONOSACCHARIDES 1. Most sugars have the general formula CH.O. 2. Sugars containing three carbons are known as trioses, those with four carbons as tetroses, those with five carbons as pentoses, and those with six carbons as hexoses. 3. Two trioses namely glyceraldehyde and dihydroxyacetone are crucial intermediates in the metabolism of glucose in the glycolytic cycle. 4. Erythrose is a tetrose that forms the raw material for the synthesis of monosaccharides. anthocyanin and lignin. 5. Pentose sugar ribose is found in every animal cell. It occurs in a number of compounds which play crucial roles in metabolism, e.g. ATP, ADP, formed. riboflavin and RNA. Its is found in DNA in its reduced form called deoxyribose 6. The hexoses comprise a large group of sugar, several of which play an important role in nutrition. 7 The hexoses are divided into aldoses or ketoses according to whether they contain an aldehyde or keto group. 8. All hexoses are aldoses (glucose, galactose and mannose), except fructose which is a ketose. 9. Simple sugar of the blood is glucose 10. Blood sugar level is a measure of glucose. 11. Immediate source of energy is glucose. 12. Glucose is stored as glycogen in liver and muscles. 13. The main cellular fuel of the body is glucose. 14. Fructose (levulose) is the fruit sugar, it is the sweetest among naturally occurring sugars. 15. Sugars having a free aldehyde or ketone group can reduce Cu2+ to Cu+ these are called reducing sugars. 16. This property is the basis of Benedict’s and Fehling's test to detect the presence of glucose in urine. 17. Galactose occurs in milk as a component of the milk sugar, lactose. 18. Certain compounds of galactose, the galactosides, occur in the brain and nervous tissue. 19. Galactose is a constituent of agar-agar and galactolipids found in plant leaves. 20. Mannose is an aldohexose, found in the polysaccharides of plants. Mannose is also found in blood serum, globulins, and certain egg proteins. 21. Mannitol is an alcool of mannose common in brown algae. OLIGOSACCHARIDES 1. Oligosaccharides are formed by condensation of 2-10 monosaccharides. 2. Disaccharides are oligosaccharides with a combination of two molecules of monosaccharides. 3. When two monosaccharide molecules link by means of 1-4 glycosidic bonds, a molecule of water is released, a disaccharide molecule is formed. 4. The common disaccharides are sucrose, maltose, lactose, and cellobiose. 5. Sucrose is made up of glucose + fructose, it occurs in sugar cane and sugar beets, sources of commercial sugar. 6. Sucrose has no free aldehyde or ketone groups, sucrose is not a reducing sugar 7. Maltose is a disaccharide that gives two molecules of glucose on hydrolysis. 8. Lactose (glucose + galactose) is present in milk. 9 Lactose does not occur in nature except as a product of the mammary gland. 10. Compared to the milk of cows, buffalo, and goats, lactose is highest in human milk. 11 The taste of Saccharine is sweet, but it’s not sugar. POLYSACCHARIDES 1. Polysaccharides are polymers of monosaccharides. 2. Glycogen and starch are both polymers of α glucose. 3. Starch common in plants and glycogen in animals are two food storage polysaccharides. 4. Glycogen is known as 'animal starch'. 5. Glycogen is related to starch as both are polysaccharides. 6. A starving man first consumes reserve glycogen. 7. Glycogen found in liver and muscles store energy in mammals. 8. Glycogen is broken down by the hormone glucagon secreted by islets of langerhans. 9. Two different polymers, amylose and amylopectin actually form a mixture called starch. 10. The basic unit of starch is glucose. 11. Two structural polysaccharides are chitin and cellulose. 12. Cellulose is an unbranched chain of glucose units joined by B (1-4) linkages. 13. Cellulose is digested by termites and sheep by harboring bacteria 14. Man cannot digest cellulose. 15. Gazing animals digest cellulose with the help of intestinal bacteria. 16. Cellulose is a homoglycan hexosan. 17. Cellulose is a constituent of the cell wall of higher plants, some algae, and some fungi. 18. Cotton contains the maximum amount of cellulose. 19. Chitin is a polysaccharide and is the principal component of the exoskeleton of insects and crustaceans, it is a polymer of N-acetyl glucosamine. 20. Inulin (Dahlia starch) is a carbohydrate, polymer of fructose. LIPIDS 1. Lipids are biological molecules, insoluble in water, but readily soluble in nonpolar organic solvents like chloroform and benzene. 2. Lipids include seven major groups of substances : fatty acids, triglycerides (neutral fats), waxes, phospholipids, glycolipids, steroids and terpenes. FATTY ACIDS 1.A fatty acid is composed of a long hydrocarbon chain ("tail") and a terminal carboxyl group ("head"). 2. Most of the fatty acids found in nature have an even number of carbon atoms (usually 14 to 24). 3. Fatty acids are either saturated (all carbon-carbon bonds are single bonds) or unsaturated (with one or more double bonds in the hydrocarbon chain). 4. The general formula of a saturated fatty acid is CH3 (CH2)n COOH. 5. If a fatty acid has only one double bond (Palmitoleic acid and oleic acid) it is said to be monounsaturated. 6. If a fatty acid has more than one double bond (2 in linoleic acid, 3 in linoleic acid and 4 in arachidonic acid), it is said to be polyunsaturated. 7. Unsaturated fatty acids are slightly more abundant in nature than saturated fatty acids, especially in higher plants. 8. The most common monounsatuated fatty acid is oleic acid. 9. Saturated fatty acids do not contain double bonds. 10. Essential fatty acids are some polyunsaturated fatty acids which cannot be synthesized in the animal body and must be supplied with food to avoid their deficiency. 11. Linoleic, linolenic and arachidonic acids are essential fatty acids for man. 12. Linolenic acid is an essential fatty acid with three double bonds 13. The number of double bonds in essential fatty acids is four 14. A rich source of polyunsaturated fatty acids in the diet is vegetable oils. 15. Sunflower oil is rich in linoleic acid and the minimum fatty acid content is in coconut oil. 16. Mustard oil is one of the most unsaturated. 17. Essential fatty acids serve as a precursor for the synthesis of prostaglandins NEUTRAL FATS (TRIGLYCERIDES) 1.The esters of fatty acids with glycerol form neutral fats. Each molecule of glycerol is capable of reacting with three molecules of fatty acids 2. A glycerol possesses three hydroxyl groups, three fatty acids attached to the glycerol and three molecules of water are removed. 3. In this reaction, the removal of water results in the formation of ester bonds. 4. Fats that are generally liquid at room temperature are called oils 5. Oils are rich in unsaturated fatty acids and have low melting points. 6. In hydrogenation the unsaturated acids become saturated acids and oil becomes solid fat. 7. Most animals use a fat molecule for long-term energy storage. 8.Fat gives more calorie per unit mass. 9. Maximum energy is produced by the oxidation of fats. 10. Fats are richly found in adipose tissue. 11. Fat yields twice as many calories per gram as carbohydrates. 12. Too much use of fats should be avoided during the summer months. WAXES 1. A combination of a long-chain fatty acid with long-chain alcohol form waxes. 2. Waxes have high melting points and are not digested by animals. 3. A common example is beeswax, a combination of palmitic acid and myricyl alcohol (C30H61OH). 4. A water-insoluble coating of waxes found on hair and skin in animals and stems and leaves and fruits of plants. 5. Waxes have an important role to play in protection. PHOSPHOLIPIDS 1. These contain not only fatty acid and alcohol but also a phosphate group. 2 Phospholipid is amphipathic because it contains both hydrophilic (watersoluble) and hydrophobic (water-insoluble) regions. 3. Phospholipids are important constituents of the ell membrane because they contain both polar and nonpolar portions. 4. Some phospholipids like lecithin have a nitrogenous compound, choline attached to them. 5. Lecithin, produced commercially from soybean seed, is an excellent emulsifying agent. GLYCOLIPIDS 1. Glycolipids contain glycerol with two polyunsaturated fatty acids (largely linoleic) joined to the 2 and 3 positions.On the first position carbon atom, one or two moles of galactose are attached. 2. Glycolipids are important constituents of certain types of membranes, especially those found in plant cells and cells of the nervous system. STEROIDS 1. Steroids are derivatives of a four-membered ring compound called phenanthrene. 2. Cholesterol is one of the most important animal steroids. It is chemically unreactive and insoluble in water. 3. Cholesterol is useful since it is a structural component of cells. it is synthesized from acetyl CoA or acetate (C2) in the liver and thus not a dietary essential. 4. Cholesterol is not found in plants, but the latter contains other steroids collectively known as phytosterols. 5. Cholesterol content is minimum in vegetable oils 6. Diosgenin, a steroid compound produced by the yam plant (Dioscorea) is used in the manufacture of anti fertility pills. 7. Hormones like androgens, estrogens, progestins, glucocorticoids, mineralocorticoids, and bile acids are steroids derived from cholesterol in animals. 8. Ergosterol is the principal plant steroid present in high concentration in yeast and upon irradiation is converted to vitamin D. 9. Bile acids are derivatives of cholesterol, synthesized in liver. They are major components of bile and aid in emulsification of fat in small intestine. TERPENES 1. Lipids constructed from the five-carbon compound isoprene are called terpenes. 2. Isoprene and its derivatives are joined in various combinations to produce substances such as vitamin A, coenzyme Q and carotenoids. PROTEINS 1. 2. 3. 4. The term protein was coined by Berzelius and Mulder. Protein is the main organic compound of a living cell. Proteins are the most diverse chemicals in a living organism. Proteins essentially contain carbon, hydrogen, oxygen and nitrogen commonly sulphur, phosphorus, iodine, and iron. 5. The smallest structural units of proteins are amino acids. 6. Formation of a protein is a dehydration synthesis. 7. Peptide bonds bind molecules of amino acids. A peptide bond is formed between two carboxyl groups of amino acids and amino acid group of the adjacent. 8. Proteins are synthesized at ribosomes. 9. RNA takes part in the synthesis of proteins. 10. Nitrogen is an important component of proteins. 11. Specific dynamic action is maximum in proteins. 12. Proteins on hydrolysis yield amino acids. AMINO ACIDS 1. Amino acids are building blocks of proteins. 2 Although about 300 amino acids occur in nature, only 20 of these enter vare into the composition of proteins. 3. Each amino acid contains a centrally located carbon atom called α carbon to which four groups are attached: a basic amino group (-NH2), an acidic carboxyl group (-COO), a hydrogen atom, and a group of varying chemical structures called a side chain H R-side chain Cα H3N+ COO (Amino Group) (Carboxyl Group) 4. With four different groups attached to it, the a-carbon is said to be asymmetric. 5. There are several ways to classify the amino acids: (i) Common amino acids found in proteins. (ii) Uncommon amino acids. (iii) Amino acids are not found in proteins. 6. Common amino acids found in proteins are grouped into: (i) Nonpolar (hydrophobic) amino acids. (ii) Polar amino acids (neutral amino acids) (iii) Acidic amino acids and (iv) Basic amino acids. 7. There are several amino acids that rarely occur in proteins. Uncommon Amino Acids Amino Acid Found in Hydroxylysine Collagen and gelatin Hydroxyproline Collagen and gelatin Methylhistidine Muscle protein Methyllysine Muscle protein Aminoadipic acid Com protein N-methylarginine Histone protein N-acetyllysine Histone protein Amino Acids not found in Proteins Gamma amino butyric acid (GABA) Histamine Serotonin Ornithine Citrulline β-Alanine 8. Glycine is the simplest amino acid with the lowest molecular weight and no asymmetrical carbon atom. 9. Glycine is involved in the formation of heme. 10.Tryptophan is an amino acid with an unusual cyclic structure, it does not possess free amino and carboxyl groups. 11. Proline is an amino acid with an unusual cyclic structure, it does not possess free amino and carboxyl groups. 12. Strictly speaking, proline is not an amino acid, but imino acid 13. Methionine and cysteine are sulphur-containing amino acids. 14. Isoleucine is an amino acid with two asymmetrical carbon atoms 15. Tyrosine gives rise to dopamine, melanin, thyroxine, adrenaline and noradrenaline. LEVELS OF PROTEIN STRUCTURE 1. Primary Structure (i) the linear sequence of amino acids in a protein molecule is referred to as the Primary structure. (ii) The first protein to have its complete amino acid sequence determined was insulin, a hormone that contains 51 amino acids (Frederic Sanger, 1956) 2. Secondary Structure (i) Secondary structure of protein molecules involves α.-helices and β sheets. (ii) Secondary structure depends on hydrogen bonds between C=0 and - NH groups. (iii) In α-helix, a single amino acids chain is coiled spirally by establishing hydrogen bonds between first and fourth amino acids. (iv) in β-pleated arrangement a sheet is produced by holding of two or more polypeptide chains in parallel or antiparallel manner. 3. Tertiary Structure (i) When the polypeptide chains of protein molecules bend and fold in order to assume a more compact three-dimensional shape, a tertiary level of structure is formed. (ii) Tertiary structure is due to a variety of bonds and interactions between amino acid side chains like disulphide bonds, electrostatic (ionic) bonds, hydrogen bonds, van der Waals' interactions and hydrophobic effect. 4. Quaternary Structure (i) Quaternary structure of a protein is an inter-relation between peptide chains having more than two peptide chains. Biological Functions of Proteins with Examples Functional Class Examples Enzymes Ribonuclease Amylase Trypsin Catalase Regulatory proteins Insulin Growth hormone Parathormone Transport proteins haemoglobin Serum albumin Glucose Transporter Storage proteins Ovalbumin Casein Ferritin Glutelins Globulins Contractile and motile Actin Myosin Tubulin Kinesin Structural proteins Collagen a-keratins Elastin Chondrin Ossein Fibroin Protective proteins Immunoglobulin Thrombin Fibrinogen Antifreeze proteins Exotic proteins Monellin Resilin Glue proteins Representative Conjugate Proteins Class Nucleoprotein Examples Ribosomes, TMV Metalloproteins Ferritin, Cytochrome Oxidase Chromoproteins Haemoglobin, Cytochrome c Phosphoproteins Casein Lipoproteins Blood plasma lipoproteins Glycoproteins Proteoglycan, Mucin Flavoproteins Succinic dehydrogenase NADH dehydrogenase Keratin is a fibrous protein. It contains large amount of sulphur. Feathers are made up of β-keratin. Structural proteins are fibrous. The most abundant protein in human body is collagen. A major component of extracellular matrix in vegetables is collagen. Enzymes are functional proteins. An enzyme is formed by chemically bonding together amino acids. 7. Silk contains protein fibroin. 8. Casien is a phosphoprotein, the best source of casein is milk. 1. 2. 3. 4. 5. 6.