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CELLULAR MACROMOLECULES

Everyday Science (PCS) Biology

Cellular Macromolecules

A small number of monomers bounded together, form a molecule called oligomer, but a molecule containing large number of monomers is called polymer. Small molecules polymerise to constitute large molecule called Macromolecules. Some of the important macromolecules discussed in this chapter are Polysaccharides, Proteins and Nuclear Acids.

Polysaccharides

The most important polysaccharides are polymers of glucose. These include cellulose, glycogen & starch. As these polysaccharides polymerise, a molecule of water is released at each condensation the bond formed during polymerization is glycosidic bond. This leads to reduction of bulk & makes the polysaccharide almost insoluble. This also reduces the effect on water potential of cell, thus making the polysaccharides ideal for storage & structural components.

Structural Classification

(a) Homosaccharides: When polysaccharides are made up of single kind of monosaccharide as in starch, glycogen & cellulose.

(b) Meter polysaccharides: When polysaccharides are made up of 2 or more kinds of monosaccharides or their derivations eg. Mucopolysaccharides, Chgitan & Peptidoglycan.

Important polysaccharides

(1) Starch : Polymer of glucose units linked together by glycosidic linkage which enzymes can break. Thus, starch can be digested. Its formed during photosynthesis by green plants & stores energy. Starch can be hydrolyzed to lower weight of polysaccharides & finally splits into maltose & glucose. The enzymes hydrolyzing starch are called Amylases. Latter can be of plant or animal origin. Partial hydrolysis of starch results in substances known as destrains.

(2) Glycogen: It’s a branched polymer of glucose found mostly in muscles and livers of animals. Its also called Animal Starch.

The above 2 polysaccharides are food storage polysaccharides unlike Cellulose which is a structural polysaccharide.

(3) Cellulose: It’s a lower polymer of glucose. It is of interest to note that although the human intestinal mucosa doesn’t secrete a cellulose splitting enzyme.

Cellulose in daily use

Cotton fibres contain more than 90% cellulose.

Wood has 25.50% cellulose. It also has hemicellulose & pectin.

Carboxy Methyl Cellulose is widely used in ice creams, cosmetic industry & medicines.

Micro organisms on fermentation produce ethyl alcohol, butyl alcohol etc.

Insulin: Homopolysacccharide of fructose units found in cell sag of some plants.

Pectin: Homopelysaccharide used in preparation of gums, jellies etc.

Chitin: Nitrogen containing polysaccharide present in cell wall of fungi and exoskeleton of arthropods. It’s a heteropolysaccharide.

Mucopolysaccharide

They contain amino sugars. Most of the mucopolysaccharides are found in association with proteins and may be called as Mucoproteins.

Mucopolysaccharides are common in cell walls of bacteria, connective tissue of animals and in body fluids. They bring lubrication in ligaments and tendons. Mucilage, slumy substance produced in plants has galactose & mannose as its components.

Mucopolysaccharides work as binding agent for proteins present in cell walls, connective tissue & interstitial spaces.

Proteins

Proteins form about 12% of cell contents. Amino acids are building blocks of proteins where they are linked together via a peptide bond. They are nitrogenous compounds containing carbon, hydrogen, oxygen & nitrogen. Phosphorus & sulpur are often also found.

The protein structure and conformation can be broadly classified under three types:

(I) According to Composition

(II) According to functions

(III) According to Shape

(A) Simple Proteins:

Those which yield only X-Helix anum acid upon hydrolysis. Some important ones are:-

1. Albumins – Found in plants and animal. Eq. Egg albumin.

2. Globulins – Found in plants and animal. Eq. Serum globulins.

3. Schleroproteins (Albuminoids): Found only in animals. Eq. keratin in hair and fingernail.

4. Glutenins: found in animals. Eq. Glytenin from wheat.

5. Histones & Prolamines.

Eq. Zein from corn and gliadin from wheat.

6. Protamines

Eq. Salmine from Salman fish sturine from Sturgeon.

(B) Conjugated Proteins

These which yield X-amino acidplus a non protein material known as prosthetic group upon hydrolysis. Some important conjugated proteins are:-

(a) Glycoproteins (Carbohydrate derivative as prosthetic group.) eq. Mucin (in saliva)

(b) Phosphoproteins:

Eq. Casein in milk.

Eq. Haemoglobin, Cytochrone

(d) Nuclcoproteins (Nucleic acids as prosthetic group)

Eq. Nuclien & Nucleohistones of glandular tissues, yeasts, chromosomes and other materials rich in cell nuclei.

1. Structural proteins – These are fibrous proteins, such a collagen which comprise half of mains total protein in form of skin, cartilage & bones.

2. Contractile proteins – Found in muscles eq. Myosin, Actin.

3. Hormones – eq. Insulin.

4. Enzymes – eq. Pepsin & Trypsin.

5. Antibedies – eq. gamma globulins in blood.

6. Blood proteins – eq. Albumin, Haemoglobin & fibrinogen.

1. Fibrous proteins:

They are thread like polypepide chains held together by hydrogen bonds.

2. Globular Proteins

These are polypeptide chains held together by Ionic, hydrogen and disulphide bonds.

Functions:

1. All enzymes are made up of protein. Enzymes are pertinacious substances which enhance the rate of biochemical reactions.

2. Collagen provides strength to skin and bones.

3. Proteins are responsible for immunological reactions (antibody formation).

4. They transmit nerve impulses.

5. Haemoglobin and Myoglobain transport proteins and O2 in blood and muscles respectively.

6. Hormones like Insulin and Parathormone are proteins and centrol metabolism.

7. Protein act as carrier molecules & binding structures for metabolites for their possible transport across membrane.

8. P-protein take part in transport of organic solutes in phloem of vascular tissue.

9. Proteins also help in muscle contraction, because they constitute the major part of muscles.

10. Proteins may act as energy source.

1. Primary Proteins: (10 Proteins) : It represents true configuration of any protein. For proper functioning, it should have a three-dimensional form. Enzyme Kibonuclease & hormone insulin are proteins with primary structure only.

2. Secondary proteins: The next level of protein structure is called Secondary. Folding & Coiling of chain beings 2⁰ level.

3. Tertiary Proteins: The formation of stable, 3-D structure by further coiling of peptide chain results in tertiary structure. Its maintained via 3 types of bonds eg. Ionic bond, hydrogen bond. Latter is the strongest of all bonds.

Classification of Protein

Nucleic Acids

Chromosomes are made up of nucleoproteins which constitute basic proteins and nucleic acids. Two kinds of nucleic acids are recognized – Deoxgibose nucleic acid (DNA) and Ribose nucleic acid (RNA).

DNA

DNA is found in cytoplasm in prokaryotes in circular form. In eukaryotes, it is mainly located in nucleus as the chief constituent of chromosomes in combination with proteins to form DNP (Deoxyribo nucleoproteins). Eukaryotes also have DNA in organelles like Mitochondna and chloroplasts.Watson & Crick proposed the double helical structure of DNA. Circular DNA is without fire terminus white linear DNA is with free terminal DNA is hereditary in function.

In 1953 American biochemist James Watson and British biophysicist Francis Crick published the first description of the structure of DNA. Their model proved to be so important for the understanding of protein synthesis, DNA replication, and mutation that they were awarded the 1962 Nobel Prize for Physiology or Medicine for their work.

Monosaccharides

Derived Monosaccharides

Oligosaccharides (210 carbon units)

Polypaccharides

Monosaccharides of Simple sugars don’t give smaller sugar units on hydrolysis.

The most abundant monosaccharide found in nature is glucose. Smallest monosaccharides are Trioses (3-carbon sugars).

Types:

1. Trioses (3 - carbon sugars) Eg Glycerldehyde, Dihydroxyacetone

2. Tetroses (4 – carbon sugars) Eg. Grythrose, Erythrulose, Threose

3. Pentose: (5 – Carbon sugars) Eg. Ribose, Deoxyribose, Xilulose, Arbinose

4. Hexose (6 – carbon sugars) Eq. Glucose/grape Sugar, Fructose/Fruit Sugar, Galactose

5. Heptose (7 – carbon sugars) Eq. Sedoheptulose

These are polysaccharides with low molecular weight. The most important and smallest are Disaccharides.

Eq. Maltose - Simplest of all disaccharides, Made up of 2 glucose units, Readily soluble in water

Eg. Sucrose - Also known as cane sugar/Table Sugar, Sweetening power of sucrose is considered to be 100, Made up of glycose & fructose, Easily soluble in water.

Eg. Lactose - Also known as Milk Sugar , Made up of glucose & galactose units, Not very soluble and not very sweet, Its not found in plants.

Trisaccharides:

Raffinose is a common trisaccharide found in plants. On hydrolysis, it gives rise to molecule each of glucose, fructose and galactose.

These are compound sugars which are formed due to larger number of monosaccharides. They have comparatively high molecular weight. These are considered as Cellular Marcromolecules

C-Value

Total value of DNA per genome of organism is called C-value. Its represented by pictograms (pg) of base pair (bp).

RNA

Its found in cytoplasm, little in nucleolus & in nucleoplasm associated with chromosomes. Its single stranded unlike DNA. It consists of pentose sugar – Ribose, nitrogenous bases – Adenine, Guanine, Cytosin & uracial.

It is involved in protein synthesis & is of 3 types:

(a) eRNA (ribosomel RNA)

(b) mRNA (messenger RNA)

Small Molecules of Life

Although living matter often contains traces of all element found in its surroundings, some 20 elements are essential for life. Based on their relative concentration found in human body, they are of following types:

(a) Major Elements : 6 elements carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus and Sulphur make up most of the body weight (98%). They are also called Protoplasmic Elements.

(b) Minor Elements

Biomolecules

The molecules found in organisms are called Biomolecules. These constitute of Inorganic Material eq. Salts, Mineral sons and water and Organic compounds as carbohydrates, lipids, amino acids, proteins etc. Organic & Inorganic compounds occur in ratio of 9:1.

Organic Compounds

Carbohydrates

They are chiefly composed of carbon hydrogen & oxygen. In some, which are derivations of biological importance, Nitrogen and Sulphur have also been detected, They are also known as Saccharides.

Major Classes

Carbohydrates can be classified into four major classes.

Functions of Carbohydrates

1. Carbohydrates in the form of sugar of starch are responsible for major calorie intake in animals, humans and micro-organisms.

2. They make up bulk of living matter in plants performing structure and food storage functions eg. Starch and glycogen.

3. Many carbohydrates become commenting in nature and work to lubricate skeletal joints.

4. Glucose – Works as beginning point of Respiration. Immediate source of energy.

5. Fructose – Component of a polysaccharide : Insulin.

6. Galactose – (Not naturally occurring sugar). Constituent of Agar-agar.

7. Luerose – Reserve storage produce of Sugarbeet and Sugarcane.

8. Lactose – Constitutes 5% of mammalian milk.

Some Important Points

Glucose, Fructose and Galactose have identical molecular formula viz C₆H₁₂O₆ but the atoms in different molecules differ in arrangement which account for difference in their chemical properties. Such substances are known as Isomers.
Sucrose is a non-reducing sugar.
Souring of milk occurs when bacteria convert lactose (of milk) into Lactic Acid.

Lipids

Fats and their derivatives are together known as Lipids. They are soluble in organic solvents but insoluble in water.

Some common lipids

Diosgenin : Used as Antifertility Drug.

Myelin : Ensheaths nerve fibre

Lecithin – Present in egg yolk and brain.

Cerebrosides: found in nervous system.

Sterols: Important constituent of hormones like Testosterones, progesterone and Cortisones.

Turpenes: impart flavour and adour to some essential oils like Camphor oil, Eucalyptus oil.

Carotene – Found in carrot

Lycopene – Found in tomato

Classification

(a) Simple Lipids

(b) Conjugated Lipids

(c) Derived Lipids

Simple Lipids

They are composed of fatty acids & alcohols. They are further of 2 sub-types: Neutral/ True fats – Composed of fatty acids and glycerol. Waxes – Composed of fatty acids with alcohol other than glycerol. They are responsible for making plant and animal tissues, heat proof.
They are made up of carbon, Hydrogen and oxygen but include proportionately less oxygen as compared to carbohydrates.
Physical nature of fat is determined by chain length of fatty acids and whether they are saturated (Not bearing double bonds between carbon atoms of molecules chain) or unsaturated (Having one or more double bounds between carbon atoms of molecular chain.)
Most of animals usually get the supply of these acids from plant and bacteria.
Due to their lower specific gravities, they float in water.
Most plant fats have unsaturated fatty acids and most animal fats have higher quantity of saturated fatty acids.
Saturated fatty acids are solids at ordinary temperatures and unsaturated fatty acids are liquid at ordinary temp.
Oils on Hydrogenation become solidified – vanaspati ghee.

Conjugated Lipids

They consist of lipids along with an additional component.

Phospholipids: Lipids bearing a phosphate group in addition to fatty acids and glycerol. It’s a major structural component of cell membranes. Some Important Phospholipids are Lecithin’s: Constituent of cytoplasm and are found in storage fats.
Glycolipids: Complex lipids containing carbohydrates.
Lipoproteins: Lipid is bound to protein and found mainly in mammalian plasma. A number of proteins in serum are known as Lipoproteins because their function is to transport lipids, without them lipids could not exist in dissolved state in blood.

Derived Lipids

These are substances formed on hydrolysis of simple or conjugated lipids which still retain properties of this class of compound.

Steroids
Sterols				Bile Acids	Sex Hormones
Cholesterol	Ergsterol	Prostaglandins	Stigmasterol and Sitsterol
Steroid found in animals only Abundant in Nervous System Processor of hormones like Progesterone, Testosterone etc	Found in cell membrane of fungi. Precessor of Vit D2.	- Hormone like compounds found in secretion of seminal vesicles (in males) and Menstrual fluid (in females). - Works in inflammatory and allergic reactions, blood clotting and muscle contraction.	Found in plants	Bile Acids in human bile. Cholic Acid Deoxycholic Acid Chenodeoxycholic Acid	Ovary: Estradial Testes: Testosterone

Functions of Lipids

1. Act as storage compounds in animals, in fruits and seeds of plants.

2. Provide food to developing embryo in plants.

3. Act as structural component in cell’s components.

4. Provide electrical and thermal insulation.

5. Act as solvent for fat soluble vitamins A, D & E.

Amino Acids

Constitute the structural framework of proteins. Infact, proteins are linear polymers made up of Amino Acids.

Types

(A) When amino group is free its said to be Basic (Lysine, Arginine) and when carboxyl group is free its said to be Acidic (Glutamic Acid, Aspartic). Neutral Amino Acid are Alanine, glycine

(B) (1) Essential Amino Acids : They can’t be synthesized by organisms in the body as they are obtained from plants. (2) Non-Essential Amino Acids :They can be synthesized by organisms in the body.

(3) Semi-Essential Amino Acids: They are needed by growing children and lactating, pregnant mothers. Eg Aeginine, Mistidine.

Some Important Points

Amino acids acts as a base in acidic solutions as acids in a base. This property is known as Amphoteric property.
simplest Amino acid : Glycine
Amino acid acting as plant growth hormone : Tryptophan
Removal of amino group leads to formation of glucose in many amino acids.
Histamine – removal of carboxyl group of amino acid in form of carbon dioxide yields this which is released in body as inflammatory response.
Non protein amino acids are components of Antibiotics.

Nucleotides

Nucleotides are made up of sugar (deoxyribose sugar in DNA and ribose in RNA), nitrogenous base and phosphoric acid.

DNA and RNA are recognized on the basis of pentose sugar and nitrogenous base responsible for farming nucleotides.

Components

(a) Sugar Molecule : Deoxymbion sugar has one oxygen less than Ribose sugar through both are pentoses.

(b) Nitrogen bases : Purines: They are dycyclic in nature. Admine ((A) and Gyamine (G) constitute purines - Pyrimidines: They are monocyclic in nature. Most commonly noticed pyrimidines in DNA are Thymine (T), Cytosine (C). In RNA, Uracil (U) replaces Thymine.

Some points:

Mannitol: Alcohol of Mannose.
Honey bees inject formic acid during their bites.
Saccharine in cancer causing sugar.
Monellin (2000 times sweeter than sugar) is sweetest chemical and is a protein obtained from African berry.

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