Introduction To Biology

Introduction To Biology

1.1   Life Components ( Biochemical Important Molecules)

The chemical molecules present in the cell and which have direct relationship with the activities  of cell are called biochemical molecules or biomolucules. Biomolucule can also be defined as the chemical compound found naturally in living organisms. The collection of molecules in a cell is called cellular pool. A cellular pool consists of:

·         Organic Compounds: Carbohydrates, Lipids, Proteins, Amino Acids and Nucleic acids.

·         Inorganic Compounds: Minerals and water.

Inorganic compounds: It includes minerals and water.

1.2   Organic Compounds

A chemical compound containing carbon is called organic compound. Methane is one of the simplest organic compound. Biomolecules consist primarily of carbon and hydrogen along with oxygen, nitrogen, phosphorus and sulpher. These elements (C,H.O and N) join in various combinations and form several types of organic compounds such as carbohydrates, proteins, enzymes, lipids and nucleic acids.

The organic molecules are further classified into two types.

A)     Micro molecules: They are small and simple molecules with low molecular weight. They are formed by basic elements like carbon, hydrogen, oxygen and nitrogen. Examples Monosaccharides, Disaccharides, fatty acids, amino acids, nucleotides, lipids.

B)      Macromolecules: They are large and complex molecules with high molecular weight. They are formed by polymerization of large number of micromolecules. Example: polysaccharides, proteins, nucleic acids.

1.2.1          Carbohydrates: These are the organic compounds of carbon,hydrogen and oxygen where the hydrogen and oxygen are present in the ratio of 2:1, as in water. They act as sources of energy for cells. The carbohydrates are classified as monosaccharides, disaccharides and polysaccharides. They are called ‘Saccharides’ (Sakcharon in Greek meaning ‘Sugar’.

Monossaccharides: Monosaccharides are the simplest form of carbohydrates with only one simple sugar. The general formula for momosccharides is CHO. Based on the number of carbon atoms, the members of monosccharides are known as trioses (C3H6O3) , tetroses (C4H8O4), pentoses (C5H10O5), hexoses (C6H12O6) and heptoses (C7H14O7), Glucose, fructose and galactose are the most common types of hexoses. They are highly soluble in water and sweet in taste.

They are also designated as aldoses and ketoses depending on whether they containaldehyde or ketone groups. All sugars contain the C=O group. This is called a carbonyl group. When carbonyl group is terminal in position and is jointed to at least one hydrogen atom it is designated as aldehyde. But when it is subterminal in position or it is present between carbon atoms it is designated as ketones.

Some Biologically Important Monosaccharides

Disaccharides: These are formed by two molecules of the monosaccharides with release of a water molecule. The most common disaccharides are maltose sucrose and lactose. They are soluble in water and sweet in taste.

Sucrose is found in the juice of plants such as sugarcane, sugar beet, pineapple and carrot roots. Lactose or milk sugar occurs about 5% in cows milk and 7% in human milk,

Some biologically important disaccharides

Polysaccharides: Polysaccharides are the condensation product of a large number of monosaccharides. The general formula for polysaccharide is (C6H10O5) n. Shorter polysaccharides with 2-10 monomeres, are called oligosaccharides. Polysaccharides are mostly insoluble in water and not sweet in taste. The most common polysaccharides found in living organisms are glycogen, starch and cellulose. Starch is the storage food of plant . Glycogen is the storage food of animal and also found in blue green algae, fungi and bacteria. Cellulose is an important constituent of plant cell wall.

     Cellulose is the main constituent of paper and cloth. It is also the basis for the manufacture of several synthesis fibres like rayon.

1.1.1          Proteins: Proteins are nitrogenous macromolecules of amino acids. The amino acids in protein are joined together by the peptide bonds between the carboxyl and amino groups. Hence, the proteins are also known as polypeptides. A covalent bond between a nitrogen atom and a carbon atom is called peptide bond. Most proteins are polymers of twenty different amino acids. 

Every cell contains protein. It is a major part of the skin, muscles, organs and glands.

 

Proteins are classified into three types:

a)      Simple proteins: These proteins are made up of amino acids only eg. Albumin, globulin, protamines, histones, glutelines, etc.

b)      Conjugate Proteins: These are the proteins which contain other substance known as prosthetic groups in addition to amino acids. Conjugate proteins are phosphoprotein, nucleoprotein, glycoprotein, chromoprotein, haemoglobin etc.

c)       Derived proteins: They are products of denaturation or of partial digestion of proteins eg. Metaproteins, proteoses and peptones.

 

Functions of proteins

I)                    Protein is the structural component of protoplasm and is thus an important consitituent of all cells and tissues.

II)                  All enzymes are derived from proteins.

III)                Protein also forms a part of membrane.

IV)               Chlorophyll consists of magnesium and proteins, while the cytochromes are made up of iron and proteins.

V)                 Protein is important for growth and development during childhood, adolescence and pregnancy.

1.1.1          Amino Acids: Amino acids are small molecules of carbon, hydrogen, oxygen and nitrogen. Sometimes, they may contain sulphur also. They are the building blocks of protein. About 20 naturally occurring amino acids are known. These are colourless, crystalline solids. They are generally soluble in water and insoluble in organic solvents. An amino acid contains one amino group (-NH2), Carboxylic group (- COOH) and R- group having variable length of atomic grouping. The R group in glycine is a hydrogen atom, CH3 in alanine, CH2OH- in serine: CH3CHOH in threonine.

Function of Amino acids:

a)      They are the building blocks of proteins.

b)      Amino acids are converted to vitamins, hormones, pigments and alkaloids.

c)       Carbon chain of many amino acids is converted into glucose after removal of amino group.

d)      When carboxyl group of amino acid is lost as carbon-dioxide biologically active amines (histamine) are formed.

Depending upon the ability of our body to synthesis them, amino acids can be divided into two types:

i)                    Essential and ii) non essential amino acids. The term essential or non essential does not mean that some are essential to our body and others are non essential.

1.1.1          Lipids : Lipids are organic compounds of carbon, hydrogen and oxygen, but have much less oxygen in comparison to carbohydrates. Lipids are esters of fatty acids and alcohol. They are insoluble in water but readily dissolve in organic solvents, such as ether. Benzene and chloroform .

Esters : Ester is an organic compound formed by a carboxylic acid and an alcohol molecule with the loss of a water molecule.

 

 

Fatty Acids: These are large molecules containing the carboxylic group- COOH.

Fatty acid molecules in living organisms commonly have up to 20 carbon atoms. Palmitic acid for example, has 16 carbon atoms.

Glycerol : It is a trihydric alcohol and can react with three molecues of fatty acids to form a fat molecule.

Lipids are Classified into three types:

1)      Simple lipids  2) Compound lipids  3) Derived lipids

1)      Simple lipids: Simple lipids are esters of fatty acids and various alcohols eg.

a)      Fats : esters of fatty acids and glycerol that are solid at room temperature.

b)      Oils : esters of fatty acids and glycerol that are liquid at room temperature

c)       Waxes : esters of fatty acids and alcohols other than glycerol.

2)      Compound Lipids : These are lipids, which contain an inorganic or organic group in addition to fatty acids and alcohol.

a)      Glycolipids : Carbohydrate+ lipid

b)      Phospholipids or phosphatides : Phosphoric acid + lipid

c)       Lipoprotien : Protein + lipid

3)      Derived Lipids: They are derived from simple or compound lipids on hydrolysis.

a)      Fatty acids of various series.

b)      Setrols : (steroids) : A steroid is a derived lipid formed of four carbon rings with an attached

c)        

R group. Cholesterol , ergosterol, diosgenin, stigmasterol, sitosterol are some important sterols. 

Cholesterol: Since cholesterol was first isolated from gallstones. It was called cholesterol which means “ Solid alcohol from bile “. Brain, nervous tissues, adrenal glands and egg yolk are rich sources of cholesterol.  

Importance of Steroids

1)      Cholesterol is a molecule of many sex hormones like testosterone, progesterone, etc.

2)      Cholesterol forms vitamin D on radiation by UV rays.

3)      Diosgenin is used in the manufacture of anti- fertility pills.

4)      Cholesterol creates abnormal thickening of the walls of arteries. It can raise the blood pressure and hence may lead to circulatory problems.

5)      It is not bad not useful as well.

Differences Between Fats and Oils

Functions Of lipids

     

         i.            Fats are abundantly found in seeds as reserve food with a large amount of energy stored in them.

       ii.            They (fats) are reserve food in plants and animals

      iii.            They form an insulating layer below the skin in animals

     iv.            Phospholipids are important constituents of cell membranes and subcellular structures

       v.            They act as cushions to absorb mechanical impact around organs like eyeballs

     vi.            Lipoprotien can prevent bacterial diseases

    vii.            Bile salts are modified cholesterol needed for digestion of fat

  viii.            Wax provides a protective and impermeable lining to edidermis and check water loss in some xerophytic plants

1.2.5 Nucleic Acids: Nucleic acids are long chain macromolecules of nucleotides . Nucleic acids were so named because they were first found in the nucleus of cells but later they are found existing outside the nucleus.

Nucliec acid was first isolated in 1869 by a Swiss physician F Miescher from the nuclei of pus cells. He called it nuclein. Altman(1889) renamed it as nucleic acid. Oswald Avery (1944) gave some evidence that nucleic acid is the carrier of genetic information.

Living organisms contain two types of nucleic acids in the form of DNA and RNA. These are long chaims macromolecules of nucleotides with high molecular weight. For example E coli has DNA molecule of 3,400,000 base pairs. In higher organisms the amount of DNA may be hundred times larger (7000 times in the case of man)

Deoxyribonucliec Acid: DNA is mainly found in the nucles of eukaryotic cell a small amount is also found in mitochondria and chloroplasts. It is also found in the cytoplasm of prokaryotic cell. It is formed by the end to end polymerization of a large number of repeated units called deoxyribonucleotides or simply nucleotides. Each nucleotide is formed by cross linking of three substances.

         i.            Deoxy-ribose-sugar: The DNA molecule contains deoxy-ribose-sugar and hence it is called deoxyribonucleic acid. Deoxyribose is a pentose sugar (with 5 carbon atoms)

       ii.            Phosphate: The phosphate in the DNA is present as phosphoric acid (H3PO4). Each phosphate group is joined to a carbon atom 3 of one deoxyribose sugar and to carbon atom 5 of another deoxyribose sugar.

      iii.            Nitrogenous Bases: The nitrogenous bases are of two types- purine and pyrimidine . Purine bases of DNA comprise mainly adenine (A) and guanine (G) while pyrimidine bases comprise cytosine (C) and thymine(T).

Nucleosides and nucleotides : A sugar molecule with the nitrogenous base forms a nucleoside and a nucleoside with a phospheat group forms a nucleotide . The nucleosides in DNA are called deoxyribonucleosides and nucleotides are called deoxyribonucleotide. 

 

Nitrogenous base+sugar = Nucleoside

Nucleoside+Phosphate+Nucleotide

Or

Nitrogenous base+sugar+phosphate=Nucleotide

ADNA Molecule is composed of:

 

DNA is a Double Helix or Double stranded structure.

Watson and Crick established the structure of the DNA molecule in 1953 on the basis of the x-ray diffraction. For this excellent discovery Watson and crick were awarded by Noble prize in 1962. According to them DNA is composed of two polynucleotide strands that form a double helix around the central axis. These two strands run in opposite directions to each other and are therefore, anti parallel.

The strands are made up of alternate bands of deoxyribose sugar and phosphate molecules.
They are joined by the phosphodiester linkages. Abond between two sugar groups and a phosphate group is called phosphodiester bond.

Each deoxyribose sugarin the strand has one N-base horizontally attached to it at carbon-1. The fourN-bases can occur in any possible sequence along the length og a strand. The N-base +deoxyribose sugar+ phosphate together form one unit or each other in a linear fashion, therefore, the resulting strand is described as the polynucleotide strand and DNA molecule as polynucleotide molecule.

The two polynucleotide strands are held together by hydrogen bonds between specific pairs of purines and pyrimidines. Purine of one polynucleotide chain pairs with pyrimidine of the other i.e adenine (A) with thymine (T) and guanine (G) with cytosine (C). A and T are held together by two hydrogen bonds and G and C by three bonds e.g (A=T) and (G=C). The sequence of bass in one polynucleotide chin automatically determines the order of bases in the other i.e the two chains are complementary to each other. For example, when adenine (a purine) occurs in one strand , thymine ( a pyrimidine) is present in the corresponding position in the opposite strand and vice versa. Similarly wherever guanine (a purine) is present in one strand, the other strand has cytosine ( a pyramidine)opposite to it and vice versa.

The two strands of a helix are of opposite polarity. If one chain runs in 3-5 direction (sugar phosphate linkage) then the other will run in 5-3 direction (sugar phosphate linkage).

Circular DNA molecule

Circular DNA molecule are found in almost all prokaryotes e.g bacteria. The molecule has two complementary strands which form a covalenty closed circular DNA. This DNA is supercoiled and highly folded. This is because the diameter of a bacterial cell (E coli) is about 1-2 microns, while the total length of the circular DNA is about 1100 microns. In several groups of small bacteria and viruses the circular DNA is single stranded. It becomes double stranded only during replication.

Functions

        I.            DNA is a genetic material hence it carries all the hereditary information from one generation to another generation.

      II.            DNA has unique properties of formation of carbon copies. This is essential for transfer of genetic information.

    III.            DNA gives rise to RNA through transcription process.

    IV.            DNA play a key role in protein synthesis.

      V.            Any change in the sequence of nitrogen bases due to addition or deletion causes mutation.

Ribonucleic Acid (RNA)

RNA is found both in the nucleus and in the cytoplasm  . It is a single stranded, long chain macromolecules of ribonucleotides. Like DNA the ribonuucleotide of RNA is also formed by cross-linking of three substances-phosphoric acid a pentose sugar (ribose sugar) and nitrogen bases.The ribose sugar differs from the deoxyribose sugar of DNA in having four rather than three hydroxyl groups. The nitrogenous bases of RNA are of two types: i) purine ii) pyrimidine

Purine bases comprise adenine A) and guanine G) while pyrimidine bases comprise cytosine C) and Uracil U).

Thus structurally DNA and RNA show two main differences:

i) DNA contains deoxyribose and RNA contains ribose.

ii) DNA contains thymine whereas the RNA contains Uracil.

A RNA molecule is composed of:

 

Being single stranded the nitrogen bases of RNA unpaired and the complementary bases found in the same strand.The four nucleotides in the RNA are A, G,C and U nucleotides. In a double stranded RNA base pairing occurs between purines and pyrimidies. Guanine(G) and Cytosine (C) are held together by three hydrogen bonds and uracil (U) adenine (A) are held together by two hydrogen bonds.

The strand is made up of alternate bands of ribose sugar and phosphate (H3PO 4) molecule . A nitrogen base a ribose sugar and a phosphate form a nucleotide and a nucleotide without the phosphate is called nucleoside.

In most of the plant viruses and half of animal virus the genetic materials is RNA rather than DNA.

 

The RNA is classified into three types.

1.       M-RNA ( messenger RNA)

2.       R- RNA (Ribosomal RNA)

3.       T- RNA ( transfer- RNA)

1.  m- RNA (messenger RNA) : It constitutes about 5%- 10% of the total RNA present in the cell m-RNA carries the genetic information from DNA for protein synthesis.

2.  r- RNA ( Ribosomol RNA) : It takes about 80% of the total RNA in the cell. It is the major component of ribosomes. It also provides proper binding sites for the mRNA on the ribosones.

3. t-RNA (Transfer RNA) It is also known as soluble RNA (sRNA) . It forms about (10%-15%) of the total cell RNA . It carries amino acid molecules to the site of protein synthesis.

Nucleotide

A nucleotide is made up of three molecules . These are:

A) Pentose sugar b) Nitrogenous bases and c) Phosphoric acid

A) Pentose Sugar: There are two kinds of pentose sugar found in nucleotides. These are ribose sugar and deoxyribose sugar. A nucleotide containing ribose sugar is called ribonucleotide. Ribonucleotide is the basic unit of ribonucleic acid (RNA) . A nucleotide containing deoxyribose sugar is called deoxyribonucleotide. Deoxyribonucleotide is the basic unit of Deoxyribonucleic acid.

B) Nitrogenous Bases: The nitrogenous are of two types purines and pyrimidines.

        I.            Purines: They have two rings in their structure eg Adenine and guanine.

      II.            Pyrimidines: They have only one ring in their structure e.g cytosine, thymine and uracil.

c) Phosphoric Acid: It contains a phosphate group. It links two nucleotides together by information of phosphodiester bond.

 

Nucleosides and Nucleotides

 A sugar molecule together with the nitrogen base forms a nucleoside. These are ATP , ADP, AMNP, MNAD, MNADP , FAD.

An ATP contains a ribose sugar the base adenine and three phosphate groups. The energy transporting portion of ATP is a bond between the terminal and middle phosphates. These bonds  on hydrolysis yield adenosine diphosphate (ADP) on removal of one phosphate and adenosine monophosphate  (AMP) on removal of two phosphate groups. ATP is universal carrier of energy in living cells. Major ATP synthesis takes place in mitochondria during respiration.