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The Role of H-Bonding in Living Organisms

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Discuss the Role of Hydrogen Bonding in living Organisms

A hydrogen bond is an intermolecular bond and is formed when a charged part of a molecule having polar covalent bonds, forms an electrostatic attraction with a molecule of opposite charge, generally with fluorine, oxygen and nitrogen. Molecules having non polar covalent bonds do not form hydrogen bonds. Hydrogen bonds are classified as weak bonds as they are easily and rapidly formed and broken, however the cumulative effects of large numbers of these bonds can be enormous.

Properties Of Water Related To Hydrogen Bonding:

Hydrogen bonding allows water to remain liquid at room temperature which is unexpected as molecules of similar size are gases at room temperature. This allows organisms to live in water and it also provides a liquid environment inside cells. Water has also a high specific heat capacity due to hydrogen bonding and it ensures a stable environmental temperature as water does not quickly heat up or cool down. Water has a high boiling point as a large amount of heat is required to overcome the hydrogen bonding. The high density of water allows many organisms to readily float on water. The buoyancy in water helps the swimming of motile gametes and in the dispersal of fruits and seeds. Hydrogen bonds hold water molecules together, therefore giving water the properties of cohesion and adhesion – leaves pull water upwards from the roots through the xylem.

Hydrogen bond

Hydrogen Bonding In Cellulose:

Cellulose is a polysaccharide and consists of linear chains of beta-glucose residues with the OH (hydroxyl) group pointing upwards and some pointing downwards. Individual cellulose chains are bound to each other by hydrogen bonds in order to form microfibrils which associate further more to form macrofibrils. These have high tensile strength and are able to withstand stretching forces as in a fully turgid plant cell.

The Presence Of Hydrogen Bonding In Proteins:

Hydrogen bonds between parts of amino acids give rise to the secondary structure of proteins. There are three types of secondary structures which are alpha-helix, beta-pleated sheet and triple helix. Hydrogen bonds are present in the N-H bond of one amino acid and the C=O bond of another. These structures are maintained by hydrogen bonds between CO and NH groups.

In tertiary structures, proteins bend and fold extensively to form three dimensional tertiary structures, which are stabilized by various bonds which are present between amino acids and proteins including polypeptide bonds, disulfide bonds, ionic bonds and hydrogen bonds. The quaternary structure involves the precise arrangement of polypeptide chains held together and stabilised by hydrophobic interactions, hydrogen bonds and ionic bonds.

Hydrogen Bonding In DNA Structure:

Hydrogen bonds hold together adenine with thymine and guanine with cytosine in DNA, and this is known as complementary base pairing. Adenine and thymine are held together by two hydrogen bonds whilst guanine and cytosine are held by three hydrogen bonds therefore, the two complementary polynucleotide strands are held together by hydrogen bonding between the nitrogenous bases of adjacent nucleotides.

The structure of tRNA:

The single strand in tRNA molecule winds up into a double helix. tRNA molecule resembles to form a clover leaf. Hydrogen bonds between base pairing result into three dimensional structures. All tRNA molecules have the same basic structure- 5’end always ends in guanine and 3’end always ends in CCA. One end of the tRNA carries the genetic code in a 3 nucleotide sequence called an anticodon (site of base pairing with mRNA)

[pic]

Hydrogen Bonding In Protein Synthesis:

During translation which occurs on ribosomes one finds a process known as elongation when there is anticodon - codon pairing. During protein synthesis, the anticodon at one end interacts with a codon in the mRNA. The tRNA will then form base pairs between the triplet anticodon. The tRNA’s must be complementary at the first two codon positions but can vary in the third codon position. At the other end of the compact shape formed there are enzymes present which join the proper amino acid to the corresponding tRNA and this reaction requires energy from ATP.

Due to the chemical nature of living organisms, hydrogen bonding is essential for the formation of biomolecules mainly proteins and chemical processes which occur in the organism. One of the most important roles of hydrogen bonding is in the structure of DNA as it holds base pairs together and this is extremely important because DNA transfers hereditary information from generation to generation, it controls the production of proteins and determines the structure of the cell.

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Alpha-Helix

Beta-pleated sheet

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