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What is molecular biology?

Molecular biology is a section of biology that considers the chemical substances that are important to life and explains living processes in terms of these chemicals.

Living things are built up of many chemical elements, the majority of which are bonded together in organic, carbon-containing compounds.

Most organic compounds in living things are carbohydrates, proteins, nucleic acid or lipids.

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Carbon, hydrogen, oxygen and nitrogen are the four most common elements found in living organisms.

Carbon, hydrogen and oxygen are found in all the key organic molecules - proteins, carbohydrates, nucleic acid and lipids. Proteins and nucleic acids also contain nitrogen.

Any compound that does not contain carbon is said to be inorganic.
-- these substances are vital to both the structure and functioning of different organisms.

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Are important because they can form four covalent bonds and allow the formation of many different, stable compounds.

As carbon atoms can also easily bond with each other, organic compounds can be formed from carbon chains that differ in shape and length.

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Do you see the bonds?
Do you know what type of carbon compounds these are? (If you don't, don't worry, just scroll down.)

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Many organic molecules are very large and complex but they are built up of small sub-units, which can be relatively simple.

Small units are called monomers, which will then be built up into larger complex molecules called polymers in a process known as polymerization.

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These form the basic molecules of life - carbohydrates, lipids, proteins and nucleic acid.

Carbohydrates are compounds that contain only the elements carbon, hydrogen and oxygen and are the most abundant group of biological molecules.

Lipids contain the same three elements but with much less oxygen than a carbohydrate of the same size. They may also contain small amounts of other elements such as phosphorus.

Proteins, however always contain nitrogen. Sulfur, phosphorus and other elements are also often present.

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These are the most abundant category of a molecule in living things. They have an important role as a source of energy for plants and animals. In plants they also have a structural function.

Monosaccharides, with the general formula: (CH²O)n, where n = the number of carbon atoms in the molecule, are monomers - single sugars made up of just one subunit.

Disaccharides are sugars that have two subunits joined together by a condensation reaction ; and polysaccharides are long molecules consisting of a chains of monosaccharides linked together.

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These are insoluble in water but do dissolve in organic solvents. Lipids are used as energy storage molecules in plants and animals.

One group known as triglyceride lipids include fats and oils.

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They are built up of building blocks called Amino Acids. The atoms occurring at the fourth bond differ in different amino acids and give each its own properties. (R)

There are more than 100 naturally occurring amino acids but only 20 are used in building the bodies of living things.

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These are found in all living cells and in viruses. There is deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

Nucleic acids are vital to inheritance and development.
They are long molecules consisting of chains of units called nucleotides. Each nucleotide consists of a pentose sugar linked to phosphoric acid and an organic base.

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In this type of reaction, two molecules can be joined to form a larger molecule, held together by strong covalent bonds. It is also an example of an anabolic reaction, which is a type of reaction that builds up monomers to form macromolecules.

Each condensation reaction requires an enzyme to catalyse the process and it produces one molecule of water.

The condensation of two monosaccharide monomers produces a disaccharide.

For example:

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These type of reactions occur every time food is digested. They involve breaking down polysaccharides, polypeptides and triglycerides into the smaller units of which they are made. It is an example of a catabolic reaction, in which macromolecules are broken down into monomers. Water molecules are used in this type of reaction. Hydrolysis reactions are the reverse of condensation reactions. Once again, enzymes are required to catalyse the reactions.

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Define And Explain Hydrolysis With Examples and Latest Expariments

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Chemical name: COOH

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Chemical name: CH₃

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Chemical name: NH₂

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Chemical name: OH
This is part of a common functional groups.

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Important: Water is the main component in living things. For instance, human cells consist of approximately 80% water.

Water provides the environment in which the biochemical reactions of life can occur. It also takes part in and is produced by many reactions.

The structure of water: two hydrogen atoms each bonded to an oxygen atom by covalent bond.

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The water molecule is unusual because there is a small positive charge on the hydrogen atom and a small negative charge on the oxygen atom. Due to this arrangement, we say it to be a polar molecule.

A weak bond can form between the negative charge of one water molecule and the positive charge of another. This type of bond is called a hydrogen bond.

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Hydrogen bonds between water molecules hold them together in a network, resulting in a phenomenon known as cohesion.

Cohesive forces give water many of its biologically important properties.

For instance, water transport in plants goes from the roots to the leafs.

Cohesion is also responsible for surface tension, which enables some small organisms to 'walk on water', and contributes to the thermal properties of water as well.

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Water also tends to be attracted and adhere to the walls of its container. There are forces of attraction known as adhesive forces, which occur between water molecules and different molecules in vessels that contain the water.
Adhesion attracts water molecules to the sides of the xylem and is important as water is drawn up the stem of the plant.
Because adhesive forces are greater in narrow tubes, as the water molecules are more in contact with the sides (SA:V ratio), therefore the adhesive forces are able to 'hold up' and support a substantial mass of water in the fine xylem vessels.

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Water is a liquid with a normal range of temperatures. A large amount of energy is needed to break the many weak hydrogen bonds between the water molecules. This means that water has a high specific heat capacity.

A stable temperature is important to living things because the range of temperatures for reactions to be occur is quite narrow. The thermal properties of water thus allow an organism to maintain a fairly constant temperature.
Water can thus be a temperature regulator.

In order for liquid water to evaporate and become vapor, many hydrogen bonds between the molecules must be broken, so evaporation requires a lot of energy. When water evaporates, it carries a great deal of heat with it.

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Water is sometimes known as a universal solvent. The polar molecules of water can interact with other polar molecules, thus allowing it to have ions, large molecules with polar side groups, to dissolve in it. This is happens due to the positive or negative charges of the solutes that will be attracted to the charges of the water molecules. So water therefore acts as an excellent transport medium and as a medium for metabolic reactions.

Hydrophilic substances such as sugars and salts dissolve well in water. Hydrophobic or 'water-hating' substances do not dissolve in water.

Uncharged and non-polar substances are not very soluble in water because water molecules would rather remain hydrogen-bond to each other than allow such molecules to come between them.

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Cholesterol is only slightly soluble in water and dissolves in the blood in very small amounts. For this reason, cholesterol is transported in the circulatory system within lipoproteins, which have an outer surface made up of amphiphatic proteins and lipids.

Hence why there is cholesterol in phospholipid bi-layer, so as to make the membrane less permeable. However, too much could affect the cell's metabolism and its reactions.