Define metabolism, anabolism and catabolism, explaining the role of ATP in these processes. Be sure to use specific examples to make your answer clear.

Biochemistry

Assignment 7

Task 1) – Define metabolism, anabolism and catabolism, explaining the role of ATP in these processes. Be sure to use specific examples to make your answer clear.

The patterns of growth and decay in an organism result from two opposing forces; anabolism (synthesis), and catabolism (decay). Metabolism, Anabolism and Catabolism are all types of process that happen in every living cell, in every living organism. They are to do with breaking down large molecules into smaller ones (decay), making larger molecules out of smaller ones (synthesis), and altering molecules so they are of use in reactions. ATP is required for all of these processes, to build molecules up, and to break them down, and especially to convert them to something else, for example in respiration when glucose is converted to glucose – 6 – phosphate. ATP and energy in the form of electrons are also produced in Catabolism. It is important when discussing this topic that we remember that organisms can neither create nor destroy energy, but simply transform it from one form to another.

Metabolism

All life forms—from single-celled algae to mammals—are dependent on many hundreds of simultaneous and precisely regulated metabolic reactions to support them from conception through growth and maturity to the final stages of life. Inside every living cell of an organism, chemical reactions take place, these chemical activities are described as ‘metabolism’. The chemical activity, or metabolism is split into two different categories, anabolism and catabolism as explained later on. All chemical reactions need ATP, energy to help them. The reactions involve bringing molecules together, or breaking them apart, this does not just happen in the cell, but requires energy to break this apart. You could see it as a builder, without energy in the form of food he would not be able to either build a wall, or knock one down although knocking it down would also produce energy. Using a specific example from the body would be respiration, the metabolic process that not only requires energy (ATP) but also produces it. In glycolysis of respiration two ATP molecules are used, and four are produced, this shows that ATP plays a major role in respiration, which is a very important metabolic reaction within the cell.

Anabolism

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Anabolism

This is one of the two parts of metabolism, and is the general term for building large molecules from smaller ones. Generally these are condensation reactions, two molecules are joined together with the release of water. A good example of this in the human body is when two small sugars (monosaccharides), join together to form a larger sugar molecule (disaccharide). In this example you can see two alpha glucose molecules joining together with the release of water to form maltose. To form the glycosidic link between these two molecules, ATP is required, without it the two molecules would not be able to join together. The smaller sugars must join together to form maltose, this is not needed in the body, but to this more glucose molecules are added with the release of water, to form glycogen. Glycogen is a very important molecule in the body because it can be stored in the liver and the muscles and can then be broken down in a catabolic reaction when there are no ‘free glucose’ molecules in the blood, but the body requires energy. Include picture pg 38. There are many processes like this one that occur in the body, another good example is the building up of amino acids to form proteins. Amino acids are carried by tRNA molecules, which join to specific mRNA molecules, to bring together a specific sequence of amino acids. ATP is required to join the amino acids together in a condensation reaction with peptide bonds, and water is lost. As amino acids are joined together they form peptides, many peptides joined together form polypeptides and eventually polypeptides join together to form proteins; the joining of all of these requires energy in condensation reactions. Amino acids on their own in the body are only good for building up to bigger molecules, once the ATP has been used to form the protein, these can then fold into primary, secondary and tertiary structures, when other strands of protein are added a quaternary structure can be formed. Proteins are the basis of enzymes, which are used to control all metabolic reactions. Proteins are also used in keratin for hair and nails, collagen which is used in tendons, ligaments bone and skin, and antibodies which are used to protect the body against diseases and bacteria.

Other anabolic reactions include the combination of fatty acids and glycerol to form lipids. Three fatty acid molecules and a glycerol molecule join together in a condensation reaction to form lipids. Triglyceride, a form of lipid is used as an energy store in animals and yields more than twice as much energy as proteins and carbohydrates. Cholesterol is another form of lipid that is important in the cell, it stabilises cell membranes and forms sex hormones in the body. Without the anabolic reactions to make proteins from amino acids there would be none of these products which are so essential in the body.

Catabolism

This is the other part of metabolism, and is the opposite of anabolism; it is the general term for breaking down large molecules into smaller ones. The main purpose of catabolism is to break down the larger molecules, producing energy in the form of ATP from ADP and inorganic phosphate. It also produces electrons, which are ‘reducing energy’ used for energy production and biosynthesis, the making of new products. Generally these are hydrolysis reactions, reactions in the presence of water taking water into the molecule as they break down. . This is true for many different reactions, breaking down proteins to amino acids, fats to fatty acids and glycerol and polysaccharides to disaccharides and finally monosaccharides.

We eat to produce energy to sustain the body’s metabolic reactions, but we cannot use the food as soon as we eat it, we must break down the food into more useable molecules. Enzymes start by breaking down the food and then it follows through the digestive system with the final products being absorbed into the blood. Protein, lipid, carbohydrates, starch, vitamins and minerals are all broken down in the body. Anabolism is the opposite to catabolism, and therefore the way proteins and fats are built up in anabolic reactions, the reverse happens in catabolism. Contained within the carbohydrate group is sugars and starches, they are made up of carbon, hydrogen and oxygen and therefore are broken down into these components during catabolism reactions. Carbon is useful in the body as a ‘building block’, it is used to build up other molecules that are needed in the body, such as nucleic acids, which are the building block for DNA. Without DNA we could not build new cells, this goes for the hydrogen and oxygen as well, both important in respiration, which fuels the process of ‘building’ a new cell. So it is important to break down the products of food in digestion so that they can be used in new processes within the body. Catabolism breaks down large molecules to form ‘building blocks’ for biosynthesis, all the metabolic reactions that occur in the body. Depending on their source of reducing power organisms can be classified as either organotrophs or lithotrophs. Organotrophs oxidise organic compounds; as an example, the complete oxidation of a typical carbohydrate (CH2O) by respiration by an organotroph can be represented as:

CH2O + O2-->CO2 + H2O.

Lithotrophs oxidise inorganic compounds for example NO2– (nitrite), is oxidized to NO3– (nitrate) in the carbon cycle.