Metabolism.pdf

Metabolism What is Metabolis m? “Metabolis m refers to a series of chemical reactions that occur in a living organis m to sustain life.” All the chemical reactions occurring in the living organisms from digestion to transportation of substances from cell to...

Metabolism What is Metabolis m? “Metabolis m refers to a series of chemical reactions that occur in a living organis m to sustain life.” All the chemical reactions occurring in the living organisms from digestion to transportation of substances from cell to cell require energy. Metabolic Process There are two types of metabolic process:  Catabolism  Anabolism Catabolism – The process involves the breakdown of large molecules such as polysaccharides, lipids, nucleic acids and proteins into smaller units like monosaccharides, fatty acids, nucleotides, and amino acids, respectively. Catabolism in Differe nt Organisms The exact nature of catabolic reactions differs from organism to organism and can be classified based on their sources of energy and carbon which are as given below- Stages of Catabolism: Catabolism can be broken down into 3 main stages. Stage 1 – Stage of Digestion The large organic molecules of organic chemistry like proteins, lipids, and polysaccharides are digested into their smaller components outside cells. This stage acts on starch, cellulose or proteins that cannot be directly absorbed by the cells. Stage 2 – Release of energy Once the molecules are broken down, these molecules are taken up by cells and converted to yet smaller molecules, usually acetyl coenzyme A, which releases some energy. Stage 3 – Energy Store d The released energy is stored by reducing the coenzyme nicotinamide adenine dinucleotide into NADH. This process provides the chemical energy necessary for the maintenance and growth of cells. Some examples of the catabolic processes include glycolysis, the citric acid cycle, the breakdown of muscle protein in order to use the amino acids as substrates for gluconeogenesis, the breakdown of fat in adipose tissue to fatty acids, a nd oxidative deamination of neurotransmitters by monoamine oxidase. Anabolism – This process is mainly involved in building up or synthesizing compounds from simpler substances required by the cells. This metabolic process requires and stores energy. This process is endergonic, which means it is not spontaneous and requires energy to progress the anabolic reaction. The complex molecules obtained are further used to store energy in the form of ATP (Adenosine Tri Phosphate). Anabolism Example Cells use an anabolic process to make polymers, repair, and grow tissues. For example:  Formation of disaccharides and water with the help of combining simple sugars C6 H12 O6 + C6H12O6 → C12 H22 O11 + H2O  Formation of dipeptides by combining Amino acids NH2 CHRCOOH + NH2 CHRCOOH → NH2CHRCONHCHRCOOH + H 2 O  Formation of lipids when glycerol reacts with fatty acids CH2 OHCH(OH)CH2OH + C17H35COOH → CH2 OHCH(OH) CH2 OOCC17H35  Process of photosynthesis to form glucose and oxygen 6CO2 + 6H2 O → C6 H12 O6 + 6O2 Some Examples of Anabolic Hormones are  Insulin – It promotes absorption of glucose  Anabolic steroids – It helps in stimulating muscle growth  Anaerobic exercise – It helps in building muscle mass Stages of Anabolism There are three stages in anabolism. They are 1. Production of precursors such as monosaccharides, nucleotides, amino acids, and isoprenoids. 2. Activation of the above-mentioned precursors into reactive forms with the help of energy from ATP. 3. Assemble the precursors to form complex molecules such as polysaccharides, nucleic ac ids, proteins, and lipids. Energy Sources for Anabolic Processes Various species depend on various sources of energy. A few have been discussed below:  Autotrophs – Formation of complex organic molecules such as proteins and polysaccharides in plant cells from simple molecules like water and carbon dioxide with the help of sunlight as an energy source.  Heterotrophs – They require complex substances such as amino acids and monosaccharides to produce these complex molecules.  Photoheterotrophs and photoautotrophs – They obtain energy from light  Chemoheterotrophs and chemoautotrophs get energy from inorganic oxidation reactions. Anabolism Functions The nutrients from food are broken down into small blocks in the catabolic pathway. Macromolecules are formed when small molecules are combined. During the anabolic pathway, energy is utilized to generate large molecules by forming chemical bonds between the smaller molecules. These macromolecules are further used to build new cells or structure the cells. Anabolism is essential for maintenance, growth, and development of cell. DNA synthesis DNA (Deoxyribonucleic acid), is a macromolecule which is made up of smaller molecules known as nucleic acids. These nucleic acids are made up of a nucleotide base attached to a phosphate and deoxyribose sugar molecule. DNA’s synthesis takes place in the nucleus of the cell before cell division. It involves the following steps:-  Unzipping the double-stranded DNA  Attaching new matching nucleotides to each strand to form two new strands  Metabolism is related to nutrition and the existence of nutrients. Bioenergetics describes the metabolism as the biochemical pathway through which the cells obtain energy. One of the major aspects is the energy formation. Anabolic Hormones Anabolic hormones stimulate anabolic processes. Examples of anabolic hormones include insulin, which promotes glucose absorption, and anabolic steroids, which stimulate muscle growth. Anabolic exercise is anaerobic exercise, such as weightlifting, which also builds muscle strength and mass. Photosynthetic carbohydrate synthesis This process in plants creates certain bacteria that produces glucose, cellulose, starch, lipids, and proteins from CO2. It uses the energy produced from the light-driven reactions of photosynthesis and creates the precursors to those large molecules via carbon assimilation within the photosynthetic carbon reduction cycle. Amino Acid Biosynthesis All amino acids are formed from intermediates within the catabolic processes of glycolysis: the citric acid cycle, or the pentose phosphate pathway. Glycolysis, glucose 6-phosphate is a precursor for histidine; 3- phosphoglycerate is a precursor for glycine and cysteine; phosphoryl pyruvate, combined with the 3- phosphoglycerate-derivative erythrose 4-phosphate, forms tryptophan, phenylalanine, and tyros ine. Pyruvate is a precursor for alanine, valine, leucine, and isoleucine. From the acid cycle, α-ketoglutarate is converted into glutamate and subsequently glutamine, proline, and arginine; and oxaloacetate is converted into aspartate and subsequently asparagine, methionine, threonine, and lysine. Glycogen Storage During periods of high blood sugar, glucose 6-phosphate from glycolysis is diverted to the glycogen- storing pathway. It is changed to glucose-1-phosphate by phosphoglucomutase and then to UDP-glucose by UTP--glucose-1-phosphate uridylyltransferase. Glycogen synthase adds this UDP -glucose to a glycogen chain. Gluconeogenesis Glucagon is traditionally a catabolic hormone but also stimulates the anabolic process of gluconeogenesis by the liver, and to a lesser extent the kidney cortex and intestines, during starvation to prevent low blood sugar. It is the process of converting pyruvate into glucose.