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Pepsin / ˈ p ɛ p s ɪ n / is an endopeptidase that breaks down proteins into smaller peptides and amino acids.It is one of the main digestive enzymes in the digestive systems of humans and many other animals, where it helps digest the proteins in food.
Digestive enzymes are classified based on their target substrates: lipases split fatty acids into fats and oils; [6] proteases and peptidases split proteins into small peptides and amino acids; [7] amylases split carbohydrates such as starch and sugars into simple sugars such as glucose, [8] and nucleases split nucleic acids into nucleotides. [9]
Glucose-6-phosphate can then progress through glycolysis. [1] Glycolysis only requires the input of one molecule of ATP when the glucose originates in glycogen. [1] Alternatively, glucose-6-phosphate can be converted back into glucose in the liver and the kidneys, allowing it to raise blood glucose levels if necessary. [2]
The endocrine part secretes insulin when the blood sugar becomes high; insulin moves glucose from the blood into the muscles and other tissues for use as energy. The endocrine part releases glucagon when the blood sugar is low; glucagon allows stored sugar to be broken down into glucose by the liver in order to re-balance the sugar levels.
Metabolism (/ m ə ˈ t æ b ə l ɪ z ə m /, from Greek: μεταβολή metabolē, "change") is the set of life-sustaining chemical reactions in organisms.The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the conversion of food to building blocks of proteins, lipids, nucleic acids, and some carbohydrates; and the ...
Glucose reacts with oxygen in the following reaction, C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O. Carbon dioxide and water are waste products, and the overall reaction is exothermic. The reaction of glucose with oxygen releasing energy in the form of molecules of ATP is therefore one of the most important biochemical pathways found in living organisms.
The parietal cell releases bicarbonate into the bloodstream in the process, which causes a temporary rise of pH in the blood, known as an alkaline tide. The acidic gastric juice also contains digestive enzymes produced by other cells in the gastric glands – gastric chief cells. Gastric chief cells secrete an inactivated pepsinogen.
If the blood glucose level falls to dangerously low levels (as during very heavy exercise or lack of food for extended periods), the alpha cells of the pancreas release glucagon, a peptide hormone which travels through the blood to the liver, where it binds to glucagon receptors on the surface of liver cells and stimulates them to break down glycogen stored inside the cells into glucose (this ...