6.9 - Enzymes In Digestion Flashcards
(30 cards)
What is the human digestive system made up of?
Long muscular tube and its associated glands
What do glands in the digestive system produce?
Enzymes that hydrolyse large molecules into small ones ready for absorption. The digestive system is therefore an exchange surface through which food substances are absorbed
What are the major parts of the digestive system?
- oesophagus
- stomach
- Ileum
- large intestine
- rectum
- salivary glands
- pancreas
What does the oesophagus do?
Carries food from the mouth to the stomach
What is the stomach?
It is a muscular sac with an inner layer that produces enzymes. Its role is to store and digest food, especially proteins. It has glands that produce enzymes which digest protein.
What is the ileum
(Small intestine) it is a long muscular tube. Food is further digested in the ileum by enzymes that are produced by its walls and by glands that pour their secretions into it. The inner walls of the ileum are folded into villi, which gives them a large surface area. The surface area of these villi is further increases by millions of tiny projections, called microvilli, on the epithelial cells of each villus. This adapts the ileum for its purpose of absorbing the products of digestion into the bloodstream
What is the large intestine?
It absorbs water. Most of the water that is absorbed is water from the secretions of the many digestive glands
What is the rectum?
Is the final section of the intestines. The faeces are stored here before periodically being removed via the anus in a process called egestion
What are the salivary glands?
They are situated near the mouth. They pass their secretions via a duct into the mouth. There secretions contain the enzymes amylase, which hydrolyses starch into maltose
What is the pancreas?
Is a large gland situated below the stomach. It produces a secretion called pancreatic juice. This secretion contains proteases to hydrolyse proteins, lipase to hydrolyse lipids and amylase to hydrolyse starch.
What are the two stages of digestion in humans?
Physical breakdown and chemical digestion
What occurs in physical breakdown?
If the food is large, it is broken down into smaller pieces by means of structures such as teeth. This makes it possible to ingest the food but also provides a large surface area for chemical digestion, food is also churned by the muscles in the stomach wall and this also physically breaks it up.
What occurs in chemical digestion?
Chemical digestion hydrolyses large, insoluble molecules into smaller soluble ones. It is carried out my enzymes. All digestive enzymes function by hydrolysis. Enzymes are specific and so it follows that more than one enzyme is needed to hydrolyse a large molecule. Usually one enzyme hydrolyses a large molecule into sections and there sections are then hydrolysed into smaller molecules by one ore more additional enzymes
What is hydrolysis?
The splitting up of molecules by adding water to the chemical bonds that hold them together
What are the 3 important types of digestive enzymes?
- Carbohydrases
- lipases
- proteases
What does carbohydrase do?
Hydrolyses carbohydrates, ultimately to monosaccharides
What does lipase do?
Hydrolyses lipids (fats and oils) into glycerol and fatty acids
What does protease do?
Hydrolyse proteins, ultimately to amino acids.
Which enzymes are involved in the complete hydrolysis of starch?
Firstly the enzyme amylase is produced in the mouth and the pancreas. Amylase hydrolyses the alternate glycosidic bonds of the starch molecule to produce the disaccharide maltose. The maltose is in turn hydrolysed into the monosaccharide a - glucose by a second enzyme, a disaccharide called maltase. Maltase is produced by the lining of ileum.
What is the process of the complete breakdown of starch in humans
- saliva enters the mouth from the salivary glands and is thoroughly mixed with the food during chewing
- saliva contains salivary amylase, this starts hydrolysing any starch in the food to maltose. It also contains mineral salts that help to maintain the pH at around neutral
- this is the optimum pH for salivary amylase to work
- the food is swallowed and enters the stomach, where the conditions are acidic. This acid denatures the amylase and prevents further hydrolysis of the starch
- after a time the food is passed into the small intestine, where is mixes with the secretion from the pancreas called pancreatic juce
- the pancreatic juice contains pancreatic amylase. This continues the hydrolysis of any remaining starch to maltose. Alkaline salts are produced by both the pancreas and the intestinal wall to maintain the pH at around neutral so that the amylase can function
- muscles in the intestinal wall push the food along the ileum. Its epithelial lining produces the disaccharide maltase
- maltose is not released into the lumen of the ileum but is part of to the cell surface membranes of the epithelial cells that line the ileum
- it is therefore referred to as a membrane bound disaccharidase
- the maltase hydrolyses the maltose from starch breakdown into a - glucose.
What other disaccharides are hydrolysed?
Sucrose and lactose
Where is sucrose found?
In many natural foods, especially fruits
Where is lactose found?
In milk, and hence in milk products, such as yoghurt and cheese
How is sucrose and lactose hydrolysed?
Each disaccharide is hydrolysed by a membrane bound disaccharidase as follows:
- sucrase hydrolyses the single glycosidic bond in the sucrose molecule, this hydrolysis produced the two monosaccharides glucose and fructose
- lactase hydrolyses the single glycosidic bond in the lactose molecule. This hydrolysis produced the two monosaccharides glucose and galactose.
