6.9 Enzymes and digestion Flashcards
What is the human digestive system made up of
A long muscular tube and its associated glands. The glands produce enzymes that hydrolyse large molecules into small ones ready for absorption
What are the major parts of the digestive system
- Oesophagus
- Stomach
- Ileum
- Large intestine
- Rectum
- Salivary glands
- Pancreas
What is the oesophagus and what is its role
Carries food from the mouth to the stomach
What is the stomach and what is its role
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 and what is its role
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.
What happens to the inner walls of the ileum
They become folded into villi, giving them a large surface area.
What increases the surface area of the ileum more
Tiny projections called microvilli.
What do the adaptations to the ileum achieve
An efficient system for absosbing the products of digestion into the blood stream
What is the large intestine and what is its role
The large intestine is a tube that absorbs water.
The water is from digestive glands
What is the rectum and what is its role
It is the final section of the intestines.
Faeces are stored here before being removed via the anus during egestion
What are the salivary glands and what are their role
Glands situated near the mouth.
They pass their secretions via a duct into the mouth. These contain amylase which hydrolyse starch into maltose
What is the pancreas and what is its role
A large gland situated below the stomach. It produces a secretion called pancreatic juice.
The pancreatic juice contains proteases to hydrolyse proteins, lipase to hydrolyse lipids and amylase to hydrolyse starch
What enzymes does the pancreas produce
Proteases (proteins to amino acids)
Lipases (fats to glycerol and fatty acids)
Amylase (starch to maltose)
What are the two stages of digestion
- Physical breakdown
2. Chemical breakdown
What is physical breakdown during digestion
If the food is large, it is broken down into smaller pieces by means of the teeth.
This ensures a large surface area for chemical digestion.
Food is also churned by the muscles in the stomach wall which also physically breaks it down
What is chemical digestion
Chemical digestion hydrolyses large, insoluble molecules into smaller, soluble ones.
How does chemical digestion occur
By enzymes, which function by hydrolysis (adding water over a chemical bond)
How do enzymes work in the digestive system
Usually one hydrolyses a large molecule into sections and these sections are then hydrolysed into smaller molecules by one or more additional enzymes
What are the three digestive enzymes
- Carbohydrases - Hydrolyse carbohydrates into monosaccharides
- Lipases - hydrolyse lipids into glycerol and fatty acids
- Proteases - hydrolyse proteins, ultimately to amino acids
What is the principle behind chemical digestion and large molecules
It usually takes more than one enzyme to completely hydrolyse a large molecule
Typically one enzyme hydrolyses the molecule into smaller sections and then other enzymes hydrolyse these sections further into monomers. These enzymes are usually produced in different parts of the digestive system
It is therefore important enzymes are added in the right order
Describe the process of starch digestion
- Saliva enters the mouth via salivary glands and is thoroughly mixed with the food during chewing
- Saliva contains salivary amylase. This hydrolyses starch into maltose. It also contains mineral salts that maintain pH around neutral - the optimum pH
- The food is swallowed and enters the acidic stomach where any enzymes are denatured, preventing further hydrolysis
- The food is passed into the small intestine, where it mixes with the pancreatic juice
- Pancreatic juice contains pancreatic amylase. This continues the hydrolysis of starch to maltose. Alkaline salts are produced by the pancreas AND intestinal wall to maintain pH around neutral
- Muscles in the intestine wall push food along the ileum. Its epithelial lining produces maltase. Maltase is not released but is instead part of the cell membrane of epithelial cells - it is a membrane-bound disacchardidase. The maltase hydrolyses maltose from
starch breakdown into alpha glucose
What is maltase
A membrane bound disacchardidase
What are two other common disaccharides in a persons diet
Sucrose
Lactose
How is sucrose digested
By membrane-bound sucrase which hydrolyses the single glycosidic bond in sucrose. This produces fructose and glucose
How is lactose digested
By membrane-bound lactase which hydrolyses the single glycosidic bond in the lactose molecule. This produces glucose and galactose
What are digested by lipids
Lipases
What are lipases, where are they found and how do they work
enzymes produced by the pancreas that hydrolyse the ester bond found in triglycerides to form fatty acids and monoglycerides.
What is a monoglyceride
A glycerol molecule with a single fatty acid molecule attached
Describe the process of lipid digestion
Lipids are firstly split up into tiny droplets called micelles by bile salts, which are produced by the liver. This process is called emulsification and increases the surface area of the lipids so that the action of lipases is sped up
How are proteins digested
By proteases
What are the different proteases
Endopeptidase
Exopeptidase
Dipeptidase
What do endopeptidases do
Hydrolyse the peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules
What do exopeptidases do
Hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases. In this way they release dipeptides and single amino acids
What do dipeptidases do
Hydrolyse the bond between the two amino acids of a dipeptide. Dipeptidases are membrane-bound, being part of the cell-surface membrane of epithelial cells lining the ileum
