Enzymes and Digestion Flashcards
What is the human digestive system made up of?
A long muscular tube and its associated glands
What do the glands in the digestive system produce?
Enzymes
What is the role of enzymes in the digestive system?
They hydrolyse large molecules into smaller ones ready for absorption
What is the digestive system?
An exchange surface through which food substances are absorbed
What are the major parts of the digestive system?
- the oesophagus
- the stomach
- the ileum
- the large intestine
- the rectum
What is the role of the oesophagus?
It carries food from the mouth to the stomach
What is the stomach?
A muscular sac with an inner layer that produces enzymes
What is the role of the stomach?
It stores and digests food (especially proteins(it has glands which produce enzymes to digest proteins))
What is the ileum?
A long muscular tube
What happens in the ileum?
Food is further digested by enzymes produced by ts walls and by its glands
What is the purpose of the ileum?
Absorbing the products of digestion into the blood stream
How is the ileum adapted to its purpose?
The inner walls are folded into villi which gives them a large surface area, the surface area of the villi is then increased by millions of tiny projections called microvili which are on the epithelial cells of each villus
What do the gland in the ileum do with the Secretions they produce?
They pour them onto the digesting food
What is the role of the large intestine?
Absorbing water
What is most of the water absorbed by the large intestine?
Water from the secretions of the many digestive glands
What is the role of the rectum?
It is where the faeces are stored before they are periodically removed via the anus in the process of egestion
Where are the salivary glands found?
Near the mouth
What do the salivary glands do?
They pass on their secretions via a duct in the mouth
What do the secretions from salivary glands contain?
The enzyme amylase which hydrolysed starch into maltose
What is the pancreas?
A large gland situated below the stomach
What does the pancreas produce?
Pancreatic juices
What does the pancreatic juice contain?
- Proteases to hydrolysed proteins
- Lipase to hydrolyse lipids
- Amylase to hydrolyse starch
What are the two stages in digestion?
- physical breakdown
- chemical digestion
Why does the physical breakdown of food take place?
To make the food possible to ingest and to provide a large surface area for chemical digestion
What are the two ways food can be physically broken down?
By the teeth and by the churning of food in the stomach by the muscles in the stomach wall
What does chemical digestion do?
It hydrolyses large, insoluble molecules into smaller, soluble ones
How is chemical digestion carried out?
By enzymes
How do all digestive enzymes function?
By hydrolysis
What is hydrolysis?
The splitting up of molecules by adding water to the chemical bonds that hold them together
What are enzymes?
Specific
What can large molecules require more than one of to be broken down?
Type of enzyme
How do enzymes usually act upon a large molecule?
A large molecule is hydrolysed into editions by one enzyme into sections and these sections can then be hydrolysed into smaller molecules by one or more additional enzyme
What is the role of carbohydrases?
They hydrolyse carbohydrates, ultimately to monosaccharides
What is the role of lipase?
They hydrolyse lipids into glycerol and fatty acids
What is the role of proteases?
They hydrolyse proteins ultimately to amino acids
Why is it important that enzymes are added to food in the correct sequence?
It usually takes multiple enzymes to completely hydrolyse a large molecule and each enzyme is specific to one substrate
How is starch broken down by the body?
- firstly amylase is produced in the mouth and the pancreas which hydrolyses the alternate glycosidic bonds so that the disaccharide maltose is produced
- maltose is hydrolysed into the monosaccharide alpha glucose by a disaccharidase called maltase which is produced in the lining get of the ileum
What is the process of carbohydrate digestion in humans?
- saliva enters the mouth from salivary glands and contains salivary amylase which is mixed with the food during chewing to start hydrolysing starch to maltose ]
- food is swallowed where is can enter the acidic conditions of the stomach
- the food is then passed to the small intestine where it mixes wit pancreatic juices that contain pancreatic amylase which can continue the hydrolysis of any remaining starch to maltose
- Muscles in the intestinal walls push the food along the ileum and the epithelial lining produces the membrane bound maltase which hydrolyses maltose into alpha glucose
What does saliva contain?
Salivary amylase
What is the optimum pH of saliva?
Around neutral
How is salivary amylase optimum pH maintained?
By mineral salts in the saliva
What happens to the salivary amylase when it reaches the stomach?
It is denatured by the acidic conditions preventing the further hydrolysis of starch
What does the pancreatic juice contain for the digestion of carbohydrates?
Pancreatic amylase
What does pancreatic amylase continue?
The hydrolysis of any remaining starch into maltose
What is the optimum pH of pancreatic amylase??
Around neutral
How is the optimum pH of pancreatic amylase maintained?
By alkaline salts produced by both the pancreas and the intestinal walls
Where is maltase produced?
In the epithelial lining of the intestinal wall
Where is maltase not released to?
The lumen of the ileum
Why is maltase not released to the lumen of the ileum?
It is part of the cell-surface membrane of the epithelial cells that line the ileum
What is maltase known as?
A membrane bound disaccharide
What does maltase hydrolyse maltose into?
Alpha-glucose
Aside from maltose, what are the two other common disaccharides in the diet that are hydrolysed in carbohydrate digestion?
Sucrose and lactose
Where is sucrose found?
In many natural foods especially fruits
Where is lactose found?
In milk and therefore in milk products such as yogurt an d cheese
What is each disaccharide hydrolysed by in carbohydrate digestion?
A membrane bound disaccharide
How does sucrase hydrolyse sucrose?
It hydrolyses the single glycosidic bond in the sucrose molecule to produce glucose and fructose
How does lactase hydrolyse lactose?
It hydrolyses the single glycosidic bond in the lactose molecule to produce glucose and galactose
What enzymes hydrolyse lipids?
Lipases
What are lipases?
Enzymes produced in the pancreas that hydrolyse the ester bond found in triglycerides to form fatty acids and monoglycerides
What is a monoglyceride?
A glyceride is a glycerol molecule with a single fatty acid molecule attached
What are lipids first split up into?
Tiny droplets called micelles
How are lipids split into micelles?
By bile salts
Where ate bile salts produced?
The liver
What is the process of lipids being split into micelles called?
Emulsification
What is the purpose of emulsification?
To increase the surface area of lipids so that the action of lipases is sped up
What is the name of the group of enzymes that hydrolyse proteins?
Peptidases (proteases)
What do endopeptidases hydrolyse?
The peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules
What do exopeptidases hydrolyse?
The peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases to progressively release dipeptides and single amino acids
What do dipeptidases hydrolyse?
The bond between the two amino acids of a dipeptide
What are dipeptidases?
Membrane bound
Where are dipeptidases found?
In the cell surface membrane of the epithelial cells lining the ileum
What happens to lactase levels as humans age?
Lactase levels naturally decrease as humans age due to milk forming a less significant role in our diets and some peoples lactase levels diminish entirely leading to lactose intolerance
What happens to undigested lactose in lactose intolerant humans?
The undigested lactose will reach the large intestines where microorganisms hydrolyse it giving rise to mall soluble molecules and a large volume of gas
Why does lactose intolerance result in diarrhoea?
Because the soluble molecules lower the water potential of the material in the colon
