3.3 Digestion and absorption Flashcards
1
Q
What is amylase?
A
- The enzyme produced in the salivary glands and pancreas.
- Amylase hydrolyses the alternate glycosidic bonds of the starch molecule to produce the disaccharide maltose.
2
Q
What is maltase?
A
- The dissacharidase maltase is produced in the lining of the ileum (small intestine)
- It is not released into the lumen but is part of the cell-surface membranes of the epithelial cells, so is referred to as a membrane-bound disaccharide
- It hydrolyses the maltose from starch into α-glucose.
3
Q
What is sucrase?
A
- Sucrose is found in many natural foods, especially fruits
- Sucrase is a membrane-bound disaccharide
- It hydrolyses the single glycosidic bond in the sucrose molecule.
- This hydrolysis produces the two monosaccharides glucose and fructose.
4
Q
What is lactase?
A
- Lactose is found in milk, and milk products.
- Lactase is a membrane-bound disaccharide
- It hydrolyses the single glycosidic bond in the lactose molecule.
- This hydrolysis produces the two monosaccharides glucose and galactose.
5
Q
What is lipase?
A
- Lipids are hydrolysed by enzymes called lipases
- Lipases are produced in the pancreas and hydrolyse the ester bond found in triglycerides to form fatty acids and monoglycerides (a glycerol molecule with a single fatty acid molecule attached)
6
Q
What are endopeptidases?
A
- They hydrolyse the peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules.
7
Q
What are exopeptidases?
A
- They hydrolyse the peptide bonds on the end amino acids of the peptide molecules formed by endopeptidases
- They progressively release dipeptides and single amino acids.
8
Q
What are dipeptidases?
A
- They hydrolyse the bond between the two amino acids of a dipeptide
- Dipeptidases are membrane-bound, being part of the cell-surface membrane of the epithelial cells lining the ileum.
9
Q
What are peptidases?
A
- Proteins are large, complex molecules that are hydrolysed by peptidases
- There are endopeptidases, exopeptidases and dipeptidases.
10
Q
Why do endopeptidases work first?
A
- This exposes more ends of the amino acid chains for the exopeptidases to work on
- It can create 4 ends, but if exopeptidases worked first, there would only be 2 ends to work on, which would be slower
11
Q
What happens during digestion?
A
During digestion, large, insoluble molecules are hydrolysed to smaller molecules that can be absorbed across the cell membrane of the intestinal epithelial cells
12
Q
What 2 stages does digestion take place?
A
- Physical breakdown
- Chemical digestion
13
Q
What is physical breakdown?
A
- If the food is large, it is broken down into smaller pieces by structures such as the teeth
- This not only makes it possible to ingest the food but also provides a large surface area for chemical digestion
- Food is churned by the muscles in the stomach wall and this also physically breaks it up
14
Q
What is chemical digestion?
A
- This hydrolyses large, insoluble molecules into smaller, soluble ones, through enzymes
- All digestive enzymes function by hydrolysis, the splitting up of molecules by adding water to chemical bonds that hold them together
- Enzymes are specific so more than one is needed to hydrolyse a large molecule
- Usually one enzyme hydrolyses a large molecule into sections and these sections are then hydrolysed into smaller molecules
15
Q
What are the three main important digestive enzymes?
A
- Carbohydrases - hydrolyse carbohydrates, ultimately to monosaccharides.
- Lipases - hydrolyse lipids into monoglycerides and fatty acids.
- Proteases - hydrolyse proteins, ultimately to amino acids.
16
Q
What is the first part of the process of carbohydrate digestion?
A
- Saliva enters the mouth from the salivary glands and is thoroughly mixed with the food during chewing.
- The salivary amylase starts hydrolysing any starch in the food to maltose. It also contains mineral salts that help to maintain the pH around neutral, the optimal pH for amylase
- The food is swallowed and enters the acidic stomach, which denatures the amylase and prevents further hydrolysis of the starch.
17
Q
What is the second part of the process of carbohydrate digestion to do with the pancreas?
A
- The food is passed into the small intestine, where it mixes with the secretion from the pancreas called the pancreatic juice.
- This contains pancreatic amylase, which continues the hydrolysis of any remaining starch to maltose.
- Alkaline salts are produced by both the pancreas and the intestinal wall to maintain pH at neutral.
- Muscles in the intestine wall push the food along the ileum, its epithelium lining produces maltase.
- This hydrolyses the maltose from starch breakdown into α-glucose.
18
Q
What is the human digestive system?
A
- 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
- The digestive system is therefore an exchange surface through which food substances are absorbed
19
Q
What is bile?
A
- It’s really alkaline
- Not an enzyme or an acid
20
Q
What is the role of bile?
A
- Emulsification
- Neutralisation of stomach acids
21
Q
What enzymes are involved in carbohydrate digestion and where are they found?
A
- amylase in the mouth
- maltase, sucrase, lactase in the membrane of small intestine
22
Q
Where are lipids digested?
A
small intestine
23
Q
What needs to happen before lipids can be digested?
A
they must be emulsified by bile salts produced by the liver. This breaks down large fat molecules into smaller, soluble molecules called micelles, increasing surface area
24
Q
How are lipids digested?
A
lipase hydrolyses the ester bond between the monoglycerides and fatty acids
25
Which enzymes are involved in protein digestion?
endopeptidases
exopeptidases
dipeptidases
26
How are certain molecules absorbed into the ileum despite a negative concentration gradient?
through co-transport
27
Which molecules require co-transport?
amino acids and monosaccharides
28
Explain how sodium ions are involved in co-transport.
Sodium ions are actively transported out of the cell into the lumen, creating a diffusion gradient. Nutrients are then taken up into the cells along with sodium ions
29
Why do fatty acids and monoglycerides not require co-transport?
the molecules are non-poplar, meaning they can easily diffuse across the membrane of the epithelial cells
