4 Stages of the Digestive System
- Food enters through the mouth and down the oesophagus.
- Food gets broken down with enzymes in the stomach and the colon.
- Food gets absorbed through the epithelial cells all around the digestive system.
- Waste material gets ejected from the anus after being stored in the rectum.
The Digestive System
- Saliva is produced which contains amylase.
- Amylase breaks down starch into maltose.
- Saliva lubricates food making it easier to pass through the oesophagus.
- Saliva is pH7 for the optimum pH of amylase.
- Relatively large circular and longitudinal muscle layer as peristalsis (the squeezing movement of the oesophagus to push food) is needed to push food down.
- Used only for transportation.
- Only mucus producing cells to protect the lining.
- Muscular walls and enzymes help with digestion.
- Pepsin is secreted here.
- There are no villi.
- Mucus layer to prevent self digestion.
- Secretes enzymes: protease, lipase, amylase.
- Pancreatic juice also contains pancreatic salts to neutralise acidity from the stomach.
- The lining is folded into villi with many microvilli to increase surface area for absorption.
- Villi with microvilli.
- Epithelial cells have many mitochondria to provide energy for active transport.
- Rich blood supply to remove absorbed molecules away quickly, maintaining a diffusion gradient.
- Each villus contains a lymph vessel for removal of absorbed lipids.
- Thin epithelial layer for short diffusion path.
- Bile is entered as soon as the stomach ends to neutralise the stomach acid.
- Bile is made in the liver and stored in the gall bladder.
- Absorbs water.
- The food therefore becomes drier and forms faeces.
- Faeces are stored here.
- They are then removed via the anus.
- Mastication (chewing by the teeth)
- Churning (in the stomach)
- Food is broken down which provides a larger surface area for chemical digestion.
- Breaks down large insoluble molecules into smaller soluble ones by hydrolysis.
- All digestive enzymes function by hydrolysis.
- The large food molecules are first hydrolysed into monosaccharide's and are then absorbed into the blood.
- Once absorbed, assimilation takes place.
- Proteins contain the elements carbon, hydrogen, oxygen and nitrogen.
- They are major structural components in tissues making them vital for growth.
- Proteins are made up from 20 different amino acids which can be assembled in any order.
- Amino acids join together by a condensation reaction to form Dipeptides.
- A peptide bond is formed.
- Made by adding more amino acids.
- Each polypeptide has its own unique sequence of amino acids. This is known as the primary structure of the protein.
- By changing just one amino acid in a polypeptide chain the complete properties of the molecule can be changed.
The Structure of Proteins
1. Primary structure
- The sequence of amino acids that make up a polypeptide chain.
2. Secondary structure
- The polypeptide chain twists into a shape called the secondary structure
- There are two main secondary structures: α-helix & β-pleated sheet
- Structure are held in place by hydrogen bonds
3. Tertiary structure
- The secondary structure is folded into a 3D shape which is held by weak chemical bonds
- In some proteins, the tertiary structure forms fibrous proteins which are insoluble
- In other proteins it can form a globular protein which is more spherical, like enzymes and hormones.
4. Quaternary structure
- Two or more polypeptide chains and non-protein groups combine.
- If the bonds which hold a protein in shape are broken, the structure of said protein will be changed.
- Denaturation can be caused by high temperature, extremes of pH and reducing agents.
The Biuret Test
- The biuret test is a test for proteins.
- E.g. Sodium hydroxide and copper sulphate are added to the sample
- if the test turns lilac, protein is present.
That's the end of the topic!
Drafted by Bonnie (Biology)