Carbohydrates, proteins and lipids Flashcards
Where does digestion start?
In the mouth
Where does it continue and finish?
Continues in the duodenum and finishes in the ileum
How many enzymes are needed for carbohydrate digestion and what are they?
Amylases and membrane-bound disaccharidases
What is digestion?
Large molecules are hydrolysed into smaller molecules that can be absorbed across the cell membrane
Where is amylase produced?
In the pancreas and salivary glands
What does amylase do?
Hydrolyses polysaccharides into disaccharide maltose by hydrolysing glycosidic bonds
What are micelles?
Water soluble vesicles formed of fatty acids, glycerol and monoglycerides.
In mammals, how does are the products of digestion absorbed?
Across the cells lining the ileum
Features of ileum wall
Covered in villi and microvilli which increases the surface area for absorption
How are amino acids and monosaccharides absorbed?
- Na plus ions are actively transported out of epithelial cells by Na and K pumps into blood
- Maintains a much higher concentration of Na plus ions in the lumen or intestine than inside epithelial cells
- Na plus ions diffuse into epithelial cells down a concentration gradient
- Occurs through co-transport protein
- Na plus ions carry either amino acids or monosaccharides into the cell
- Pass into blood plasma via facilitated diffusion using carrier proteins
How are lipids absorbed?
- Micelles break down when in contact with ileum walls releasing MG and FA.
- They are non-polar so they diffuse across the cell sf membrane into epithelial cells
- Transported to ER to be reformed into triglycerides
- Continues in Golgi apparatus
- TG associate with lipoproteins to form chylomicrons
- These move out of the cell by exocytosis and move to lymphatic capillaries
Chylomicrons pass these capillaries into bloodstream - Enzymes in epithelial cells of blood capillaries hydrolyse TG in the chylomicrons to diffuse into the cell.
What is a bolus?
Small ball of chewed food
What is peristalsis?
Rhythmic contractions which push the food down to the stomach
What does bile do?
It Emulsifies fats and neutralises stomach acid.
Where is bile produced?
In the liver, stored in gall bladder and passed down bile duct
What is the alimentary canal?
Referred to as the gut. Indigestible material can pass through the whole tube without crossing the cell membrane.
Where does peristalsis occur?
Oesophagus
What are the enzymes involved in protein digestion?
Endopeptidases, exopeptidases and dipeptidases
What do endopeptidases do?
Hydrolyse peptide bonds between amino acids in the centre of a protein molecule to form a group of peptide bonds.
What do exopeptidases do?
Hydrolyse peptide bonds in the terminal end of the peptide molecules formed by endopeptidases. It releases dipeptides and single amino acids which are usually embedded in the membrane.
What to dipeptidases do?
Hydrolyse bonds between two amino acids of a dipeptide. These are membrane-bound on the lining of the ileum.
What happens in protein digestion?
Many proteins are soluble which aids digestion. It begins in the stomach with the secretion of gastric juice, which contains pepsin. Food then passes into the duodenum, or small intestine, where pepsin works alongside Trypsin to further break the protein down into polypeptides. These polypeptides are then further broken down into amino acids by various exopeptidases and dipeptidases, and are then absorbed into the bloodstream through the walls of the small intestine.
What are the adaptations of the ileum?
Folded walls with villi and microvilli, thin walls lined with epithelial cells and a rich blood supply of capillaries to maintain a conc gradient.
What do bile salts do?
They help break down large lipid molecules and are both hydrophilic and hydrophobic.
How are lipids hydrolysed?
By enzyme called lipase
Where are lipases produced?
Produced in the pancreas
What do lipases do?
They hydrolyse the ester bond found in triglycerides to form fatty acids and monoglycerides
What is starch broken down into?
Amylases breaks it down into maltose.
What is maltose hydrolysed into?
It’s further broken down into alpha glucose by maltase.
Where is maltase made?
By the lining of the ileum
What happens in carbohydrate digestion?
- Saliva enters the mouth from salivary glands and is mixed with food during chewing
- Saliva contains salivary amylase which hydrolyses any starch into maltose
- Saliva also contains mineral salts to maintain PH 7 which is optimum for amylase
- The food is then swallowed and enters the stomach. The HCL denatures the salivary amylases preventing further hydrolysis of the starch.
- Food passes from the stomach into small intestine and mixes with pancreatic juices.
- Contains pancreatic amylase which continues to hydrolyse starch into maltose. Alkaline salts are produced by the pancreas and intestinal wall to neutralise the acidic PH
- Muscles in the intestinal wall push the food along the ileum. Epithelium lining produces disaccharidase maltase.
- Maltase hydrolyses the maltose into alpha glucose.
