Unit 1. Digestion And Carbohydrates Flashcards
How does the digestive system break down food both chemically and physically?
Physical - food broken into smaller pieces by teeth in mouth, then moves to stomach where broken down further by churning movement of stomach muscles. Breaking food down into smaller molecules gives it a larger surface area making chemical digestion faster.
Chemical - polymers in food = insoluble so have to be hydrolysed into smaller more soluble molecules by adding water. (Happens during chemical digestion - hydrolysis catalysed by digestive enzymes).
What is the role of enzymes in digestion?
They catalyse hydrolysis
Three classes:
1. Carbohydrases catalyse the hydrolysis of carbohydrates.
2. Proteases catalyse the hydrolysis of proteins.
3. Lipases catalyse the hydrolysis of lipids.
What are the structure and function of major parts of the digestive system?
Mouth - teeth used to break down food, tongue used to push food down oesophagus (mechanical digestion). Saliva secreted makes food easier to swallow - enzymes start chemical digestion.
Oesophagus - tube which takes food from mouth to stomach using waves of muscle contractions called peristalsis (contraction and relaxation of muscle in digestive organs). Mucus also secreted from tissue in walls - lubricate foods passage downwards.
Stomach - small sac with lots of folds to allow expansion, entrance and exit controlled by sphincter muscles. Walls produce gastric juices (hydrochloride acid, pepsin, mucus) which help to break down food. Pepsin hydrolyses proteins into smaller polypeptide chains - turns food into acidic conditions called chyme.
Small intestine - two main parts - duodenum and ileum. Chyme is moved along small intestine by peristalsis. In duodenum bile and pancreatic juice neutralise acidity of chyme and break it down into smaller molecules. In ilium small soluble molecules are absorbed through villi which line but wall.
Large intestine - absorbs water, salts and minerals. Has folded wall which provides large surface area for absorption. Bacteria that decomposes its un digested nutrients are found in large intestine.
Rectum - faeces stored, pass through sphincter muscles at anus during defecation (pooing).
How are large molecules like carbohydrates constructed?
Monosaccharides are formed by condensation reactions, a molecule of water is released during this process and a glycosidic bond is formed between monosaccharides. Polysaccharide formed when more than two monosaccharides join together.
What is the structure of a monosaccharide?
The monosaccharide glucose is a hexose sugar - a monosaccharide with six carbon atoms in each molecule (alpha glucose).
Maltose hydrolysed by Maltese into glucose + glucose
Sucrose hydrolysed by sucrose into glucose + fructose
Lactose hydrolysed by lactase into glucose + galactose
How would you carry out the Benedict’s test for reducing and non-reducing sugars?
Reducing sugars (all monosaccharides some disaccharides):
Add Benedict’s reagent to sample and heat
If reducing sugar present it gradually turns brick red (formation of red precipitate), if no reducing sugar present sample will stay blue.
Non-reducing sugar (e.g sucrose - need to first be broken down into monosaccharides):
Get new sample of test solution and boil it with dilute hydrochloride acid.
Neutralise it with sodium hydrogencarbonate
Heat sample with Benedict’s reagent, if it turns brick red non-reducing sugar present, if stays blue no non-reducing sugar present.
How does salivary amylase act in the mouth to hydrolyse starch?
Salivary glands release the enzyme amylase which break down the starch into maltose.
How is starch digestion completed in the small intestine?
Maltose is then broke down into alpha glucose molecules by maltase which is released by the intestinal epithelial.
How are the disaccharides digested?
Broken down by hydrolysis by enzymes released by the intestinal epithelial.
What is lactose intolerance?
Lactose is broken down by enzyme lactase, if you don’t have enough of the enzyme lactase you won’t be able to break down lactose properly. Condition called lactose-intolerance.
Undigested lactose is fermented by bacteria - can cause stomach cramps, wind and diarrhoea.
How are monosaccharides linked together to form disaccharides?
Monosaccharides are joined together by condensation reactions - molecule of water is released. A glycosidic bond is formed between monosaccharides.
(Disaccharide- when two Monosaccharides join together, polysaccharide when more than two monosaccharides join together).
How are alpha-glucose molecules linked to form starch?
Starch is made from two polysaccharides (both composed of long chain alpha glucose linked by glycosidic bonds) - amylopectin and amylose
What is the test for starch?
The iodine test - add iodine dissolves in potassium iodine solution to the test sample. If starch is present sample will change from browny orange to a dark blue-black colour.
