Carbohydrates

Simple starch

1. Starch. 2. Hydrolysed by amylase, broken down to maltose. 3. Maltase hydrolyses maltose to form alpha-glucose molecules.

Monosaccharides

1. Sweet tasting soluble substances. 2. General formula = (CH2O)n 3. Glucose, fructose and galactose. 4. Glucose is a hexose sugar = C6H12O6 5. Structure of glucose

Polysaccharides

1. Very large molecules. 2. Insoluble = makes them suitable for storage. 3. When hydrolysed, they break down into monosaccharides + disaccharides.

Explain why these people get diarrhoea when they drink milk containing lactose.

= Low / decreased water potential (in gut) = Water enters gut / lumen / leaves cells by osmosis

Formula for lactose

C12H22O11

What is starch?

1. A polysaccharide. 2. Made up of a mixture of two polysaccharides = amylose + amylopectin. 3. Both are composed of long chains of alpha glucose, linked together by glycosidic bonds formed in condensation reactions.

Parts of digestive system

1. Oesophagus = food from mouth to stomach = thick muscular wall. 2.

Assimilation

Incorporating absorbed molecules into body tissues.

Sucrose and maltose are...

SOLUBLE IN WATER

Absorption

Taking soluble molecules into the body.

Induced fit' and the 'lock and key' are two models used to explain enzyme action. Describe how 'induced fit' is different from the 'lock and key' model

1. Active site not totally complementary/does not match exactly; 2. = Flexible: Wraps round substrate/ Enzyme changes

Test for reducing sugars

1. All monosaccharides and some disaccharides. 2. Maltose = reducing sugar. 3. Add Benedict's reagent and heat. 4. Brick red (formation of precipitate) = reducing sugar present. 5. Nothing = remains blue.

Chemical digestion

1. Breaks down large, insoluble molecules into smaller ones. 2. Carried out by enzymes = hydrolases. 3. All function by hydrolysis. 4. Carbohydrases = break down carbohydrates to monosaccharides. 5. Lipases = break down lipids (fats and oils) itno glycerol and fatty acids. 6. Proteases = break down proteins into amino acid. 7. Once large molecules have been hydrolysed = absorbed by various means into the blood. 8. Carried to different parts of the body and are often built up again into large molecules.

Starch digestion - Enzymes are specific. - As a result it takes more than one enzyme to break down a large molecule.

1. Enzyme amylase = produced in the mouth (salivary amylase) and the pancreas (pancreatic amylase). 2. Food taken into mouth, chewed, broken into smaller pieces = large SURFACE AREA, 3. Saliva enters mouth from salivary glands, starts hydrolysing any starch in food to maltose. 4. Food is swallowed, enters stomach, acid denatures amylase, prevents further hydrolysis of starch. 5. Food is passed into small intestine, pancreatic amylase continues hydrolysis of remaining starch into maltose. 6. Muscle cells in the intestinal wall push food along small intestine. 7. Cells in intestinal epithelial lining produce the enzyme maltase. 8. Maltase hydrolyses the maltose from starch breakdown into alpha glucose + alpha glucose.

Digestion of carbs

1. Enzymes are released by the intestinal epithelium 2. Break down disaccharides by hydrolysis 3. Hydrolysis = The breaking down of large molecules into smaller ones, by addition of water molecules. 4. When water is added to a disaccharide under suitable conditions it breaks the glycosidic bond, releasing the constituent monosaccharides. 5. Maltose = hydrolysed by maltase = glucose + glucose. 6. Sucrose = hydrolysed by sucrase = glucose + fructose. 7. Lactose = hydrolysed by lactase = glucose + galactose. 8. I.e. Sucrose hydrolyses the single glycosidic bond in the sucrose molecule to produce the tow monosaccharides that make up sucrose.

Physical digestion

1. Food broken into smaller pieces by teeth. 2. Further broken down in stomach by churning movement of stomach muscles. 3. Breaking down food into smaller pieces gives it a larger surface area = makes chemical digestion faster.

Test for starch

1. Iodine test. 2. Add iodine dissolved in potassium iodide solution to test sample. 3. If starch is present = sample turns from browny orange to dark blue/black colour.

Lactose-intolerance

1. Lactose =sugar found in milk. 2. Digested by the enzyme lactase. 3. If your production of lactase enzyme is greatly reduced, you are not able to break down the lactose in milk properly. 4. Undigested lactose is fermented by bacteria in the large intestine. 5. This gives rise to a large volume gas = results in bloating, nausea, diarrhoea and cramps. 6. Avoid food containing lactose, or milk can be treated with purified lactase.

Carbohydrate formation

1. Monosaccharides are joined together by condensation reactions. 2. Molecule of water is released. 3. Disaccharide = 2 monosaccharides 4. Polysaccharide = +2 monosaccharides

Use BR test to show something contains MORE reducing sugar

1. More RS produces MORE precipitate, redder. 2. Standardise test, same amount of Br + banana

Disaccharides

1. Pairs of monosaccharides can be combined to form a disaccharide. 2. Glucose + glucose =maltose 3. Glucose + fructose = sucrose 4. Glucose + galactose = lactose 5. Formula = 6. OH from one glucose and the H of another OH of the one next to it. 6. It looks like -O-

What causes starch hydrolysis to be slow in chilled bananas

1. Process controlled by enzymes (amylase) 2. Lower temp = less KE 3. Fewer collisions/less ESCS formed

Test for non-reducing sugars

1. Some disaccharides = non-reducing sugars. 2. Sucrose. 3. These do not change colour of Benedict's reagent when heated with it. 4. Boil sample with dilute hydrochloric acid. 5. Neutralise by adding sodium hydrogencarbonate. 6. Add Benedict's reagent and heat. 7. Red = non-reducing sugar. 8. Blue = neither reducing, nor non-reducing sugar.

You could use the test to compare the amount of reducing sugar in two different brands of biscuit. Suggest how.

1. Standardised technique e.g. same amount of biscuit / same volume of benedict's / heat for same period of time. 2. Compare colour / compare mass (of precipitate) / rate of colour production / different colours / use a colorimeter.

All lactose molecules have the same chemical structure. Starch molecules from different organisms may be different from each other. Give one way in which starchmolecules may be different from each other.

Different number of glucose (units) (Different proportions of) amylose/amylopectin; Different number of branches in molecule/ branches in different places