Enzymes and The Digestive System

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What is the definition of digestion?
The breakdown of large, complex, insoluble molecules into smaller, simpler, soluble molecules by mechanical and chemical means.
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Foods need to contain...
- Proteins
- Carbohydrates
- Lipids
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An example of an unsaturated fat is..
Walnuts, vegetable oil
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An example of a saturated fat is..
Butter, lard
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Carbohydrates contain..
Carbon, hydrogen and oxygen
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The mouth
The first part of the digestive system where food enters the body. It has a pH of 7.5 and assists in mechanical and chemical breakdown. Amylase enzymes are produced by the salivary glands.
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The oesophagus
The tube from the mouth to the stomach. The muscles in the oesophagus contract and relax (peristalsis) to slowly transport food.
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The stomach
Produces protease and pepsin. pH1-2. Has hydrochloric acid (stomach acid) to assist chemical breakdown. Mucus lining prevents HCl from burning the stomach itself.
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The liver
Produces bile of pH8.5-9 to neutralise stomach acid. Converts ammonia into urea.
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The gallbladder
Stores bile produced by the liver and secretes it into the small intestine accordingly. Emulsifies lipids into small droplets. Bile neutralises the stomach acid in the small intestine to create alkaline conditions for enzyme function.
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The pancreas
Produces insulin to control blood glucose levels. Signals to liver, muscle and fat cells when to absorb glucose from the blood. Allows glucose to be used in respiration. Produces lipase, protease, carbohydrase and amylase. Secretes enzymes into the duoden
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The small intestine
pH7. Food is transported through the small intestine by peristalsis. Nutrients (vitamins and minerals) from the food are absorbed through the thin lining of the small intestine to enter the bloodstream. Carbohydrase, lipase, protease and amylase continue
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The large intestine
Reabsorbs any water from undigested food. Food, fibre and waste is left to harden and form faecal matter.
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The rectum
When the faeces has hardened it is transported to and stored in the rectum.
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The anus
Faeces is excreted.
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How long does digestion take?
Anywhere between 24 to 72 hours.
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What is the definition of an enzyme?
A biological catalyst made of protein that speeds up a chemical reaction without being used up itself.
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Enzymes are sensitive to..
- pH
- temperature (digestive enzymes work best at 37°C)
- their substrate
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How an enzyme binds together to its substrate is known as the..
Lock and key hypothesis (because the enzyme is specific to its substrate)
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The place where an enzyme binds to its substrate is..
The active site
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The products of digestion are..
- Glucose
- Amino acids
- Fatty acids
- Glycerol
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Protease breaks down..
Proteins into amino acids
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Amylase breaks down..
Starch into maltose and sugars
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Carbohydrase breaks down..
Carbohydrates into simple sugars
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Lipase breaks down..
Lipids into fatty acids and glycerol
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Why is the emulsification of fats important?
It breaks large particulates of fat down into smaller, more digestible droplets. It gives enzymes a larger surface area to work on.
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How do you test for starch?
(RP)
- Prep a food sample and transfer 5cm^3 to a test tube.
- Add a few drops of iodine solution and shake gently.
- A positive test will turn from orange to blue-black
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How do you test for proteins?
(RP)
- Prep a food sample and transfer 2cm^3 to a test tube
- Add 2cm^3 of Biuret solution and mix by gently shaking
- A positive test will change from blue to purple.
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How do you test for lipids?
(RP)
- Prep a food sample and transfer 5cm^3 to a test tube
- Use a pipette to add 3 drops of Sudan III stain solution to the test tube and gently shake
- A positive test will make the mixture separate into 2 layers. The top layer will be bright red.
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What is the formula for the rate of reaction?
Rate = 1000 / time (in secs)
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How does temperature affect enzyme reaction rates?
As the temp increases, the molecules move and collide more (kinetic energy is gained). It reaches an optimum (typically around 37-40°C) where the enzyme and substrate are best matched and reactions reach their peak. They then denature and the enzyme shape
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How does pH affect enzyme reaction rates?
Different enzymes function best at different pH values. Every enzyme has an optimum pH where reactions peak and denature when the pH is too high/low as the active site changes shape.
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How do you investigate the effect of pH on amylase?
(RP)
- Put a drop of iodine into each well of a spotting tile
- Put a Bunsen burner on a heatproof mat with a tripod and gauze over the top of it.
- Put a beaker of water on the tripod and heat it until it is 35°C (measured by a thermometer). Keep this temp
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How do you investigate the effect of pH on amylase?
(RP)
- constant
- Use a syringe to add 1cm^3 of amylase solution and 1cm^3 of buffer solution (pH5) to boiling tube
- Put the tube into the beaker
- Use another syringe to add 5cm^3 of a starch solution to the boiling tube
- Mix the contents in boiling tube
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How do you investigate the effect of pH on amylase?
(RP)
- Use continuous sampling to record how long it takes for the amylase to break down the starch
- Use a dropping pipette to take a sample from the boiling tube every 30s and put a drop into a well
- When the iodine remains orange starch is not present
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How do you investigate the effect of pH on amylase?
(RP)
- Repeat with different buffer solutions of different pH values.
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How do you test for glucose?
(RP)
- Prep a food sample and transfer 5cm^3 to a test tube.
- Prep a water bath to be set at 80°C
- Add approx 10 drops of Benedict's solution with a pipette to the test tube
- Place the test tube in the water bath for 5 minutes with the tube pointed away
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How do you test for glucose?
(RP)
- from you
- A positive test will change from blue to green, yellow or brick red depending on how sugary the food is
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Card 2

Front

Foods need to contain...

Back

- Proteins
- Carbohydrates
- Lipids

Card 3

Front

An example of an unsaturated fat is..

Back

Preview of the front of card 3

Card 4

Front

An example of a saturated fat is..

Back

Preview of the front of card 4

Card 5

Front

Carbohydrates contain..

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Preview of the front of card 5
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