Paper 1: Topic 2 Organisation - Digestive system & enzymes (LV) Flashcards
Define the term enzyme
A biological catalyst that speeds up the rate of a chemical reaction without being altered or used up itself in the reaction
State what type of molecule enzymes are
Proteins
A large molecule made from many amino acids joined together
Hint: remember all proteins are made by ribosomes
State 4 factors that affect the activity of enzymes
pH
temperature
concentration of enzyme
concentration of substrate
Define the term substrate
A chemical that is used in the reaction and is converted to the product
Define the term product
The chemical that is made at the end of a chemical reaction
State the two different types of chemical reaction
Catabolic
Anabolic
Define the terms
a) catabolic reaction
b) anabolic reaction
a) catabolic:
A chemical reaction that breaks down the substrate(s) into smaller product(s)
b) anabolic:
A chemical reaction that builds up smaller substrates into a larger molecule (the product)
Define the term metabolism
The sum total of all the chemical reactions that take place inside a cell
Describe the structure of an enzyme
An enzyme has a dip on its surface (called the active site)
The active site has a complementary shape to its specific substrate
Explain why enzymes are specific
Each enzyme has an active site that is unique to specific substrates for one chemical reaction
The active site is only complementary to one substrate
Hence each enzyme can only catalyse one specific reaction
Describe the relationship between the active site and the substrate
They are complementary to each other
Hint: do NOT say they are the same as each other
Name the model that describes how enzymes work
Lock and key theory
IMPORTANT:
When annotating a diagram remember to add descriptions onto your diagram e.g.
- the active site is complementary to the substrate
- the substrate is specific to the enzyme’s active site
Explain the lock and key theory model
The active site on an enzyme acts as a lock
The complementary substrate acts as a key that fits into the active site (lock)
This forms the enzyme-substrate complex
The chemical reaction then takes place
The substrate is converted to the product
The product is released
The enzyme remains unaltered and can carry out further identical reactions
Define the term enzyme-substrate complex
An enzyme that has it specific substrate bound to its active site
Explain the effect of low temperatures on enzyme activity
- At low temperatures both the substrate and enzyme have very little kinetic energy
- There are very few collisions between the substrate and the active site
- Very few enzyme-substrate complexes form
- Hence very little product is made in any given period of time
- The enzyme is described as inactive
- The rate of reaction is very low
Explain the effect of high temperatures on enzyme activity
- At high temperatures both the substrate and enzyme have a high amount of kinetic energy
- There are many collisions between the substrate and the active site
- However the high temperature changes the shape of the enzyme
- This alters the shape of the active site
- The substrate is no longer complementary to the active site
- NO enzyme-substrate complexes form
- NO product is made in any given period of time
- The enzyme is described as denatured
- The rate of reaction is zero
Why is it incorrect to say an enzyme is dead?
All enzymes are just proteins
They are not living and so can’t be killed
They are just specialised chemical molecules
Describe the effect the optimum temperatures on enzyme activity
- At the optimum temperatures both the substrate and enzyme have very high kinetic energy
- There are many collisions between the substrate and the active site
- High numbers of enzyme-substrate complexes form
- Hence a lot of product is made in any given period of time
- The enzyme is described as working at its maximum rate
- The rate of reaction is at its maximum
What is the typical optimum temperature for human enzymes?
37oC
Describe how an enzyme is denatured and the effect this has
How an enzyme is denatured:
- At high temperatures the bonds holding the enzyme in its specific shape break
- This changes the shape of the enzyme including the shape of the active site
The effect of denatureing an enzyme:
- The active site is no longer complementary to its substrate
- So no reaction can take place and no product is made
Name an human enzyme that works at an optimal pH of 1-2 (acidic)
Pepsin
Remember this enzyme is found in the stomach and must be able to work efficiently in acidic conditions due to the hydrochloric acid in the stomach
State 2 human enzymes that work at an optimal pH of 7 (neutral)
Amylase
Catalase
Lipase
Carbohydrases
Proteases (except trypsin)
How do you calculate the rate of reaction?
Amount of product formed divided by the time
In an experiment how can you control the temperature to ensure you are carrying out a fair test?
Use a thermostatically controlled water bath
Hint: don’t just say water bath
In an experiment how can you control the pH to ensure you are carrying out a fair test?
Use buffer solutions to keep the pH of the experiment constant
Buffers work by keeping the pH constant
State the 3 main groups of enzymes that are involved in digestion
Lipases
Carbohydrases
Proteases
Describe the action of a protease enzyme
Proteases break proteins down into amino acids
Describe the action of a lipase enzyme
Lipases break lipids down into 3 fatty acids and 1 glycerol
Hint: remember to state the number of each type of product made
Describe the action of a carbohydrase enzyme
Carbohydrases break complex carbohydrase down into simpler sugars e.g. glucose
Give an example of a carbohydrase.
State its substrate and product
Carbohydrase = amylase
Substrate = starch
Product = maltose
State 3 places in the human body where amylase is produced
Mouth (salivary amylase)
Pancreas
Small intestine
State 3 places in the human body where proteases are produced
Pancreas
Stomach
Small intestine
State 2 places in the human body where lipase is produced
Pancreas
Small intestine
Which 2 organs in the human body produce carbohydrases, lipases and proteases
Pancreas
Small intestine
Describe what happens to the fatty acids and glycerol that are produced after digestion
- The fatty acids and glcyerol are absorbed into the blood stream
- This absorption occurs in the small intestine
- They are absorbed into the lacteals
- They are then used by cells to make new lipids
- The new lipids are used to make new cell membranes for the production of new cells or stored for energy
Describe what happens to the amino acids that are produced after digestion
- The amino acids are absorbed into the blood stream
- This absorption occurs in the small intestine
- They are absorbed into the blood plasma
- They are then used by cells to make new proteins
- The proteins are then used to make new cells for tissue growth and organ growth
Describe what happens to the simple sugars that are produced after digestion
The simple sugars are absorbed into the blood stream
This absorption occurs in the small intestine
They are absorbed into the plasma
They are then used by cells to make new carbohydrates
The new carbohydrates are used in respiration to produce ATP
What is the function/role of bile?
Bile emulsifies lipids
It breaks large lipids into smaller droplets of lipid
This increases the surface area for the lipase enzymes
Hence the rate of reaction increases
How does the emulsification of lipids affect the activity of lipases?
Emulsifying the fats into smaller droplets increases the surface area
This increases the activity of lipase
Explain why the pH falls (becomes more acidic) in during a reaction catalysed by lipase
Lipase breaks down lipids into 3 fatty acids and glycerol
As more lipids are broken down more fatty acids are produced
The greater the accumulation of fatty acids the more the pH decreases (becomes more acidic)
State where bile is stored
Gall bladder
Explain why it is important bile is released into the small intestine to allow digestion to occur
- The contents of the stomach are acidic (from the hydrochloric acid)
- The acidic contents pass into the small intestine
- The enzymes in the small intestine have an alkaline optimal pH
- The bile neutralises the acid to create the optimal pH for the enzymes of the small intestine
State where bile is produced
Liver
What test would you use to detect the presence of reducing sugars?
Benedict’s test
Describe the results of a positive Benedict’s test
The solution would change from blue to green to yellow to orange to brick red
What colour is a negative Benedict’s test?
Blue
Describe how to carry out a Benedict’s test
- Prepare the sample to be tested (if this is a solid food substance it will need to be ground up and mixed with a little water first and then filtered)
- Add 5 cm3 of the food sample to a test tube
- Add 10 drops of Benedict’s solution
- Heat the food sample in a water bath at 75oC for 5 minutes
State 3 safety precautions you should take when carrying out a Benedict’s test
- Wear safety goggles
- Make sure the test tube is pointing away from you in the water bath
- Do not ingest the Benedict’s solution – it is harmful
What test would you use to detect the presence of starch?
Iodine solution
Describe the results of a positive starch test
A blue-black solution
What colour is a negative starch test?
A yellow-brown solution
Describe how to carry out a starch test
- Prepare the sample to be tested (if this is a solid food substance it will need to be ground up and mixed with a little water first and then filtered)
- Place the food sample in the well of a spotting tile
- Add a few drops of iodine solution onto the food sample with a pipette
- Observe the colour change
State 2 safety precautions you should take when carrying out a starch test
Wear safety goggles
Do not ingest the iodine solution – it is harmful
What test would you use to detect the presence of lipids?
Sudan III stain solution
Describe the results of a positive Sudan III test
2 layers will form
The top layer will be bright red
Describe the results of a negative Sudan III test
No separate red layer will form
Describe how to carry out a Sudan III test
- Prepare the sample to be tested (if this is a solid food substance it will need to be ground up and mixed with a little water first. It does NOT need to be filtered)
- Place the food sample in a test tube
- Add 3 drops of Sudan III stain solution onto the food sample with a pipette
- Gently shake the test tube
- Observe the colour change
What test would you use to detect the presence of proteins?
Biuret reagent
Describe the results of a positive Biuret test
Purple solution
Describe the results of a negative Biuret test
Blue solution
Describe how to carry out a Biuret test
- Prepare the sample to be tested (if this is a solid food substance it will need to be ground up and mixed with a little water first and then filtered)
- Add 5 cm3 of the food sample to a test tube
- Add 5 cm3 of Biuret solution
- Gently shake the test tube
- Observe the colour change
Give 2 properties that amino acids, glycerol, simple sugars and fatty acids have that enable them to be absorbed into the plasma
Small and soluble
Explain the purpose of digestion
To use enzymes to break down large insoluble molecules into small and soluble molecules that can be absorbed into the bloodstream
