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Mrs P's GCSE Biology > Paper 1: Topic 2 Organisation - Digestive system & enzymes (LV) > Flashcards

Paper 1: Topic 2 Organisation - Digestive system & enzymes (LV) Flashcards

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1
Q

Define the terms

a) enzyme
b) active site

A

Enzyme: A biological catalyst that speeds up the rate of a chemical reaction without being altered or used up itself in the reaction

Active site: a small dent on the surface of the enzyme where the substrate binds to form and ESC and where the chemical reaction takes place.

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2
Q

State what type of molecule enzymes are

A

Proteins

A large molecule made from many amino acids joined together

Hint: remember all proteins are made by ribosomes

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3
Q

State 4 factors that affect the activity of enzymes

A

pH

temperature

concentration of enzyme

concentration of substrate

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4
Q

Define the term substrate

A

A chemical that is used in the reaction and is converted to the product

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5
Q

Define the term product

A

The chemical that is made at the end of a chemical reaction

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6
Q

State the two different types of chemical reaction

A

Catabolic

Anabolic

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7
Q

Define the terms

a) catabolic reaction
b) anabolic reaction

A

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)

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8
Q

Define the term metabolism

A

The sum total of all the chemical reactions that take place inside a cell which includes all the catacbolic and anabolic reactions

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9
Q

Describe the structure of an enzyme

A

An enzyme has a dip on its surface (called the active site)

The active site has a complementary shape to its specific substrate

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10
Q

Explain why enzymes are specific

A

Each enzyme has an active site that is uniq​ue 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

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11
Q

Describe the relationship between the active site and the substrate

A

They are complementary to each other

Hint: do NOT say they are the same as each other

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12
Q

Name the model that describes how enzymes work

A

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
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13
Q

Explain the lock and key theory model

A

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

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14
Q

Define the term enzyme-substrate complex

A

An enzyme that has it specific substrate bound to it’s active site

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15
Q

Explain the effect of low temperatures on enzyme activity

A
  • 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
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16
Q

Explain the effect of high temperatures on enzyme activity

A
  • 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
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17
Q

Why is it incorrect to say an enzyme is dead?

A

All enzymes are just proteins

They are not living and so can’t be killed

They are just specialised chemical molecules

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18
Q

Describe the effect the optimum temperatures on enzyme activity

A
  • 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
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19
Q

What is the typical optimum temperature for human enzymes?

A

37oC

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20
Q

Describe how an enzyme is denatured and the effect this has

A

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
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21
Q

Name an human enzyme that works at an optimal pH of 1-2 (acidic)

A

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

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22
Q

State 2 human enzymes that work at an optimal pH of 7 (neutral)

A

Amylase

Catalase

Lipase

Carbohydrases

Proteases (except trypsin)

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23
Q

How do you calculate the rate of reaction?

A

Amount of product formed divided by the time

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24
Q

In an experiment how can you control the temperature to ensure you are carrying out a fair test?

A

Use a thermostatically controlled water bath

Hint: don’t just say water bath

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25
Q

In an experiment how can you control the pH to ensure you are carrying out a fair test?

A

Use buffer solutions to keep the pH of the experiment constant

Buffers work by keeping the pH constant

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26
Q

State the 3 main groups of enzymes that are involved in digestion

A

Lipases

Carbohydrases

Proteases

27
Q

Describe the action of a protease enzyme

A

Proteases break proteins down into amino acids

28
Q

Describe the action of a lipase enzyme

A

Lipases break lipids down into 3 fatty acids and 1 glycerol

Hint: remember to state the number of each type of product made

29
Q

Describe the action of a carbohydrase enzyme

A

Carbohydrases break complex carbohydrates (called polysaccharides) down into simpler sugars (called monosaccharides) e.g. glucose

30
Q

Give an example of a carbohydrase.

State its substrate and product

A

Carbohydrase = amylase

Substrate = starch

Product = maltose

31
Q

State 3 places in the human body where amylase is produced

A

Mouth (salivary amylase)

Pancreas

Small intestine

32
Q

State 3 places in the human body where proteases are produced

A

Pancreas

Stomach

Small intestine

33
Q

State 2 places in the human body where lipase is produced

A

Pancreas

Small intestine

34
Q

Which 2 organs in the human body produce carbohydrases, lipases and proteases

A

Pancreas

Small intestine

35
Q

Describe what happens to the fatty acids and glycerol that are produced after digestion

A
  • 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
36
Q

Describe what happens to the amino acids that are produced after digestion

A
  • 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
37
Q

Describe what happens to the simple sugars that are produced after digestion

A

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

38
Q

What is the function/role of bile?

A

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

39
Q

How does the emulsification of lipids affect the activity of lipases?

A

Emulsifying the fats into smaller droplets increases the surface area

This increases the activity of lipase

40
Q

Explain why the pH falls (becomes more acidic) in during a reaction catalysed by lipase

A

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)

41
Q

State where bile is stored

A

Gall bladder

42
Q

Explain why it is important bile is released into the small intestine to allow digestion to occur

A
  • 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
43
Q

State where bile is produced

A

Liver

44
Q

What test would you use to detect the presence of reducing sugars?

A

Benedict’s test

45
Q

Describe the results of a positive Benedict’s test

A

The solution would change from blue to green to yellow to orange to brick red

46
Q

What colour is a negative Benedict’s test?

A

Blue

47
Q

Describe how to carry out a Benedict’s test

A
  1. 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)
  2. Add 5 cm3 of the food sample to a test tube
  3. Add 10 drops of Benedict’s solution
  4. Heat the food sample in a water bath at 75oC for 5 minutes
48
Q

State 3 safety precautions you should take when carrying out a Benedict’s test

A
  1. Wear safety goggles
  2. Make sure the test tube is pointing away from you in the water bath
  3. Do not ingest the Benedict’s solution – it is harmful
49
Q

What test would you use to detect the presence of starch?

A

Iodine solution

50
Q

Describe the results of a positive starch test

A

A blue-black solution

51
Q

What colour is a negative starch test?

A

A yellow-brown solution

52
Q

Describe how to carry out a starch test

A
  1. 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)
  2. Place the food sample in the well of a spotting tile
  3. Add a few drops of iodine solution onto the food sample with a pipette
  4. Observe the colour change
53
Q

State 2 safety precautions you should take when carrying out a starch test

A

Wear safety goggles

Do not ingest the iodine solution – it is harmful

54
Q

What test would you use to detect the presence of lipids?

A

Sudan III stain solution

55
Q

Describe the results of a positive Sudan III test

A

2 layers will form

The top layer will be bright red

56
Q

Describe the results of a negative Sudan III test

A

No separate red layer will form

57
Q

Describe how to carry out a Sudan III test

A
  1. 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)
  2. Place the food sample in a test tube
  3. Add 3 drops of Sudan III stain solution onto the food sample with a pipette
  4. Gently shake the test tube
  5. Observe the colour change
58
Q

What test would you use to detect the presence of proteins?

A

Biuret reagent

59
Q

Describe the results of a positive Biuret test

A

Purple solution

60
Q

Explain the purpose of digestion (3 key points)

A
  • To use enzymes to break down large insoluble molecules
  • into small and soluble molecules
  • that can be absorbed into the bloodstream
61
Q

Describe the results of a negative Biuret test

A

Blue solution

62
Q

Describe how to carry out a Biuret test

A
  1. 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)
  2. Add 5 cm3 of the food sample to a test tube
  3. Add 5 cm3 of Biuret solution
  4. Gently shake the test tube
  5. Observe the colour change
63
Q

Give 2 properties that amino acids, glycerol, simple sugars and fatty acids have that enable them to be absorbed into the plasma

A

Small and soluble

Mrs P's GCSE Biology (26 decks)

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