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AQA A Level Biology > 3.1 Chapter 1- Biological Molecules > Flashcards

3.1 Chapter 1- Biological Molecules Flashcards

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1
Q

What is indirect evidence for evolution?

A
  • All life on Earth shares a common chemistry. This is indirect evidence for evolution, as it suggests all life has a common ancestor.
  • Despite the extensive variety of life, the cells of all living organisms contain only a few groups of carbon-based organic compounds that interact in similar ways.
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2
Q

Why is the biochemical basis of life similar?

A
  • Based on carbon atoms- organic
  • Contain versatile bonds that readily link with each other and form chains.
  • Few other atoms attach to carbon.
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3
Q

Define a monomer

A

A small repeating unit from which polymers are made.

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4
Q

Define a polymer.

A

A chain of many monomers joined together by bonds. e.g. amino acids forming proteins with peptide bonds.

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5
Q

What must you remember to mention when talking about polymers?

A

The bonds e.g. glycosidic, phosphodiester

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6
Q

Define a condensation reaction.

A

The joining of 2 molecules/ monomers together forming a chemical bond and releasing water.

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7
Q

Define hydrolysis

A

The breaking of a chemical bond (between monomers) using a water molecule.

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8
Q

What are the monomers of carbohydrates?

A

Monosaccharides

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9
Q

What are the features of monosaccharides?

A
  • Soluable
  • Sweet tasting
  • General formula (CH2O) n
  • Reducing sugars
  • e.g. glucose, galactose, fructose
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10
Q

What type of molecules are monosaccharides?

A

Hydrocarbons- made from only carbon, oxygen and hydrogen.

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11
Q

What is the general formula of a monosaccharide?

A

(CH2O) n

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12
Q

What is another name for hexose?

A

Glucose

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13
Q

Name the each monosaccharides from 3 to 7 carbons.

A

3- triose
4- tetrose
5- pentose
6- hexose= glucose
7- heptose

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14
Q

What is the name for a bond between a monosaccharide?

A

Glycosidic bond

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15
Q

What are alpha and beta glucose?

A

Structural isomers

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16
Q

Draw alpha and beta glucose.

A

Answer on revision card.

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17
Q

Describe the test for reducing sugars and how it works.

A
  1. Dissolve the sample
  2. Add an equal volume of Benedicts reagent
  3. Heat to over 70°C
  4. If present, the solution will turn from blue to brick red

All monosaccharides are reducing sugars. Test works by reducing Cu2+ ions to Cu+ turning them from blue to red. High concentration means more red substrate.

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18
Q

What are the uses of carbohydrates?

A
  • Used as respiratory substrate
  • Form structural components in plasma membranes and cell walls
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19
Q

How disaccharides formed and broken?

A

Formed by the concentration reaction of two monosaccharides, forming a glycosidic bond and water.
Broken by hydrolysis requiring water.

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20
Q

What type of sugar are disaccharides?

A

Reducing or non-reducing sugars

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21
Q

What are the components of:
Maltose
Sucrose
Lactose

A
  • Maltose- 2 alpha glucose- forms α1-4 glycosidic bond
  • Sucrose- alpha glucose and fructose
  • Lactose- alpha glucose and galactose
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22
Q

Complete the equation (written and formula):
2α glucose —>

A

2α glucose —> maltose + water
2C6H12O6 —> C12H22O11 + H2O

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23
Q

Describe the test for non-reducing sugars.

A
  1. Perform the test for reducing sugars make sure it’s negative
  2. Take new sample, dissolve and add an equal volume of HCl/ acid
  3. Boil/ heat to hydrolyse the disaccharide
  4. Add sodium hydrogen carbonate to neutralise. Test the solution is alkaline using indicator paper.
  5. Add Benedict’s reagent and heat over 70°
  6. They reducing sugar is present. The solution turns from blue to brick red. Red precipitate/ colour.
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24
Q

Draw glucose and how it forms into maltose

A

Answer on revision card
Remember to label α1-4 glycosidic bond

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25
Q

What type of test is Benedicts?

A

Semi quantitative

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26
Q

How can the Benedicts test be measured quantitatively?

A
  • High concentration means more red substrate
  • Measured by filtering, drying and finding the weight of the precipitate
  • Can be measured using a colorimeter.
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27
Q

What is the colorimeter used to measure in Benedict’s/ in general?

A

Used to measure the colour change of the Benedict’s reagent test and therefore the concentration of reducing sugars.
Makes the test more quantitive.
In general measures the percentage absorption or transmission of a particular wavelength of light emitted by a solution

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28
Q

What do reducing sugars do to the Benedict’s solution ?

A

Reduce blue Cu2+ to red Cu+ forming a red precipitate.

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29
Q

How do you measure the Benedict’s test with a colorimeter and what results would you see?

A
  1. The Benedict’s solution is filtered to remove the red precipitate, leaving just the blue solution. The more glucose means the solution is lighter blue as the solution is more reduced
  2. The cuvette is filled 3/4 full of blue liquid and a separate cuvette is filled 3/4 full of distilled water
  3. The colorimeter is set to red and the water is placed inside to calibrate it to 0. The solution is then added and the percentage absorption is measued.
  4. The red light is absorbed by the blue as this is a complimentary colour, the less blue that means the more red light transmitted and less absorbed. This means more red precipitate was produced, and there was a great quantity of reducing sugar.
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30
Q

What would you do with the results from the colorimeter test of Benedict’s?

A

The results of the unknown solution will be used to plot a calibration curve At different glucose concentrations, which can then be used to find the glucose concentration of an unknown substance.

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31
Q

How are polysaccharides formed and what is their property?

A

Formed in the condensation reaction of many monosaccharide monomers, forming water and glycosidic bonds. Insoluble.

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32
Q

What can polysaccharides be hydrolysed into?

A

Hydrolyse into disaccharides or monosaccharides

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33
Q

Describe the structure of starch

A

Polysaccharide made of repeating units of alpha (α) glucose joined together by glycosidic bonds in a condensation reaction
Made of amylose (unbranched and coiled helical structure due to hydrogen bonds) and amylopectin (branched).

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34
Q

What is starch hydrolysed into by amylase and why?

A

Starch is hydrolysed into maltose by amylase.
This enables the maltose to be absorbed and transported around the body and enables it to be further hydrolysed into glucose for respiration as starch cannot be absorbed and is egested.

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35
Q

Describe starch’s purpose and how it suits it.

A

Storage of alpha glucose in plants, e.g. seeds.
- Insoluble- doesn’t affect water potential or osmosis
- Large- can’t cross cell membrane and leave cell
- Compact- coiled and branched, helical structure of amylose stores lots of glucose molecules in a small space
- Branched endings- more ends- fast enzyme action- easily hydrolysed for rapid glucose release due to branched ends of amylopectin meaning enzymes can attach and work simultaneously.

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36
Q

Describe the test for starch

A

Add two drops of iodine and see if the colour turns from brown orange to black blue

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37
Q

Describe the structure of glycogen

A

Polysaccharide polymer made of alpha (α) glucose monomers joined together in a condensation reaction to form glycosidic bonds. 1-4 and 1-6 glycosidic bonds. Shorter chained and more highly branched than starch. Similar structure to amylopectin.

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38
Q

What is glycogen used for and how does it suit its purpose?

A

Used for alpha glucose/carbohydrate storage in animals and bacteria. e.g. in the liver. Hydrolyses into glucose. Small amount of glycogen because main storage molecule in animals is fat.
- Insoluble- Doesn’t affect water potential or osmosis
- Compact- stores lots of glucose in a small space
- Highly branched- made of amylopectin, More ends to be acted on simultaneously by enzymes. More rapid as animals have a higher metabolic rate so quicker energy release.

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39
Q

Describe the structure of cellulose

A
  • Polysaccharide with beta (β) glucose monomers
  • Position of hydrogen and hydroxyl groups on carbon atom 1 inverted every other monomer
  • Only 1-4 glycosidic bonds
  • Straight unbranched chains, parallel to each other
  • Joined together by hydrogen bond cross linkages to add strength- weak on their own but strong together
  • Group to form strong, microfibrils and fibres
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40
Q

Describe the function of cellulose and how it suits that function

A
  • Forms plant cell walls
  • Provide structural support and rigidity to the plant cell
  • Long straight chains linked together by many hydrogen bonds to form fibrils that provide strength
  • The cell from bursting under osmosis and exerts an inward pressure to stop water influx
  • Makes yourself turgid and rigid, creating a maximum surface area for photosynthesis
  • Permeable to water- allows water movement
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41
Q

Describe the overall features of lipids

A

Insoluble in water, soluble in organic solvents

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42
Q

What are lipids roles/ what are they used for?

A
  • Cell (plasma) membranes- help form bilayer
  • Used in certain hormones and respiratory structures.
  • Energy source- 2x energy as glucose and produces water
  • Waterproofing- waxy cuticle and oil on the skin
  • Electrical and heat insulation
  • Protecting delicate organs
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43
Q

Describe how triglycerides are made and their structure.

A
  • Made of one glycerol and three fatty acids
  • Formed in a condensation reaction forming ester bonds and three molecules of water. Reversed by hydrolysis.
  • A fatty acid is made of a carboxyl (COOH) and an R group
  • Variation is found in the R group of fatty acids
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44
Q

Explain why triglycerides are insoluble.

A

The 3 fatty acid tails are hydrophobic.

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45
Q

Explain how triglycerides can vary.

A
  • Vary in the R group of fatty acids.
  • Saturated- no carbon to carbon double bonds- saturated by hydrogen
  • Unsaturated- carbon to carbon double bonds
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46
Q

Describe the features of triglycerides.

A
  • Good source of energy- high ratio of energy storing carbon-hydrogen bonds to carbon. Produce two times energy of carbohydrates
  • Low mass to energy ratio- high energy in a small volume- reduces the mass animals have to carry.
  • Insoluble- large and non-polar and don’t affect osmosis or water potential.
  • Important source of water- high ratio of carbon to oxygen, so release water when oxidised.
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47
Q

What do triglycerides form in water (and draw)?

A
  • Form Insoluble droplets aka micelles
  • See revision card for drawing
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48
Q

Draw a triglyceride

A

Answer on revision card.

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49
Q

Describe the structure of a phospholipid.

A
  • Similar to triglycerides, except one fatty acid is replaced with a phosphate.
  • Hydrophilic phosphate heads- attract water- interact with water but not fat- negatively charged.
  • Two hydrophobic fatty acid tails- repel water- orient away from water but mix with fat
  • Polar molecule- head as close to the water as possible. Tails far away.
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50
Q

Describe the features and functions of a phospholipid bilayer.

A
  • Polar molecules form a bilayer.
  • Phosphate heads face outwards, fatty acid tails face inwards.
  • Helps form the cell surface membrane
  • Forms a hydrophobic barrier- the centre blocks water soluble substances
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51
Q

Why are phospolipids useful in cell membranes?

A
  • Provide flexibility
  • Transfer lipid soluble substances
  • The hydrophilic phosphate heads hold the phospholipids at the surface of the cell-surface membrane.
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52
Q

What do phospholipids easily form?

A

Glycolipids with carbohydrates

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53
Q

Draw and label a phospholipid.

A

‘Drawing on revision card
Labels should include:
Uncharged hydrophobic fatty acid ‘tails’
Negatively charged hydrophobic phosphate ‘head’

54
Q

Describe the test for lipids

A
  1. Take a dry, grease free test tube
  2. Add a sample and double the volume of ethanol
  3. Shake to dissolve lipid in sample
  4. Then add equal volume of water to ethanol and shake
  5. If a milky white emulsion forms lipids are present
    Control- process repeated using water instead of sample- solution should be clear.
55
Q

What are amino acids?

A

The monomers which proteins are made from through condensation reactions.

56
Q

What do amino acids provide indirect evidence for?

A

Evolution- There are only twenty different types of naturally occurring amino acids.

57
Q

Describe the structure of an amino acid.

A
  • Amine (NH2) group at one end
  • Carboxyl group (COOH) at other end
  • Single hydrogen molecule and carbon at centre
  • R group/ R side chain- where amino acids differ/ vary
58
Q

Draw and label an amino acid

A

Answer on revision card
Labels should include:
Amine group
Carboxyl group
R side chain- only place amino acids differ

59
Q

What does the condensation reaction of two amino acids form? How can this be broken.

A
  • Forms a peptide bond between the amine and carboxyl groups
  • Creates a dipeptide
  • Releases water.
  • Peptide bonds can be broken by hydrolysis using water.
60
Q

Draw a dipeptide

A

Answer on revision card.

61
Q

What is the order of what amino acids form?

A

Amino acids form polypeptide chains that form proteins.

62
Q

What do proteins do?

A

Proteins form many cell structures. They are important as enzymes, chemical messengers and components in the blood.

63
Q

Why is a protein’s shape important?

A

A protein shape determines its function. Structure and shapes have to be specialised e.g. enzymes

64
Q

What are amino acids polymerised into and how are they arranged?

A

Polymerised in condensation reactions to form polypeptides and peptide bonds between the amine (NH2) group and the carboxyl group (COOH). Each amino acid is orientated in the same direction and in each chain there is a free amine group at one end and a free carboxyl group at the other.

65
Q

What are proteins made of?

A

One or more polypeptide chains of amino acids. Often more than one.

66
Q

What is a simple protein made of?

A

One polypeptide chain

67
Q

What is the overall structure of a protien determined by?

A

The relative positions of amino acids and the bonds between them (hydrogen, disulfide bridges, ionic).

68
Q

Describe the primary structure.

A

The sequence of amino acids in a polypeptide chain- specific order.

69
Q

What is the primary structure determined by?

A

DNA and genes that code for the protein- in base sequences of triplets- every three bases codes for one amino acid.

70
Q

Why is the primary structure important?

A
  • The sequence of amino acids determines the end shape and function of the protein.
  • A change in just one amino acid along sequence changes the shape of the whole protein and stops it from functioning.
  • The protein shape is specific to its function.
  • A change in the primary structure produces different bonds in different places (ionic, hydrogen, disulfide bridges) that produces a different teritary structure.
71
Q

What can the same amino acids form?

A

The same amino acids can form different sequences- primary structures.

72
Q

Describe the secondary structure.

A

Hydrogen bonds form between amino acids. Form between NH/ the hydrogen in the amine group and the double bonded oxygen and carbon in the carboxyl group. Forms a twisted 3D shape. e.g. alpha helix/ beta pleated sheet.

73
Q

Describe the tertiary structure.

A
  • More complex and specific 3D structure.
  • Formed by further twisting coiling and folding the polypeptide. Bonds between amino acids do this.
  • Disulphide bridges are strong and easily broken, formed from two sulfurs.
  • Ionic bonds are formed from the carboxyl and amine group not in peptide bonds- easily broken by a pH change.
  • Hydrogen bonds are common and weak.
74
Q

What is the final structure in simple proteins?

A

The tertiary structure.

75
Q

Describe the quanternary structure.

A

Several (more than one) different linked polypeptide chain formed by bonds between polypeptides (hydrogen, disulfide bridges, ionic bonds), the way they are assembled together and bonds to non-protein (prosthetic) groups associated with the molecules.

76
Q

Why is the sequence of amino acids more important than the tertiary structure?

A

Although 3D structures important to have protein functions. The sequence of amino acids determines the 3D shape.

77
Q

What is the test for proteins?

A

The biuret test:
1. Add a few drops of sodium hydroxide to make the solution alkaline.
2. Then add copper II sulphate (biuret reagent)
3. If proteins are present, the solution turns from blue to purple.

78
Q

What are enzymes?

A

Enzymes are biological catalysts and globular proteins

79
Q

What is the function of enzymes.

A

Biological catalysts that increase the rate of reaction of metabolic reactions without undergoing permanent change and can therefore be reused.

80
Q

What do enzymes catalyse and where do they function?

A
  • Catalyse metabolic reactions:
  • At a cellular level e.g. respiration and for the organism as a whole e.g. digestion.
  • Help produce structures, e.g. proteins and functions, e.g. respiration.
  • Functions can be intracellular (in the cell) or extracellular (outside the cell).
81
Q

Describe the structure of enzymes.

A

Enzymes are globular proteins with a specific 3D tertiary structure as a result of their primary structure (sequence of amino acids)

82
Q

Describe the active site.

A

The functional region of an enzyme with a specific shape where substrates bind to. A small depression made of a few amino acids specific to the substrate.

83
Q

Describe substrates.

A

Molecules on which enzymes act. Fits into the active site held by temporary bond between amino acids and the substrate to form enzyme substrate complexes.

84
Q

What is activation energy?

A

The minimum amount of energy needed for a reaction to start. Often in the form of heat.

85
Q

What is required for a reaction to occur?

A

The activation energy and a successful collision.

86
Q

How do enzymes increase the rate of reaction?

A
  1. Catalyse reactions
  2. Form enzyme substrate compexes
  3. Lower the activation energy
  4. Induced fit causes the active site of the enzyme to change shape
  5. The enzyme substrate complex causes bonds to form/ break by putting tension on/ bending the bonds or weakening the bonds.
  6. Joining- being attached to the enzyme holds the substrates close together and reduces the repulsive forces.
    Breaking- the active site put strain on the bonds of the substrate, so they break more easily.
87
Q

What do enzymes do to the activation energy and what does this enable?

A

Enzymes lower the activation energy so reactions can happen at lower temperatures and this speeds up the rate of reaction. This enables metabolic processes to happen rapidly at the low body temperatures e.g. 37°C. Without this reactions would be too slow to sustain life.

88
Q

Draw the graph of the effect of enzymes on activation energy

A

Answer on revision card

89
Q

How do enzymes lower the activation energy?

A

Joining- overcoming repulsion forces between molecules by holding them close together.
Breaking- puts strain on the bonds of the substrate to break it apart.

90
Q

Why have models changed over time and give an example

A
  • Accepted theories change as new evidence comes to light.
  • For example, the lock and key model, where the enzyme and substrate have rigid complementary shapes has been replaced by the induced fit model where the enzymes shape changes slightly.
91
Q

Describe the induced fit model

A

The enzyme is flexible and mould around the substrate. This only occurs with the specific substrate the enzyme is complementary to otherwise, the enzyme maintains its usual shape. As the enzyme changes shape, it puts strain on the substrate and reduces the activation energy.

92
Q

Describe how the induced fit model works to catalyse a reaction.
| Hint: 4 steps

A
  1. Substrate binds to the active site and enzyme-substrate complexes form
  2. Active site changes shape (slightly) so it is complementary to substrate
  3. This breaks/forms bonds in the substrate
  4. This reduces activation energy
93
Q

When does the enzyme only change shape in the induced fit model?

A

In the presence of the enzymes complimentary substrate.

94
Q

How does the enzyme lower the activation energy in the induced fit model?

A

Joining- being attached to the enzyme holds the substrates close together and reduces the repulsive forces.
Breaking- the active site put strain on the bonds of the substrate, so they break more easily.

95
Q

What structure are properties of enzymes related to?

A

The tertiary structure of the active site.

96
Q

Enzymes are h_____ s_______ fill in the blanks and explain what this means.

A

Highly specific.
Usually only catalyse one reaction and have only one complimentary substrate that will fit into the active site.

97
Q

What is the active site determined by?

A

The tertiary structure, which is determined by the primary structure (sequence of amino acids). Different for different types of enzyme.

98
Q

What happens if the substrate does not fit the active site?

A

Enzyme substrate complexes do not form and the reaction isn’t catalysed.

99
Q

What happens if the tertiary structure of an enzyme is changed and what could the change be caused by?

A
  • The shape of the active site changes.
  • The substrate won’t fit as the active site is no longer complimentary.
  • Enzyme substrate complex are not formed.
  • The enzyme can’t carry out its function and catalyse the reaction.

Caused by:
- pH or temperature changes
- Changes in the primary structure due to mutations causing a change in the tertiary structure.

100
Q

What will any change in an enzymes environment do?

A

Change the shape of the enzyme, even colliding with the substrate.

101
Q

What is necessary for an enzyme to work?

A

The enzyme must come in to come physical contact with the substrate and have an active site that fits the substrate. Change rate means one of these factors is affected.

102
Q

How can you measure enzyme controlled reactions?

A

Measuring the time it takes to:
- Make a product, e.g. hydrogen peroxide to oxygen and water catalysed by catalase- measure oxygen using gas syringe
- Breakdown of product, e.g. the reduction of starch to maltose by amylase- use a spotting tile and iodine and see when turns blue black.

103
Q

How do you describe an enzyme reaction over time without a factor?
Hint: 5 steps

A
  1. At first, lots of substrate and no product (remember to name the substrate and product).
  2. It’s easy for the substrate to reach an empty active site. All the active sites are filled/ occupied and the substrate is rapidly acted upon. Rate of reaction is at its peak.
  3. The amount of substrate decreases and the amount of product increases over time, there is less substrate and more product.
  4. This makes it more difficult for the substrate to come in contact with the enzyme, as there are fewer and the products get in the way. It takes longer for the substrates to be broken down. The rate slows and the gradient decreases.
  5. The rate of reaction becomes so low the changing concentration can’t be measured. The graph flats and all the substrate is used up.
104
Q

What must you remember to mention when describing enzyme-controlled reactions?

A

The enzyme and substrates names.

105
Q

How do you measure rate of change?

A

Find the gradient of the tangent of the graph. Use the normal to help you find the tangent and draw an equal distance from where it touches the curve.

106
Q

What variables are changed when investigating enzymes?

A

Only one variable is changed the rest are controlled.

107
Q

Why can an enzyme be used effectively at low concentrations

A

The enzymes are never used up.

108
Q

Describe the effect of increasing enzyme concentration on the rate of reaction.

A
  1. If the substrate is in excess, an increase in the enzyme is proportional to the rate of reaction increase as there are more substrates than active sites. Enzymes are more likely to collide with the substrate and form enzyme substrate complexes.
  2. If the substrate is limited, there are more enzymes than substrate. The substrate is the limiting factor, and adding more enzyme has no further effect, as there are empty active sites.
109
Q

Draw the graph of the effect of enzyme concentration on the rate of reaction and label

A

Answer on revision card.
Labels should include:
* A steady increase as more active sites available.
* An increase in enzyme concentration has no further effect.

110
Q

Describe the effect of increasing substrate concentration on the rate of reaction and draw the graph.

A
  • At first, a higher substrate concentration increases the rate of reaction proportionally. The more substrate, the more likely a collision will occur, and enzyme substrate complexes will form.
  • More active sites are occupied until the maximum/ saturation point is reached, at this point, all active sites are full/ occupied.
  • After the saturation point there are more substrates than enzymes. All active sites are full and enzyme concentration is the limiting factor. Adding more substrate has no effect on the rate of reactions
111
Q

Summarise the effect of increasing substrate concentration while keeping enzyme concentration constant on the time to fully catalyse the substrate.

A

As substrate concentration increases, time to catalyse substrate increases.

112
Q

What is another symbol for the maximum point?

A

Vmax

113
Q

How do enzyme inhibitors work?

A

Prevent the enzyme from forming enzyme substrate complexes.

114
Q

How do competitive inhibitors work?

A
  • Competitive inhibitors have a molecular shape similar to the substrate.
  • The competitive inhibitors compete with the substrate to bind with the active site.
  • The competitive inhibitor blocks the active site, so no substrate molecules can fit. Prevents/ reduces enzyme substrate complexes forming. Reduces amount of substrate catalysed
  • Not permanent.
115
Q

How does a change in substrate concentration affect competitive inhibition?

A
  • The amount of inhibition is relative to the amount of inhibitor vs. the amount of substrate.
  • An increased amount of inhibitor means there’s less chance of the substrate reaching the active site.
  • An increased substrate means there’s more chance of binding to the active site and the effect of the inhibitor is reduced.
116
Q

Draw and label the graph for competitive enzyme inhibition.

A

Answer on revision card.

117
Q

How do non-competitive inhibitors work?

A

Bind the enzyme away from the active site and alter the shape of the enzyme and active site, changing the tertiary structure. The enzyme is no longer complementary to the substrate so substrate can’t fit and the enzyme can’t catalyse the reaction. No enzyme substrate complexes form.

118
Q

Draw and label the graph for non-competitive inhibition

A

Answer on revision card.

119
Q

What is the effect of substrate concentration on non-competitive inhibitors?

A

No effect- the graph shows increasing the substrate concentration doesn’t increase/ change the rate of reaction so it does not overcome inhibition

120
Q

What do the end products of metabolic pathways sometimes act as and describe a metabolic pathway?

A
  • End products of metabolic pathways sometimes act as inhibitors and regulate their own production.
  • Metabolic pathways are a series of metabolic reactions.
121
Q

Why can substances that bind to enzymes sometimes improve the rate of reaction?

A
  • Co-enzymes improve the rate of reaction
  • Bind to the enzyme away from active site and alter the tertiary structure
  • This causes the active site to change site
  • This makes the active site more complementary to the substrate so more successful enzyme-substrate complexes form
122
Q

What is the formula for and how do you calculate PH?

A

-log10H+
Approximately equal to standard form.

123
Q

What is pH?

A

A measure of hydrogen ion concentration. Inversely proportional to the number of hydrogen ions.

124
Q

What is optimum pH?

A

pH where enzymes work fastest. Different for different enzymes.

125
Q

How does pH affect the reaction?

A
  • At the optimum pH the rate is fastest.
  • An increase or decrease from the optimum pH e.g. by adding acid/ alkali reduces the rate.
  • A lower or higher pH alters the charges in amino acids in the active site.
  • The change in pH causes H+ and OH- ions to disrupt the ionic and hydrogen bonds in the enzymes tertiary structure causing them to break and change the active site’s tertiary structure.
  • The enzyme at first finds it difficult to bind to the substrate then cannot bind at all. The enzyme is no longer complementary to the substrate. The substrate can’t attatch to the active site and enzyme substrate complexes don’t form. The enzyme is denatured and the rate decreases to zero.
126
Q

When is a solution acidic and when is a solution alkali?

A
  • Acidic- below pH 7
  • Alkaline- above pH 7
127
Q

Draw and label the graph of the effect of pH on the rate of reaction of enzymes.

A

Answer on revision card.

128
Q

How does temperature affect the rate of reaction?

A
  • At low temperatures e.g. in fridge/ freezer- low kinetic energy so fewer enzyme substrate complexes form
  • An increased temperature increases the kinetic energy of the enzymes and substrates. Molecules move faster and are more likely to collide and form enzyme substrate complexes. Collisions happen more frequently. The energy of collisions increases- more likely to result in a reaction and enzyme substrate complexes. The graph has a positive gradient.
  • The enzyme meets the up its optimum temperature where the rate is highest. The graph peaks.
  • After the optimum, higher temperatures e.g. by boiling cause hydrogen and other bonds in the enzyme to break changing the tertiary strucuture and shape of the enzyme and it’s active site. The enzyme finds it more difficult to form enzyme substrate complexes, the rate of reaction decreases and the gradient of the graph becomes negative.
  • Firstly, the substrate doesn’t fit as easily and this slows the rate of reaction. After a certain point the enzyme is so changed it stops working and denatures. The enzyme is no longer complementary to the substrate and the rate of reaction declines to zero.
129
Q

Draw and label the graph of the effect of temperature on the rate of reaction of enzymes.

A

Answer on revision card.

130
Q

Why is the human body temperature different to the optimum temperature of its enzymes?

A
  • Enzymes optimum temperature is 40°C despite the human body temperature being 35°C.
  • This difference ensures the safety of the enzyme as any rise in temperature from the optimum could denature the enzyme
  • This also ensures that less energy and food is needed to gain higher temperature.
  • It’s also is important to ensure the other proteins do not denature.
  • This is also the same for bacteria- isolated enzymes can’t be tested on their own- all enzymes/ protiens needed to provide bigger picture
131
Q

How do you analyse graphs of rates of reaction?

A
  1. Compare the rate of reaction at the start of the graph and at the end of the graph, and explain the difference.
  2. Look at where the maximum is and explain why
  3. If given different graphs compare and explain the difference.
  4. Identify any effect that denatures the enzyme where reactions stop sooner.
  5. Mention why a reaction is stopped Is it because the enzyme has denatured or because the substrate has been used up.
132
Q

How can optimum pH and temperature vary?

A

Different for different enzymes

AQA A Level Biology (11 decks)

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