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AS AQA Biology - Burnley College (2023-24) > Biological Molecules 3.1 > Flashcards

Biological Molecules 3.1 Flashcards

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1
Q

GCSE recap

What process in plants produces glucose?

A

Photosynthesis

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2
Q

GCSE Recap

Is starch soluble or insoluble?

A

Insoluble

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3
Q

GCSE Recap

What process is glucose used for by both plants and animals?

A

Respiration

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4
Q

GCSE Recap

What is the function of cellulose?

A

To provide strength and rigidity to the plant cell wall

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5
Q

GCSE recap

How do you test for starch?

A

1. Add (two drops of) iodine solution to the sample solution.

2. A blue/black/purple colour indicates the presence of starch.

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6
Q

GCSE Recap

Metabolism includes the conversion of glucose into which larger biological molecules?

A

Starch
Glycogen
Cellulose

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7
Q

AS (Monomers & Polymers AO1)

Define a monomer (1 mark)

A

Small repeating units from which larger molecules called polymers are made

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8
Q

AS (Monomers & Polymers AO1)

Define a polymer (1 mark)

A

Molecules made from a large number of monomers (3 or more) joined together

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9
Q

AS (Monomers & Polymers AO1)

Give 3 examples of monomers

A

Glucose / Galactose / Fructose
Nucleotides
Amino acids

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10
Q

AS (Monomers & Polymers AO1)

Which of the below molecules is NOT a polymer?

Glycogen
Triglyceride
Cellulose
Starch
DNA
Polypeptides/proteins

A

Triglyceride

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11
Q

AS (Monomers & Polymers AO1)

Molecules with carbon-carbon and carbon-hydrogen bonds are referred to as ……………………

A

Organic molecules

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12
Q

AS (Monomers & Polymers AO1)

What type of reaction joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water (H2O).

A

Condensation

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13
Q

AS (Monomers & Polymers AO1)

Describe a hydrolysis reaction (1 mark)

A

Breaks a chemical bond between two molecules & involves the use of a water molecule (H2O).

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14
Q

AS (Carbohydrates AO1)

What are the monomers from which larger carbohydrates called polysaccharides are made

A

Monosaccharides

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15
Q

AS (Carbohydrates AO1)

List 3 common monosaccharides

A

Glucose, galactose and fructose

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16
Q

AS (Carbohydrates AO1)

What bond is formed as result of a condensation reaction between two monosaccharides?

A

Glycosidic bond

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17
Q

AS (Carbohydrates AO1)

What is the name of the disaccharide formed by condensation reaction with two glucose molecules?

A

Maltose

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18
Q

AS (Carbohydrates AO1)

What monosaccharides are joined by a condensation reaction to form lactose?

A

Glucose

Galactose

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19
Q

AS (Carbohydrates AO1)

What disaccharide is formed by condensation reaction with glucose and fructose?

A

Sucrose

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20
Q

AS (Carbohydrates AO1)

TRUE or FALSE:

Many glycosidic bonds are found in a disaccharide?

A

FALSE

There is only 1 glycosidic bond in a disaccharide

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21
Q

AS (Carbohydrates AO1)

Write out a chemical equation for the formation of a disaccharide (1 mark)

A

For every bond formed, a condensation reaction produces one molecule of water.

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22
Q

AS (Carbohydrates AO1)

Which isomer of glucose is shown below?

A

Alpha glucose

Remember: Alpha Below Beta Above (ABBA) on C1

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23
Q

AS (Carbohydrates AO1)

Which isomer of glucose is shown below?

A

Beta glucose

Remember: Alpha Below Beta Above (ABBA) on C1

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24
Q

AS (Carbohydrates AO1)

Draw out the full chemical structure of alpha glucose

A

Remember: Alpha Below Beta Above (ABBA) on C1

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25
Q

AS (Carbohydrates AO1)

What polymer is formed by the condensation of many glucose units?

A

Polysaccharides

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26
Q

AS (Carbohydrates AO1)

Which 2 polysaccharides are formed by the condensation of α-glucose?

A

Glycogen

Starch

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27
Q

AS (Carbohydrates AO1)

What polysaccharide is formed by the condensation of many β-glucose units?

A

Cellulose

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28
Q

AS (Carbohydrates AO1)

Plant cells produce which 2 polysaccharides?

A

Starch

Cellulose

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29
Q

AS (Carbohydrates AO1)

Glycogen is found in which animal organs?

A

Liver

Muscle

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30
Q

AS (Carbohydrates AO1)

Explain how starch is related to its function (3 marks)

A

Any three from:

  1. Insoluble (in water), so doesn’t affect water potential/osmosis;
  2. Coiled / (α-)helix / helical structure, so makes molecule compact;
  3. Polymer of (α-)glucose so provides glucose for respiration;
  4. Branched / more ends for fast breakdown / enzyme action;
  5. Large (molecule), so can’t cross the cell membrane
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31
Q

AS (Carbohydrates AO1)

Explain how glycogen is related to its function (5 marks)

A
  1. Helix/coiled/branched so compact;
  2. Polymer of (alpha) glucose so easily hydrolysed;
  3. (Highly) branched so more ends for faster hydrolysis;
  4. (alpha) Glucose (polymer) so provides respiratory substrate for energy (release);
  5. Insoluble so does not affect water potential/osmosis;
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32
Q

AS (Carbohydrates AO1)

What bonds does cellulose contain?

A

Beta (1,4) glycosidic

(many weak) Hydrogen

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33
Q

AS (Carbohydrates AO1)

Explain how the structure of cellulose is related to its function in plant cell walls (3-4 marks)

A
  1. Long / straight / unbranched chains of beta glucose
  2. (joined by weak) hydrogen bonds;
  3. Forms microfibrils;
  4. Provide rigidity / strength;
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34
Q

AS (Carbohydrates AO1)

Compare the structure of starch and cellulose

A

1.Both polysaccharides;
OR Both are glucose polymers
OR Both are made of glucose monomers;

  1. Both contain glycosidic bonds (between monomers);
  2. Both contain carbon, hydrogen and oxygen/C, H and O;
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35
Q

AS (Carbohydrates AO1)

Contrast the structure of starch and cellulose

A
  1. Starch made of α-glucose whereas cellulose made of β-glucose;
  2. Starch (molecule) is helical/coiled whereas cellulose (molecule) is straight;
  3. Starch (molecule) is branched whereas cellulose is not/unbranched;
  4. Cellulose has microfibrils whereas starch does not;
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36
Q

AS (Carbohydrates AO1)

Draw out the formation of a glycosidic bond between two alpha glucose molecules

A
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37
Q

AS (Carbohydrates AO1)

What bonds do starch and glycogen contain?

A

alpha (1,4) glycosidic

alpha (1,6) glycosidic

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38
Q

AS (Carbohydrates AO1)

Describe the biochemical test for a reducing sugar (3 marks).

A

1. Add equal volumes of Benedict’s solution and sample to a test tube

2. Heat to 95⁰C.

3. Formation of a brick red precipitate if a reducing sugar is present.

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39
Q

AS (Carbohydrates AO1)

List all the reducing sugars

A

Glucose
Fructose
Galactose
Maltose
Lactose

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40
Q

AS (Carbohydrates AO1)

Rank the below colours of precipitate by concentration - lowest to highest - of reducing sugar following the Benedict’s test.

Brick red
Green/yellow
Orange

A

Lowest: green/low
Medium: orange
Highest concentration: brick red

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41
Q

AS (Carbohydrates AO1)

Following the Benedict’s test for a reducing sugar, what would a negative result look like?

A

Solution remains blue

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42
Q

AS (Carbohydrates AO1)

TRUE or FALSE:

The Benedict’s test is quantitative?

A

FALSE

The different coloured precipitates are semi-quantitative

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43
Q

AS (Carbohydrates AO1)

TRUE or FALSE:

A sample containing sucrose will produce a coloured precipiate following the Benedict’s test?

A

FALSE

Sucrose is a non-reducing sugar

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44
Q

AS (Carbohydrates AO1)

Describe a biochemical test to show that a solution contains a non-reducing sugar (3 marks).

A

1. Boil with acid AND neutralise;

Accept named examples, eg hydrochloric acid (HCl), sodium hydrogen carbonate (NaHCO3)

2. Heat (to 95oC) with Benedict’s (solution);

3. Red precipitate
(indicates non-reducing sugar is present);

Accept other colours eg. green/orange

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45
Q

AS (Carbohydrates AO1)

Describe how scientists produce a calibration curve to obtain estimates maltose concentration for an unknown sample (4 marks).

Do not include details of how to perform a Benedict’s test in your answer.

A

1 Make/use maltose solutions of known/different concentrations

2. Carry out Benedict’s test on each solution;

3. (Use colorimeter to) measure colour/colorimeter value (e.g. absorbance) of each solution and plot calibration curve;

4. Details of curve:
concentration on x-axis,
colorimeter value on y-axis,
draw a line of best fine.

5. Estimate concentration of sample by using calibration curve i.e. read off Y axis value to estimate concentration using the x axis

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46
Q

AS (Carbohydrates AO1)

A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution (2 marks).

A

1. Filter AND dry (the precipitate);

Accept: correct reference to evaporation after filtration

2. Find mass/weight;

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47
Q

AS (Carbohydrates AO1)

Explain how you would use the graph to determine the maltose concentration with a light absorbance of 0.45 arbitary units?

A

Line of best fit drawn;

Read off Y axis value at 0.45 (to estimate concentration using the x axis)

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48
Q

AS (Carbohydrates AO1)

What is an arbitary unit? (AU)

A

A relative unit of measurement to show the ratio of amount of substance;

This allows comparisons.

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49
Q

AS (Carbohydrates AO1)

Using a colorimeter rather than relying on the Benedict’s test results alone improves the repeatability of the student’s results.

Give one reason why.

A

1. Quantitative OR
(Colour change is) subjective;

Accept: accurate/precise

2. Standardises (the) method;

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50
Q

AS (Lipids AO1)

Name two groups of lipids

A

Triglycerides
Phospholipids

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51
Q

AS (Lipids AO1)

What are triglycerides are made up of?

A

One molecule of glycerol
and
three molecules of fatty acid

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52
Q

AS (Lipids AO1)

What is the name of the bond formed when a condensation reaction joins together glycerol to three fatty acids?

A

Ester

There are 3 ester bonds in a triglyceride

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53
Q

AS (Lipids AO1)

Identify the carboxyl group and hydrocarbon chain in the fatty acid

A
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54
Q

AS (Lipids AO1)

A

Everything other than the COOH inside drawn box;

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55
Q

AS (Lipids AO1)

Complete the diagram to produce a triglyceride

A
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56
Q

AS (Lipids AO1)

Saturated or unsaturated fatty acid?

A

Saturated fatty acid

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57
Q

AS (Lipids AO1)

Saturated or unsaturated fatty acid?

A

Unsaturated fatty acid

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58
Q

AS (Lipids AO1)

What is an unsaturated fatty acid?

A

Fatty acids with double bonds between the carbon atoms in the hydrocarbon chain.

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59
Q

AS (Lipids AO1)

What is an saturated fatty acid?

A

Fatty acids have no double bonds between carbons in the hydrocarbon chain.

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60
Q

AS (Lipids AO1)

Describe the emulsion test for a lipid (3 marks)

A

1. Add ethanol to sample and mix
(to dissolve the lipid)

2. Then add water and mix

3. A white emulsion will be visible if fat is present

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61
Q

AS (Lipids AO1)

If the sample is a seed - which contains oils - what must you first do before starting the emulsion test?

A

Crush seeds before adding ethanol.

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62
Q

AS (Lipids AO1)

Describe how a triglyceride molecule is formed (3 marks)

A

1. One glycerol and three fatty acids;

2. Condensation (reactions) and removal of three molecules of water;

3. Ester bond(s) (formed);

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63
Q

AS (Lipids AO1)

What molecules are represented by P and Q?

A

P = Glycerol

Q = Fatty acids (chains)

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64
Q

AS (Lipids AO1)

Compare the structure of triglycerides and phospholipids.

A

Both contain ester bonds (between glycerol and fatty acid);

Both contain glycerol;

Fatty acids on both may be saturated or unsaturated;

Both contain C, H and O whereas phospholipids also contain P; Must relate to element.

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65
Q

AS (Lipids AO1)

Compare the properties of triglycerides and phospholipids.

A

Both are insoluble in water;

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66
Q

AS (Lipids AO1)

Contrast the structure of triglycerides and phospholipids.

A

Triglyceride has three fatty acids whereas phospholipid has two fatty acids;

Triglyceride has no phosphate group whereas phospholipids has 1 phosphate group;

Triglycerides have 3 ester bonds whereas phospholipids have 2;

Both contain C, H and O whereas phospholipids also contain P; Must relate to element.

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67
Q

AS (Lipids AO1)

Contrast the properties of triglycerides and phospholipids.

A

Triglycerides are hydrophobic/non-polar whereas phospholipids have hydrophilic/polar and hydrophobic region;

Phospholipids form bilayer whereas triglycerides don’t;

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68
Q

AS (Lipids AO1)

Triglycerides are hydrophobic or hydrophilic

A

Hydrophobic

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69
Q

AS (Lipids AO1)

Explain the arrangement of phospholipids in a cell-surface membrane.

A
  1. (As a) Bilayer
  2. Hydrophobic (fatty acid) tails point away/are repelled from water

OR

Hydrophilic (phosphate) heads point to/are in/are attracted to water;

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70
Q

AS (Lipids AO1)

TRUE or FALSE
Phospholipids are hydrophobic AND hydrophilic

A

TRUE

Hydrophobic fatty acids tails and hydrophilic phosphate head

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71
Q

AS (Lipids AO1)

Explain the arrangement of phospholipids in a cell-surface membrane (3 marks)

A

1. Phospholipid both hydrophobic and hydrophilic
OR
Phospholipid polar
OR
Phosphate group is charged;

2. Triglycerides only hydrophobic
OR Fatty acid/triglyceride is non-polar;

3. Hydrophilic/phosphate group attracts water (to either side of bilayer)

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72
Q

AS (Lipids AO1)

Draw and label a simple diagram of the phospholipid bilayer

A
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73
Q

AS (Lipids AO1)

Draw and label a simple diagram of a single phospholipid molecule

A
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74
Q

AS (Water AO1)

Explain the importance of water as a metabolite

A

This means water can be involved in metabolic reactions such as condensation and hydrolysis.

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75
Q

AS (Water AO1)

Explain the importance of water as a solvent

A

This allows metabolic reactions to occur AND also allows the transport of substances.

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76
Q

AS (Water AO1)

Explain the importance of the high specific heat capacity of water

A

This ‘buffers’ changes in temperature.

It requires lots of energy to break the hydrogen bonds in water

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77
Q

AS (Water AO1)

Explain the importance of the large latent heat of vaporisation of water

A

This provides a cooling effect (through evaporation).

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78
Q

AS (Water AO1)

Explain the importance of Cohesion
between water molecules

A

This supports the formation of continuous columns of water (which is needed to move water up the xylem).

Cohesion also produces surface tension which supports small organisms on the surface of water e.g., pond skaters.

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79
Q

AS (Carbohydrates AO1)

Describe how the results from the colorimeter can identify the fruit juice containing the higher sugar content.

A

High(er) absorbance (has more sugar)

OR

Low(er) transmission (has more sugar);

More sugar = darker precipitate (brick red) which absorbs more light

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80
Q

AS (Carbohydrates AO1)

What term is used to describe the different structures of α-glucose and β-glucose?

A

Isomer

Isomers have same molecular formula but different arrangement of atoms

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81
Q

AS (Lipids AO1)

The general structure of a fatty acid is RCOOH.

Name the group represented by COOH.

A

Carboxyl

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82
Q

AS (Carbohydrates AO1)

The student controlled variables in the test using Benedict’s solution.

Give two variables the student controlled.

A
  1. Benedict’s (solution) volume;
  2. Benedict’s (solution) concentration;
  3. (Fruit) juice volume;
  4. (Water bath/water/solution) temperature;
  5. Duration of heating (in water bath);
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83
Q

AS (Carbohydrates AO2)

A

Carbon = 18

Hydrogen = 32

Oxygen = 16

Two glycosidic bonds formed, so two molecules of water produced

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84
Q

AS (Carbohydrates AO2)

Galacto-oligosaccharides (GOS) are polymers of galactose.

Explain why GOS are described as polysaccharides (2).

A

1. Galactose is a monosaccharide/monomer;

2. Polysaccharide is a carbohydrate polymer;

3. Several monosaccharides / monomers / galactose joined by condensation reactions

OR monosaccharides / monomers / galactose joined by glycosidic bonds;

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85
Q

AS (Carbohydrates AO2)

Galacto-oligosaccharides (GOS) are polymers of galactose.

Give two differences between the structures of GOS and lactose.

A

1. Lactose contains (alpha) glucose and GOS does not

OR Lactose contains (alpha)glucose + galactose and GOS contains only galactose;

2. Lactose is a disaccharide and GOS is a polysaccharide;

3. Lactose has one glycosidic bond and GOS has many glycosidic bonds;

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86
Q

AS (Proteins AO1)

Draw out and label an amino acid

A
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87
Q

AS (Proteins AO1)

What are the monomers from which proteins (aka polypeptides) are made?

A

Amino acids

88
Q

AS (Proteins AO1)

TRUE OR FALSE:
The twenty amino acids that are common in all organisms differ only in their variable/side group.

A

TRUE

89
Q

AS (Proteins AO1)

What type of reaction joins amino acids to form a peptide bond.

A

Condensation

1 molecule of water is produced for every peptide formed

90
Q

AS (Proteins AO1)

What is formed by the condensation of two amino acids?

A

Dipeptides
& 1 water molecule

91
Q

AS (Proteins AO1)

What is formed by the condensation of many (3 or more) amino acids?

A

Polypeptides

Plus 1 molecule of water produced for every peptide formed

92
Q

AS (Proteins AO1)

Draw a dipeptide and label the peptide bond

A
93
Q

AS (Proteins AO1)

Describe how a peptide bond is formed between two amino acids to form a dipeptide (2 marks).

A
  1. Condensation (reaction) / loss of water.
  2. Between amine/NH2 and carboxyl/COOH groups.
94
Q

AS (Proteins AO1)

List the levels of organisation of protein structure

A

The PRIMARY structure

The SECONDARY structure

The TERTIARY structure

The QUATERNARY structure

95
Q

AS (Proteins AO1)

Describe the primary structure of all proteins

A

1. number AND sequence/order of amino acids (in a polypeptide chain);

2. (Joined by) peptide bonds;

96
Q

AS (Proteins AO1)

Describe how monomers join to form the primary structure of a protein (3 marks).

A
  1. Condensation reaction between amino acids
  2. Forming peptide bond
  3. Creating a specific number AND sequence of amino acids
97
Q

AS (Proteins AO1)

What bonds maintain the secondary structure of proteins?

A

(Many weak) hydrogen bonds

98
Q

AS (Proteins AO1)

The secondary structure of a polypeptide is produced by bonds between amino acids. Describe how (2 marks).

A
  1. Hydrogen bonds
  2. Between NH / amine and C=O / carboxyl groups of amino acids

this forms alpha helix and beta pleated sheets

99
Q

AS (Proteins AO1)

Which level of protein structure?

A

Secondary

100
Q

AS (Proteins AO1)

The tertiary structure is held together by which bonds between R groups of different amino acids.

A

Hydrogen
Ionic
Disulphide bridges

101
Q

AS (Proteins AO1)

Which level of protein structure?

A

Tertiary

102
Q

AS (Proteins AO1)

Fill in the blank:

Quatenary proteins contain ………………….. polypeptide chains

A

two or more

OR

more than one

103
Q

AS (Proteins AO1)

The quaternary structure is held together by which bonds between the polypeptide chains.

A

Hydrogen
Ionic
Disulphide bridges

104
Q

AS (Proteins AO1)

TRUE or FALSE:

Quaternary proteins also contains non-protein groups (prosthetic groups).

A

TRUE

e.g. Heamoglobin contains a red haem group where oxygen binds

105
Q

AS (Proteins AO1)

Two proteins have the same number and type of amino acids but different tertiary structures. Explain why (2 marks).

A
  1. Different primary structure / different sequence of amino acids
  2. Forms ionic / hydrogen / disulphide bridges in different places
106
Q

AS (Proteins AO1)

Describe the structure of a protein (5 marks).

A

1. Polymer of amino acids

2. Amino acids joined by peptide bonds

3. Formed by a condensation reaction

4. Primary structure is number AND order/sequence of amino acids

5. Secondary structure is folding of polypeptide chain due to hydrogen bonding

6. Tertiary structure is formed by interactions between R groups e.g. due to hydrogen / ionic / disulphide bonds

7. Quaternary structure more than one OR two or more polypeptide chains

107
Q

AS (Proteins AO1)

Describe how you would test for the presence of protein (2 marks).

A
  1. Add Biuret reagent
  2. Positive result = purple/lilac (solution)
108
Q

AS (Proteins AO1)

A dipeptide consists of two amino acids joined by a peptide bond.

Describe two other ways in which all dipeptides are similar.

A

1.  Amine/NH2 (group at end);

2.  Carboxyl/COOH (group at end);

3.  Two R groups;

4.  All contain C and H and N and O;

109
Q

AS (Proteins AO1)

A dipeptide consists of two amino acids joined by a peptide bond.

Describe one way in which they might differ.

A

Variable/different R group(s);

110
Q

AS (Proteins AO2)

A solution contained a mixture of three different amino acids. A scientist passed an electric current through the solution to separate the amino acids.

Explain what the positions of the spots in the below diagram show about these amino acids.

A
  1. Moved to negative (electrode) because positive(ly charged);
  2. (Spots move) different distances/rates because (amino acids) different charge/mass;
  3. Two spots (not three) because (amino acids) same charge/mass
111
Q

AS (Proteins AO1)

TRUE OR FALSE:

All proteins have a specific tertiary structure which gives them a specific shape which is necessary for them to carry out their function.

A

True

112
Q

AS (Proteins AO1)

Rank the bonds found in the tertiary structure of protein by strength

A

Disulphide = strongest

Ionic (broken by changes in pH)

Hydrogen = weakest (broken by changes in temperature)

113
Q

AS (Proteins AO1)

What is denaturation of proteins?

A

A permanent change in its tertiary structure

114
Q

AS (Proteins AO1)

If you added the Biuret reagent to a solution containing enzymes, what would the result be?

A

Purple/lilac = positive result

because enzymes are proteins.

115
Q

AS (Enzymes AO1)

Each enzyme lowers the ______________________ of the reaction it catalyses.

A

activation energy

116
Q

AS (Enzymes AO1)

TRUE OR FALSE:

Enzymes are proteins which have a specific tertiary structure which gives them a specific 3D shape.

A

TRUE

117
Q

AS (Enzymes AO1)

Active sites have a unique shape which is _______________ to only one substrate.

A

COMPLEMENTARY

118
Q

AS (Enzymes AO1)

When an enzyme active site binds to a substrate it forms an _______________.

A

enzyme substrate complex

119
Q

AS (Enzymes AO1)

In humans, the enzyme maltase breaks down maltose to glucose. Explain why maltase only breaks down maltose (2 marks).

A
  1. Maltase has a specific tertiary structure that contains an active site;
  2. Active site complementary to only maltose / substrate
120
Q

AS (Enzymes AO1)

Describe the induced fit model of enzyme action (3 marks).

A
  1. Active site is initially NOT complementary to the substrate
  2. The substrate enters the enzyme’s active site and induces the change in the shape of the active site so now complementary
  3. Enzyme substrate complex forms which stresses the bonds in the substrate and lowers the activation energy
  4. When the product leaves the active site, it then returns to its previous shape.
121
Q

AS (Enzymes AO1)

Describe one similarity between the induced-fit model of enzyme action and the lock and key model of enzyme action.

A

Substrate binds to active site

OR

Enzyme-substrate complex (formed);

122
Q

AS (Enzymes AO1)

Describe one difference between the induced-fit model of enzyme action and the lock and key model of enzyme action.

A

Active site changes shape with induced-fit, whereas does not change in lock and key

OR

(Initially) active site not complementary to substrate with induced-fit, whereas is complementary in lock and key

123
Q

AS (Enzymes AO1)

In humans, the enzyme maltase breaks down maltose to glucose. This takes place at normal body temperature. Explain why (3 marks).

A
  1. Description of induced fit - binding of substrate causes active site to change shape (now complementary to substrate);
  2. This forms an enzyme-substrate complex which stresses bonds in the substrate (so more easily broken);
  3. Which lowers activation energy required for reaction;
124
Q

AS (Enzymes AO1)

Explain how the active site of an enzyme causes a high rate of reaction (3 marks).

A
  1. Description of induced fit - binding of substrate causes active site to change shape (now complementary to substrate);
  2. This forms an enzyme-substrate complex which stresses bonds in the substrate (so more easily broken);
  3. Which lowers activation energy required for reaction;
125
Q

AS (Enzymes AO1)

How can you measure the rate of enzyme-controlled reactions?

A

formation of products OR

disappearance or breakdown of the substrate

(in a defined period of time)

KEY POINT: Calculating the rate of any process ALWAYS requires time.

126
Q

AS (Enzymes AO1)

How do you calculate the rate of an enzyme controlled reaction

A

DY (substrate or product) / DX (always time)

(Change in Y over change ix X)

127
Q

AS (Enzymes AO1)

Calculate the rate of reaction:

A
DY (change in Y) / DX (change in X)
128
Q

AS (Enzymes AO1)

What factors affect enzyme controlled reactions?

A

Temperature
pH
Substrate concentration
Enzyme concentration

129
Q

AS (Enzymes AO1)

Fill in the gaps:

As the temperature increases the enzymes and substrates have more [1].

Therefore they move around more and are more likely to successfully collide and form [2].

A
  1. knetic energy
  2. enzyme-substrate complexes
130
Q

AS (Enzymes AO1)

What is enzyme denaturation?

A

A permanent change to the tertiary structure of the enzyme (inc the shape of the active site).

Active is no longer complementary to its substrate, so fewer enzyme substrate complexes form.

131
Q

AS (Enzymes AO1)

Which bonds can be broken in the enzymes tertiary structure by increases in temperature?

A

(mainly) weak hydrogen

ionic

132
Q

AS (Enzymes AO1)

pH is a measure of________________.

A

hydrogen ion concentration

Increase H+ ions (low pH) , decrease H+ ions (high pH)

133
Q

AS (Enzymes AO1)

TRUE or FALSE:

Both increases and decreases in the pH can denature an enzyme

A

TRUE

134
Q

AS (Enzymes AO1)

Describe and explain the effect of increasing substrate concentration on the rate of an enzyme controlled reaction (2 marks).

A

Increases then plateaus

Because all enzyme active sites are occupied

Plateaus because all the substrate has been used up

135
Q

AS (Enzymes AO1)

What is the limiting factor at the red arrow?

A

Substrate concentration

136
Q

AS (Enzymes AO1)

What is the limiting factor at the red arrow?

A

Enzyme concentration

137
Q

AS (Enzymes AO1)

Why is the initial rate of reaction faster?

A

because there’s lots of substrate and therefore more enzyme substrate complexes form.

138
Q

AS (Enzymes AO1)

Why does the rate of reaction plateau?

A

because the substrate has been used up

139
Q

AS (Enzymes AO1)

Inhibitors __________ the rate of reaction

A

decrease

140
Q

AS (Enzymes AO1)

Competitive inhibitors have a __________________________ shape to the substrate

A

similar

141
Q

AS (Enzymes AO1)

Fill in the blanks:

Because they have a similar shape to the substrate, competitive inhibitors can bind to the enzyme’s [1].
.
Competitive inhibitors reduce [2] forming.

This reduces the [3].

A
  1. active site
  2. enzyme substrate complexes
  3. rate of reaction
142
Q

AS (Enzymes AO1)

___________________ substrate concentration can overcome competitive inhibition

A

Increasing

143
Q

AS (Enzymes AO2)

A
  1. (Allopurinol) is a similar shape to xanthine;
  2. (Allopurinol) enters active site / is a competitive inhibitor;
  3. Less xanthine binds so fewer enzyme substrate complexes and therefore fewer uric acid crystals formed;
144
Q

AS (Enzymes AO1)

Which type of inhibitor binds to the allosteric site (away from the active site).

A

non-competitive

145
Q

AS (Enzymes AO1)

What happens after a non-competitive inhibitor binds to the allosteric site?

A

1.Change thes shape of the active site so that it is no longer complementary to the substrate.

2. Fewer enzyme substrate complexes form and the rate of reaction is decreased.

146
Q

AS (Enzymes AO1)

TRUE OR FALSE:

Increasing substrate concentration can overcome non-competitive inhibition.

A

FALSE

This is because the active site has changed shape

147
Q

AS (Enzymes AO2)

Explain the results in the below graph
(2 marks).

A

1. (Rate of) increase in concentration of maltose slows as substrate/starch is used up

OR

High initial rate as plenty of starch/substrate/more E-S complexes;

2. No increase after 25 minutes/at end/levels off because no substrate/starch left;

148
Q

AS (Enzymes AO1)

What does the addition of a buffer do in an enzyme controlled reaction?

A

Maintains a constant pH

This prevents the enzyme from denaturing

149
Q

AS (Enzymes AO1)

A competitive inhibitor decreases the rate of an enzyme-controlled reaction.

Explain how (3 marks).

A
  1. Inhibitor similar shape to substrate;
  2. Binds to active site;
  3. Reduces enzyme-substrate complex forming;
150
Q

AS (Enzymes AO1)

Describe how a non-competitive inhibitor can reduce the rate of an enzyme-controlled reaction (3 marks).

A
  1. Attaches to the enzyme at the allosteric site (other than the active site);
  2. Changes shape of the active site

OR Changes tertiary structure (of enzyme);

  1. (So active site and substrate) no longer complementary so less/no substrate can fit/bind;
151
Q

AS (Enzymes AO2)

A

(With inhibitor) increase substrate/lipid (concentration) does not increase rate of reaction

OR

(With inhibitor) increase substrate/lipid (concentration) does not increase lipase activity

OR

High substrate (concentration) does not overcome inhibition

152
Q

Structure of DNA and RNA (AO1)

DNA holds ____________ information

A

genetic

153
Q

Structure of DNA and RNA (AO1)

RNA transfers genetic information from ____________ to the ribosomes

A

DNA

154
Q

Structure of DNA and RNA (AO1)

Ribosomes are formed from which components?

A

rRNA and proteins.

155
Q

Structure of DNA and RNA (AO1)

Both DNA and RNA are polymers of ______________.

A

nucleotides

156
Q

Structure of DNA and RNA (AO1)

Draw out and label a DNA nucleotide

A
157
Q

Structure of DNA and RNA (AO1)

What is the name of the pentose sugar found in a RNA nucleotide?

A

Ribose

158
Q

Structure of DNA and RNA (AO1)

What is the name of the pentose sugar found in a DNA nucleotide?

A

Deoxyribose

159
Q

Structure of DNA and RNA (AO1)

Draw out and label a RNA nucleotide

A
160
Q

Structure of DNA and RNA (AO1)

What is the name of the nitrogenous base specific to RNA?

A

Uracil

161
Q

Structure of DNA and RNA (AO1)

What is the name of the nitrogenous base specific to DNA?

A

Thymine

162
Q

Structure of DNA and RNA (AO1)

What is the name of the bond that links together nucelotides?

A

Phosphodiester

163
Q

Structure of DNA and RNA (AO1)

What enzyme catalyses the formation of a phosphodiester bond via a condestation reaction of DNA nucleotides?

A

DNA polymerase

164
Q

Structure of DNA and RNA (AO1)

Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule (2 marks).

A
  1. Condensation (reaction);
  2. (Between) phosphate and deoxyribose;
  3. (Catalysed by) DNA polymerase;
165
Q

Structure of DNA and RNA (AO1)

Fill in the blanks

A DNA molecule is a double helix with two [1] chains held together by [2] bonds between specific [3] base pairs.

A

1 - polynucleotide

2 - hydrogen

3 - complementary

166
Q

Structure of DNA and RNA (AO1)

The double helix structure for DNA was put foward by which scientists?

A

Watson & Crick

167
Q

Structure of DNA and RNA (AO1)

In the DNA double helix, adenine forms a complementary base pair with?

A

thymine

168
Q

Structure of DNA and RNA (AO1)

In the DNA double helix, guanine forms a complementary base pair with?

A

cytosine

169
Q

Structure of DNA and RNA (AO1)

Describe the structure of DNA (5 marks)

A
  1. Polymer of nucleotides;
  2. Each nucleotide formed from deoxyribose, a phosphate (group) and a nitrogenous base;
  3. Phosphodiester bonds (between nucleotides);
  4. Double helix/2 strands held by hydrogen bonds;
  5. (Hydrogen bonds/ complementary pairing) between adenine, thymine and cytosine, guanine;
170
Q

Structure of DNA and RNA (AO1)

What are the functions of the sugar-phosphate backbone and double helix structure?

A
  1. Provides strength and stability;
  2. Protects information coded in the bases and hydrogen bonding between bases;
171
Q

Structure of DNA and RNA (AO1)

What is the function of DNA being a long molecule?

A

Can store a lot of information

172
Q

Structure of DNA and RNA (AO1)

What is the function of helix structure in DNA?

A

Makes it compact

(more nucleotides can fit into a smaller space)

173
Q

Structure of DNA and RNA (AO1)

What is the function of the the base sequence of DNA?

A

Codes for the sequence of amino acids in the primary structure of proteins

174
Q

Structure of DNA and RNA (AO1)

What is the function of the DNA helix being double stranded?

A

Allows semi-conservative replication because both strands can act as a template;

175
Q

Structure of DNA and RNA (AO1)

Complementary base pairing between – adenine and thymine & cytosine and guanine allows ____________ .

A

accurate replication

176
Q

Structure of DNA and RNA (AO1)

What is the function of (weak) hydrogen bonds between complementary bases in DNA?

A

Easily broken (by DNA helicase) and allows separation of strands for semi-conservative replication;

177
Q

Structure of DNA and RNA (AO1)

A

Thymine = 18%

Guanine = 32%

178
Q

Structure of DNA and RNA (AO1)

What are the structural differences between a DNA molecule and a mRNA molecule (4 marks).

A

1. DNA has deoxyribose whereas mRNA has ribose;
2. DNA has thymine whereas mRNA has uracil;
3. DNA long whereas mRNA short;
4. DNA is double stranded / double helix whereas mRNA is single stranded
5. DNA has hydrogen bonds whereas mRNA has no hydrogen bonds
OR
DNA has (complementary) base pairing whereas mRNA does not;

179
Q

Structure of DNA and RNA (AO1)

What are the structural differences between a DNA molecule and a mRNA molecule (4 marks).

A

1. DNA has deoxyribose whereas mRNA has ribose;
2. DNA has thymine whereas mRNA has uracil;
3. DNA long whereas mRNA short;
4. DNA is double stranded / double helix whereas mRNA is single stranded
5. DNA has hydrogen bonds whereas mRNA has no hydrogen bonds
OR
DNA has (complementary) base pairing whereas mRNA does not;

180
Q

Structure of DNA and RNA (AO1)

Give structural similarities between a DNA molecule and a mRNA molecule (4 marks).

A

1. Both polymers of nucleotides;

2. Nucleotides have pentose, (nitrogen-containing organic) base and a phosphate (group);

3. Both Cytosine, guanine and adenine (as bases);

4. Both have phosphodiester bonds;

181
Q

DNA replication (AO1)

The semi-conservative replication of DNA ensures ___________________ .

A

genetic continuity between generations of cells

OR

genetically identical cells following mitosis

182
Q

DNA replication (AO1)

What is the role of DNA helicase during semi-conservative DNA replication?

A

Breaks hydrogen bonds
(to unwind DNA / separate strands);

183
Q

DNA replication (AO1)

Following semi-conservative replication, a new molecule of DNA will consist of _______________.

A

half “original” strand and half “new” stranded.

184
Q

DNA replication (AO1)

Describe the process of semi-conservative replication of DNA (5 marks).

A
  1. DNA helicase unwinds DNA/double helix
    OR DNA helicase breaks hydrogen bonds;
  2. Both strands act as templates;
  3. (Free DNA) nucleotides line up in complementary base pairs / Adenine to Thymine and Guanine to Cytosine;
  4. DNA polymerase joins nucleotides (of new strand);
  5. Forming phosphodiester bonds;
  6. Each new DNA molecule consists of one
    old/original/template strand and one new strand;
185
Q

DNA replication (AO1)

What is the name of the scientisis who provided the evidence for the semi-conservative model of replication.

A

Meselson & Stahl

186
Q

DNA replication (AO1)

What organism did Meseleson and Stahl use for their experiment?

A

Bacteria (E.coli)

187
Q

DNA replication (AO1)

Meselson & Stahl experiment

In generation ‘0’, all the bacteria (e.coli) were grown with which isotope of nitrogen?

A

N15

188
Q

DNA replication (AO1)

Meselson & Stahl experiment

In generation ‘1’, all the bacteria (e.coli) were grown with which isotope of nitrogen?

A

N14

189
Q

DNA replication (AO1)

Meselson & Stahl experiment

Which nitrogen isotope is heavier?

A

N15

190
Q

DNA replication (AO1)

Meselson & Stahl experiment

Put ticks for which generation the different DNA molecules will be found.

A
191
Q

Structure of DNA and RNA (AO1)

A
  1. Hydrogen (bonds);
  2. Phosphodiester (bonds);
192
Q

DNA replication (AO1)

In the process of semi-conservative DNA replication, the two strands within a DNA molecule are separated. Each then acts as a template for the formation of a new complementary strand.

Describe how the separation of strands occurs (2 marks).

A
  1. DNA helicase;
  2. Breaks hydrogen bonds between complementary base pairs
193
Q

DNA replication (AO1)

Describe the role of DNA polymerase in the semi-conservative replication of DNA (2 marks).

A
  1. Joins (adjacent DNA) nucleotides;
  2. (Catalyses) condensation (reactions);
  3. (Catalyses formation of) phosphodiester bonds (between adjacent nucleotides);
194
Q

DNA replication (AO1)

Use your knowledge of semi-conservative replication of DNA to suggest:

the role of the single-stranded DNA fragments (2 marks)

A

1.   Act as template;

2.   Determines order of nucleotides/bases;

195
Q

DNA replication (AO1)

Use your knowledge of semi-conservative replication of DNA to suggest:

the role of the DNA nucleotides (1 mark)

A

Forms complementary pairs / Adenine to Thymine, Guanine to Cytosine

196
Q

Structure of DNA and RNA (AO1)

DNA is a polymer of nucleotides. Each nucleotide contains an organic base.

Explain how the organic bases help to stabilise the structure of DNA (2 marks).

A
  1. Hydrogen bonds between the complementary base pairs holds two strands together
  2. Many hydrogen bonds provides strength
197
Q

ATP (AO1)

Draw out and label the structure of adenosine triphosphate (ATP)

A
198
Q

ATP (AO1)

What are the products of ATP hydrolysis?

A

adenosine diphosphate (ADP)
AND
an inorganic phosphate group (Pi)

199
Q

ATP (AO1)

What is the name of the enzyme that catalyses ATP hydrolysis?

A

ATP hydrolase

200
Q

ATP (AO1)

ATP is mostly produced in the mitochondria via which process?

A

Aerobic respiration

Smaller amounts of ATP are produced by anaerobic respiration

201
Q

ATP (AO1)

Describe how an ATP molecule is formed from its component molecules (4 marks).

A
  1. and 2. Accept for 2 marks correct names of three components: adenine, ribose, three phosphates;

OR accept suitably labelled diagram

  1. Condensation reaction (releases 1 water molecule);
  2. ATP synthase;
202
Q

ATP (AO1)

Adding an inorganic phosphate to a biological molecules is known as phosphorylation. This makes the molecule ______________ .

A

more reactive

203
Q

ATP (AO1)

ATP is useful in many biological processes. Explain why (4 marks).

A
  1. Releases energy in small amounts;
  2. (Broken down) in a one step / immediate energy compound / makes energy available rapidly;
  3. Phosphorylates / adds phosphate makes (phosphorylated substances) more reactive / lowers activation energy;
  4. Reformed / made again / resynthesised;
204
Q

ATP (AO1)

TRUE or FALSE

Adding a phosphate group to an enzyme can help lower the activation energy.

A

TRUE

205
Q

ATP (AO1)

Give two ways in which the properties of ATP make it a suitable source of energy in biological processes (2 marks).

A
  1. Energy released in small amounts;
  2. Involves a single reaction
    (and therefore energy is immediately available);
  3. Soluble;
206
Q

ATP (AO1)

Humans synthesise more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP (2 marks).

A
  1. ATP cannot be stored / is an immediate source of energy;
  2. ATP only releases a small amount of energy at a time;
207
Q

ATP (AO1)

Adenosine triphosphate (ATP) is a nucleotide derivative.

Contrast the structures of ATP and a nucleotide found in DNA to give two differences.

A
  1. ATP has ribose whereas DNA nucleotide has deoxyribose;
  2. ATP has 3 phosphate (groups) whereas DNA nucleotide has 1 phosphate (group);
  3. ATP – base always adenine whereas in DNA nucleotide nitrogenous base can be different / varies;
208
Q

ATP (AO1)

A

Quaternary

Condensation/phosphorylation

Release/loss/formation

(Aerobic) respiration

209
Q

Past Paper Question (AO1)

A

B - is a monomer in an enzyme’s active site

D - is a monomer in cellulose

C - is produced during photosynthesis and respiration

B - forms a polymer that gives a positive result with a biuret test

210
Q

Inorganic ions (AO1)

Describe the role(s) of iron ions in cells

A
  1. (forms part of) Haemoglobin which binds to oxygen / transports oxygen
211
Q

Inorganic ions (AO1)

Describe the role(s) of sodium ions in cells

A
  1. Sodium moved out by active transport/Na – K pump;
  2. Creates a sodium concentration/diffusion gradient;
  3. Co-transport of glucose/amino acids (into cells);
  4. Affects osmosis/water potential;
212
Q

Inorganic ions (AO1)

Describe the role(s) of phosphate ions in cells

A
  1. Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides;
  2. Used in/to produce ATP;
  3. Phosphorylates other compounds (usually) making them more reactive;
  4. Hydrophilic/water soluble part of phospholipid bilayer/membrane;
  5. Affects osmosis/water potential;
213
Q

Inorganic ions (AO1)

Describe the role(s) of hydrogen ions (protons) in cells

A

Its concentration affects the acidity of solutions (pH);

a low pH (acidic) has a higher concentration of H+ ions;

A high pH (alkali) has a lower concentration of H+ ions;

214
Q

Inorganic ions (AO1)

Explain a property of iron ions that enables these ions to carry out their role in red blood cells (2 marks).

A
  1. (Is) charged/polar

OR (Is) part of haem(oglobin);

  1. (So) binds to oxygen

OR (So) transports oxygen;

215
Q

AS (Enzymes AO1)

Explain how two enzymes with different amino acid sequences can catalyse the same reaction (2 marks).

A

1. Both active sites have similar/identical tertiary structures
OR
Both have active sites that are complementary to different parts of the substrate;

Accept attach/bind for complementary

2. Form enzyme-substrate complexes (with the same substrate);

AS AQA Biology - Burnley College (2023-24) (5 decks)

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